LINUX

TheUltimateStepbyStepGuidetoQuicklyandEasilyLearningLinux

TEDDAWSON

©Copyright2015byWECANTBEBEATLLC

ChapterOne:LINUXHISTORY

ChapterTwo:LINUXDISTRIBUTION(DISTRO)

Introduction

GUIDETOCHOOSINGDISTRIBUTION

LinuxMint

Ubuntu

DebianGNU/Linux

Mageia

Fedora

openSUSE

ArchLinux

CentOS

PCLinuxOS

SlackwareLinux

FreeBSD

ChapterThree:LICENSING

COMMUNITY

DEVELOPMENT

ChapterFour:INSTALLINGDEBIAN8

WhatisDebian

CustomizingyourSystem

Terminal

Installsudo

Setupthenetwork

Setupyourhostsfile

LoginviaSSH!

Installingthebasics

InstallingMySQL

SettingupMySQL

ChapterFive:INSTALLINGCENTOS7

InstallationofCenOS7

Step1:DownloadtheISOImage

Step2:MakeabootableDrive

Step3:BeginInstallation

Step4:SelectLanguageandKeyboard

Step5:ChangetheInstallationDestination

Step6:SelectthePartitioningScheme

Step7:CreateaSwapSpace

Step8:CreateaMountpoint

Step9:AcceptChanges

Step10:SetDateandTime

Step11:BeginInstallation

Step12:SetUpRootPassword

Step13:CreateaUserAccount

Step14:CompleteInstallation

ChangeandSetHostnameCommand

Method#1:hostnamectl

HowdoIseethehostnames?

HowdoIdeleteaparticularhostname?

HowdoIchangehostnameremotely?

Method#2:nmtui

Method#3:nmcli

Toviewthehostnameusingnmcli:

Tosetthehostnameusingnmcli:

ChapterSix:LINUXANDUNIXMANCOMMAND

Syntax

Description

GeneralOptions

MainModesofOperation

FindingManualPages

ControllingFormattedOutput

SectionNumbers

ExitStatus

Environment

Files

Examples

ChapterSeven:LINUXDIRECTORYCOMMAND

sampleoutputs

ListonlyfilesinUnix

Task:Createaliasestosavetime

ChapterEight:WORKINGWITHFILES

UNIXFileNames

LookingattheContentsofFiles

CatCommand

MoreCommand

HeadCommand

TailCommand

Copying,Erasing,Renaming

CopyingFiles

ErasingFiles

RenamingaFile

UsingtheCommandLine

StandardInputandStandardOutput

Redirection

UsingPipesandFilters

SomeAdditionalFileHandlingCommands

WordCount

ComparingtheContentsofTwoFiles:thecmpanddiffCommands

ChapterNine:NAVIGATIONANDFILEMANAGEMENT

PrerequisitesandGoals

NavigationandExploration

Findingwhereyouarewiththe“pwd”command

LookingattheContentsofDirectorieswith“ls”

MovingAroundtheFilesystemwith“cd”ViewingFiles

FileandDirectoryManipulation

CreateaFilewith“touch”

CreateaDirectorywith“mkdir”

MovingandRenamingFilesandDirectorieswith“mv”

CopyingFilesandDirectorieswith“cp”

RemovingFilesandDirectorieswith“rm”and“rmdir”

EditingFiles

ChapterTen:UNIXSHELLSCRIPTING

ShellScriptingIntroduction

ChapterEleven:SHELLBASICOPERATOR

ArithmeticOperators

RelationalOperators:

BooleanOperators

StringOperators

FileTestOperators

RunThe.ShFileShellScriptInLinux/Unix

.shAsRootUser

chmodCommand:RunShellScriptInLinux

ChapterTwelve:SHELLEMBEDDINGANDOPTIONS

Shellinstalling

Backticks

Backticksorsinglequotes

ShellAlternatives

Practice:ShellInstalling

ChapterThirteen:SHELLHISTORYSEARCHCOMMAND

EmacsLine-EditModeCommandHistorySearching

fccommand

Deletecommandhistory

FILENAMEGLOBBINGWITH*,?,[]

Chapterfourteen:UNIX-SHELLINPUT/OUTPUTREDIRECTIONS

ChapterFifteen:UNIXSHELLFUNCTION

CreatingFunctions

Example

PassParameterstoaFunction

ReturningValuesfromFunctions

Example

NestedFunctions

FunctionCallfromPrompt

Unix-PipesandFilters

ThegrepCommand

ThesortCommand

ThepgandmoreCommands

ChapterSixteen:UNIXUSEFULCOMMAND

FilesandDirectories

Manipulatingdata

MessagesbetweenUsers

ChapterSeventeen:REGULAREXPRESSION

Invokingsed

ThesedGeneralSyntax

DeletingAllLineswithsed

ThesedAddresses

ThesedAddressRanges

TheSubstitutionCommand

SubstitutionFlags

UsinganAlternativeStringSeparator

ReplacingwithEmptySpace

AddressSubstitution

TheMatchingCommand

UsingRegularExpression

UsingMultiplesedCommands

BackReferences

ChapterEighteen:FILESYSTEMBASICS

DirectoryStructure

ThedfCommand

TheduCommand

MountingtheFileSystem

UnmountingtheFileSystem

UserandGroupQuotas

ChapterNineteen:UNIX-USERADMINISTRATION

ManagingUsersandGroups

ModifyaGroup

DeleteaGroup:

CreateanAccount

ModifyanAccount

DeleteanAccount

ChapterTwenty:SYSTEMPERFORMANCE

PerformanceComponents

Unix-SystemLogging

The/etc/syslog.conffile

LoggingActions

LogRotation

ImportantLogLocations

ChapterTwenty-one:UNIXSIGNALSANDTRAPS

LISTofSignals

DefaultActions

SendingSignals

TrappingSignals

CleaningUpTemporaryFiles

IgnoringSignals

ResettingTraps

ABOUTTHEAUTHOR

LINKSANDRESOURCESDEDICATION

SPECIALTHANKS

ChapterOne:LINUXHISTORY

Thehistory of Linux began in 1991with the commencement of a personal

projectbyFinnishstudentLinusTorvalds tocreateanewfreeoperatingsystem

kernel.Sincethen,theresultingLinuxkernelhasbeenmarkedbyconstantgrowth

throughout its history. Since the initial release of its source code in 1991, it has

grown from a small number of C files under a license prohibiting commercial

distributiontothe3.18versionin2015withmorethan18millionlinesofsource

code under the GNU General Public License (GPL). He wrote the program

specificallyforthehardwarehewasusingandindependentofanoperatingsystem

because he wanted to use the functions of his new PC with an Intel 80386

processor.DevelopmentwasdoneonMINIXusingtheGNUCcompiler.TheGNU

CCompiler is still themain choice for compiling Linux today. The code can be

builtwithothercompilers,suchastheIntelCCompiler.AsTorvaldswroteinhis

book ‘Just forFun,’he eventually endedupwritinganoperating systemkernel.

On25August1991(age21),heannouncedthisnewsysteminaUsenetpostingto

thenewsgroup“comp.os.minix.”

TorvaldsfirstpublishedtheLinuxkernelunderitsownlicense,whichhada

restriction on commercial activity. The software used with the kernel was

developedaspartoftheGNUprojectlicensedundertheGNUGPL,afreesoftware

license. The first release of the Linux kernel, Linux 0.01, included a binary of

GNU’sBash shell. In the “Notes forLinux release0.01”,Torvalds lists theGNU

softwarethatisrequiredtorunLinux:Sadly,akernelbyitselfgetsyounowhere.

To get a working system, you need a shell, compilers, a library, etc. These are

separatepartsandmaybeunderstricter (oreven looser)copyright.Mostof the

toolsusedwithLinuxareGNUsoftwareandareundertheGNUcopyright.These

tools are not in the distribution - askme (or GNU) formore info. In 1992, he

suggested releasing the kernel under the GNU GPL. He first announced this

decisioninthereleasenotesofversion0.12.InthemiddleofDecember1992,he

publishedversion0.99usingtheGNUGPL.LinuxandGNUdevelopersworkedto

integrateGNUcomponentswithLinux tomakea fully functional freeoperating

system.Torvaldshasstated,“MakingLinuxGPL’dwasdefinitelythebestthingI

everdid.”Torvaldsinitiallyusedthedesignation“Linux”onlyfortheLinuxkernel.

Thekernelwas,however,frequentlyusedtogetherwithothersoftware,especially

thatoftheGNUproject.ThisquicklybecamethemostpopularadoptionofGNU

software.InJune1994inGNU’sBulletin,Linuxwasreferredtoasa“freeUNIX

clone,” and theDebianproject began calling its productDebianGNU/Linux. In

May1996,RichardStallmanpublishedtheeditorEmacs19.31,inwhichthetype

ofsystemwasrenamedfromLinuxtoLignux.Thisspellingwasintendedtorefer

specificallytothecombinationofGNUandLinux,butthiswassoonabandonedin

favor of “GNU/Linux.” This name garnered varying reactions. The GNU and

Debianprojectsusethename,althoughmostpeoplesimplyusetheterm“Linux”

torefertothecombination.

The largestpartof theworkonLinux isperformedby thecommunity: the

thousands of programmers around the world that use Linux to send their

suggestedimprovementstothemaintainers.Variouscompanieshavealsohelped

notonlywiththedevelopmentofthekernelsbutalsowiththewritingthebodyof

auxiliarysoftware,whichisdistributedwithLinux.AsofFebruary2015,over80%

ofLinuxkerneldevelopersarepaid.Itisreleasedbothbyorganizedprojectssuch

asDebianandbyprojectsconnecteddirectlywithcompaniessuchasFedoraand

openSUSE.Themembersoftheserespectiveprojectsmeetatvariousconferences

and fairs, in order to exchange ideas. One of the largest of these fairs is the

LinuxTaginGermany(currentlyinBerlin),whereabout10,000peopleassemble

annually,inordertodiscussLinuxandtheprojectsassociatedwithit.TheOpen

Source Development Lab (OSDL) was created in the year 2000, and is an

independentnonprofitorganization,whichpursues thegoalofoptimizingLinux

foremployment indatacentersand in thecarrier range. It servedas sponsored

working premises for Linus Torvalds and also for Andrew Morton (until the

middleof2006whenMorton transferred toGoogle).Torvaldsworked full-time

onbehalfofOSDL,developingtheLinuxkernels.

Chronology

1991:The Linux kernel is publicly announced on 25 August by 21-year-old

FinnishstudentLinusBenedictTorvalds.

1992:The Linux kernel is re-licensed under the GNU GPL. The first Linux

distributionsarecreated.

1993:Over100developersworkontheLinuxkernel.Withtheirassistance,the

kernel is adapted to the GNU environment, which creates a large

spectrumofapplicationtypesforLinux.Theoldestcurrently(asof2015)

existingLinuxdistribution,Slackware,isreleasedforthefirsttime.Later

that sameyear, theDebianproject is established.Today it is the largest

distributioncommunity.

1994:Torvalds judges all components of the kernel to be fully matured: he

releasesversion1.0ofLinux.TheXFree86projectcontributesagraphical

userinterface(GUI).CommercialLinuxdistributionmakersRedHatand

SUSEpublishversion1.0oftheirLinuxdistributions.

1995:LinuxisportedtotheDECAlphaandtheSunSPARCsystems.Overthe

followingyears,itisportedtoanever-greaternumberofplatforms.

1996:Version 2.0 of the Linux kernel is released. The kernel can now serve

several processors at the same time using symmetric multi-processing

(SMP),andtherebybecomesaseriousalternativeformanycompanies.

1998:Many major companies such as IBM, Compaq, and Oracle announce

theirsupportforLinux.TheCathedralandtheBazaarwerefirstpublished

asanessay(laterasabook),resultinginNetscapepubliclyreleasingthe

sourcecodetoitsNetscapeCommunicatorwebbrowsersuite.Netscape’s

actionsandcreditingoftheessaybringsLinux’sopensourcedevelopment

modeltotheattentionofthepopulartechnicalpress.Inaddition,agroup

ofprogrammersbegandevelopingthegraphicaluserinterfaceKDE.

1999:A group of developers began work on the graphical environment

GNOME, destined to become a free replacement for KDE,which at the

timedependedonthethenproprietary,QtGUItoolkit.Duringthisyear,

IBMannouncedanextensiveprojectforthesupportofLinux.

2000:DellannouncesthatitisnowtheNo.2providerofLinux-basedsystems

worldwideandthefirstmajormanufacturertoofferLinuxacrossits full

productline.

2002:Themediareported,“MicrosoftkilledDellLinux.”

2004:The XFree86 team splits up and joins with the existing X standards

bodytoformtheX.OrgFoundation,whichresultsinasubstantiallyfaster

developmentoftheXserverforLinux.

2005:The project openSUSE begins free distribution from Novell’s

community. In addition, the project OpenOffice.org introduces version

2.0whichthenstartedsupportingOASISOpenDocumentstandards.

2006:OraclereleasesitsowndistributionofRedHatEnterpriseLinux.Novell

and Microsoft announce cooperation for better interoperability and

mutualpatentprotection.

2007:DellstartsdistributinglaptopswithUbuntupre-installed.

2009:RedHatsmarketcapitalizationequalsSuns,interpretedasasymbolic

momentforthe“Linux-basedeconomy.”

2011:Version3.0oftheLinuxkernelisreleased.

2012:TheaggregateLinuxservermarket revenueexceeds thatof therestof

theUNIXmarket.

2013:Google’s Linux-based Android claims 75% of the Smartphone market

share,intermsofthenumberofphonesshipped.

2014:Ubuntuclaims22,000,000users.

2015:Version4.0oftheLinuxkernelisreleased.

Chapter Two:LINUX DISTRIBUTION(DISTRO)

Introduction

The bewildering choice and the ever increasing number of Linux

distributions canbe confusing for thosewhoarenew toLinux.This iswhy this

bookwas created. It lists 10 Linux distributions (plus an honorablemention of

FreeBSD,by far themostpopular of all of theBSDs), it is considered tobe the

mostwidely-usedbyLinuxusersaroundtheworld.Therearenofigurestoback

up this claim, and there are many other distributions that might suit your

particularpurposebetter,butasageneralrule,allofthesearepopularandhave

veryactive forumsormailing listswhereyoucanaskquestions ifyougetstuck.

Ubuntu,LinuxMint,andPCLinuxOSareconsideredtheeasiestfornewuserswho

wanttogetproductiveinLinuxassoonaspossiblewithouthavingtomasterallof

itscomplexities.Ontheotherendofthespectrum,SlackwareLinux,ArchLinux,

and FreeBSD are more advanced distributions that require a deeper

understanding, before they can be used effectively. openSUSE, Fedora, Debian

GNU/Linux and Mageia can be classified as good “middle-road” distributions.

CentOS is an enterprise distribution, suitable for those who prefer stability,

reliability,andlong-termsupporttocutting-edgefeaturesandsoftware.

GUIDETOCHOOSINGDISTRIBUTION

LinuxMint

LinuxMint,adistributionbasedonUbuntu,wasfirst launchedin2006by

Clement Lefebvre, a French-born IT specialist living in Ireland. Originally

maintainingaLinuxwebsitededicatedtoprovidinghelp,tipsanddocumentation

to new Linux users, the author saw the potential of developing a Linux

distributionthatwouldaddressthemanyusabilitydrawbacksassociatedwiththe

generally more technical, mainstream products. Since its beginnings, the

developers have been adding a variety of graphical “mint” tools for enhanced

usability; this includes mintDesktop - a utility for configuring the desktop

environment,mintMenu-anewandelegantmenustructureforeasiernavigation,

mintInstall - an easy-to-use software installer, and mintUpdate - a software

updater. Mint’s reputation for ease of use has been further enhanced by the

inclusionofproprietaryandpatent-encumberedmultimediacodecsthatareoften

absentfromlargerdistributionsduetopotentiallegalthreats.Perhapsoneofthe

bestfeaturesofLinuxMintisthefactthatthedeveloperslistentotheusersand

arealwaysfast in implementinggoodsuggestions.WhileLinuxMint isavailable

as a free download, the project generates revenue from donations, advertising,

andprofessionalsupportservices.

Pros:Superbcollectionof“minty”toolsdevelopedin-house,hundredsofuser-

friendlyenhancements,theinclusionofmultimediacodecs,opentousers’

suggestions.

Cons:Thealternative“community”editionsdonotalwaysincludethelatest

features;theprojectdoesnotissuesecurityadvisories.

Ubuntu

ThelaunchofUbuntuwasfirstannouncedinSeptember2004.Althougha

relative newcomer to the Linux distribution scene, the project took off like no

other, with its mailing lists soon filled with discussions by eager users and

enthusiastic developers. In the years that followed,Ubuntu grew to become the

most popular desktop Linux distribution and has contributed greatly toward

developing an easy-to-use and free desktop operating system that can compete

wellwith any of the proprietary ones available on themarket.On the technical

sideofthings,UbuntuisbasedonDebian“Sid”(unstablebranch),butwithsome

prominentpackages,suchasGNOME,Firefox,andLibreOffice,updatedtotheir

latestversions.Itusesacustomuserinterfacecalled“Unity.”Ithasapredictable,

6-month release schedule,with anoccasionalLongTermSupport (LTS) release

that issupportssecurityupdatesfor5years,dependingontheedition(non-LTS

releasearesupportedfor9months).OtherspecialfeaturesofUbuntuincludean

installable live DVD, creative artwork, desktop themes, migration assistant for

Windows users, support for the latest technologies, such as 3D desktop effects,

easyinstallationofproprietarydevicedriversforATIandNVIDIAgraphicscards,

wirelessnetworking,andon-demandsupportfornon-freeorpatent-encumbered

mediacodecs.

Pros:Fixed release cycleand supportperiod; long-termsupport (LTS)variants

with5yearsofsecurityupdates;novice-friendly;awealthofdocumentation,both

officialanduser-contributed.

Cons: Lacks compatibility with Debian; frequent major changes tend to drive

some users away, the Unity user interface has been criticized as being more

suitable for mobile devices rather than desktop computers; non-LTS releases

comewithonly9monthsofsecuritysupport.

DebianGNU/Linux

DebianGNU/Linuxwasfirstannouncedin1993.Itsfounder,IanMurdock,

envisaged the creation of a completely non-commercial product developed by

hundreds of volunteer developers.With skeptics far outnumbering optimists at

thetime,itseemeddestinedtodisintegrateandcollapse,buttherealitywasvery

different.Debiannotonlysurvived,itthrivedand,inlessthanadecade,itbecame

the largest Linux distribution and possibly the largest collaborative software

productevercreated!ThefollowingnumberscanillustratethesuccessofDebian

GNU/Linux.Over1,000volunteerdevelopersdevelopit,itssoftwarerepositories

containcloseto50,000binarypackages(compiledfor8processorarchitectures)

andisresponsibleforinspiringover120Debian-baseddistributionsandliveCDs.

These figures are unmatched by any other Linux-based operating system. The

actualdevelopmentofDebiantakesplace inthreemainbranches(or four ifone

includesthebleeding-edge“experimental”branch)ofincreasinglevelsofstability:

“unstable”(alsoknownas“sid”),“testing”and“stable.”However,thislengthyand

complexdevelopmentstylehassomedrawbacks:thestablereleasesofDebianare

not particularly up-to-date, and they age rapidly, especially since new stable

releases are only published once every 1 - 3 years. Users who prefer the latest

packagesandtechnologiesareforcedtousethepotentiallybuggyDebiantesting

distributions or unstable branches. The highly democratic structures of Debian

have led to controversial decisions and have led to infighting among the

developers. This has contributed to stagnation and reluctance to make radical

decisionsthatwouldtaketheprojectforward.

Pros: Very stable; remarkable quality control; includes over 30,000 software

packages; supports more processor architectures than any other Linux

distribution.

Cons:Conservative-duetoitssupportformanyprocessorarchitectures,newer

technologiesarenotalwaysincluded;slowreleasecycle(onestablereleaseevery1

-3years);discussionsondevelopermailing listsandblogscanbeunculturedat

times.

Mageia

Mageia

Mageiamaybe thenewestdistributiononthis list,but itsrootsgobackto

July1998whenGaëlDuval launchedMandrakeLinux.Atthetime, itwasjusta

branch of Red Hat Linux with KDE as the default desktop, better hardware

detection,andsomeuser-friendlyfeatures,butitgainedinstantpopularitydueto

positive reviews in the media. Mandrake was later turned into a commercial

enterprise and renamed toMandriva (to avoid some trademark-related hassles

andtocelebrateitsmergerwithBrazil’sConectiva)beforealmostgoingbankrupt

in2010.ARussianventurecapitalfirmeventuallysavedit,butthiscameatacost

when thenewmanagementdecided to layoffmostof the establishedMandriva

developersinthecompany’sParisheadquarters.Uponfindingthemselvesoutof

work, they decided to form Mageia, a community project that is a logical

continuationofMandrakeandMandriva,perhapsmoreso thanMandriva itself.

Mageiaisprimarilyadesktopdistribution.Itsbest-lovedfeaturesarecutting-edge

software, a superb system administration suite (Mageia Control Centre), the

ability to attract a large number of volunteer contributors, and extensive

internationalization support. It features one of the easiest, but more powerful

systeminstallersonitsinstallationDVD,whileitalsoreleasesasetofliveimages

withbothKDEorGNOMEdesktopsandcomprehensive languagesupport,with

theabilitytoinstallitontoaharddiskdirectlyfromthelivedesktopsession.The

distribution’s well-established package management features, with powerful

command-lineoptionsandagraphicalsoftwaremanagementmodule,alloweasy

access to thousands of software packages. The unique Mageia Control Center

continues to improvewith each release, offering apowerful tool for configuring

justaboutanyaspectoftheircomputerwithouteverreachingfortheterminal.

Pros:Beginner-friendly;excellentcentralconfigurationutility;verygoodout-of-

the-boxsupportfordozensoflanguages;installablelivemedia.

Cons:Lacks reputationandmindshare following its split fromMandriva, some

concernover thedevelopers’ ability tomaintain thedistribution long-termon a

volunteerbasis.

Fedora

AlthoughFedorawasformallyonlyunveiled inSeptember2004, itsoriginsdate

back to 1995when itwas launched by twoLinux visionaries—BobYoung and

MarcEwing—under thenameofRedHatLinux.The company’s first product,

RedHatLinux 1.0 “Mother’sDay,”was released the sameyearandwasquickly

followedbyseveralbug-fixupdates.In1997,RedHatintroduceditsrevolutionary

RPM package management system with dependency resolution and other

advanced features which greatly contributed to the distribution’s rapid rise in

popularityand itsovertakingofSlackwareLinuxas themostwidely-usedLinux

distribution in theworld. In later years, RedHat standardized on a regular, 6-

month release schedule. In2003, just after the release ofRedHatLinux9, the

company introducedsomeradicalchanges to itsproduct line-up. It retainedthe

Red Hat trademark for its commercial products, notably Red Hat Enterprise

Linux, and introduced Fedora Core (later renamed to Fedora), a Red Hat

sponsored, but community-oriented distribution designed for the “Linux

hobbyist”.Aftertheinitialcriticismofthechanges,theLinuxcommunityaccepted

the“new”distributionasthelogicalcontinuationofRedHatLinux.Afewquality

releaseswasall it took forFedora toregain its formerstatusasoneof thebest-

lovedoperatingsystemsonthemarket.Atthesametime,RedHatquicklybecame

thebiggestandmostprofitableLinuxcompany in theworld,withan innovative

productline-up,excellentcustomersupport,andotherpopularinitiatives,suchas

itsRedHatCertifiedEngineer (RHCE)certificationprogram.AlthoughFedora’s

directionisstilllargelycontrolledbyRedHat,Inc.andtheproductissometimes

seen—rightlyorwrongly—asatestbedforRedHatEnterpriseLinux,thereisno

denyingthatFedoraisoneofthemostinnovativedistributionsavailabletoday.Its

contributions to the Linux kernel, glibc and GCC are well-known and its more

recent integration of SELinux functionality, virtualization technologies, system

servicemanager, cutting-edge journaled file systems, and other enterprise-level

features aremuch appreciatedby the company’s customers.On anegative side,

Fedorastill lacksacleardesktop-orientedstrategy thatwouldmake theproduct

easiertouseforthosebeyondthe“Linuxhobbyist”target.

Pros: Highly innovative; outstanding security features; a large number of

supportedpackages;strictadherencetothefreesoftwarephilosophy;availability

ofliveCDsfeaturingmanypopulardesktopenvironments.

Cons: Fedora’s priorities tend to lean towards enterprise features, rather than

desktopusability;somebleedingedgefeatures,suchasearlyswitchtoKDE4and

GNOME3,occasionallyalienatedesktopusers.

openSUSE

The beginnings of openSUSE date back to 1992 when four German Linux

enthusiasts — Roland Dyroff, Thomas Fehr, Hubert Mantel and Burchard

Steinbild—launchedtheprojectunderthenameofSUSE(SoftwareundSystem

Entwicklung)Linux.Intheearlydays,theyoungcompanysoldsetsoffloppydisks

containingaGermaneditionofSlackwareLinux,but itwasn’t longbeforeSUSE

Linuxbecameanindependentdistributionwiththelaunchofversion4.2inMay

1996. In the following years, the developers adopted the RPM package

management format and introduced YaST, an easy-to-use graphical system

administrationtool.Frequentreleases,excellentprinteddocumentation,andeasy

availabilityofSUSELinuxinstoresacrossEuropeandNorthAmericaresultedin

growingpopularityofthedistribution.SUSELinuxwasacquiredbyNovell,Inc.in

late2003,and then fell into thehandsofAttachmate inNovember2010.Major

changes in the development, licensing and availability of SUSE Linux followed

shortly after the first acquisition - YaST was released under the GPL, the ISO

images were freely distributed from public download servers, and, most

significantly, the development of the distribution was opened to public

participationforthefirsttime.SincethelaunchoftheopenSUSEprojectandthe

releaseofversion10.0inOctober2005,thedistributionbecamecompletelyfree

in both senses of theword. The openSUSE code has become a base system for

Novell’scommercialproducts, firstnamedasNovellLinux,but laterrenamedto

SUSE Linux Enterprise Desktop and SUSE Linux Enterprise Server. Today,

openSUSE has a large following of satisfied users. The principal reason for

openSUSEreceivinghighmarksfromitsusersarepleasantandpolisheddesktop

environments (KDE and GNOME), an excellent system administration utility

(YaST), and, for those who buy the boxed edition, some of the best-printed

documentation available. However, the infamous deal between Novell and

Microsoft, which apparently concedes to Microsoft’s argument that it has

intellectual property rights over Linux, has resulted in condemnation by many

Linux personalities and has prompted some users to switch distributions.

AlthoughNovellhasdownplayedthedeal,andMicrosofthasyet toexerciseany

rights, this issue remains a thorn in the side of the otherwise very community-

friendlyLinuxCompany.

Pros: Comprehensive and intuitive configuration tool; large repository of

softwarepackages,excellentwebsiteinfrastructure,andprinteddocumentation.

Cons: Novell’s patent deal with Microsoft in November 2006 seemingly

legitimizedMicrosoft’sintellectualpropertyclaimsoverLinux;itsresource-heavy

desktopset-upandgraphicalutilitiesaresometimesseenas“bloatedandslow.”

ArchLinux

The KISS (Keep It Simple, Stupid) philosophy of Arch Linux was devised

aroundtheyear2002byJuddVinet,aCanadiancomputersciencegraduatewho

launched thedistribution thesameyear.Forseveralyears it livedasamarginal

project designed for intermediate and advanced Linux users and only shot to

stardom when it began promoting itself as a “rolling-release” distribution that

onlyneedstobeinstalledonceandisthenkeptup-to-datethankstoitspowerful

packagemanagerandanalwaysfreshsoftwarerepository.Asaresult,ArchLinux

“releases”arefewandfarbetweenandarenowlimitedtoabasicinstallationDVD

thatisissuedonlywhenconsiderablechangesinthebasesystemwarrantafresh

install. Besides featuring the much-loved “rolling-release” update mechanism,

Arch Linux is also renowned for its fast and powerful package manager called

“Pacman”,theabilitytoinstallsoftwarepackagesfromsourcecode,easycreation

of binary packages thanks to its AUR infrastructure, and the ever increasing

software repository of well-tested packages. Its highly regarded documentation,

complementedbytheexcellentArchLinuxHandbookmakesitpossibleforeven

less experienced Linux users to install and customize the distribution. The

powerful tools available at the user’s disposalmean that the distro is infinitely

customizabletotheminutestdetailandthatnotwoinstallationscanpossiblybe

the same. On the negative side, any rolling-release update mechanism has its

dangers:ahumanmistakecancreepin,a libraryordependencygoesmissing,a

newversionof anapplicationalready in the repositoryhas a yet-to-be-reported

criticalbug…Itisnotunheardoftoendupwithanunbootablesystemfollowinga

Pacmanupgrade.Assuch,ArchLinuxisthekindofdistributionthatrequiresits

users to be alert and to have enough knowledge to fix any such problems. In

addition,theinfrequentinstallmediareleasesmeanthatitissometimesnolonger

possible tousetheoldmediato install thedistributiondueto importantsystem

changesorlackofhardwaresupportintheolderLinuxkernel.

Pros:Excellentsoftwaremanagementinfrastructure;unparalleledcustomization

andtweakingoptions;superbonlinedocumentation.

Cons:Occasionalinstabilityandriskofbreakdown.

CentOS

Launched in late 2003, CentOS is a community project with the goals of

rebuilding the source code for Red Hat Enterprise Linux (RHEL) into an

installable Linux distribution and to provide timely security updates for all

included software packages. To put inmore bluntly, CentOS is anRHEL clone.

Theonlytechnicaldifferencebetweenthetwodistributionsisbranding-CentOS

replaced all Red Hat trademarks and logos with its own. Nevertheless, the

relations between Red Hat and CentOS remain amicable, and many CentOS

developers are in active contact with, or even employed directly by, Red Hat.

CentOSisoftenseenasareliableserverdistribution.Itcomeswiththesamewell-

testedandstableLinuxkernelandsetofsoftwarepackagesthatformthebasisof

itsparent,RedHatEnterpriseLinux.Despitebeingacommunityprojectrunby

volunteers, it has gained a reputation for being a solid, free alternative tomore

costlyserverproductsonthemarket,especiallyamongexperiencedLinuxsystem

administrators. CentOS is also suitable as an enterprise desktop solution,

specifically where stability, reliability and long-term support are preferred over

latestsoftwareandnewfeatures,likeRHEL,CentOSincludesapproximately7-10

years of security updates.Despite its advantages,CentOSmightnot be thebest

solution inalldeploymentscenarios.Thoseuserswhopreferadistributionwith

thelatestLinuxtechnologiesandnewestsoftwarepackagesshouldlookelsewhere.

MajorCentOSversions,whichfollowRHELversioning,areonlyreleasedevery2-

3years,while“point”releases(e.g.5.1)tendtoarrivein6-9monthintervals.The

point releases do not usually contain any major features (although they do

sometimes include support for more recent hardware), and only a handful of

softwarepackagesmaygetupdatedtonewerversions.TheLinuxkernel,thebase

system, and most application versions remain unchanged, but occasionally a

newerversionofanimportantsoftwarepackage(e.g.LibreOfficeorFirefox)may

be provided on an experimental basis. As a side project, CentOS also builds

updatedpackagesfortheusersofitsdistributions,buttherepositoriescontaining

themarenotenabledbydefaultastheymaybreakupstreamcompatibility.

Pros:Extremelywelltested,stableandreliable;freetodownloadanduse;comes

with7+yearsoffreesecurityupdates.

Cons:LackslatestLinuxtechnologies;occasionallytheprojectfailstoliveupits.

PCLinuxOS

Bill “Texstar” Reynolds first introduced PCLinuxOS in 2003. Prior to

creatinghisowndistribution,Texstarwasalreadyawell-knowndeveloperinthe

MandrakeLinux community of users for building up-to-dateRPMpackages for

the popular distribution and providing them as a free download. In 2003, he

decidedtobuildanewdistribution, initiallybasedonMandrakeLinux,butwith

several significant usability improvements. The goals? It should be beginner-

friendly, have out-of-the box support for proprietary kernel modules, browser

plug-in andmedia codecs, and should function as a live CDwith a simple and

intuitive graphical installer. Several years and development releases later,

PCLinuxOS is rapidly approaching its intended state. In terms of usability, the

projectoffersout-of-the-boxsupport formanytechnologiesthatmostWindows-

to-Linuxmigrants would expect from a new operating system.On the software

sideofthings,PCLinuxOSisaKDE-orienteddistribution,withacustomizedand

always up-to-date version of the popular desktop environment. Its growing

softwarerepositorycontainsotherdesktopsandoffersagreatvarietyofdesktop

packages for many common tasks. For system configuration, PCLinuxOS has

retainedmuchofMandriva’sexcellentControlCentrebuthasreplaceditspackage

management system with APT and Synaptic, a graphical package management

front-end.Onthenegativeside,PCLinuxOSlacksanyformofroadmaporrelease

goals.Despitegrowingcommunityinvolvement,mostdevelopmentanddecision-

making remains in the hands of Texstar, who tends to be conservative when

judging the stability of a release. As a result, the development process of

PCLinuxOS is often arduous. For example, despite frequent calls for a 64-bit

edition, the developers held off producing a 64-bit build until fairly recently.

Furthermore,theprojectdoesnotprovideanysecurityadvisories,relyinginstead

ontheusers’willingnesstokeeptheirsystemup-to-dateviatheincludedpackage

managementtools.

Pros:Out-of-the-boxsupport forgraphicsdrivers,browserplug-ins,andmedia

codecs;rolling-releaseupdatemechanism;up-to-datesoftware.

Cons: no out-of-the-box support for non-English languages; lacks release

planningandsecurityadvisories.

SlackwareLinux

Slackware Linux, created by Patrick Volkerding in 1992, is the oldest

survivingLinux distribution. Separated from the now-discontinued SLSproject,

Slackware 1.0 came on 24 floppy disks and was built on top of Linux kernel

version 0.99pl11-alpha. It quickly became themost popular Linux distribution;

with some estimates putting its market share as much as 80% of all Linux

installationsin1995.ItspopularitydecreaseddramaticallywiththearrivalofRed

Hat Linux and other, user-friendlier distributions, but Slackware Linux still

remains a much-appreciated operating system among the more technically

oriented system administrators and desktop users. Slackware Linux is a highly

technical, clean distribution, with only a limited number of custom utilities. It

usesasimple,text-basedsysteminstallerandacomparativelyprimitivepackage

management system that does not resolve software dependencies. As a result,

Slackwareisconsideredoneofthecleanestandleastbuggydistributionsavailable

today-thelackofSlackware-specificenhancementsreducesthelikelihoodofnew

bugs being introduced into the system. The entire system configuration is

completedbyediting text files.There isasaying in theLinuxcommunity that if

youlearnRedHat,you’llknowRedHat,but ifyoulearnSlackware,you’llknow

Linux.This isparticularly true todaywhenmanyotherLinuxdistributionskeep

developingheavilycustomizedproductstomeettheneedsoflesstechnicalLinux

users.While thisphilosophyof simplicityhas its fans, the fact is that in today’s

world,SlackwareLinuxisincreasinglybecominga“coresystem”uponwhichnew,

customsolutionsarebuilt,ratherthanacompletedistributionwithawidevariety

ofsupportedsoftware.Theonlyexceptionistheservermarket,whereSlackware

remainspopular,thoughevenhere,thedistribution’scomplexupgradeprocedure

and lack of officially supported automated tools for security updates make it

increasingly uncompetitive. Slackware’s conservative attitude towards the

system’sbasecomponentsmeans that it requiresmuchmanualpost-installation

workbeforeitcanbeturnedintoamoderndesktopsystem.

Pros: Consideredhighly stable, clean and largely bug-free, strong adherence to

UNIXprinciples.

Cons:Limitednumberofofficiallysupportedapplications;conservativeinterms

ofbasepackageselection;complexupgradeprocedure.

FreeBSD

FreeBSD,an indirectdescendantofAT&TUNIXvia theBerkeleySoftware

Distribution(BSD),hasalongandturbulenthistorydatingbackto1993.Unlike

Linuxdistributions,whicharedefinedasintegratedsoftwaresolutionsconsisting

of theLinuxkernelandthousandsofsoftwareapplications,FreeBSDisa tightly

integratedoperatingsystembuiltfromaBSDkernelandtheso-called“userland”

(thereforeusableevenwithoutextraapplications).Thisdistinctionis largely lost

onceinstalledontheaveragecomputersystem-likemanyLinuxdistributions,a

largecollectionofeasilyinstalled,(mostly)opensourceapplicationsareavailable

for extending the FreeBSD core, but these are usually provided by third-party

contributors and aren’t strictly part of FreeBSD. FreeBSD has developed a

reputation for being a fast, high-performance and extremely stable operating

system, especially suitable for web serving and similar tasks. Many large web

searchenginesandorganizationswithmission-criticalcomputinginfrastructures

havedeployedandusedFreeBSDontheircomputersystemsforyears.Compared

to Linux, FreeBSD is distributed under a much less restrictive license, which

allows virtually unrestricted use and modification of the source code for any

purpose.EvenApple’sMacOSX isknown tohavebeenderived fromFreeBSD.

Besidesthecoreoperatingsystem,theprojectalsoprovidesover24,000software

applications in binary and source code forms for easy installation on top of the

core FreeBSD. While FreeBSD can certainly be used as a desktop operating

system, although it doesnot comparewell tomorepopularLinuxdistributions.

The text-mode system installer offers little in terms of hardware detection or

system configuration, leaving much of the dirty work to the user in a post-

installationsetup. In termsof support formodernhardware,FreeBSDgenerally

lags behind Linux, especially in supporting cutting-edge desktop and laptop

gadgets,suchaswirelessnetworkcardsordigitalcameras.Thoseusersseekingto

exploit the speed and stability of FreeBSD on a desktop or workstation should

consider one of the available desktop FreeBSD projects, rather than FreeBSD

itself.

Pros: Fast and stable; availability of over 24,000 software applications (or

“ports”)forinstallation;verygooddocumentation.

Cons: Tends to lag behind Linux in terms of support for new and exotic

hardware, limited availability of commercial applications; lacks graphical

configurationtools.

ChapterThree:LICENSING

CodeiscontributedtotheLinuxkernelunderanumberof licenses,butall

codemustbecompatiblewithversion2oftheGNU(GPLv2),whichisthelicense

coveringthekerneldistributionasawhole.Inpractice, thatmeansthatallcode

contributions are covered either by GPLv2 (with, optionally, language allowing

distributionunderlaterversionsoftheGPL)orthethree-clauseBSDlicense.Any

contributions,whicharenotcoveredbyacompatiblelicense,willnotbeaccepted

into the kernel. Copyright assignments are not required (or requested) for code

contributed to the kernel. All code merged into the mainline kernel retains its

original ownership; as a result, the kernel now has thousands of owners. One

implicationofthisownershipstructureisthatanyattempttochangethelicensing

ofthekernelisdoomedtoalmostcertainfailure.Therearefewpracticalscenarios

where the agreement of all copyright holders could be obtained (or their code

removed from the kernel). Therefore, there is no prospect of a migration to

version 3 of the GPL in the foreseeable future. It is imperative that all code

contributedtothekernelbelegitimatelyfreesoftware.Forthatreason,codefrom

anonymous(orpseudonymous)contributorswillnotbeaccepted.

Allcontributorsarerequiredto“signoff”ontheircode,statingthatthecode

canbedistributedwiththekernelundertheGPL.Codewhichitsowner,hasnot

licensedas free software, orwhich risks creating copyright-relatedproblems for

the kernel (such as codewhich derives from reverse-engineering efforts lacking

proper safeguards) cannot be contributed. Questions about copyright-related

issues are common on Linux development mailing lists. Such questions will

normally receive no shortage of answers, but one should bear inmind that the

peopleansweringthosequestionsarenotlawyersandcannotprovidelegaladvice.

IfyouhavelegalquestionsrelatingtoLinuxsourcecode,thereisnosubstitutefor

talkingwithalawyerwhounderstandsthisfield.Relyingonanswersobtainedon

technicalmailinglistsisariskyaffair.

COMMUNITY

Linuxcommunitiescomeintwobasicforms:developeranduser.

OneofthemostcompellingfeaturesofLinuxisthatitisaccessibletodevelopers;

anybodywiththerequisiteskillscanimproveLinuxandinfluencethedirectionof

itsdevelopment.Proprietaryproductscannotofferthiskindofopenness,whichis

acharacteristicofthefreesoftwareprocess.Developercommunitiescanvolunteer

to maintain and support whole distributions, such as the Debian or Gentoo

Projects. Novell and Red Hat also support community-driven versions of their

products, openSUSE and Fedora, respectively. The improvements to these

communitydistrosarethenincorporatedintothecommercialserveranddesktop

products. The Linux kernel itself is primarily supported by its developer

community and is one of the largest and most active free software projects in

existence.Atypicalthree-monthkerneldevelopmentcyclecaninvolveover1000

developersworkingformorethan100differentcompanies(orfornocompanyat

all).

WiththegrowthofLinuxhascomeanincreaseinthenumberofdevelopers

(and companies) wishing to participate in its development. Hardware vendors

want to ensure that Linux supports their products well, making their products

attractive to Linux users. Embedded systems vendors, who use Linux as a

componentinanintegratedproduct,wantLinuxtobeascapableandwellsuited

tothetaskathandaspossible.Distributorsandothersoftwarevendorswhobase

theirproductsonLinuxhaveaclearinterestinthecapabilities,performance,and

reliability of the Linux kernel. Other developer communities focus on different

applications and environments that run on Linux, such as Firefox, OpenOffice,

GNOME, and KDE. End users, too, can make valuable contributions to the

development of Linux. With online communities such as Linux.com,

LinuxQuestions, and themany and varied communities hosted by distributions

and applications, the Linux user base is often a very vocal, but usually positive

advocateandguidefortheLinuxoperatingsystem.TheLinuxcommunityisnot

justaonlinepresence.LocalgroupsknownasLinuxUsersGroups(LUGs)often

meet to discuss issues regarding theLinux operating system, andprovide other

localuserswithfreedemonstrations,training,technicalsupport,andinstall-fests.

DEVELOPMENT

Linux is an operating system comprised of many different development

languages.Avery largepercentageof thedistributions’ code iswritten in either

theC (52.86%)orC++ (25.56%) languages.All of the restof the code falls into

single-digit percentages, with Java, Perl, and Lisp rounding out the top 5

languages.TheLinuxkernel itselfhasanevenmoredominantCpresence,with

over 95 percent of the kernel’s code written in that language. However, other

languagesmakeupthekernelaswell,makingitmoreheterogeneousthanother

operating systems. The kernel community has evolved its own distinct way of

operating which allows it to function smoothly (and produce a high-quality

product) inanenvironmentwherethousandsof linesofcodearebeingchanged

everyday.ThismeanstheLinuxkerneldevelopmentprocessdiffersgreatlyfrom

proprietarydevelopmentmethods.

The kernel’s development process may come across as strange and

intimidating tonewdevelopers,but therearegoodreasonsandsolidexperience

behindit.Adeveloperwhodoesnotunderstandthekernelcommunity’sways(or,

worse,who tries to flout or circumvent them)will becomevery frustrated .The

developmentcommunity,whilebeinghelpfultothosewhoaretryingtolearn,has

little time for those who will not listen or who does not care about the

developmentprocess.WhilemanyLinuxdevelopers,stillusetext-basedtoolssuch

asEmacsorVimtodeveloptheircode,Eclipse,Anjuta,andNetbeansallprovide

morerobustintegrateddevelopmentenvironments.

ChapterFour:INSTALLINGDEBIAN8

WhatisDebian

Debianisanall-volunteerorganizationdedicatedtodevelopingfreesoftware

and promoting the ideals of the Free Software community. The Debian Project

began in 1993, when Ian Murdock issued an open invitation to software

developers tocontribute toacompleteandcoherentsoftwaredistributionbased

on the relatively new Linux kernel. That relatively small band of dedicated

enthusiasts,originallyfundedbytheFreeSoftwareFoundationandinfluencedby

theGNU philosophy, has grown over the years into an organization of around

1026DebianDevelopers.

DebianGNU/Linux

The combination of Debian’s philosophy, methodology, GNU tools, the

Linux kernel, and other important free software, form a unique software

distribution called Debian GNU/Linux. This distribution is made up of a large

number of software packages. Each package in the distribution contains

executables, scripts, documentation, and configuration information, and has

amaintainer who is primarily responsible for keeping the package up-to-date,

tracking bug reports, and communicating with the upstream author(s) of the

packagedsoftware.Theextremelylargeuserbase,combinedwithabugtracking

systemensures thatproblemsare foundand fixedquickly.Debian’sattention to

detail allows them to produce a high-quality, stable, and scalable distribution.

Installations can be easily configured to servemany roles, from stripped-down

firewallstoscientificdesktopworkstationstohigh-endnetworkservers.Debianis

especiallypopularamongstadvancedusersbecauseofitstechnicalexcellenceand

its deep commitment to the needs and expectations of the Linux community.

Debianalso introducedmany features toLinux that arenowcommonplace.For

example, Debian was the first Linux distribution to include a package

managementsystemfortheeasyinstallationandremovalofsoftware.Itwasalso

the first Linux distribution that could be upgraded without requiring re-

installation. Debian continues to be a leader in Linux development. Its

developmentprocessisanexampleofjusthowwelltheOpenSourcedevelopment

modelcanwork—evenforverycomplextaskssuchasbuildingandmaintaininga

completeoperatingsystem.

ThefeaturethatmostdistinguishesDebianfromotherLinuxdistributionsis

itspackagemanagementsystem.ThesetoolsgivestheadministratorofaDebian

systemcompletecontroloverthepackagesinstalled,includingtheabilitytoinstall

asinglepackageorautomaticallyupdate theentireoperatingsystem.Individual

packagescanalsobeprotectedfrombeingupdated.Youcaneventellthepackage

management system about software you have compiled yourself and what

dependenciesitfulfills.Toprotectyoursystemagainst“Trojanhorses”andother

malevolent software,Debian’s servers verify that uploaded packages come from

registeredDebianmaintainers.Debianpackagersalsotakegreatcaretoconfigure

theirpackagesinasecuremanner.Whensecurityproblemsinshippedpackages

doappear,fixesareusuallyavailableveryquickly.

InstallingDebian8asaVirtualMachine.

First,youwillneedtodownloadandinstallVirtualBox,theOraclesoftware

thatallowsyoutorunanyOSon…anyotherOS,asavirtualenvironment.This

procedureisalotsaferthanadualboot:noneedtofoolaroundwithbootsector

ordiskpartitions,allisvirtuallycreated.ThecounterpartisthatthetwoOS’s

shareyourcomputerresources.Toavoidanyperformanceissue,wewillchoosea

lightweightbutefficientdesktopenvironment.ThisbookwillusetheXFCE

Debianedition,thatyoucandownloadusingthislinkbelow:

https://www.debian.org/CD/torrent-cd/

XFCEisnotthenewestdesktopenvironment,howeveritisamongthemost

powerful, lightweight, and customizable,while being easy to usewith its classic

desktopmetaphor.ImagineanimprovedversionofWindowsXP,agreatwayto

getstartedwithLinux.

CreateyourVirtualSystem

Once installed, startVirtualBox and follow these steps.Wewill begin the

VMconfiguration:

New>Name,Type(debian),Version64

General>Advanced>ActivateclipboardandDrag’n’drop

System>checkmemory,deactivateFloppy,checkthenbofCPU(2)

Display>maxvideomemory,enable3Dacceleration

Storage>selectyourDebianISOunder“ControllerIDE”

SharedFolders>choosewhichfoldertosharebetweenthesystems.We

willgetbacktothisfunctionlater.

Wearenowreadytorunthedistributioninstallation.

RunDebianinstaller

Selectyourvirtualmachineandclickthe‘Start’icon.TheDebiangraphicinstallerisstraightforward:justfollowthesteps,whenaskedenterarootpassword;createyouruser(name,username,andpassword).Onceyougettothepartitioning,select‘Guided,useentiredisk,allinonepartition.’Ifyouwishtomodifythesizeoftheswappartition,youmayselectthemanualpartitioning,orproceedlaterwithParted,thepartitioningutilitytool.

Proxy,part#1:selectyournetworkmirror.Ifyouneedtoconfigureaproxy,usethefollowingsyntaxintherequiredfield:http://user:pass@host:port/.

Proceedtotheinstallation.Onceithasfinished,youwillhavetochoosewheretoinstallGrub(thebootloaderpackage):becausethisisaVMinstall,choose/dev/sda(ata-VBOX_HARDDISK).Thiswouldbethetrickypartifyouwereinstallingonadual-boot,systemsoenjoythecomfortofaVM!

NowreboottheVM.

FirstBootandUpdates

AtstartuptheGrubmenuisdisplayed,stickwiththedefaultentryandwaitforyoursystemtoinitialize.AtXFCEfirststart,youwillbeaskedtochoosebetweentwopanelsetups,selectthedefaultconfig.

Check your time configuration. If incorrect, launch as root a dpkg-

reconfiguretzdataandselectyourcountry.

Proxy, part #2 (if needed): during install, you entered your proxy addressforaptconnection(repositoriesconnection).Itishasbeenwritteninsidethefile/etc/apt/apt.conf, and can bemodified any time. I usenanoas command linetexteditor,changeatwill.

Nowaddtheproxysettingfortheentiresystem:

Congratulations, youarenowa confirmedLinuxuser!Nowwecanupdate

andinstallsomeuseful tools, thenwewillmodifythedefaultUI.Tousethefull

capacity of your VM you need to install a complementary VirtualBox extension

calledGuestAdditions.Todoso,somedependenciesarerequired.

Checkyoursources,removetheCDentries,addthecontribandnon-freerepos:

Updateyoursystem:

InstalltheGuestAdditionsrequirements

InserttheGuestAdditionsCDimage(Host+D),gototherootofthemounteddriveandexecutethe

program:

CustomizingyourSystem…togetsomethingthatlooksalittlemoremodern.

Terminal

TheterminalisoneofthemostusefultoolsonaLinuxsystem.Spendsometime

making it pleasant to look at: enable your prompt color ink .bashrc, add your

aliases,andenablecolorsandautocompletioninrootbash.

uncommentthe“force_colored_prompt=yes”line

[root]$nano.bashrc

#setafancyredprompt

PS1=’${debian_chroot:+($debian_chroot)}\[33[01;31m\]\u@\h\[33[00m\]:\[33[01;34m\]\w\[33[00m\]\$‘

#enableauto-completion

if

[-f/etc/bash_completion]&&!shopt-oqposix;

then./etc/bash_completion

fi

Fonts

Enablefonthinting intheAppearancePanel togetthebest fontrenderingfor

your system. Settings > Appearance > Fonts > Enable anti-aliasing + Hinting

Slight+Sub-pixelorderRGB.ThisshouldbeenoughinJessie,noneedtocreatea

fonts.conffileorinstalltheInfinalityengine.

IThemesandicons

GTK Themes, windows decoration and iconsets are the most important

elementstocustomizingyourdesktop.Startwithinstallingsomecomplementary

gtkenginesthatareneededbysomethemes:

[root]$apt-getinstallgtk2-engines-murrinegtk2-engines-pixbufdmz-cursor-theme

Installsudo

Debiandoesn’tcomewithsudooutofthebox,thisisahandylittletoolfor

temporarilygivingyourootaccess.

Replace USERNAME with your username. The NOPASSWD flag removes the

requirementtoenterapasswordeverytimeyouusesudo.Thisisnotagoodidea

onaproductionserver!

Rebootyourmachinetomakethechangestakeeffect:$reboot

Fromnowonalloperationsthatrequirerootshouldberunwiththesudoprefix,

withouthavingtoenterthepasswordeachtime.

Setupthenetwork

LogintoyournewVMusingtheusernameandpasswordyouchoseduring

installation.We’regoingtoaddanetworkconnectiontoyourVMthatwillallow

youtooeasilySSHintotheserver.

HitCTRL+X,thenYandENTERtosavechanges.ShutdowntheVM.

AtthemainVirtualBoxscreen,hittheSettingsbutton.ThenselectNetworkfromthelist on the left, chooseAdapter 2 from the tabs, check ‘Enable Network Adapter’ andchoose‘Host-onlyAdapter’fromthedropdown,thenclickOK.

WhatwehavedoneissetupyourVMtouseastaticIPaddress.Thisisagoodidea

becauseitallowsustoalwaysaccessourVMusingasingleIPaddress/hostname

withouthavingtolookitupeachtimeweboot.

Bydefault,VirtualBoxutilizes the 192.168.56.1 address in yournetwork, and itassignsIPaddressesinthe192.168.56.1xxrangetoallyourVMs.

Byediting/etc/network/interfaceswetoldtheOSthatitshouldexpectanetworkresourcetobeavailableatthataddress.

Setupyourhostsfile

Nowyourserverisconfiguredletsaddthehostnametoyourhostsfile!

Simplyaddthefollowingentry intoyourhostsfile.Thisshouldbedoneonyour

hostmachine–beitWindowsorMacOSXorLinux,nottheVMitself.

KeepinmindthatforeverydomainyousetuponyourVM,youwillneedtoaddit

toyourhostsfile.

LoginviaSSH!

NowthatyouhavesetupthenetworkadapterinVirtualBox,andaddedthe

correct settings to theVM interfaces file, you’re ready toactuallySSH intoyour

server andbegin installing everything!Youmaybewonderingwhy youneed to

SSHandnotsimplyuse theVMwindow.ThereasonIdo it thisway is that the

serverdoesnotsupportcopy/paste!There’salotoftypingaheadandhavingthe

abilitytosimplycopy/pasteintoyourterminalisgoingtospeedthingsupquitea

bit!

ForSSHonWindows,IuseKiTTy.It’sanSSHclientthataddssomeniftyfeatures

to PuTTY. There is also Poderosa. For Mac/Linux just use the terminal! Since

you’vealreadyaddedthecorrectlinestoyourhostsfile,youcansettheaddressto

connect to as debian-vm (or whatever you chose during setup). Make sure to

actually start the VM from VirtualBox before attempting to login. Just start it,

thereisnoneedtologinfromtheVirtualBoxserverwindow.

Installingthebasics

Firstthingsfirst,we’regoingtoinstallthebasicnecessities,likemake,curl,

wget,aswellastheApacheServer,Mercurial,GitandSubversion:

EditthenewApache2configfile,$sudonano/etc/apache2/httpd.confandadd

YounowhavetheApacheserverupandrunning!Justpointyourbrowserto

http://debian-vmandbeholdthemagic.

NowletsenableApache’sModRewritemodule:

InstallingMySQL

WewillbeinstallingMySQL5.1fromrepo,asthisistheeasiestwayandworksfairlywell.

On the screens asking for aMySQL password, leave it blank and hit Enter.Sincethisisonlyforalocalserverthereisnopointinsettingupapassword.DoNOTuseablankpasswordinproductionenvironments.

SettingupMySQL

WeneedtoupdatetheIPaddressthatMySQLwilllistentoforconnectionsby

editingthemy.cnffile.

$sudonano/etc/mysql/my.cnf

Doasearchforbind-address(CTRL+W)andchangethesettingto:

Nowlet’sgrantrootMySQLuserallpermissions:

ChapterFive:INSTALLINGCENTOS7

This is a community-supported distribution derived from sources freely

providedtothepublicbyRedHatforRedHatEnterpriseLinux(RHEL).Assuch,

CentOS Linux aims to be functionally and compatible with RHEL. The CentOS

Project mainly changes packages to remove upstream vendor branding and

artwork. CentOS Linux is free and free to redistribute. Each CentOS version is

maintainedforupto10years(bymeansofsecurityupdates—thedurationofthe

support interval by Red Hat has varied over time with respect to Sources

released).AnewCentOSversionisreleasedapproximatelyevery2yearsandeach

CentOSversionisperiodicallyupdated(roughlyevery6months)tosupportnewer

hardware. This results in a secure, low-maintenance, reliable, predictable and

reproducibleLinuxenvironment.

InstallationofCenOS7

Finally,themuch-awaitedCentOS7isout.CentOS(CommunityEnterprise

OperatingSystem)areforkedfromRedHatLinux,aLinuxDistrofinetunedfor

servers.YouwilllearnhowtoinstallCentos7inafeweasysteps.

Step1:DownloadtheISOImage

TogetacopyofCentOS7downloadfromthelinkbelow:

http://mirror.centos.org/centos/7/

CentOS7 isonlyavailable for64-bitplatforms; currently there isno32-bit ISO

image.Thisisprimarilyduetothefactthatmostproductionserversare64-bit.

Step2:MakeabootableDrive

AfteryoudownloadtheISOimage,makeabootableUSBdriveusingUnetbootin.

Alternatively, you can burn a DVD using Brasero or your favorite CD/DVD

burningsoftware.

Step3:BeginInstallation

Tobegininstallation,clickontheInstalltoHardDriveicononthedesktop.

Step4:SelectLanguageandKeyboard

Selectyourpreferredlanguage.

Step5:ChangetheInstallationDestination

By default, the Anaconda installer will choose automatic partitioning foryour hard disk. Click on the INSTALLATION DESTINATION icon to change to custompartitioning.

Select theharddrivewhere youwant to installCentOS7 andunderOther StorageOptions,choose‘Iwillconfigurepartitioning’thenclickDone.

Step6:SelectthePartitioningScheme

Next, select the partitioning scheme to use for the mountpoints. In this case,chooseStandardPartition.

Step7:CreateaSwapSpace

You can create a swap space in one of the partitions and set the desiredcapacity,whichisdependentonhowmuchRAM,thesystemhas.ChoosetheFileSystem for swap spaceas swap, and select theReformat option.Youcanalsonameyour swap space to whatever name you like but a name like swap is moredescriptive.

Step8:CreateaMountpoint

The next step is to create themountpointwhere the root partitionwill be

installed.Dependingonyourrequirements,youmightneedtoputtheboot,home

androotpartitionsondifferentmountpoints.Inthisinstance,weshallonlycreate

onemountpoint/.

Next,settheLabelandDesiredCapacitytowhateveryouwish.Aruleofthumbistousedescriptive names for the label especially if the computer is to bemanaged bydifferent system administrators. Choose the file system as ext4 and select theReformatoption.

Step9:AcceptChanges

After Steps 7 and 8 have successfully completed click on Done button. Apromptwindowwillappearwithasummaryofthechangesthatwilltakeplace.IfyouaresatisfiedwiththemclickAcceptChanges.

Step10:SetDateandTime

Click on theClock icon under the localizationmenu and select your time zonefromthemapoftheworld,thenclickDone.

Step11:BeginInstallation

ClickontheBeginInstallationbutton.

Installationwill begin immediately and as it proceeds youwill need to set up auseraccountaswellastherootpassword.

Set

Step12:SetUpRootPassword

ClickontheROOTPASSWORDoptionandenterapasswordandconfirmationofthesamethenclickDone.

Step13:CreateaUserAccount

Thenextstep is tocreateauseraccount.Enter thedetailsand if this isan

administrator account, check Make this user administrator and Require apasswordtousethisaccountforsecuritypurposes.

Step14:CompleteInstallation

Theinstallershouldfinishinstallingthesoftwareandbootloader.

Hopefully,oncetheinstalliscompleteyouwillgetasuccessmessage,afterwhich

you can click Quit. Now logout from the live system and login to your newinstallation.Finally,onceyoulogintoyourCentOS7accepttheEULAagreement

andenjoy!

ChangeandSetHostnameCommand

OnaCentOSLinux7server,youcanuseanyoneofthefollowingtoolstomanage

hostnames:

hostnamectl:Controlthesystemhostname.Thisistherecommended

method.

nmtui:Controlthesystemhostnameusingtextuserinterface(TUI).

nmcli:ControlthesystemhostnameusingCLIpartofNetworkManager.

Method#1:hostnamectl

Letusseehowtousethehostnamectlcommand.

HowdoIseethehostnames?

Sampleoutputs:Statichostname:server1.cyberciti.biz

Prettyhostname:SenatorPadméAmidala’sLaptop

Transienthostname:r2-d2

Iconname:computer

Chassis:n/a

MachineID:b5470b10ccfd49ed8e4a3b0e953a53c3

BootID:f79de79e2dac4670bddfe528e826b61f

Virtualization:oracle

OperatingSystem:CentOSLinux7(Core)

CPEOSName:cpe:/o:centos:centos:7

Kernel:Linux3.10.0-229.1.2.el7.x86_64

Architecture:x86_64

HowdoIdeleteaparticularhostname?

Thesyntaxis:#hostnamectlset-hostname””

#hostnamectlset-hostname””—static

#hostnamectlset-hostname””–pretty

HowdoIchangehostnameremotely?

Useanyofthefollowingsyntax:#sshroot@server-ip-herehostnamectlset-hostnameserver1

ORsetserver1ashostnameonaremoteservercalled192.168.1.42usingssh:#hostnamectlset-hostnameserver1-Hroot@192.168.1.42

Method#2:nmtui

Youcansethostnameusingthenmtuicommand,whichhastextuserinterfacefornewusers:#nmtui

Sampleoutputs:

UsetheDownarrowkey>selectthe‘Setsystemhostname’menuoption>Click

theOKbutton:

Youwillseetheconfirmationboxasfollows:

Finally,restartthehostnamedservicebytypingthefollowingcommand:

#systemctlrestartsystemd-hostnamed

Toverifythechanges,enter:

#hostnamectlstatus

Method#3:nmcli

Thenmcliisacommand‐linetoolforcontrollingNetworkManagerandreportingnetworkstatus.

Toviewthehostnameusingnmcli:

Thesyntaxis:#nmcligeneralhostname

Tosetthehostnameusingnmcli:

Thesyntaxis:#nmcligeneralhostnameR2-D2

#nmcligeneralhostnameserver42.cyberciti.biz

Finally,restartthesystemd-hostnamedservice:#systemctlrestartsystemd-hostnamed

Chapter Six: LINUX AND UNIXMANCOMMAND

OnLinuxandotherUnix-likeoperatingsystems,manistheinterfaceusedtoview

thesystem’sreferencemanuals.

Syntaxman[-Cfile][-d][-D][—warnings[=warnings]][-Rencoding][-Llocale]

[-msystem[,…]][-Mpath][-Slist][-eextension][-i|-I]

[—regex|—wildcard][—names-only][-a][-u][—no-subpages][-Ppager]

[-rprompt][-7][-Eencoding][—no-hyphenation][—no-justification]

[-pstring][-t][-T[device]][-H[browser]][-X[dpi]][-Z]

[[section]page…]…

man-k[aproposoptions]regexp…

man-K[-w|-W][-Slist][-i|-I][—regex][section]term…

man-f[whatisoptions]page…

man-l[-Cfile][-d][-D][—warnings[=warnings]][-Rencoding]

[-Llocale][-Ppager][-rprompt][-7][-Eencoding][-pstring][-t]

[-T[device]][-H[browser]][-X[dpi]][-Z]file…

man-w|-W[-Cfile][-d][-D]page…

man-c[-Cfile][-d][-D]page…

man[-hV]

Description

Manisthesystem’smanualviewer;itcanbeusedtodisplaymanualpages,

scroll up and down, search for occurrences of specific text, and other useful

functions.Eachargumentgiventomanisnormallythenameofaprogram,utility

or function. The pages associatedwith each of these arguments are then found

anddisplayed.Asectionnumber,ifprovided,willdirectmantolookonlyinthat

section of the manual. The default action is to search in all of the available

sections,followingapre-definedorderandtoshowonlythefirstpagefound,even

ifpagesexistinseveralsections.

GeneralOptions

-h,—help Printahelpmessageandexit.

-V,—version Displayversioninformationandexit.

-Cfile,—config- Useconfigurationfilefileratherthanthe

file=file defaultof~/.manpath.

-d,—debug Printdebugginginformation.

-D,—default Thisoption,whenused,isnormally

specifiedasthefirstoption;it

resetsman‘sbehaviourtoitsdefault.Its

useistoresetthoseoptionsthatmayhave

beensetin$MANOPT.Anyoptionsthat

follow-Dwillhavetheirusualeffect.

—

warnings[=warnings]

Enablewarningsfromthegrofftext

formatter.Thismaybeusedtoperform

sanitychecksonthesourcetextofmanual

pages.warningsisacomma-separated

listofwarningnames;ifitisnotsupplied,

thedefaultis“mac“.Seethe“Warnings”

nodeinthegroffinfopageforalistof

availablewarningnames.

MainModesofOperation

-f,—whatis Equivalenttothewhatiscommand;displaysashortdescriptionfromthemanualpage,ifavailable.

-k,—apropos Equivalenttotheaproposcommand;Searchtheshortmanualpagedescriptionsforkeywordsanddisplayanymatches.

-K,—global-apropos

Searchfortextinallmanualpages.Thisisabrute-forcesearch,andislikelytotakesometime;ifyoucan,youshouldspecifyasectiontoreducethenumberofpagesthatneedtobesearched.Searchtermsmaybesimplestrings(thedefault),orregularexpressionsifthe—regexoptionisused.

-l,—local-file Activate‘local’mode.Formatanddisplaylocalmanualfilesinsteadofsearchingthroughthesystem’smanualcollection.Eachmanualpageargumentwillbeinterpretedasannroffsourcefileinthecorrectformat.Nocatfileisproduced.Ifadash(‘-‘)islistedasoneofthearguments,inputwillbetakenfromstdin.Whenthisoptionisnotused,andmanfailstofindthepagerequired,beforedisplayingtheerrormessageitattemptstoactasifthisoptionwassupplied,usingthenameasafilenameandlookingforanexactmatch.

-w,—where,—location

Don’tactuallydisplaythemanualpages;insteadprintthelocation(s)ofthesourcenrofffilesthatwouldbeformatted.

-W,—where-cat,—location-cat

Don’tactuallydisplaythemanualpages,butdoprintthelocation(s)ofthecatfilesthatwouldbedisplayed.If-wand-Warebothspecified,printboth,separatedbyaspace.

-c,—catman Thisoptionisnotforgeneraluseandshouldonlybeusedbythecatmanprogram.

-Rencoding,—recode=encoding

Insteadofformattingthemanualpageintheusualway,outputitssourceconvertedtothespecifiedencoding.Ifyoualreadyknowtheencodingofthesourcefile,youcanalsousemanconvdirectly.However,thisoptionallowsyoutoconvertseveralmanualpagestoasingleencodingwithouthavingtoexplicitlystatetheencodingofeach,providedthattheywerealreadyinstalledinastructuresimilartoamanualpagehierarchy.

FindingManualPages

-Llocale,—

locale=locale

manwillnormallydetermineyour

currentlocalebyacalltotheC

functionsetlocalewhichchecksthe

valuesofvariousenvironment

variables,possibly

including$LC_MESSAGESand$LANG.

Totemporarilyoverridethe

determinedvalue,usethisoptionto

supplyalocalestringdirectlytoman.

Notethatitwillnottakeeffectuntilthe

searchforpagesactuallybegins.

Outputsuchasthehelpmessagewill

alwaysbedisplayedintheinitially

determinedlocale.

-msystem[,…],—

systems=system[,

…]

Ifthissystemhasaccesstootheroperating

system’smanualpages,theycanbeaccessed

usingthisoption.Tosearchforamanualpage

from(forexample)the“NewOS”manualpage

collection,usetheoption-mNewOS.

Thesystemspecifiedcanbeacombinationof

commadelimitedoperatingsystemnames.To

includeasearchofthenativeoperating

system’smanualpages,includethesystem

namemanintheargumentstring.This

optionwilloverride

the$SYSTEMenvironmentvariable.

-Mpath,—

manpath=path

Specifyanalternatemanpathtouse.This

optionoverridesthe$MANPATH

environmentvariableandcausesoption-mto

beignored.

Apathspecifiedasamanpathmustbethe

rootofamanualpagehierarchystructured

intosectionsasdescribedintheman-db

manual(under“Themanualpagesystem”).

Toviewmanualpagesoutsidesuch

hierarchies,seethe-loption.

-Slist,-slist,—

sections=list

listisacolon-orcomma-separatedlistof

`orderspecific’manualsectionstosearch.

Thisoptionoverrides

the$MANSECTenvironmentvariable.

(The–sspellingisforcompatibility

withSystemV.)

-esub-

extension,—

extension=sub-

extension

Somesystemsincorporatelargepackagesof

manualpages,suchasthosethataccompany

theTclpackage,intothemainmanualpage

hierarchy.Togetaroundtheproblemof

havingtwomanualpageswiththesamename

suchasexit,theTclpageswereusuallyall

assignedtosectionl(lowercaseL).However,

itisnowpossibletoputthepagesinthe

correctsection,andtoassignaspecific

“extension”tothem,inthiscase,exit(3tcl).

Undernormaloperation,manwill

displayexitinpreferencetoexit(3tcl).To

negotiatethissituationandtoavoidhavingto

knowwhichsectionthepageyourequire

residesin,itisnowpossibletogivemana

sub-extensionstringindicatingwhichpackage

thepagemustbelongto.Usingtheabove

example,supplyingtheoption-e

tcltomanwillrestrictthesearchtopages

havinganextensionof*tcl.

-i,—ignore-case Ignorecasewhensearchingformanualpages.

Thisisthedefault.

-I,—match-case Searchformanualpagescase-sensitively.

—regex Showallpageswithanypartofeithertheir

namesortheirdescriptionsmatchingeach

pageargumentasaregularexpression,as

withapropos.Sincethereisusuallyno

reasonablewaytopicka“best”pagewhen

searchingforaregularexpression,thisoption

implies-a.

—wildcard Showallpageswithanypartofeithertheir

namesortheirdescriptionsmatchingeach

pageargumentusingshell-stylewildcards,as

withapropos—wildcard.Thepage

argumentmustmatchtheentirenameor

description,ormatchonwordboundariesin

thedescription.Sincethereisusuallyno

reasonablewaytopicka“best”pagewhen

searchingforawildcard,thisoptionimplies-

a.

—names-only Ifthe—regexor—wildcardoptionisused,

matchonlypagenames,notpage

descriptions,aswithwhatis.Otherwise,this

optionhasnoeffect.

-a,—all Bydefault,manwillexitafterdisplayingthe

mostsuitablemanualpageitfinds.Usingthis

optionforcesmantodisplayallthemanual

pageswithnamesthatmatchthesearch

criteria.

-u,—update Thisoptioncausesmantoperformaninode-

levelconsistencycheckonitsdatabasecaches

toensurethattheyareanaccurate

representationofthefilesystem.Itwillonly

haveausefuleffectifmanisinstalledwith

thesetuidbitset.

—no-subpages Bydefault,manwilltrytointerpretpairsof

manualpagenamesgivenonthecommand

lineasequivalenttoasinglemanualpage

namecontainingahyphenoranunderscore.

Thissupportsthecommonpatternof

programsthatimplementanumberof

subcommands,allowingthemtoprovide

manualpagesforeachthatcanbeaccessed

usingsimilarsyntaxaswouldbeusedto

invokethesubcommandsthemselves.For

example,thecommand:

man-awgitdiff

displaysthemanualpage:

/usr/share/man/man1/git-diff.1.gz

Todisablethisbehavior,usethe—no-

subpagesoption.

Forexample:

man-aw—no-subpagesgitdiff

Willinsteadshowthemanualpagesfor

bothgitanddiff:

/usr/share/man/man1/git.1.gz

/usr/share/man/man3/Git.3pm.gz

/usr/share/man/man1/diff.1.gz

ControllingFormattedOutput

-Ppager,—pager=pager

Specifywhichoutputpagertouse.Bydefault,manusespager-s.Thisoptionoverridesthe$MANPAGERenvironmentvariable,whichinturnoverridesthe$PAGERenvironmentvariable.Itisnotusedinconjunctionwith-for-k.

Thevaluemaybeasimplecommandnameoracommandwitharguments,andmayuseshellquoting(backslashes,singlequotes,ordoublequotes).Itmaynotusepipestoconnectmultiplecommands;ifyouneedthat,useawrapperscript,whichmaytakethefiletodisplayeitherasanargumentoronstandardinput.

-rprompt,—prompt=prompt

Ifarecentversionoflessisusedasthepager,manwillattempttosetitspromptand

somesensibleoptions.Thedefaultpromptlookslike:

Manualpagename(sec)linex

wherenamedenotesthemanualpagename,secdenotesthesectionitwasfoundunderandxthecurrentlinenumber.Thisisachievedbyusingthe$LESSenvironmentvariable.

Supplying-rwithastringwilloverridethisdefault.Thestringmaycontainthetext$MAN_PNwhichwillbeexpandedtothenameofthecurrentmanualpageanditssectionnamesurroundedby“(”and“)”.Thestringusedtoproducethedefaultcouldbeexpressedas;

\Manual\page\\$MAN_PN\?ltline\%lt?L/%L.:

byte\%bB?s/%s..?\(END):?pB\%pB\%..

(presshforhelporqtoquit)

Itisbrokenintothreelineshereforthesakeofreadabilityonly.Foritsmeaningseethemanpageforless.

Theshellfirstevaluatesthepromptstring.Alldoublequotes,back-quotesandbackslashesinthepromptmustbeescapedbyaprecedingbackslash.Thepromptstringmayendinanescaped$whichmaybefollowedbyfurtheroptionsforless.Bydefault,mansetsthe-ix8options.

Ifyouwanttooverrideman’spromptstringprocessingcompletely,usethe$MANLESSenvironmentvariabledescribedbelow.

-7,—ascii WhenviewingapureASCIImanualpageona7-bitterminalorterminalemulator,somecharactersmaynotdisplaycorrectlywhenusingthelatin1devicedescriptionwithGNUnroff.ThisoptionallowspureASCIImanpagestobedisplayedinASCIIwiththelatin1device.Itwillnottranslate

anylatin1text.Thefollowingtableshowsthetranslationsperformed:somepartsofitmayonlybedisplayedproperlywhenusingGNUnroff’slatin1device.Thisoptionisignoredwhenusingoptions-t,-H,-T,or-ZandmaybeuselessforversionsofnroffotherthanGNU’s.

-Eencoding,—encoding=encoding

Generateoutputforacharacterencodingotherthanthedefault.Forbackwardcompatibility,encodingmaybeannroffdevicesuchasascii,latin1,orutf8aswellasatruecharacterencodingsuchasUTF-8.

—no-hyphenation,—nh

Normally,nroffwillautomaticallyhyphenatetextatlinebreakseveninwordsthatdonotcontainhyphens,ifitisnecessarytodolayoutthrewordsonalinewithoutexcessivespacing.Thisoptiondisablesautomatichyphenation,sowordswillonlybehyphenatediftheyalreadycontainhyphens.Ifyouarewritingamanpageandsimplywanttopreventnrofffromhyphenatingawordataninappropriatepoint,donotusethisoption,butconsultthenroffdocumentationinstead;forinstance,youcanput“\%”insideawordtoindicatethatitmaybehyphenatedatthatpoint,orput“\%”atthestartofawordtopreventitfrombeinghyphenated.

—no-justification,—nj

Normally,nroffwillautomaticallyjustifytexttobothmargins.Thisoptiondisablesfulljustification,leavingjustifiedonlytotheleftmargin,sometimescalled“ragged-right”text.

Ifyouarewritingamanpageandsimplywanttopreventnrofffromjustifyingcertainparagraphs,donotusethisoption,butconsultthenroffdocumentation;forinstance,youcanusethe“.na”,“.nf”,“.fi”,and“.ad”requeststotemporarilydisableadjustingandfilling.

-pstring,—preprocessor=string

Specifythesequenceofpreprocessorstorunbeforenroffortroff/groff.Notallinstallationswillhaveafullsetofpreprocessors.Someofthepreprocessorsandthelettersusedtodesignatethemare:eqn(e),grap(g),pic(p),

tbl(t),vgrind(v),refer(r).Thisoptionoverridesthe$MANROFFSEQenvironmentvariable.zsoelimisalwaysrunasthefirstpreprocessor.

-t,—troff Usegroff-mandoctoformatthemanpagetostandardoutput.Thisoptionisnotrequiredinconjunctionwith-H,-T,or-Z.

-T[device],—troff-device[=device]

Thisoptionisusedtochangegroff(orpossiblytroff’s)outputtobesuitableforadeviceotherthanthedefault.Itimplies-t.Examplesincludedvi,latin1,ps,utf8,X75andX100.

-H[browser],—html[=browser]

ThisoptionwillcausegrofftoproduceHTMLoutput,andwilldisplaytheoutputinawebbrowser.Thechoiceofbrowserisdeterminedbytheoptionalbrowserargumentifoneisprovided,bythe$BROWSERenvironmentvariable,orbyacompile-timedefaultifthatisunset(usuallylynx).Thisoptionimplies-t,andwillonlyworkwithGNUtroff.

-X[dpi],—gxditview[=dpi]

Thisoptiondisplaystheoutputofgroffinagraphicalwindowusingthegxditviewprogram.Thedpi(dotsperinch)maybe75,75-12,100,or100-12,defaultingto75;the-12variantsusea12-pointbasefont.Thisoptionimplies-TwiththeX75,X75-12,X100,orX100-12devices,respectively.

-Z,—ditroff groffwillruntroffandthenuseanappropriatepost-processortoproduceoutputsuitableforthechosendevice.Ifgroff-mandocisgroff,thisoptionispassedtogroffandwillsuppresstheuseofapost-processor.Itimplies-t.

SectionNumbers

The section numbers of the manual are listed below. While reading

documentation,ifyouseeacommandnamefollowedbyanumberinparentheses,

the number refers to one of these sections. For example, man is the

documentation of man found in section number1. Some commands may have

documentation in more than one section, so the numbers after the command

namemaydirectyoutothecorrectsectiontofindaspecifictypeofinformation.

Thesectionnumbers,andthetopicstheycover,areasfollows:

section# Topic

1 Executableprogramsorshellcommands

2 Systemcalls(functionsprovidedbythekernel)

3 Librarycalls(functionswithinprogramlibraries)

4 Specialfiles(usuallyfoundin/dev)

5 Fileformatsandconventionseg/etc/passwd

6 Games

7 Miscellaneous(includingmacropackagesand

conventions),e.g.man,groff

8 Systemadministrationcommands(usuallyonly

forroot)

9 Kernelroutines[Nonstandard]

ExitStatus

Whenitterminates,manwillreturnoneofthefollowingexitstatus:

0 Returneduponsuccessfulprogramexecution.

1 Returnediftherewasausage,syntax,orconfigurationfile

error.

2 Returnediftherewasanoperationalerror.

3 Returnedifachildprocessreturnedanon-zeroexitstatus.

16 Returnedifoneormoreofthepages,files,orkeywords

searchedfordidnotexistorwasnotmatched.

Environment

manmakesuseofthefollowingenvironmentvariables:

MANPATH If$MANPATHisset,itsvalueis

usedasthepathtosearchfor

manualpages.

MANROFFOPT Thecontentsof$MANROFFOPTare

addedtothecommandlineevery

timemaninvokestheformatter

(nroff,troff,orgroff).

MANROFFSEQ If$MANROFFSEQisset,itsvalueis

usedtodeterminethesetof

preprocessorstopasseachmanual

pagethrough.Thedefault

preprocessorlistissystem-dependent.

MANSECT If$MANSECTisset,itsvalueisa

colon-delimitedlistofsectionsanditis

usedtodeterminewhichmansections

tosearchandinwhatorder.

MANPAGER,PAGER If$MANPAGERor$PAGERisset

($MANPAGERisusedin

preference),itsvalueisusedasthe

nameoftheprogramusedtodisplay

themanpage.Bydefault,pager-sis

used.Thevaluemaybeasimple

commandnameoracommandwith

arguments,andmayuseshellquoting

(backslashes,singlequotes,ordouble

quotes).Itmaynotusepipesto

connectmultiplecommands;ifyou

needthat,useawrapperscript,which

maytakethefiletodisplayeitherasan

argumentoronstandardinput.

MANLESS If$MANLESSisset,manwillnot

performanyofitsusualprocessingto

setupapromptstringfor

thelesspager.Instead,thevalueof

$MANLESSwillbecopiedverbatim

into$LESS.Forexample,ifyouwant

tosetthepromptstring

unconditionallyto“mypromptstring”,

set$MANLESSto‘-Psmyprompt

string’.

BROWSER If$BROWSERisset,itsvalueisa

colon-delimitedlistofcommands,each

ofwhichinturnisusedtotrytostarta

webbrowserforman—html.Ineach

command,%sisreplacedbya

filenamecontainingtheHTMLoutput

fromgroff,%%isreplacedbyasingle

percentsign(%),and%cisreplaced

byacolon(:).

SYSTEM If$SYSTEMisset,itwillhavethe

sameeffectasifithadbeenspecified

astheargumenttothe-moption.

MANOPT If$MANOPTisset,itwillbeparsed

priortomanscommandlineandis

expectedtobeinasimilarformat.As

alloftheothermanspecific

environmentvariablescanbe

expressedascommandlineoptions,

andarethuscandidatesforbeing

includedin$MANOPTitisexpected

thattheywillbecomeobsolete.Note:

allspacesthatshouldbeinterpretedas

partofanoption’sargumentmustbe

escaped(precededwithabackslash).

MANWIDTH If$MANWIDTHisset,itsvalueis

usedasthelinelengthforwhich

manualpagesshouldbeformatted.Ifit

isnotset,manualpageswillbe

formattedwithalinelength

appropriatetothecurrentterminal

(usinganioctlifavailable,thevalue

of$COLUMNS,orfallingbackto80

charactersifneitheris

available).catpageswillonlybesaved

whenthedefaultformattingcanbe

used,thatiswhentheterminalline

lengthisbetween66and80

characters.

MAN_KEEP_FORMATTING Normally,whenoutputisnotbeing

directedtoaterminal(suchastoafile

orapipe),formattingcharactersare

discardedtomakeiteasiertoreadthe

resultwithoutspecialtools.However,

if$MAN_KEEP_FORMATTINGis

settoanynon-emptyvalue,these

formattingcharactersareretained.

Thismaybeusefulforwrappers

aroundmanthatcaninterpret

formattingcharacters.

MAN_KEEP_STDERR Normally,whenoutputisbeing

directedtoaterminal(usuallya

pager),anyerroroutputfromthe

commandusedtoproduceformatted

versionsofmanpagesisdiscardedto

avoidinterferingwiththepager’s

display.Programssuchasgroffoften

producerelativelyminorerror

messagesabouttypographical

problemssuchaspooralignment,

whichareunsightlyandgenerally

confusingwhendisplayedalongwith

themanpage.However,youmight

wanttoseethemanyway,so

if$MAN_KEEP_STDERRissettoa

non-emptyvalue,erroroutputwillbe

displayedasusual.

LANG,LC_MESSAGES Dependingonthesystemand

implementation,eitherorboth

of$LANGand$LC_MESSAGESwill

beinterrogatedforthecurrent

messagelocale,manwilldisplayits

messagesinthatlocale(ifavailable).

Files

Thesefilesareusedbyman:

/etc/manpath.config Theman-

dbconfiguration

file.

/usr/share/man Aglobalmanual

pagehierarchy.

/usr/share/man/index.

(bt|db|dir|pag)

Atraditionalglobal

indexdatabase

cache.

/var/cache/man/index.

(bt|db|dir|pag)

AnFHScompliant

globalindex

databasecache.

Examples

manman

Viewthemanpageforthemancommand.

man—nh—njman

Chapter Seven: LINUX DIRECTORYCOMMAND

LinuxorUNIX-likesystemsuse the ls command to list filesanddirectories.However, ls does not have an option to list only directories. You can usecombination of ls and grep to list directory names only. You can use the findcommandtoo.Inthisquicktutorial,youwilllearnhowtolistonlydirectoriesin

LinuxorUNIX.

ListalldirectoriesinUnix

Typethefollowingcommand:

$ls-l|grep`^d’ls-l|egrep`^d’

Trythefollowinglscommandtolistdirectoriesinthecurrentdirectory:

$ls-d*/

sampleoutputs

ListonlyfilesinUnix

Typethefollowingcommand:$ls-l|egrep-v‘^d’

$ls-l|egrep-v‘^d’

Thegrepcommandisusedtosearchesinput.Itwillfilteroutdirectorynames

bymatchingfirstcharacter‘d’.Toreversetheeffecti.e.justtodisplay

filesyouneedtopassthe-voption.Itinvertsthesenseofmatching,to

selectnon-matchinglines.

Task:Createaliasestosavetime

Youcancreatetwoaliasestolistonlydirectoriesandfiles.aliaslf=“ls-l|egrep-v‘^d’”

aliasldir=“ls-l|egrep‘^d’”

Putabovetwoaliasesinyourbashshellstartupfile:$cd

$vi.bash_profile

Appendtwolines:aliaslf=“ls-l|egrep-v‘^d’”

aliasldir=“ls-l|egrep‘^d’”

Saveandclosethefile.

Nowjusttypelf-tolistfilesandldir-tolistdirectoriesonly:$cd/etc

$lf

Sampleoutput:

-rw-r—r—1rootroot21492006-09-0423:25adduser.conf

-rw-r—r—1rootroot442006-09-2905:11adjtime

-rw-r—r—1rootroot1972006-09-0423:48aliases

-rw––-1rootroot1442002-01-1813:43at.deny

-rw-r—r—1rootroot1622006-09-2223:24aumixrc

-rw-r—r—1rootroot282006-09-2223:24aumixrc1

Listdirectorynamesonly:$cd/etc

$ldir

Sampleoutput:drwxr-xr-x4rootroot40962006-09-2216:41alsa

drwxr-xr-x2rootroot40962006-09-2020:59alternatives

drwxr-xr-x6rootroot40962006-09-2216:41apm

drwxr-xr-x3rootroot40962006-09-0702:51apt

drwxr-xr-x2rootroot40962006-09-0801:46bash_completion.dUsefindcommandtolisteitherfilesordirectories

Thefindcommandcanbeusedasfollows:tolistalldirectoriesin/nas,enter:find/nas-typed

find/nas-typed-ls

find.-typed-ls

Sampleoutput:10707858drwxrwxrwt8rootroot4096Jul507:12.

10707978drwx––2rootroot4096Jul407:22./orbit-root

10708438drwxr-xr-x2rootroot4096Jun1618:55./w

10707898drwxr-xr-x10rootroot4096Jun1714:54./b

10713408drwxr-xr-x2rootroot4096Jun1618:55./b/init.d

10715818drwxr-xr-x3rootroot4096Jun1618:55./b/bind

10715848drwxr-xr-x2rootroot4096Jun1618:55./b/bind/bak

10716178drwxr-xr-x2rootroot4096Jun1618:55./b/fw

10716288drwxr-xr-x8rootroot4096Jun1618:55./b/scripts

ChapterEight:WORKINGWITHFILES

ThischapterwillfirstdescribegeneralcharacteristicsofUnixcommands.Itwill

thendiscusscommands,whicharecommonlyusedtocreateandmanipulatefiles.

AsummaryofsomeofthemostcommonlyusedUNIXcommandsispresentedin

CommandComparisons.

UNIXFileNames

ItisimportanttounderstandtherulesforcreatingUNIXfiles:UNIXiscase

sensitive! For example, “fileName” is different from “filename.” It is

recommended that you limit names to the alphabetic characters, numbers,

underscore(_),anddot(.).Dots(.)usedinUNIXfilenamesaresimplycharacters

andnotdelimitersbetweenfilenamecomponents;youmayincludemorethanone

dotinafilename.Includingadotasthefirstcharacterofafilenamemakesthefile

invisible(hidden)tothenormallscommand;usethe-aflagofthelscommandto

displayhidden files.Althoughmany systemswill allowmore, the recommended

length is 14 characters per file name. Unix shells typically include several

important wildcard characters. The asterisk (*) is used to match 0 or more

character (e.g., abc* will match any file beginning with the letters abc), the

questionmark(?)isusedtomatchanysinglecharacter,andtheleft([)andright

(])squarebracketsareusedtoencloseastringofcharacters,anyoneofwhichis

tomatch.Executethefollowingcommandsandobservetheresults:

lsm*

ls*.f

ls*.?

ls[a-d]*

NotesforPCusers:Unixusesforwardslashes(/)insteadofbackslashes(\)fordirectories

LookingattheContentsofFiles

You can examine the contents of files using a variety ofcommands.cat,more,pg,head,andtailaredescribedhere.Of course, youcanalwaysuseaneditor;touseviin“read-only”modetoexaminethecontentsofthefile“argtest”,enter:

vi-Rargtest

Youcannowuse the standardvi commands tomove through the file;however,

youwillnotbeabletomakeanychangestothecontentsofthefile.Thisoptionis

usefulwhenyousimplywanttolookatafileandwanttoguaranteethatyoumake

nochangeswhiledoingso.

Usethevi“””commandtoexitfromthefile.

CatCommand

cat is a utility used to conCATenate files. Thus, it can be used to join filestogether,butitisperhapsmorecommonlyusedtodisplaythecontentsofafileonthescreen.

Observetheoutputproducedbyeachofthefollowingcommands:

cd;cdxmp

catcars

cat-vetcars

cat-ncars

The semicolon (;) in the first line of this example is a command separatorwhich enables entry of more than one command on a line. Whenthe<Return>keyispressedfollowingthisline,thecommandcdisissuedwhichchangestoyourhomedirectory.Thenthecommand“cdxmp”isissuedtochangeinto the subdirectory “xmp.” Entering this line is equivalent to having enteredthese commands sequentially on separate lines. These two commands areincludedintheexampletoguaranteethatyouareinthesubdirectorycontaining“cars”andtheotherexamplefiles.Youneednotenterthesecommandsifyouarealreadyinthe“xmp”directorycreatedwhenyoucopiedtheexamplefile.

The “-vet” option enables display of tab, end-of-line, and other non-printablecharacterswithinafile;the“-n”optionnumberseachlineasitisdisplayed.

Youcanalsousethecatcommandtojoinfilestogether:

catpage1

catpage2

catpage1page2>document

catdocument

Note: If the file “document” had previously existed, it will be replaced by the

contentsoffiles“page1”and“page2.”

Cautionstousingthecatcommand:Thecatcommandshouldonlybeusedwith “text” files; it should not be used to display the contents of binary (e.g.,compiledCorFORTRANprograms).Unpredictableresultsmayoccur,includingtheterminationofyourlogonsession.Usethecommand“file*”todisplaythecharacteristicsoffileswithinadirectorypriortousingthecatcommandwithanyunknownfile.Youcanusetheod(enter“manod”fordetailsonuseofOctalDump)commandtodisplaythecontentsofnon-textfiles.Forexample,todisplaythecontentsof“a.out”inbothhexadecimaland

characterrepresentation,enter:

od-xca.out

Warning:cat(andotherUnixcommands)candestroyfilesifnotusedcorrectly.Forexample,asillustratedintheSobellbook,thecat(alsocpandmv)commandcan overwrite and thus destroy files. Observe the results of the followingcommand:

catletterpage1>letter

Typically, UNIX does not return a message when a command executes

successfully. Here the UNIX operating system will attempt to complete the

requested command by first initializing the file “letter” and then writing the

currentcontentsof“letter”(nownothing)and“page1”intothisfile.Since“letter”

has been reinitialized and is also named as a source file, an error diagnostic is

generated. Part of the UNIX philosophy is “No news is good news.” Thus, the

appearance of a message is a warning that the command was not completed

successfully.

Now use the “cat” command to individually examine the contents of the files“letter” and “page1.” Observe that the file “letter” does not contain the originalcontentsofthefiles“letter”and“page1”aswasintended.

Usethefollowingcommandtorestoretheoriginalfile“letter”:

cp~aixstu00/xmp/letter.

MoreCommand

You may type or browse files using the more command. The “more”commandisusefulwhenexaminingalargefileasitdisplaysthefilecontentsonepage at a time, allowing each page to be examined at will. As withthemancommand,youmustpressthespacebartoproceedtothenextscreenofthefile.Onmanysystems,pressingthe<b>keywillenableyoutopagebackwardsinthefile.Toterminatemoreatanytime,press<q>.

Toexamineafilewiththemorecommand,simplyenter:

morefile_name

Themancommanduses themorecommand todisplay themanualpages; thus,thecommandsyouarefamiliarwithusingmanwillalsoworkwithmore.Not all Unix systems include the more command; some implementthe pg command instead. VTAIX includes both the more and pg commands.When using the pg command, press <Return> to page down through a fileinsteadofusingthespacebar.

Observetheresultsofenteringthefollowingcommands:

moreargtest

pgargtest

HeadCommand

Theheadcommandisusedtodisplaythefirst fewlinesofafile.Thiscommand

canbeusefulwhenyouwishtolookforspecificinformation,inthebeginningof

thefile.Forexample,enter:

headargtest

TailCommand

Thetailcommandisusedtodisplaythelastlinesofafile.Thiscommandcanbeusefultomonitorthestatusofaprogram,whichappendsoutputtotheendofafile.Forexample,enter:

tailargtest

Copying,Erasing,Renaming

Warning:ThetypicalUnixoperatingsystemprovidesno‘unerase’or ‘undelete’command.Ifyoumistakenlydeleteafileyouaredependentuponthebackupsyou

orthesystemadministratorhavemaintainedinordertorecoverthefile.Youneed

to be careful when using commands like copy and move, which may result in

overwritingexisting files. If youareusing theCorKornShell, you can createa

command alias , which will prompt you for verification before overwriting fileswiththesecommands.

CopyingFiles

Thecpcommandisusedtocopyafileorgroupoffiles.Youhavealreadyseenanexampleapplicationofthecpcommandwhenyoucopiedthesamplefilestoyouruserid.Now let’smakea copyofoneof these files.Recall thatyoucanobtaina

listingof the files in the currentdirectoryusing thels command.Observe theresultsfromthefollowingcommands:

lsl*

cpletterletter.2

lsl*

Note:Unlikemanyotheroperatingsystems,suchasPC/DOS,youmustspecify

thetargetwiththecopycommand;itdoesnotassumethecurrentdirectoryifno

“copy-to”targetisspecified.

ErasingFiles

Unixusesthecommandrm(ReMove)todeleteunwantedfiles.Toremovethefile“letter.2”whichwehavejustcreated,enter:

rmletter.2

Enterthecommand“lsl*”todisplayalistofallfilesbeginningwiththeletter“l.”Note that letter.2 is no longer present in the current directory. The removecommand can be used with wildcards in filenames; however, this can bedangerous as you might end up erasing files you had wanted to keep. It isrecommendedthatyouusethe“-i”(interactive)optionofrmforwildcarddeletes—youwillthenbepromptedtorespondwitha“y”or“Y”foreachfileyouwishtodelete.

RenamingaFile

The typical Unix operating system utilities do not include a renamecommand;however,wecanusethemv(MoVe)command(seeforadditionalusesof this command) to “move”WorkingwithDirectories) a file fromonename toanother.Observetheresultsofthefollowingcommands:

ls[d,l]*

mvletterdocument

ls[d,l]*

mvdocumentletter

ls[d,l]*

Note: The first mv command overwrites the file “document” which you hadcreatedinanearlierexercisebyconcatenating“page1”and“page2.”Nowarningis

issuedwhenthemvcommandisusedtomoveafileintothenameofanexistingfile.Ifyouwouldliketobepromptedforconfirmationifthemvcommandweretooverwriteanexisting file,use the “-i” (interactive) optionof themv command,e.g.:

mv-ipage1letter

Youwillnowbetoldthatthefile“letter”alreadyexistsandyouwillbeaskedifyouwish toproceedwith themvcommand.Answeranythingbut “y”or “Y” and thefile“letter”willnotbeoverwritten.

UsingtheCommandLine

The command interpreter (shell) provides the mechanism by which input

commandsare interpretedandpassed to theUnixkernelorotherprograms for

processing.Observetheresultsofenteringthefollowingcommands:

./filesize

./hobbit

./add2

ls-F

Observethat“filesize”isanexecutableshellscript,whichdisplaysthesizeoffiles.

Also note that “./hobbit” and “./add2” generate error diagnostics as there is no

command or file with the name “hobbit” and the file “add2” lacks execute

permission.

StandardInputandStandardOutput

Asyouhavecansee,Unixexpectsstandardinputtocomefromthekeyboard,e.g.,

enter:

cat

my_text

<Ctrl-D>

Standardoutputistypicallydisplayedontheterminalscreen,e.g.,enter:

catcars

Standard error (a listing of program execution error diagnostics) is typically

displayedontheterminalscreen,e.g.,enter:

lsxyzpqrz

Redirection

As illustrated above, many Unix commands read from standard input

(typically the keyboard) and write to standard output (typically the terminal

screen).Theredirectionoperatorsenableyoutoreadinputfromafile(<)orwrite

program output to a file (>).When output is redirected to a file, the program

outputreplacestheoriginalcontentsofthefileifitalreadyexists;toaddprogram

outputtotheendofanexistingfile,usetheappendredirectionoperator(>>).

Observetheresultsofthefollowingcommand:

./a.out

YouwillbepromptedtoenteraFahrenheittemperature.Afterenteringanumeric

value,amessagewillbedisplayedonthescreeninformingyouoftheequivalent

Centigradetemperature.Inthisexample,youenteredanumericvalueasstandard

input via the keyboard and the output of the program was displayed on the

terminalscreen.

Inthenextexample,youwillreaddatafromafileandhavetheresultdisplayedon

thescreen(standardoutput):

catdata.in

./a.out<data.in

Nowyouwillreadfromstandardinput(keyboard)andwritetoafile:

./a.out>data.two

35

catdata.two

Nowreadfromstandardinputandappendtheresulttotheexistingfile:

./a.out<data.in>>data.two

As another example of redirection, observe the result of the following two

commands:

ls-la/etc>temp

moretemp

Herewehaveredirectedtheoutputofthelscommandtothefile“temp”andthenusedthemorecommandtodisplaythecontentsofthisfileapageatatime.Inthenextsection,wewillseehowtheuseofpipescouldsimplifythisoperation.

UsingPipesandFilters

AfilterisaUnixprogram,whichacceptsinputfromstandardinputandplacesits

outputinstandardoutput.FiltersaddpowertotheUNIXsystemasprogramscan

bewrittentousetheoutputofanotherprogramasinputandcreateoutput,which

canbeusedbyyetanotherprogram.Apipe(indicatedbythesymbol“|”—vertical

bar)isusedbetweenUNIXcommandstoindicatethattheoutputfromthefirstis

to be used as input by the second. Compare the output from the following two

commands:

ls-la/etc

ls-la/etc|more

The first commanddisplays of all the files in the in the “/etc” directory in longformat.Itisdifficulttomakeuseofthisinformationsinceitscrollsrapidlyacrossthe screen. In the second line, the results of the ls command are piped intothemorecommand.Wecannowexaminethisinformationonescreenatatimeandcanevenbackuptoapriorscreenofinformationifwewishto.AsyoubecamemorefamiliarwithUNIX,youwillfindthatpipingoutputtothemorecommandcanbeveryusefulinavarietyofapplications.

Thesortcommandcanbeusedtosortthelinesinafileinadesiredorder.Nowenterthefollowingcommandsandobservetheresults:

who

sortcars

who|sort

Thewhocommanddisplays a list of users currently logged onto the system thesort command enables us to sort the information. The second command sortsthe lines in the file cars alphabetically by first field and displays the result instandard output. The third command illustrates how the result of the whocommandcanbepassedtothesortcommandpriortobeingdisplayed.Theresultisalistingofloggedonusersinalphabeticalorder.

The following example uses the “awk” and “sort” commands to select andreorganizetheoutputgeneratedbythe“ls”command:

ls-l|awk‘/:/{print$5,$9}’|sort-nr

Note:Curlybracesdonotnecessarilydisplaycorrectlyonalloutputdevices. In

theaboveexample,thereshouldbealeftcurlybraceinfrontofthewordprintand

arightcurlybracefollowingthenumber9.

Observethat theoutputdisplaysthe filesizeandfilenameindecreasingorderofsize. Here the ls command first generates a “long” listing of the files in thecurrentdirectory,whichispipedtothe“awk”utility,whoseoutputisthenpipedtothe“sort”command.

“awk” is a powerful utility which processes one or more program lines to findpatternswithinafileandperformselectiveactionsbasedonwhatisfound.Slash(/) characters are used as delimiters around the pattern to bematched and theactiontobetakenisenclosedincurlybraces.Ifnopatternisspecified,alllinesinthefileareprocessedandifnoactionisspecified,alllinesmatchingthespecifiedpattern are output. Since a colon (:) is used here, all lines containing fileinformation (the time column corresponding to each file contains a colon) areselectedandtheinformationcontainedinthe5thand9thcolumnsareoutputtothesortcommand.

Note:Ifthelscommandonyoursystemdoesnotincludeacolumnlistinggroupmembership, use{print$4,$8} instead of the “print” command option ofawklistedabove.

Herethe“sort”commandoptions“-nr”specify that theoutput from“awk”besortedinreversenumericorder,i.e.,fromlargesttosmallest.

Theprecedingcommandissomewhatcomplexanditiseasytomakeamistakein

enteringit.Ifthiswereacommandyouwouldusefrequently,wecouldincludeit

inashellscriptasinsamplefile“filesize”.Tousethisshellscript,simplyenterthe

command:

./filesizeor

shfilesize

Ifyouexaminethecontentsof this filewiththecatorvicommands,youwillseethatitcontainsnothingmorethepipingofthelscommandtoawkandthenpipingtheoutputtosort.Theteeutilityisusedtosendoutputtobothafileandthescreen:

who|teewho.out|sort

catwho.out

Hereyoushouldhaveobservedthatalistofloggedonuserswasdisplayedonthe

screen in alphabetical order and that the file “who.out” contained an unsorted

listingofthesameuserids.

SomeAdditionalFileHandlingCommands

WordCount

Thecommandwcdisplaysthenumberoflines,words,andcharactersinafile.

Todisplaythenumberoflines,words,andcharactersinthefilefile_name,enter:

wcfile_name

ComparingtheContentsofTwoFiles:thecmpanddiffCommands

Thecmpanddiffcommandsareusedtocomparefiles;the“comp”commandisnotusedtocomparefiles,butto“composeamessage.”

Thecmp command can be used for both binary and text files. It indicates thelocation(byteandline)wherethefirstdifferencebetweenthetwofilesappears.

Thediffcommandcanbeusedtocomparetext filesanditsoutputshowsthelineswhicharedifferentinthetwofiles:alessthansign(“<“)appearsinfrontoflines fromthe first filewhichdiffer fromthose in thesecondfile,agreater thansymbol(“>”)precedeslinesfromthesecondfile.Matchinglinesarenotdisplayed.

Observetheresultsofthefollowingcommands:

cmppage1page2

diffpage1page2

Lines1and2ofthesetwofilesareidentical, lines3differbyonecharacter,and

pageonecontainsablanklinefollowinglinethree,whilepage2doesnot.

ChapterNine:NAVIGATIONANDFILEMANAGEMENT

IfyoudonothavemuchexperienceworkingwithLinuxsystems,youmaybe

overwhelmed by the prospect of controlling an operating system from the

commandline.Inthisbook,wewillattempttogetyouuptospeedwiththebasics.

PrerequisitesandGoals

In order to follow alongwith this book, youwill need to have access to a

Linuxserver.Youwillalsowanttohaveabasicunderstandingofhowtheterminal

worksandwhatLinuxcommandslooklike.Thisbookcoversterminalbasics,so

youshouldcheckitoutifyouarenewtousingterminals.Allofthematerialinthis

book can be accomplished with a regular, non-root (non-administrative) user

account. You can learn how to configure this type of user account by following

yourdistribution’sinitialserversetupguide(Ubuntu14.04,CentOS7).Whenyou

arereadytobegin,connecttoyourLinuxserverusingSSHandcontinuebelow.

NavigationandExploration

The most fundamental skills you need to master are navigating the

filesystem.Wewilldiscussthetoolsthatallowyoutodothisinthissection.

Findingwhereyouarewiththe“pwd”command

When you log onto your server, you are typically dropped into your useraccountshomedirectory.Ahomedirectory is thedirectory set aside for youraccount to store files and create directories. It is the location in the filesystemwhere you have full dominion. To find out where your home directory is inrelationship to the rest of the filesystem, you can use the pwd command. Thiscommanddisplaysthedirectorythatwearecurrentlyin:pwd

Youshouldgetbacksomeinformationthatlookslikethis:

/home/demo

Thehomedirectoryisnamedaftertheuseraccount,sotheaboveexampleiswhat the value would be if you were logged into the server with an accountcalled demo. This directory is within a directory called/home, which is itselfwithinthetop-leveldirectory,whichiscalled“root”representedbyasingleslash“/”.

LookingattheContentsofDirectorieswith“ls”

Nowthatyouknowhowtodisplaythedirectorythatyouarein,wecanshow

youhowtolookatthecontentsofadirectory.

Currently,yourhomedirectorydoescontainmuch,sowewillgotoanother,more populated directory to explore. Type the following command in yourterminaltochangedirectory(wewillexplainthedetailsofmovingdirectoriesinthe next section). Afterward, we will use pwd to confirm that we successfullymoved:cd/usr/share

pwd

/usr/share

Nowthatweareinanewdirectory,letuslookatwhat’sinside.Todothis,wecanusethelscommand:ls

addusergroffpam-configs

applicationsgrubperl

apportgrub-gfxpayload-listsperl5

appshalpixmaps

apti18npkgconfig

aptitudeiconspolkit-1

apt-xapian-indexinfopopularity-contest

…

Asyoucansee,therearemanyitemsinthisdirectory.Wecanaddsomeoptionalflagstothecommandtomodifythedefaultbehavior.Forinstance,tolistallofthecontentsinanextendedform,wecanusethe-lflag(for“long”output):ls-l

total440

drwxr-xr-x2rootroot4096Apr172014adduser

drwxr-xr-x2rootroot4096Sep2419:11applications

drwxr-xr-x6rootroot4096Oct918:16apport

drwxr-xr-x3rootroot4096Apr172014apps

drwxr-xr-x2rootroot4096Oct918:15apt

drwxr-xr-x2rootroot4096Apr172014aptitude

drwxr-xr-x4rootroot4096Apr172014apt-xapian-index

drwxr-xr-x2rootroot4096Apr172014awk

…

Thisviewgivesusplentyofinformation,mostofwhichlooksratherunusual.Thefirstblockdescribesthefiletype(ifthefirstcolumnisa“d”theitemisadirectory,if it is a “-“, it is a normal file) and permissions. Each subsequent column,separatedbywhite space,describes thenumberofhard links, theowner, groupowner, item size, last modification time, and the name of the item. We willdescribesomeoftheseatanothertime,butfornow,justknowthatyoucanviewthisinformationwiththe-lflagofls.Togetalistingofallfiles,includinghiddenfilesanddirectories,youcanaddthe-aflag.Sincetherearenorealhiddenfilesinthe/usr/sharedirectory, let’sgobacktoourhomedirectoryandtrythatcommand.Youcangetbacktothehomedirectorybytypingcdwithnoarguments:cd

ls-a

....bash_logout.bashrc.profile

As you can see, there are three hidden files in this demonstration, alongwith .and ..,whicharespecial indicators.Youwill findthatoften,configurationfilesarestoredashiddenfiles.

Thedotanddoubledotentries,arebuilt-inmethodsofreferringtorelated

directories.Thesingledotindicatesthecurrentdirectory,andthedoubledot

indicatesthisdirectory’sparentdirectory.Thiswillcomeinhandyinthenext

section.

MovingAroundtheFilesystemwith“cd”

Wehavealreadychangeddirectoriestwicetodemonstratesomepropertiesofls.Let’stakeabetterlookatthecommandhere.

Beginbygoingbacktothe/usr/sharedirectorybytypingthis:

cd/usr/share

This isanexampleofchangingadirectorybygivinganabsolutepath.InLinux,

everyfileanddirectoryisunderthetop-mostdirectory,whichiscalledthe“root”

directory,butreferredtobyasingleleadingslash“/”.Anabsolutepathindicates

thelocationofadirectoryinrelationtothistop-leveldirectory.Thisletsusrefer

to directories in an unambiguous way from any place in the filesystem. Every

absolutepathmustbeginwithaslash.

The alternative is to use relative paths. Relative paths refer to directories in

relationtothecurrentdirectory.Fordirectoriesclosetothecurrentdirectory in

thehierarchy,thisisusuallyeasierandshorter.Anydirectorywithinthecurrent

directory canbe referencedbynamewithout a leading slash.We can change to

thelocaledirectorywithin/usr/sharefromourcurrentlocationbytyping:

cdlocale

Wecanlikewisechangemultipledirectorylevelswithrelativepathsbyprovidingtheportionof thepaththatcomesafter thecurrentdirectory’spath.Fromhere,wecangettotheLC_MESSAGESdirectorywithintheendirectorybytyping:

cden/LC_MESSAGES

Tomoveuponedirectorylevel,weusethespecialdoubledotindicatorwetalkedaboutearlier.Forinstance,wearenowinthe/usr/share/locale/en/LC_MESSAGESdirectory.Tomoveuponelevel,wecantype:cd..

Thistakesustothe/usr/share/locale/endirectory.Ashortcutthatyousawearlierthatwillalwaystakeyoubacktoyourhome

directoryistousecdwithoutprovidingadirectory:cd

pwd

/home/demo

ViewingFiles

Inthelastsection,welearnedhowtonavigatethefilesystem.Inthissection,wewilldiscussdifferentwaystoviewfiles.Incontrasttosomeoperatingsystems,Linux and other Unix-like operating systems rely on plain text files for vastportions of the system. The main way that we will view files is withthelesscommand.Thisiswhatwecalla“pager,”becauseitallowsustoscrollthroughpagesofafile.Whilethepreviouscommandsimmediatelyexecutedandreturnedyou to the command line,less is an application thatwill continue torunandoccupythescreenuntilyouexit.

Wewillopenthe/etc/servicesfile,whichisaconfigurationfilethatcontainsthesystemsservicesinformation:less/etc/services

Thefilewillbeopenedinless,allowingyoutoseetheportionofthedocumentthatfitsintheterminalwindow:#Networkservices,Internetstyle

#

#NotethatitispresentlythepolicyofIANAtoassignasinglewell-known

#portnumberforbothTCPandUDP;hence,officiallyportshavetwoentries

#eveniftheprotocoldoesn’tsupportUDPoperations.

#

#Updatedfromhttp://www.iana.org/assignments/port-numbersandother

#sourceslikehttp://www.freebsd.org/cgi/cvsweb.cgi/src/etc/services.

#Newportswillbeaddedonrequestiftheyhavebeenofficiallyassigned

#byIANAandusedinthereal-worldorareneededbyadebianpackage.

#Ifyouneedahugelistofusednumberspleaseinstallthenmappackage.

tcpmux1/tcp#TCPportservicemultiplexer

echo7/tcp

…

Toscroll,youcanusetheupanddownarrowkeysonyourkeyboard.Topagedownonewholescreens-worthofinformation,youcanuseeitherthespacebar,the“PageDown”buttononyourkeyboard,ortheCTRL-fshortcut.Toscrollbackup,youcanuseeitherthe“PageUp”button,ortheCTRL-bkeyboardshortcut.Tosearchforsometextinthedocument,youcantypeaforwardslash“/”followedbythesearchterm.Forinstance,tosearchfor“mail”,wewouldtype:/mailThiswillsearchforwardthroughthedocumentandstopatthefirstresult.Togettoanotherresult,youcantypethelower-casenkey:n

Tomovebackwardstothepreviousresult,useacapitalNinstead:N

Whenyouwishtoexitthelessprogram,youcantypeqtoquit:q

Whilewefocusedonthelesstool inthissection, therearemanyotherwaysofviewingafile.Thecatcommanddisplaysafile’scontentsandreturnsyoutothepromptimmediately.Theheadcommand,bydefault,showsthefirst10linesofafile. Likewise, the tail command shows the last 10 lines. These commandsdisplayfilecontentsinawaythatisusefulfor“piping”tootherprograms.Wewilldiscussthisconceptinafutureguide.

Feelfreetoseehowthesecommandsdisplaythe/etc/servicesfiledifferently.

FileandDirectoryManipulation

We learned in the last section how to view a file. In this section, we will

demonstratehowtocreateandmanipulatefilesanddirectories.

CreateaFilewith“touch”

Manycommandsandprogramscancreate files.Themostbasicmethodofcreatinga file iswiththetouchcommand.Thiswillcreateanempty fileusingthenameandlocationspecified.

First,weshouldmakesureweareinourhomedirectory,sincethis isa locationwherewehavepermissiontosavefiles.Then,wecancreateafilecalledfile1bytyping:cd

touchfile1

Now,ifweviewthefilesinourdirectory,wecanseeournewlycreatedfile:

ls

file1

Ifweusethiscommandonanexistingfile,thecommandsimplyupdatesthedata

ourfilesystemstoresonthetimewhenthefilewaslastaccessedandmodified.

Wecanalsocreatemultiplefilesatthesametime.Wecanuseabsolutepathsaswell.Forinstance,ifouruseraccountiscalleddemo,wecouldtype:touch/home/demo/file2/home/demo/file3

ls

file1file2file3

CreateaDirectorywith“mkdir”

Similartothetouchcommand,themkdircommandallowsustocreateemptydirectories.

For instance, to create a directory within our home directory called test,wecouldtype:cd

mkdirtest

Wecanmakeadirectorywithinthetestdirectorycalledexamplebytyping:mkdirtest/example

For the above command to work, the test directory must already exist. Totell mkdir that it should create any directories necessary to construct a givendirectory path, you can use the -p option. This allows you to create nesteddirectories in one step. We can create a directory structure that looks likesome/other/directoriesbytyping:mkdir-psome/other/directories

The command will make the some directory first, then it will createthe other directory in the some directory. Finally, it will createthedirectoriesdirectoryintheotherdirectory.

MovingandRenamingFilesandDirectorieswith“mv”

Wecanmoveafiletoanewlocationusingthemvcommand.Forinstance,wecanmovefile1intothetestdirectorybytyping:mvfile1test

For this command,we list all items thatwewant tomove,with the location to

move them to.We canmove that fileback to our home directory by using the

specialdotreferencetorefertoourcurrentdirectory.Weshouldmakesureweare

inourhomedirectory,andthenexecutethecommand:

cd

mvtest/file1.

This may seem unintuitive at first, but the mv command is also usedtorename files and directories. In essence,moving and renaming are both justadjustingthelocationandnameforanexistingitem.

Sotorenamethetestdirectorytotesting,wecouldtype:mvtesttesting

Note:ItisimportanttorealizethatyourLinuxsystemwillnotpreventyoufrom

certain destructive actions. If you are renaming a file and choose a name

that already exists, the previous file will be overwritten by the file you are

moving.Thereisnowaytorecoverthepreviousfileifyouaccidentallyoverwrite

it.

CopyingFilesandDirectorieswith“cp”

Withthemvcommand,wecouldmoveorrenameafileordirectory,butwecouldnotduplicateit.Thecpcommandcanmakeanewcopyofanexistingitem.

Forinstance,wecancopyfile3toanewfilecalledfile4:

cpfile3file4

Unlikethemvoperation,afterwhichfile3wouldno longerexist,wenowhavebothfile3andfile4.

Note:Aswith themvcommand, it ispossible tooverwrite a file if youarenotcareful about the filename you are using as the target of the operation. Forinstance, if file4 already existed in the above example, its contents would becompletelyreplacedbythecontentsoffile3.Inordertocopydirectories,youmustincludethe-roptioninthecommand.Thisstandsfor“recursive,”asitcopiesthedirectory,plusallofthedirectory’scontents.

This option is necessarywith directories, regardless of whether the directory isempty. For instance, to copy the some directory structure to a new structurecalledagain,wecouldtype:

cp-rsomeagain

Unlikewithfiles,withwhichanexistingdestinationwouldleadtoanoverwrite,if

thetargetisanexistingdirectory,thefileordirectoryiscopiedintothetarget:

cpfile1again

Thiswillcreateanewcopyoffile1andplaceitinsideoftheagaindirectory.

RemovingFilesandDirectorieswith“rm”and“rmdir”

Todeleteafile,youcanusethermcommand.

Note:Beextremelycarefulwhenusinganydestructivecommandlikerm.Thereisno “undo” command for these actions so it is possible to accidentally destroy

importantfilespermanently.

Toremovearegularfile,justpassittothermcommand:

cd

rmfile4

Likewise,toremoveemptydirectories,wecanusethermdircommand.Thiswillonly succeed if there is nothing in the directory in question. For instance, to

removetheexampledirectorywithinthetestingdirectory,wecantype:

rmdirtesting/example

If you wish to remove a non-empty directory, you will have to use

therm command again. This time, you will have to pass the-roption, whichremovesallofthedirectory’scontentsrecursively,plusthedirectoryitself.

For instance, to remove the again directory and everything within it, we cantype:

rm-ragain

Onceagain, it isworth reiterating that thesearepermanent actions.Be entirely

surethatthecommandyoutypedistheonethatyouwishtoexecute.

EditingFiles

Currently, we know how to manipulate files as objects, but we have not

learnedhowtoactuallyeditandaddcontenttothem.Thenanocommandisoneofthesimplestcommand-lineLinuxtexteditors,andisagreatstartingpointfor

beginners. It operates somewhat similarly to the less program we discussedearlier, in that it occupies the entire terminal for the duration of its use.

Thenanoeditorcanopenexistingfiles,orcreateafile.Ifyouwanttocreateanewfile,youcangiveitanamewhenyoucallthenanoeditor,orlateron,whenyouwishtosaveyourcontent.

Wecanopenthefile1fileforeditingbytyping:

cd

nanofile1

Thenanoapplicationwillopenthe file (which iscurrentlyblank).The interfacelookssomethinglikethis:

GNUnano2.2.6File:file1

[Read0lines]

^GGetHelp^OWriteOut^RReadFile^YPrevPage^KCutText^CCurPos

^XExit^JJustify^WWhereIs^VNextPage^UUnCutText^TToSpell

Alongthetop,wehavethenameoftheapplicationandthenameofthefileweare

editing.Inthemiddle,thecontentofthefile,currentlyblank,isdisplayed.Along

the bottom, we have a number of key combinations that indicate some basic

controlsfortheeditor.Foreachofthese,the^charactermeanstheCTRLkey.

Togethelpfromwithintheeditor,type:

CTRL-G

When you are finished browsing the help, type CTRL-X to get back to yourdocument.

Typeinormodifyanytextyouwouldlike.Forthisexample,wewilljusttypethese

twosentences:

Hellothere.

Hereissometext.

Tosavetype:

CTRL-O

Thisistheletter“o,”notazero.Itwillaskyoutoconfirmthenameofthefileyouwishtosaveto:

FileNametoWrite:file1

^GGetHelpM-DDOSFormatM-AAppendM-BBackupFile

^CCancelM-MMacFormatM-PPrepend

Asyoucansee,theoptionsatthebottomhavealsochanged.Thesearecontextual,

meaningtheywillchangedependingonwhatyouaretryingtodo.If file1 isstill

thefileyouwishtowriteto,hit“ENTER.”

Ifwemakeadditionalchangesandwishtosavethefileandexittheprogram,we

will see a similar prompt. Add a new line, and then try to exit the program by

typing:

CTRL-X

Ifyouhavenotsavedaftermakingyourmodification,youwillbeaskedwhetheryouwishtosavethemodificationsyoumade:

Savemodifiedbuffer(ANSWERING“No”WILLDESTROYCHANGES)?

YYes

NNo^CCancel

Youcan type “Y” to saveyourchanges, “N” todiscardyour changesandexit, or“CTRL-C”tocanceltheexitoperation.Ifyouchoosetosave,youwillbegiventhesamefileprompt thatyoureceivedbefore,confirmingthatyouwant tosave thechangestothesamefile.PressENTERtosavethefileandexittheeditor.

Youcanseethecontentsofthefileyoucreatedusingeitherthecatcommandtodisplay the contents, or theless command to open the file for viewing. Afterviewingwithless,rememberthatyoushouldhitqtogetbacktotheterminal.lessfile1

Hellothere.

Hereissometext.

Anotherline.

ChapterTen:UNIXSHELLSCRIPTING

Time isprecious. Itdoesnotmakesense towaste time typinga frequentlyused sequence of commands at a commandprompt,more especially if they areabnormally long or complex. Scripting is a way bywhich one can alleviate thisproblem by automating these command sequences in order tomake life at theshelleasierandmoreproductive.Scriptingisallaboutmakingthecomputer,thetool,dothework.BytheendofthistutorialyouwillhaveagoodunderstandingofthekindofscriptinglanguagesavailableforUnixandhowtoapplythemtoyourproblems. UNIX contains many wonderful and strange commands that can beveryusefulintheworldofscripting,themoretoolsyouknowandthebetteryouknowthem,themoreuseyouwillfindforthem.MostoftheUnixcommandsandmany of the built-in commands haveman pages;manpages contain the usageinstructionspertainingtotheparenttool.Theyarenotalwaysveryclearandmayrequirereadingseveraltimes.InordertoaccessamanpageinUnixthefollowingcommandsequenceisapplied:

mancommand

Ifamanpageexistsforthecommandspecifiedtheinternalviewerwillbeinvoked

andyouwillbeabletoreadaboutthevariousoptionsandusageinstructions.

ShellScriptingIntroduction

UNIXuses shells to accept commandsgivenby theuser; there arequite a

few different shells available. The most commonly used shells are SH (Bourne

SHell) CSH (C SHell) and KSH (Korn SHell), most of the other shells you

encounterwillbevariantsoftheseshellsandwillsharethesamesyntax,KSHis

basedonSHasisBASH(Bourneagainshell).TCSH(ExtendedCSHell)isbased

onCSH.

Thevariousshellsallhavebuiltinfunctionswhichallowforthecreationofshell

scripts, that is, the stringing together of shell commands and constructs to

automaterepetitivetasksinordertomakelifeeasierfortheuser.

With all these different shells available, what shell should we use? This is

debatable. For the purpose of this tutorial we will be using SH because it is

practicallyguaranteedtobeavailableonmostUnixsystemsandbesupportedby

theSHbasedshells.YourdefaultshellmaynotbeSH.Fortunatelywedonothave

tobeusingaspecificshell inordertoexploit itsfeaturesbecausewecanspecify

theshellwewanttointerpretourshellscriptwithinthescriptitselfbyincluding

thefollowinginthefirstline.

#!/path/to/shell

Usuallyanythingfollowing(#) is interpretedasacommentand ignoredbut if it

occurson the first linewitha (!) following it is treatedasbeing special and the

filename following the (!) is considered topoint to the locationof the shell that

shouldinterpretthescript.

Whena script is “executed”, it isbeing interpretedbyan invocationof the shell

that is running it.Hence, theshell issaid toberunningnon-interactively,when

theshellisused“normally”itissaidtoberunninginteractively.

Note: There aremany variations of the basic commands and extra information

which is too specific tobementioned in this short tutorial, you should read the

manpageforyourshelltogetamorecomprehensiveideaoftheoptionsavailable

to you. This tutorial will concentrate on highlighting the most often used and

usefulcommandsandconstructs.

CommandRedirectionandPipelines

By default a normal command accepts input from standard input, which we

abbreviatetostdin,standardinputisthecommandlineintheformofarguments

passed to the command. By default a normal command directs its output to

standard output, which we abbreviate to stdout, standard output is usually the

console display. For some commands thismay be the desired action but other

timeswemaywishtogetour input foracommandfromsomewhereother than

stdin and direct our output to somewhere other than stdout. This is done by

redirection:

We use> to redirect stdout to a file, for instance, if we wanted to redirect a

directorylistinggeneratedbythelswecoulddothefollowing:

ls>file

Weuse<tospecifythatwewantthecommandimmediatelybeforetheredirectionsymboltogetitsinputfromthesourcespecifiedimmediatelyafterthesymbol,forinstance,wecouldredirect the input togrep(whichsearches forstringswithinfiles)sothatitcomesfromafilelikethis:

grepsearchterm<file

Weuse>>toappendstdouttoafile,forexample,ifwewantedtoappendthedatetotheendofafilewewouldredirecttheoutputfromdatelikeso:

date>>file

One can redirect standard error (stderr) to a file by using2>, if we wanted to

redirectthestandarderrorfromcommandAtoafilewewoulduse:

commmandA2>

Pipes are another form of redirection that are used to chain commands so that

powerfulcompositecommandscanbeconstructed, thepipesymbol ’|’ takes the

stdoutfromthecommandprecedingitandredirectsittothecommandfollowing

it:

ls-l|grepsearchword|sort-r

The example above firsts requests a long (-l directory listing of the currentdirectory using the ls command, the output from this is then pipedto grepwhich filters out all the listings containing the searchword and thenfinally pipes this through to sortwhich then sorts the output in reverse (-r,sortthenpassestheoutputonnormallytostdout.

Variables

When a script starts, all environment variables are turned into shell variables.

Newvariablescanbeinstantiatedlikethis:

name=value

Youmustdoitexactlylikethat,withnospaces,thenamemustonlybemadeupof

alphabeticcharacters,numericcharactersandunderscores;itcannotbeginwitha

numericcharacter.Youshouldavoidusingkeywordslikefororanythinglikethat,

theinterpreterwillletyouusethembutdoingsocanleadtoobfuscatedcode;)

Variablesarereferencedlikethis:$name,hereisanexample:#!/bin/sh

msg1=Hello

msg2=There!

echo$msg1$msg2

This would echo “Hello There!” to the console display, if you want to assign a

stringtoavariableandthestringcontainsspacesyoushouldenclosethestringin

doublequotes(“),thedoublequotestelltheshelltotakethecontentsliterallyand

ignore keywords, however, a few keywords are still processed. You can still

use$withina(“)quotedstringtoincludevariables:

#!/bin/sh

msg1=“one”

msg2=”$msg1two”

msg3=”$msg2three”

echo$msg3

Wouldecho“onetwothree”tothescreen.Theescapecharactercanalsobeused

withinadoublequotedsectiontooutputspecialcharacters,theescapecharacter

is”",itoutputsthecharacterimmediatelyfollowingitliterallyso\wouldoutput\.

A special case is when the escape character is followed by a newline; the shell

ignoresthenewlinecharacter,whichallowsthespreadingoflongcommandsthat

mustbeexecutedonasingle line inrealityovermultiple lineswithinthescript.

Theescapecharactercanbeusedanywhere,exceptwithinsinglequotes.

Surroundinganythingwithsinglequotescausesittobetreatedasliteraltextthat

will be passed on exactly as intended, this can be useful for sending command

sequencestootherfilesinordertocreatenewscriptsbecausethetextbetweenthe

singlequoteswillremainuntouched.Forexample:

#!/bin/sh

echo‘msg=“HelloWorld!”’>hello

echo‘echo$msg’>>hello

chmod700hello

./hello

Thiswouldcause“msg=“HelloWorld!”tobeechoedandredirectedtothefilehello,“echo $msg”would then be echoed and redirected to the file hello but this timeappendedtotheend.Thechmodlinechangesthefilepermissionsofhellosothatwecanexecuteit.Thefinallineexecuteshellocausingitoutput“HelloWorld.”Ifwehadnotusedliteralquoteswewouldnothavehadtouseescapecharacterstoensurethat($)and(“)wereechoedtothefile,thismakesthecodealittleclearer.

Avariablemaybereferencedlikeso${VARIABLENAME},thisallowsonetoplace

characters immediately preceding the variable

like${VARIABLENAME}aaawithout the shell interpreting aaa asbeingpart of

thevariablename.

CommandLineArguments

Command line arguments are treated as special variables within the script, the

reason I am calling them variables is because they can be changed with

the shift command. The command line arguments are enumerated in the

followingmanner$0,$1,$2,$3,$4,$5,$6,$7,$8and$9.$0isspecialinthatit

corresponds to the name of the script itself.$1 is the first argument,$2 is the

second argument and so on. To reference after the ninth argument you must

enclosethenumberinbracketslikethis${nn}.Youcanusetheshiftcommandto

shiftthearguments1variabletotheleftsothat$2becomes$1,$1becomes$0and

soon,$0getsscrappedbecauseithasnowheretogo,thiscanbeusefultoprocess

alltheargumentsusingaloop,usingonevariabletoreferencethefirstargument

andshiftinguntilyouhaveexhaustedtheargumentslist.

Aswellasthecommandlineargumentstherearesomespecialbuilt-invariables:

$#representstheparametercount.Usefulforcontrollingloop

constructsthatneedtoprocesseachparameter.

$@expandstoalltheparametersseparatedbyspaces.Usefulfor

passingalltheparameterstosomeotherfunctionorprogram.

$-expandstotheflags(options)theshellwasinvokedwith.Usefulfor

controllingprogramflowbasedontheflagsset.

$$expandstotheprocessidoftheshellinnovatedtorunthescript.

Usefulforcreatinguniquetemporaryfilenamesrelativetothis

instantiationofthescript.

Note:Thecommand lineargumentswillbe referred toasparameters fromnow

on, this is because SH also allows the definition of functions which can take

parametersandwhencalledthe$nfamilywillberedefined,hencethesevariables

arealwaysparameters,itsjustthatinthecaseoftheparentscripttheparameters

arepassedvia thecommand line.Oneexception is$0which isalwaysset to the

nameoftheparentscriptregardlessofwhetheritisinsideafunctionornot.

CommandSubstitution

In thewords of the SHmanual “Command substitution allows the output of a

commandtobesubstitutedinplaceofthecommandnameitself”.Therearetwo

waysthiscanbedone.Thefirstistoenclosethecommandlikethis:

$(command)

Thesecondistoenclosethecommandinbackquoteslikethis:

`command`

The command will be executed in a sub-shell environment and the standard

output of the shell will replace the command substitution when the command

finishes.

ArithmeticExpansion

Arithmeticexpansionisalsoallowedandcomesintheform:

$((expression))

Thevalueoftheexpressionwillreplacethesubstitution.Eg:

!#/bin/sh

echo$((1+3+4))

Willecho“8”tostdout

ControlConstructs

TheflowofcontrolwithinSHscriptsisdoneviafourmainconstructs;if…then…

elif…,else…,do…,while…,for…andcase….

If..Then..Elif..Else

Thisconstructtakesthefollowinggenericform;thepartsenclosedwithin([)and

(])areoptional:

iflist

thenlist

[eliflist

thenlist]…

[elselist]

fi

When aUnix command exits it exitswithwhat is known as an exit status, this

indicatestoanyonewhowantstoknowthedegreeofsuccessacommand,usually

whenacommandexecuteswithouterroritterminateswithanexitstatusofzero.

Anexitstatusofsomeothervaluewouldindicatesthatanerrorhasoccurred,the

details ofwhich are specific to the command.The commands’manpagesdetail

theexitstatusmessages.

AlistisdefinedintheSHas“asequenceofzeroormorecommandsseparatedbynewlines,semicolons,orampersands,andoptionallyterminatedbyoneofthesethree characters.” Hence in the generic definition of the if above the list willdeterminewhichof theexecutionpaths thescript takes.Forexample, there isacommandcalledtestonUNIX,whichevaluatesanexpressionandifitevaluatestrue will return zero and will return one otherwise, this is how we can testconditionsinthelistpart(s)oftheifconstructbecausetestisacommand.

Wedonotactuallyhavetotypethetestcommanddirectlyintothelisttouseit;it can be implied by encasing the test case within ([) and (]) characters, asillustratedbythefollowing(silly)example:

#!/bin/sh

if[“$1”=“1”]

then

echo“Thefirstchoiceisnice”

elif[“$1”=“2”]

then

echo“Thesecondchoiceisjustasnice”

elif[“$1”=“3”]

then

echo“Thethirdchoiceisexcellent”

else

echo“Iseeyouwerewiseenoughnottochoose”

echo“Youwin”

fi

Whatthisexampledoesiscomparethefirstparameter(commandlineargument

inthiscase)withthestrings“1”,“2”and“3”usingtests’(=)testwhichcompares

two strings for equality, if any of them match it prints out the corresponding

message.Ifnoneofthemmatchitprintsoutthefinalcase.OKtheexampleissilly

andactuallyflawed(theuserstillwinseveniftheytypein(4)orsomething)butit

illustrateshowtheifstatementworks.

Noticethattherearespacesbetween(if)and([),([)andthetestandthetestand

(]), these spacesmust be present otherwise the shellwill complain. Theremust

alsobespacesbetweentheoperatorandoperandsofthetestotherwiseitwillnot

workproperly.Noticehow it startswith (if)andendswith (fi),also,noticehow

(then)isonaseparatelinetothetestaboveitandthat(else)doesnotrequirea

(then)statement.Youmustconstructthisconstructexactlylikethisforittowork

properly.

It isalsopossibletointegratelogicalANDandORintothetesting,byusingtwo

testsseparatedbyeither“&&”or“||”respectively.Forexample,wecouldreplace

thethirdtestcaseintheexampleabovewith:

elif[“$1”=“3”]||[“$1”=“4”]

thenecho“Thethirdchoi…

Thescriptwouldprintout“Thethirdchoiceisexcellent”ifthefirstparameterwas

either“3”OR“4”.Toillustratetheuseof“&&”wecouldreplacethethirdtestcase

with:

elif[“$1”=“3”]||[“$2”=“4”]

thenecho“Thethirdchoi…

The scriptwouldprint out “The third choice is excellent” if andonly if the first

parameterwas“3”ANDthesecondparameterwas“4”.

“&&”and“||”arebothlazilyevaluatingwhichmeansthat inthecaseof“&&”, ifthefirsttestfailsitwon’tbotherevaluatingthesecondbecausethelistwillonlybetrueiftheyBOTHpassandsinceonehasalreadyfailedthereisnopointwastingtimeevaluatingthesecond.Inthecaseof“||”ifthefirsttestpassesitwon’tbotherevaluatingthesecondtestbecauseweonlyneedONEoftheteststopassforthewholelisttopass.Seethetestmanpageforthelistoftestspossible(otherthanthestringequalitytestmentionedhere).

Do…While

TheDo…Whiletakesthefollowinggenericform:

whilelist

dolist

done

Inthewordsof theSHmanual“Thetwolistsareexecutedrepeatedlywhilethe

exitstatusofthefirstlistiszero.”Thereisavariationonthisthatusesuntilinplaceofwhilewhichexecutesuntiltheexitstatusofthefirstlistiszero.Hereisanexampleuseofthewhilestatement:

#!/bin/sh

count=$1#Initialisecounttofirstparameter

while[$count-gt0]#whilecountisgreaterthan10do

do

echo$countsecondstillsuppertime!

count=$(expr$count-1)#decrementcountby1

sleep1#sleepforasecondusingtheUnixsleepcommand

done

echoSuppertime!!,YEAH!!#werefinished

Ifcalledfromthecommandlinewithanargumentof4thisscriptwilloutput

4secondstillsuppertime!

3secondstillsuppertime!

2secondstillsuppertime!

1secondstillsuppertime!

Suppertime!!,YEAH!!

Youcanseethatthistimewehaveusedthe-gtofthetestcommandimplicitlycalledby‘[‘and‘]’,whichstandsforgreaterthan.Paycarefulattentiontotheformattingandspacing.

For

Thesyntaxoftheforcommandis:

forvariableinword…

dolist

done

The SHmanual states “Thewords are expanded, and then the list is executed

repeatedlywiththevariablesettoeachwordinturn.”Awordisessentiallysome

othervariablethatcontainsalistofvaluesofsomesort,theforconstructassigns

eachofthevaluesinthewordtovariableandthenvariablecanbeusedwithinthe

bodyoftheconstruct,uponcompletionofthebodyvariablewillbeassignedthe

nextvalue inworduntil therearenomorevalues inword.Thisexampleshould

makethisclearer:

#!/bin/sh

fruitlist=“ApplePearTomatoPeachGrape”

forfruitin$fruitlist

do

if[“$fruit”=“Tomato”]||[“$fruit”=“Peach”]

then

echo“Ilike${fruit}es”

else

echo“Ilike${fruit}s”

fi

done

Inthisexample, fruitlist isword, fruit isvariableand thebodyof the statement

outputs how much this person loves various fruits but includes an if… then…

else statement to dealwith the correct addition of letters to describe the plural

version of the fruit, notice that the variable fruit was expressed

like ${fruit} because otherwise the shell would have interpreted the preceding

letter(s) as being part of the variable and echoed nothing because we have not

definedthevariablesfruitsandfruitesWhenexecutedthisscriptwilloutput:

IlikeApples

IlikePears

IlikeTomatoes

IlikePeachs

IlikeGrapes

Withintheforconstruct,doanddonemaybereplacedby’{‘and’}’.

Case

Thecaseconstructhasthefollowingsyntax:

casewordin

pattern)list;;

…

esac

Anexampleofthisshouldmakethingsclearer:

!#/bin/sh

case$1

in

1)echo‘FirstChoice’;;

2)echo‘SecondChoice’;;

*)echo‘OtherChoice’;;

esac

“1”,“2”and“*”arepatterns,wordiscomparedtoeachpatternandifamatchis

found the body of the corresponding pattern is executed, we have used “*” to

represent everything, since this is checked last we will still catch “1” and “2”

becausetheyarecheckedfirst. Inourexampleword is“$1”, the firstparameter,

hence if thescript is ranwith theargument “1” itwilloutput “FirstChoice”, “2”

“SecondChoice”andanythingelse“OtherChoice”.Inthisexamplewecompared

against numbers (essentially still a string comparison however) but the pattern

canbemorecomplex,seetheSHmanpageformoreinformation.

Functions

ThesyntaxofanSHfunctionisdefinedasfollows:

name()command

Itisusuallylaidoutlikethis:

name(){

commands

}

Afunctionwillreturnwithadefaultexitstatusofzero,onecanreturndifferent

exitstatusesbyusingthenotationreturnexitstatus.Variablescanbedefined

locallywithinafunctionusinglocalname=value.Theexamplebelowshowsthe

useofauserdefinedincrementfunction:

IncrementFunctionExample#!/bin/sh

inc(){ #Theincrementisdefinedfirstsowecanuseit

echo$(($1+$2))#Weechotheresultofthefirstparameterplusthesecondparameter

}

#Wechecktoseethatallthecommandlineargumentsarepresent

if[“$1”””]||[“$2”=””]||[“$3”=””]

then

echoUSAGE:

echo”counterstartvalueincrementvalueendvalue”

else

count=$1#Renamearevariableswithclearernames

value=$2

end=$3

while[$count-lt$end]#Loopwhilecountislessthanend

do

echo$count

count=$(inc$count$value) #Callincrementwithcountandvalueasparameters

done#sothatcountisincrementedbyvalue

fi

inc(){

echo$(($1+$2))

}

Thefunction isdefinedandopenedwith inc(){, the lineecho$(($1+$2))uses

the notation for arithmetic expression substitution which is $((expression)) to

enclose the expression, $1 + $2 which adds the first and second parameters

passedtothefunctiontogether,theechobitatthestartechoesthemtostandard

output,wecancatch thisvaluebyassigning the functioncall toavariable,as is

illustratedbythefunctioncall.

count=$(inc$count$value)

We use command substitution which substitutes the value of a command to

substitute the value of the function call whereupon it is assigned to

thecount variable.The commandwithin the command substitutionblock is inc

$count $value, the last two values being its parameters. Which are then

referenced from within the function using $1 and $2.We could have used the

othercommandsubstitutionnotationtocallthefunctionifwehadwanted:

count=`inc$count$value`

Hereisanotherexampleillustratingthescopeofvariables:

VariableScope,Example

#!/bin/sh

inc(){

localvalue=4

echo“valueis$valuewithinthefunction\n”

echo“\b\$1is$1withinthefunction”

}

value=5

echovalueis$valuebeforethefunction

echo“\$1is$1beforethefunction”

echo

echo-e$(inc$value)

echo

echovalueis$valueafterthefunction

echo“\$1is$1afterthefunction”

inc(){

localvalue=4

echo“valueis$valuewithinthefunction\n”

echo“\b\$1is$1withinthefunction”

}

Weassigna localvaluetothevariablevalueof4.Thenextthree linesconstruct

theoutput,rememberthatthisisbeingechoedtoabufferandwillbereplacethe

function call with all that was passed to stdout within the function when the

function exits. So, the calling code will be replaced with whatever we direct to

standardoutputwithinthefunction.Thefunctioniscalledlikethis:

echo-e$(inc$value)

Wehavepassedtheoption-etotheechocommandwhichcausesittoprocessC-style backslash escape characters, so we can process any backslash escapecharacterswhichthestringgeneratedbythefunctioncallcontains.Ifwejustechothe lines we want to be returned by the function it will not pass the newlinecharacterontothebufferevenifweexplicitlyincludeitwithanescapecharacterreference sowhatwe do is actually include the sequence of characters thatwill

produceanewlinewithinthestringsothatwhenitisechoedbythecallingcodewith the -e the escape characters will be processed and the newlines will beplacedwherewewantthem.echo“valueis$valuewithinthefunction\n”

Notice how the newline has been inserted with \n, the first two backslashesindicate that we want to echo a backslash because within double quotes abackslash indicates to process the next character literally, we have to do thisbecauseweareonlybetweendoublequotesandnottheliteral-textsinglequotes.Ifwehadusedsinglequoteswewouldhadhavetoechothebitwiththenewlineinseparately from the bit that contains $value otherwise $value would not beexpanded.echo“\b\$1is$1withinthefunction”

This is our second line, and is contained within double quotes so that thevariable $1 will be expanded, \b is included so that \b will be placed in theechoedlineandourcallingcodeprocessesthisasabackspacecharacter.Ifwedonotdo that the shellprefixesa space to the second line, thebackspace removesthisspace.

Theoutputfromthisscriptcalledwith2asthefirstargumentis:

valueis5beforethefunction

$1is2beforethefunction

valueis4withinthefunction

$1is5withinthefunction

valueis5afterthefunction

$1is2afterthefunction

Tip:Youcanuse“.DIRECTORY/common.sh”toimportfunctionsfromascriptcalled common.sh in DIRECTORY, a quick example is shown below, first istest.sh:#!/bin/sh

../common.sh

if[“$1”=””];then

echoUSAGE:

echo“shtest.shtype”

exit

fi

if`validtype$1`;then

echoValidtype

else

echoInvalidtype

fi

Hereiscommon.sh:#!/bin/sh

validtype(){

if[“$1”=“TYPEA”]||

[“$1”=“TYPEB”]||

[“$1”=“TYPEC”]||

[“$1”=“TYPED”]||

[“$1”=“TYPEE”];

then

exit0

else

exit1

fi

}

ChapterEleven:SHELLBASICOPERATOR

Each shell supports various operators. This chapter is based on default shell

(Bourne)sowearegoingtocoveralltheimportantBourneShelloperatorsinthis

tutorial.

Wewilldiscussthefollowingoperators−

ArithmeticOperators.

RelationalOperators.

BooleanOperators.

StringOperators.

FileTestOperators.

The Bourne shell did not originally have any mechanism to perform simplearithmeticbutitusesexternalprograms,eitherawkorthemustsimplerprogramexpr.

Hereissimpleexampletoaddtwonumbers–

#!/bin/sh

val=`expr2+2`

echo“Totalvalue:$val”

Thisproducesthefollowingresult−Totalvalue:4

Note:

Theremustbespacesbetweenoperatorsandexpressionsforexample

2+2isnotcorrect,itshouldbewrittenas2+2.

Completeexpressionsshouldbeenclosedbetween“,invertedcommas.

ArithmeticOperators

ThefollowingarearithmeticoperatorssupportedbytheBourneShell.

Assumevariable‘a’holds10andvariable‘b’holds20then−

Example,usingallthearithmeticoperators−

#!/bin/sh

a=10

b=20

val=`expr$a+$b`

echo“a+b:$val”

val=`expr$a-$b`

echo“a-b:$val”

val=`expr$a\*$b`

echo“a*b:$val”

val=`expr$b/$a`

echo“b/a:$val”

val=`expr$b%$a`

echo“b%a:$val”

if[$a==$b]

then

echo“aisequaltob”

fi

if[$a!=$b]

then

echo“aisnotequaltob”

fi

Thisproducesthefollowingresult−a+b:30

a-b:-10

a*b:200

b/a:2

b%a:0

aisnotequaltob

Note:

Theremustbespacesbetweenoperatorsandexpressionsforexample2+2isnotcorrect,whereasitshouldbewrittenas2+2.

Completeexpressionshouldbeenclosedbetween“,invertedcommas.

Youshoulduse\onthe*symbolformultiplication.

Theif…then…fistatementisadecision-makingstatement,whichwillbeexplainedinthenextchapter.

Operator Description Example

+ Addition-Addsvaluesoneithersideoftheoperator

`expr$a+$b`willgive30

- Subtraction-Subtractsrighthandoperandfromlefthandoperand

`expr$a-$b`willgive-10

* Multiplication-Multipliesvaluesoneithersideoftheoperator

`expr$a\*$b`willgive200

/ Division-Divideslefthandoperandbyrighthandoperand

`expr$b/$a`willgive2

% Modulus-Divideslefthandoperandbyrighthandoperandandreturnsremainder

`expr$b%$a`willgive0

= Assignment-Assignrightoperandinleftoperand

a=$bwouldassignvalueofbintoa

== Equality-Comparestwonumbers,ifbotharesamethenreturnstrue.

[$a==$b]wouldreturnfalse.

!= NotEquality-Comparestwonumbers,ifbotharedifferentthenreturnstrue.

[$a!=$b]wouldreturntrue.

It is very important to note that all the conditional expressions should be put

insidesquarebraceswithonespacesaroundthem, forexample [$a==$b] is

correctwhereas[$a==$b]isincorrect.

Allthearithmeticalcalculationsaredoneusinglongintegers.

RelationalOperators:

Bourne Shell supports the following relational operators, which are specific tonumericvalues.Theseoperatorswillnotworkforstringvaluesunlesstheirvalueisnumeric.Forexample,thefollowingoperatorscheckarelationbetween10and20aswell as inbetween “10” and “20”butnot inbetween “ten” and “twenty”.Assumevariableaholds10andvariablebholds20then−

Thisexampleusesalltherelationaloperators−#!/bin/sh

a=10

b=20

if[$a-eq$b]

then

echo“$a-eq$b:aisequaltob”

else

echo“$a-eq$b:aisnotequaltob”

fi

if[$a-ne$b]

then

echo“$a-ne$b:aisnotequaltob”

else

echo“$a-ne$b:aisequaltob”

fi

if[$a-gt$b]

then

echo“$a-gt$b:aisgreaterthanb”

else

echo“$a-gt$b:aisnotgreaterthanb”

fi

if[$a-lt$b]

then

echo“$a-lt$b:aislessthanb”

else

echo“$a-lt$b:aisnotlessthanb”

fi

if[$a-ge$b]

then

echo“$a-ge$b:aisgreaterorequaltob”

else

echo“$a-ge$b:aisnotgreaterorequaltob”

fi

if[$a-le$b]

then

echo“$a-le$b:aislessorequaltob”

else

echo“$a-le$b:aisnotlessorequaltob”

fi

Thisproducesthefollowingresult−10-eq20:aisnotequaltob

10-ne20:aisnotequaltob

10-gt20:aisnotgreaterthanb

10-lt20:aislessthanb

10-ge20:aisnotgreaterorequaltob

10-le20:aislessorequaltob

Note:

Theremustbespacesbetweenoperatorsandexpressionsforexample

2+2isnotcorrect,whereasitshouldbewrittenas2+2.

if…then…else…fistatementisadecisionmakingstatementwhich

willbeexplainedinthenextchapter.

Operator Description Example

-eq Checksifthevalueoftwooperandsareequal,ifyesthenconditionbecomestrue.

[$a-eq$b]isnottrue.

-ne Checksifthevalueoftwooperandsareequal,ifvaluesarenotequalthenconditionbecomestrue.

[$a-ne$b]istrue.

-gt Checksifthevalueofleftoperandisgreaterthanthevalueofrightoperand,ifyesthenconditionbecomestrue.

[$a-gt$b]isnottrue.

-lt Checksifthevalueofleftoperandislessthanthevalueofrightoperand,ifyesthenconditionbecomestrue.

[$a-lt$b]istrue.

-ge Checksifthevalueofleftoperandisgreaterthanorequaltothevalueofrightoperand,ifyesthenconditionbecomestrue.

[$a-ge$b]isnottrue.

-le Checksifthevalueofleftoperandislessthanorequaltothevalueofrightoperand,ifyesthenconditionbecomes

[$a-le$b]istrue.

true.

It is very important to note that all the conditional expressions should be put

insidesquarebraceswithonespacesaroundthem, forexample [$a<=$b] is

correctwhereas[$a<=$b]isincorrect.

BooleanOperators

TheBourneShellsupportsthefollowingbooleanoperators.

Assumevariable‘a’holds10andvariable‘b’holds20then−

Thisexampleusesallthebooleanoperators−#!/bin/sh

a=10

b=20

if[$a!=$b]

then

echo“$a!=$b:aisnotequaltob”

else

echo“$a!=$b:aisequaltob”

fi

if[$a-lt100-a$b-gt15]

then

echo“$a-lt100-a$b-gt15:returnstrue”

else

echo“$a-lt100-a$b-gt15:returnsfalse”

fi

if[$a-lt100-o$b-gt100]

then

echo“$a-lt100-o$b-gt100:returnstrue”

else

echo“$a-lt100-o$b-gt100:returnsfalse”

fi

if[$a-lt5-o$b-gt100]

then

echo“$a-lt100-o$b-gt100:returnstrue”

else

echo“$a-lt100-o$b-gt100:returnsfalse”

fi

Thisproducesthefollowingresult−10!=20:aisnotequaltob

10-lt100-a20-gt15:returnstrue

10-lt100-o20-gt100:returnstrue

10-lt5-o20-gt100:returnsfalse

Note:

Theremustbespacesbetweenoperatorsandexpressionsforexample

2+2isnotcorrect,whereasitshouldbewrittenas2+2.

Operator Description Example

! Thisisalogicalnegation.Thisinvertsatrueconditionintofalseandviceversa.

[!false]istrue.

-o ThisisalogicalOR.Ifoneoftheoperandsweretruethenconditionwouldbetrue.

[$a-lt20-o$b-gt100]istrue.

-a ThisisalogicalAND.Ifboththeoperandsweretruethenconditionwouldbetrueotherwise,itwouldbefalse.

[$a-lt20-a$b-gt100]isfalse.

StringOperators

TheBourneShellsupportsthefollowingstringoperators.

Assumevariable‘a’holds“abc”andvariable‘b’holds“efg”then−

Thisexampleusesallthestringoperators−#!/bin/sh

a=“abc”

b=“efg”

if[$a=$b]

then

echo“$a=$b:aisequaltob”

else

echo“$a=$b:aisnotequaltob”

fi

if[$a!=$b]

then

echo“$a!=$b:aisnotequaltob”

else

echo“$a!=$b:aisequaltob”

fi

if[-z$a]

then

echo“-z$a:stringlengthiszero”

else

echo“-z$a:stringlengthisnotzero”

fi

if[-n$a]

then

echo“-n$a:stringlengthisnotzero”

else

echo“-n$a:stringlengthiszero”

fi

if[$a]

then

echo“$a:stringisnotempty”

else

echo“$a:stringisempty”

fi

Thisproducesthefollowingresult−abc=efg:aisnotequaltob

abc!=efg:aisnotequaltob

-zabc:stringlengthisnotzero

-nabc:stringlengthisnotzero

abc:stringisnotempty

Note:

Theremustbespacesbetweenoperatorsandexpressionsforexample

2+2isnotcorrect,whereasitshouldbewrittenas2+2.

Operator Description Example

= Checksifthevalueoftwooperandsisequal,ifyesthenconditionbecomestrue.

[$a=$b]isnottrue.

!= Checksifthevalueoftwooperandsareequal,ifvaluesarenotequalthenconditionbecomestrue.

[$a!=$b]istrue.

-z Checksifthegivenstringoperandsizeiszero.Ifitiszerolengththenitreturnstrue.

[-z$a]isnottrue.

-n Checksifthegivenstringoperandsizeisnon-zero.Ifitisnon-zerolengththenitreturnstrue.

[-z$a]isnotfalse.

str Checkifstrisnottheemptystring.Ifitisemptythenitreturnsfalse.

[$a]isnotfalse.

FileTestOperators

ThefollowingoperatorstestvariouspropertiesassociatedwithaUnixfile.

Assumeavariablefileholdsanexistingfilename“test”whosesizeis100bytesandhasread,writeandexecutepermissions−

Thisexampleusesallthefiletestoperators−#!/bin/sh

file=“/var/www/tutorialspoint/unix/test.sh”

if[-r$file]

then

echo“Filehasreadaccess”

else

echo“Filedoesnothavereadaccess”

fi

if[-w$file]

then

echo“Filehaswritepermission”

else

echo“Filedoesnothavewritepermission”

fi

if[-x$file]

then

echo“Filehasexecutepermission”

else

echo“Filedoesnothaveexecutepermission”

fi

if[-f$file]

then

echo“Fileisanordinaryfile”

else

echo“Thisisspecialfile”

fi

if[-d$file]

then

echo“Fileisadirectory”

else

echo“Thisisnotadirectory”

fi

if[-s$file]

then

echo“Filesizeiszero”

else

echo“Filesizeisnotzero”

fi

if[-e$file]

then

echo“Fileexists”

else

echo“Filedoesnotexist”

fi

Thisproducesthefollowingresult−Filehasreadaccess

Filehaswritepermission

Operator Description Example

-bfile Checksiffileisablockspecialfileifyesthenconditionbecomestrue.

[-b$file]isfalse.

-cfile Checksiffileisacharacterspecialfileifyesthenconditionbecomestrue.

[-c$file]isfalse.

-dfile Checkiffileisadirectoryifyesthenconditionbecomestrue.

[-d$file]isnottrue.

-ffile Checkiffileisanordinaryfileasopposedtoadirectoryorspecialfileifyesthenconditionbecomestrue.

[-f$file]istrue.

-gfile ChecksiffilehasitssetgroupID(SGID)bitsetifyesthenconditionbecomestrue.

[-g$file]isfalse.

-kfile Checksiffilehasitsstickybitsetifyesthenconditionbecomestrue.

[-k$file]isfalse.

-pfile Checksiffileisanamedpipeifyesthenconditionbecomestrue.

[-p$file]isfalse.

-tfile Checksiffiledescriptorisopenandassociatedwithaterminalifyesthenconditionbecomestrue.

[-t$file]isfalse.

-ufile Checksiffilehasitssetuserid(SUID)bitsetifyesthenconditionbecomestrue.

[-u$file]isfalse.

-rfile Checksiffileisreadableifyesthenconditionbecomestrue.

[-r$file]istrue.

-wfile Checksiffileiswritableifyesthenconditionbecomestrue.

[-w$file]istrue.

-xfile Checksiffileisexecuteifyesthen [-x$file]is

Filehasexecutepermission

Fileisanordinaryfile

Thisisnotadirectory

Filesizeiszero

Fileexists

Note:

Theremustbespacesbetweenoperatorsandexpressionsforexample

2+2isnotcorrect,whereasitshouldbewrittenas2+2.

RunThe.ShFileShell

ScriptInLinux/Unix

After downloading

thesoftware,the.shfileis

nothing but the shell

script to install a given

application or to perform

other tasks under UNIX

like operating systems.

Theeasiestwaytorun.sh

shell script in Linux or

UNIX is to type either of

the following commands.

Open the terminal (your

shellprompt)andtypethe

command:

shfile.sh

ORbashfile.sh

.shAsRootUser

Sometimes you will need

to install an application

that requires root level

conditionbecomestrue. true.

-sfile Checksiffilehassizegreaterthan0ifyesthenconditionbecomestrue.

[-s$file]istrue.

-efile Checksiffileexists.Istrueeveniffileisadirectorybutexists.

[-e$file]istrue.

privileges.

Rootaccess isdisabledby

default on many Linux

and UNIX like systems.

Simply use sudo or su as

follows:

sudobashfilename.sh

Type your password. Another option is to use the su command as follows tobecomesuperuser:su-

Typerootuserpasswordandfinallyrunyourscript:bashfilename.sh

chmodCommand:RunShellScriptInLinux

Anotherrecommendedoptionistosetanexecutablepermissionusingthechmodcommandasfollows:chmod+xfile.sh

Nowyoucanrunthe.shfile../file.sh

ChapterTwelve:SHELLEMBEDDINGANDOPTIONS

Thischapterinvestigatestykeshells,implantedshellsandshellalternatives.

Shellinstalling

Shellscanbe installedtoworkonacommandline; thecommandlinecanbring

forthnewprocedurescontainingaforkofthepresentshell.Youcanusevariables

todemonstratethatthenewshellsaremade.Thevariable$var1justexistsinthe

(interim)subshell.

[paul@RHELv4u3gen]$reverberation$var1

[paul@RHELv4u3gen]$reverberation$(var1=5;echo$var1)

5

[paul@RHELv4u3gen]$reverberation$var1

[paul@RHELv4u3gen]$

You can install a shell into an inserted shell; this is called settled implantingof

shells.

paul@deb503:~$A=shell

paul@deb503:~$ reverberation $C$B$A $(B=sub;echo $C$B$A; reverberation$(C=sub;echo$C$B$A))

shellsubshellsubsubshell

Backticks

Single installation can change your present index and uses backticks instead of

dollarsectiontoimplant.

[paul@RHELv4u3~]$reverberation`cd/andsoforth;ls-d*|greppass`

passwd-passwd.OLD

[paul@RHELv4u3~]$

Thebackticks/()andthe$()documentationcanbeusedtoimplantashell.

Backticksorsinglequotes

Putting the installing between backticks utilizes one character not exactly the

dollarandbracketcombo.Becautiousontheotherhand,backticksarefrequently

mistakenforsinglequotes.

Thespecializedcontrastinthemiddleof”and`iscritical![paul@RHELv4u3gen]$reverberation`var1=5;echo$var1`

[paul@RHELv4u3gen]$reverberation‘var1=5;echo$var1’

var1=5;echo$var1

[paul@RHELv4u3gen]$

ShellAlternatives

Both set and unset are built-in shell commands, which are used to setalternativestothebashshell.Thefollowingcasewillclearupthis.Theshellwilltreatunsetvariablesasanunimportantvariable.Bysetting the-ualternative,theshellwilltreatanyreferencetounsetvariablesasanerror.[paul@RHEL4b~]$reverberation$var123

[paul@RHEL4b~]$set-u

[paul@RHEL4b~]$reverberation$var123

-bash:var123:unboundvariable

[paul@RHEL4b~]$set+u

[paul@RHEL4b~]$reverberation$var123

[paul@RHEL4b~]$

Torundownallthesetchoicesforyourshell,usereverberation$-.Thenoclobber

(or-C).

[paul@RHEL4b~]$reverberation$-

himBH

[paul@RHEL4b~]$set-C;set-u

[paul@RHEL4b~]$reverberation$-

himuBCH

[paul@RHEL4b~]$set+C;set+u

[paul@RHEL4b~]$reverberation$-

himBH

[paul@RHEL4b~]$

Whenwritingasetwithoutalternatives,yougetarundownofallvariableswithout

capacity,whentheshellisinposixmode,youcansetbashinposixmodewriting

set-oposix.

Practice:ShellInstalling

1. Discovertherundownofshellchoicesinthemanpageofbash.Whatis

thecontrastbetweensituated-uandset-onounset?

2. Actuatenounsetinyourshell.Testifitdemonstratesanerrormessage

whenusingnon-existingvariables.

3. Deactivatenounset.

4. Executedisc/varandlsinaninstalledshell.

Thereverberationcommand isexpected todemonstrate theaftereffectsofthe ls command. Precluding will cause the shell to execute the firstdocumentasacommand.

5. Addthevariableembvarintoaninsertedshellandreverberationit.Doesthevariableexistinyourpresentshellnow?

6. Clarifywhat“set-x”does.Canthisbeuseful?

(Optional)

7. Giventheaccompanyingscreenshot,addfourcharacterstothe

commandsothattheaggregateyieldisFirstMiddleLast.

[paul@RHEL4b~]$reverberateFirst;resoundMiddle;reverberate

Last.

8. Displayalonglisting(ls-l)ofthepasswdcommandutilizingthewhichcommandinsideaninstalledshell.

15.4.Arrangement:shellinserting

1. Discovertherundownofshellalternativesinthemanpageofbash.

Whatisthedistinctionbetweensituated

uandset-onounset?

Checkthemanofbashandlookfornounset-bothmeanthesamething.

2. Addnounsettoyourshell.Testthatitdemonstratesalapsemessage

whenutilizingnonexistingvariables.

set-u

Or

set-onounset

Bothlineshavethesameimpact.

3. Deactivatenounset.

set+u

Or

set+onounset

4. Executealbum/varandlsinanimplantedshell.

reverberation$(cd/var;ls)

Thereverberationcommandisusedtodemonstratetheconsequenceofthe

lscommand.Precludingwillmaketheshelltoexecutethefirstdocumentas

acommand.

5.Makethevariableembvarinanimplantedshellandreverberationit.Doesthevariableexistinyourpresentshell?

reverberation$(embvar=emb;echo$embvar) ;reverberation$embvar#the

lastresoundfizzles

$embvardoesnotexistinyourpresentshell

6. Clarifywhat“set-x”does.Isthisuseful?

Itshowsshelldevelopmentforinvestigatingyourcommand.

(Optional)

7. Giventheaccompanyingscreenshot,addfourcharacterstothe

commandlinesothattheaggregateyieldisFirstMiddleLast.

[paul@RHEL4b~]$reverberateFirst;resoundMiddle;reverberateLast

reverberation-nFirst;resound-nMiddle;resoundLast

8. Showalongposting(ls-l)ofthepasswdcommandusingthe“whichcommand”insideanimplantedshell.

ls-l$(whichpasswd

Almostall-modernshellallowsyoutosearchcommandhistoryifenabledbythe

user.Historycommandcandisplaythehistorylistwithlinenumbers,listedwitha

*havebeenmodifiedbyuser.

ChapterThirteen:SHELLHISTORYSEARCHCOMMAND

Typehistoryatashellprompt:$history

Output:6du-c

7du-ch

8ls[01-15]*-2008

9ls-ld[01-15]*-2008

10ls-ld[1-15]*-2008

11ls-ld[0]*-2008

12ls-ld[01]*-2008

13rm-vrf[01]*-2008

14du-ch

15ls

16cd

17umount/mnt

18df-H

19vnstat

20yumupdate

21vnstat-m

22vnstat-m-ieth0

….

…

996pingrouter.nixcraft.in

997sshvivek@p1.vpn.nixcraft.in

998alias

999~/scripts/clean.rss—fetch

1000vnstat

1001~/scripts/clean.rss—update

Tosearchforaparticularcommand,enter:$history|grepcommand-name

$history|egrep-i‘scp|ssh|ftp’

EmacsLine-EditModeCommandHistorySearching

Tofindthecommandcontainingstring,hit[CTRL]+[r]followedbysearchstring:(reverse-i-search):

Toshowthepreviouscommand,hit[CTRL]+[p].Youcanalsouseuparrowkey.CTRL-p

Toshowthenextcommand,hit[CTRL]+[n].Youcanalsousedownarrowkey.CTRL-n

fccommand

fcstandsforeitherthefindcommandorthefixcommand.Forexampletolistthelast10commands,enter:$fc-l10

tolistcommands130through150,enter:$fc-l130150

tolistallcommandssincethelastcommandbeginningwithssh,enter:$fc-lssh

Youcaneditcommands1through5usingvitexteditor,enter:$fc-evi15

Deletecommandhistory

The-coptioncausesthehistorylisttobeclearedbydeletingalloftheentries:$history-c

FILENAMEGLOBBINGWITH*,?,[]

Sometimesyouwanttomanipulateagroupoffiles,e.g.,deleteallofthem,

without having to perform the command on each file separately. For example,

supposewewanttodeleteallofthe.cfilesinadirectory.Awildcardisapattern,

whichmatchessomethingelse.Twocommonlyused*nixwildcardsare*(star)

and?(questionmark).

Star(*)meanszeroormorecharacters

QuestionMark(?)meansexactlyonecharacter

Brackets([])representasetofcharacters

Commandsinvolvingfilenamesspecifiedwithwildcardsareexpandedbytheshell

(this is calledglobbingafter thenameof a formerprogramcalledglobwhich

usedtodothisoutsidetheshell).

The‘*’

‘file*’willmatchanyfilenamewhichstartswiththecharacters“file”,andthenis

followedbyzeroormoreoccurrencesofanycharacter.

Examples

SupposeFred’shomedirectorycontainsthefiles,

file01.cpp

file02.cpp

file03.cpp

file1.cpp

file01.o

file02.o

file03.o

file1.o

Todeleteallofthe.cfiles,type,

$rm*.c

Todeletefile01.cppandfile01.o,$rmfile01.*

The‘?’

‘?’Representsasinglecharacter.

Examples

ConsideragainFred’shomedirectoryfromthepreviousexample.

Deletefile01.o,file02.oandfile03.o,butnotfile1.o,

$rmfile??.o

Deletefile01.o,butnotfile01.cpp,$rmfile01.?

The‘[]’Glob

A set of characters can be specified with brackets [ ]. ‘[ab]‘ meansthesinglecharactercanbe‘a‘OR‘b’.Rangescanalsobespecified(ex:‘[1-57-9]‘represents1-5OR7-9).

Examples

Deletefile02.cppandfile03.cppfromFred’sdirectory,

$rmfile0[23].cpp

ThiswilldeleteanyfilesthatstartwithforF(rememberlinuxiscasesensitive),$rm[fF]*

Todeleteallfilesthatstartwiththestring“file”followedbyasinglelettertype,$rmfile[a-zA-Z]

Thea-zandA-Zinthelastexamplemeansallthelettersintherangelowercasea-z

oruppercaseA-Z.

Thereismuchmoretowildcardmatching,butthisisenoughtogetyoustarted.

MoreExamples

Removeallfilesthatareexactly1character,

$rm?

Let’s say you have a directory named ‘9-15-2007-Backup-Really-Long-Name-blah…’Rather than typing thewhole name, you could just type a subset of thestringanduseitwiththecdcommand.

$cd9-15-2007*

Ifyouhavemultiplefoldersthatstartwith9-15-2007,yourdirectorywillbe

changedtothefirstonealphabetically.

Youcanusefilenameglobbingonmostcommandsthatacceptfilesasarguments.

Chapterfourteen:UNIX-SHELLINPUT/OUTPUTREDIRECTIONS

Timeisprecious.Itdoesnotmakesensetowastetimetypingafrequentlyusedsequenceofcommandsatacommandprompt,moreespeciallyiftheyareabnormallylongorcomplex.Scriptingisawaybywhichonecanalleviatethisproblembyautomatingthesecommandsequencesinordertomakelifeattheshelleasierandmoreproductive.Scriptingisallaboutmakingthecomputer,thetool,dothework.BytheendofthistutorialyouwillhaveagoodunderstandingofthekindofscriptinglanguagesavailableforUnixandhowtoapplythemtoyourproblems.UNIXcontainsmanywonderfulandstrangecommandsthatcanbeveryusefulintheworldofscripting,themoretoolsyouknowandthebetteryouknowthem,themoreuseyouwillfindforthem.MostoftheUnixcommandsandmanyofthebuilt-incommandshavemanpages;manpagescontaintheusageinstructionspertainingtotheparenttool.Theyarenotalwaysveryclearandmayrequirereadingseveraltimes.InordertoaccessamanpageinUnixthefollowingcommandsequenceisapplied

ChapterFifteen:UNIXSHELLFUNCTION

Functionsenableyoutobreakdowntheoverallfunctionalityofascriptintosmaller, logical subsections, which are then called upon to perform theirindividual taskswhenneeded.Using functions toperformrepetitive tasks isanexcellentway to create code reuse.Code reuse is an important part ofmodernobject-oriented programming principles. Shell functions are similar tosubroutines,procedures,andfunctionsinotherprogramminglanguages.

CreatingFunctions

Todeclareafunction,simplyusethefollowingsyntax−function_name(){

listofcommands

}

Thenameofyourfunctionisfunction_name,andthatiswhatyouwillusetocall

it from elsewhere in your scripts. The function name must be followed by

parentheses,whicharefollowedbyalistofcommandsenclosedwithinbraces.

Example

Exampleusingfunction−

#!/bin/sh

#Defineyourfunctionhere

Hello(){

echo“HelloWorld”

}

#Invokeyourfunction

Hello

Output$./test.sh

HelloWorld

$

PassParameterstoaFunction

You can define a function, which would accept parameters while calling

thosefunctions.Theseparameterswouldberepresentedby$1,$2andsoon.The

followingisanexamplewherewepasstwoparametersZaraandAliandthenwe

captureandprinttheseparametersinthefunction.

#!/bin/sh

#Defineyourfunctionhere

Hello(){

echo“HelloWorld$1$2”

}

#Invokeyourfunction

HelloZaraAli

Output$./test.sh

HelloWorldZaraAli

$

ReturningValuesfromFunctions

Ifyouexecuteanexitcommandfrominsideafunction,itseffectisnotonlytoterminateexecutionofthefunctionbutalsooftheshellprogramthatcalledthefunction. If you insteadwant to just terminate execution of the function, thenthereisawaytocomeoutofadefinedfunction.Basedonthesituationyoucanreturnanyvaluefromyourfunctionusingthereturncommandwhosesyntaxisasfollows−returncode

Here code can be anything you choose, but obviously you should choosesomethingthatismeaningfulorusefulinthecontextofyourscriptasawhole.

Example

Followingfunctionreturnsavalue1−#!/bin/sh

#Defineyourfunctionhere

Hello(){

echo“HelloWorld$1$2”

return10

}

#Invokeyourfunction

HelloZaraAli

#Capturevaluereturnedbylastcommand

ret=$?

echo“Returnvalueis$ret”

Output$./test.sh

HelloWorldZaraAli

Returnvalueis10

$

NestedFunctions

Oneofthemoreinterestingfeaturesoffunctionsisthattheycancallthemselves

aswellascallotherfunctions.Afunctionthatcallsitselfisknownasarecursive

function.

Thefollowingexampledemonstratesanestingoftwofunctions−

#!/bin/sh

#Callingonefunctionfromanother

number_one(){

echo“Thisisthefirstfunctionspeaking…”

number_two

}

number_two(){

echo“Thisisnowthesecondfunctionspeaking…”

}

#Callingfunctionone.

number_one

OutputThisisthefirstfunctionspeaking…

Thisisnowthesecondfunctionspeaking…

FunctionCallfromPrompt

Youcanputdefinitionsforcommonlyusedfunctionsinsideyour.profilesothey

willbeavailablewheneveryoulogin.Alternatively,youcangroupthedefinitions

inafile,saytest.sh,andthenexecutethefileinthecurrentshellbytyping−

$.test.sh

Thishas theeffectof causingany functionsdefined inside test.sh tobe read in

anddefinedtothecurrentshellasfollows−

$number_one

Option Description

-v Printalllinesthatdonotmatchpattern.

-n Printthematchedlineanditslinenumber.

-l Printonlythenamesoffileswithmatchinglines(letter“l”)

Thisisthefirstfunctionspeaking…

Thisisnowthesecondfunctionspeaking…

$

Toremovethedefinitionofafunctionfromtheshell,youusetheunsetcommand

withthe.foption.Thisisthesamecommandyouusetoremovethedefinitionof

avariabletotheshell.

$unset.ffunction_name

Unix-PipesandFilters

You can connect two commands together so that the output from oneprogram becomes the input of the next program. Two or more commandsconnectedinthiswayformapipe.Tomakeapipe,putaverticalbar(|)onthecommand line between two commands.When a program takes its input fromanotherprogram,performssomeoperationonthatinput,andwritestheresulttothestandardoutput,itisreferredtoasafilter.

ThegrepCommand

Thegrepprogramsearchesafileorfilesforlinesthathaveacertainpattern.Thesyntaxis−$greppatternfile(s)

The name “grep” derives from the ed (a UNIX line editor) commandg/re/p,whichmeans,“globallysearchforaregularexpressionandprintalllinescontaining it.” A regular expression is either plain text (a word, for example)and/orspecialcharactersusedforpatternmatching.Thesimplestuseofgrepistolookforapatternconsistingofasingleword.Itcanbeusedinapipesothatonly those lines of the input files containing a given string are sent to thestandardoutput.Ifyoudonotgivegrepafilenametoread,itreadsitsstandardinput;thatisthewayallfilterprogramswork−$ls-l|grep“Aug”

-rw-rw-rw-1johndoc11008Aug614:10ch02

-rw-rw-rw-1johndoc8515Aug615:30ch07

-rw-rw-r—1johndoc2488Aug1510:51intro

-rw-rw-r—1caroldoc1605Aug2307:35macros

$

There are various options,whichyoucanusealongwithgrepcommand–

Next, let’s use a regularexpression that tellsgrep tofind lines with “carol”,followed by zero or more

-c Printonlythecountofmatchinglines.

-i Matcheitherupper-orlowercase.

Option Description

-n Sortnumerically(example:10willsortafter2),ignoreblanksandtabs.

-r Reversetheorderofsort.

-f Sortupper-andlowercasetogether.

+x Ignorefirstxfieldswhensorting.

other characters abbreviatedin a regular expression as“.*”), then followedby“Aug”.Hereweareusing-ioptionto

havecaseinsensitivesearch−$ls-l|grep-i“carol.*aug”

-rw-rw-r—1caroldoc1605Aug2307:35macros

$

ThesortCommand

Thesort command arranges lines of text alphabetically or numerically. Theexamplebelowsortsthelinesinthefoodfile−$sortfood

AfghaniCuisine

BangkokWok

BigAppleDeli

IsleofJava

Mandalay

SushiandSashimi

SweetTooth

TioPepe‘sPeppers

$

Thesort command arrangeslines of text alphabetically bydefault. There are manyoptionsthatcontrolthesorting−

Morethantwocommandsmaybe linked by a pipe. Taking aprevious pipe exampleusinggrep,wecanfurthersortthefilesmodifiedinAugustby

orderofsize.

Thefollowingpipeconsistsofthecommandsls,grep,andsort−$ls-l|grep“Aug”|sort+4n

-rw-rw-r—1caroldoc1605Aug2307:35macros

-rw-rw-r—1johndoc2488Aug1510:51intro

-rw-rw-rw-1johndoc8515Aug615:30ch07

-rw-rw-rw-1johndoc11008Aug614:10ch02

$

ThispipesortsallfilesinyourdirectorymodifiedinAugustbyorderofsize,and

prints themtotheterminalscreen.Thesortoption+4nskips four fields(fields

areseparatedbyblanks)thensortthelinesinnumericorder.

ThepgandmoreCommands

A long output would normally zip by you on the screen, but if you run textthroughmoreorpgasafilter,thedisplaystopsaftereachscreenoftext.Letusassumethatyouhavealongdirectorylisting.Tomakeiteasiertoreadthesortedlisting,pipetheoutputthroughmoreasfollows−$ls-l|grep“Aug”|sort+4n|more

-rw-rw-r—1caroldoc1605Aug2307:35macros

-rw-rw-r—1johndoc2488Aug1510:51intro

-rw-rw-rw-1johndoc8515Aug615:30ch07

-rw-rw-r—1johndoc14827Aug912:40ch03

.

.

.

-rw-rw-rw-1johndoc16867Aug615:56ch05

—More—(74%)

Thescreenwillfillupwithonescreenoftextconsistingoflinessortedbyorderoffilesize.Atthebottomofthescreenis themorepromptwhereyoucantypeacommandtomovethroughthesortedtext.Whenyouaredonewiththisscreen,youcanuseanyofthecommandslistedinthediscussionofthemoreprogram.

ChapterSixteen:UNIXUSEFULCOMMAND

This quick guide lists commands, including a syntax andbrief description. Formoredetailedinformationcheckoutcommandsmanpage.$mancommand

FilesandDirectories

Thesecommandsallowyoutocreatedirectoriesandhandlefiles.

Command Description

cat DisplayFileContents

cd ChangesDirectorytodirname

chgrp Changefilegroup

chmod ChangingPermissions

cp Copysourcefileintodestination

file Determinefiletype

find Findfiles

grep Searchfilesforregularexpressions.

head Displayfirstfewlinesofafile

ln Createsoftlinkonoldname

ls Displayinformationaboutfiletype.

mkdir Createanewdirectorydirname

more Displaydatainpaginatedform.

mv Move(Rename)aoldnameto

newname.

pwd Printcurrentworkingdirectory.

rm Remove(Delete)filename

Command Description

awk Patternscanningandprocessinglanguage

cmp Comparethecontentsoftwofiles

comm. Comparesorteddata

cut Cutoutselectedfieldsofeachlineofafile

diff Differentialfilecomparator

expand Expandtabstospaces

join Joinfilesonsomecommonfield

Perl Datamanipulationlanguage

sed Streamtexteditor

sort Sortfiledata

split Splitfileintosmallerfiles

tr Translatecharacters

uniq Reportrepeatedlinesinafile

wc Countwords,lines,andcharacters

vi Opensvitexteditor

vim Opensvimtexteditor

fmt Simpletextformatter

spell Checktextforspellingerror

rmdir Deleteanexistingdirectoryprovided

itisempty.

tail Printslastfewlinesinafile.

touch Updateaccessandmodificationtime

ofafile.

Manipulatingdata

The contents of files can be

compared and altered with the

followingcommands.

CompressedFiles

Filesmaybecompressedtosavespace. Compressed files can becreatedandexamined−

ispell Checktextforspellingerror

Emacs GNUprojectEmacs

ex,edit Lineeditor

Emacs GNUprojectEmacs

Command Description

gompress Compressfiles

gunzip Uncompressgzippedfiles

gzip GNUalternativecompression

method

uncompress Uncompressfiles

unzip List,testandextractcompressed

filesinaZIParchive

zcat Catacompressedfile

zcmp Comparecompressedfiles

zdiff Comparecompressedfiles

zmore Fileperusalfilterforcrtviewingof

compressedtext

GettingInformation

VariousUnixmanualsanddocumentationareavailableon-line.ThefollowingShellcommandsgiveinformation−

Command Description

apropos Locatecommandsbykeywordlookup

info Displayscommandinformationpages

online

Command Description

ftp Filetransferprogram

rcp Remotefilecopy

rlogin RemotelogintoaUNIXhost

rsh Remoteshell

tftp Trivialfiletransferprogram

telnet Maketerminalconnectiontoanotherhost

ssh Secureshellterminalorcommandconnection

scp Secureshellremotefilecopy

sftp secureshellfiletransferprogram

man Displaysmanualpagesonline

whatis Searchthewhatisdatabasefor

completewords.

yelp GNOMEhelpviewer

NetworkCommunication

The following commands are used to send and receive files froma localUNIX

hoststotheremotehostsaroundtheworld.

Some of these commandsmay

berestrictedonyourcomputer

forsecurityreasons.

MessagesbetweenUsers

TheUNIXsystemsupportson-

screen messaging to other

usersandworldwideelectronic

mail−

Command Description

Evolution GUImailhandlingtoolonLinux

mail Simplesendorreadmailprogram

nesg Permitordenymessages

parcel Sendfilestoanotheruser

Pine Vdu-basedmailutility

Talk Talktoanotheruser

write Writemessagetoanotheruser

ProgrammingUtilities

The following programming tools and languages are available based on which

versionofUnixyouareusing

Command Description

dbx Sundebugger

gdb GNUdebugger

make Maintainprogramgroupsand

compileprograms.

nm Printprogram’snamelist

size Printprogram’ssizes

strip Removesymboltableandrelocation

bits

cb Cprogrambeautifier

cc ANSICcompilerforSunsSPARC

systems

Ctrace Cprogramdebugger

Gcc GNUANSICCompiler

Indent IndentandformatCprogramsource

Bc Interactivearithmeticlanguage

processor

Gcl GNUCommonLisp

Perl Generalpurposelanguage

Php Webpageembeddedlanguage

Command Description

chfn Changeyourfingerinformation

chgrp Changethegroupownershipofafile

chown Changeowner

date Printthedate

determin Automaticallyfindterminaltype

du Printamountofdiskusage

echo Echoargumentstothestandard

options

exit Quitthesystem

Py Pythonlanguageinterpreter

Asp Webpageembeddedlanguage

CC C++compilerforSunsSPARC

systems

g++ GNUC++Compiler

Javac JAVAcompiler

appletvieweir JAVAappletviewer

Netbeans Javaintegrateddevelopment

environmentonLinux

Sqlplus RuntheOracleSQLinterpreter

Sqlldr RuntheOracleSQLdataloader

MySql RunthemysqlSQLinterpreter

MiscCommands

Thesecommandslistoraltersysteminformation−

td>groups

finger Printinformationaboutlogged-in

users

groupadd Createausergroup

Showgroup

memberships

homequota Showquotaandfileusage

iostat ReportI/Ostatistics

kill Sendasignaltoaprocess

last Showlastloginsofusers

logout logoffUNIX

lun ListusernamesorloginID

netstat Shownetworkstatus

passwd Changeuserpassword

passwd Changeyourloginpassword

printenv Displayvalueofashellvariable

ps Displaythestatusofcurrentprocesses

ps Printprocessstatusstatistics

quota–v Displaydiskusageandlimits

reset Resetterminalmode

script Keepscriptofterminalsession

script Savetheoutputofacommandor

process

setenv Setenvironmentvariables

sty Setterminaloptions

time Timeacommand

top Displayallsystemprocesses

tset Setterminalmode

tty Printcurrentterminalname

umask Showthepermissionsthataregivento

viewfilesbydefault

uname Displaynameofthecurrentsystem

uptime Getthesystemuptime

useradd Createauseraccount

users Printnamesofloggedinusers

vmstat Reportvirtualmemorystatistics

w Showwhatloggedinusersaredoing

who Listloggedinusers

ChapterSeventeen:REGULAREXPRESSION

A regular expression is a string that can be used to describe severalsequencesofcharacters.RegularexpressionsareusedbyseveraldifferentUnixcommands, includinged,sed,awk,grep,and, to amore limited extent,vi.Heresedstandsforstreameditorastreamorientededitor,whichwascreatedexclusively for executing scripts. Thus, all the input you feed into it passesthroughandgoestoSTDOUTanditdoesnotchangetheinputfile.

Invokingsed

Beforewestart, letustakemakesureyouhavealocalcopyof/etc/passwdtextfiletoworkwithsed.Asmentionedpreviously,sedcanbe invokedbysendingdatathroughapipetoitasfollows−$cat/etc/passwd|sed

Usage:sed[OPTION]…{script-other-script}[input-file]…

-n,—quiet,—silent

suppressautomaticprintingofpatternspace

-escript,—expression=script

………………………….

Thecatcommanddumpsthecontentsof/etc/passwdtosed throughthepipeintosed’spatternspace.Thepatternspace is the internalworkbuffer thatsedusestodoitswork.

ThesedGeneralSyntax

Generalsyntaxforsed

/pattern/action

Here,patternisaregularexpression,andactionisoneofthecommands

giveninthefollowingtable.Ifpatternisomitted,actionisperformedforevery

lineaswehaveseenabove.

Theslashcharacters(/)thatsurroundthepatternarerequiredbecausetheyare

usedasdelimiters.

Range Description

P Printstheline

D Deletestheline

s/pattern1/pattern2/ Substitutesthefirstoccurrenceof

pattern1withpattern2.

DeletingAllLineswithsed

Invokesedagain,butthistimetellsedtousetheeditingcommanddeleteline,denotedbythesingleletterd−$cat/etc/passwd|sed‘d’

$

Insteadof invokingsedbysendinga file to it throughapipe,youcan instructsed to read the data from a file, as in the following example. The followingcommanddoesexactly thesamethingas thepreviousexample,without thecatcommand−$sed-e‘d’/etc/passwd

$

ThesedAddresses

sedalsounderstandssomethingcalledaddresses.Addressesareeitherparticularlocations in a file or a range where a particular editing command should beapplied.Whensedencountersnoaddresses,itperformsitsoperationsoneverylineinthefile.

Thefollowingcommandaddsabasicaddresstothesedcommandyouhavebeenusing–

$cat/etc/passwd|sed‘1d’|more

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

bin:x:2:2:bin:/bin:/bin/sh

sys:x:3:3:sys:/dev:/bin/sh

sync:x:4:65534:sync:/bin:/bin/sync

games:x:5:60:games:/usr/games:/bin/sh

man:x:6:12:man:/var/cache/man:/bin/sh

mail:x:8:8:mail:/var/mail:/bin/sh

news:x:9:9:news:/var/spool/news:/bin/sh

backup:x:34:34:backup:/var/backups:/bin/sh

$

Noticethatthenumber1isaddedbeforethedeleteeditcommand.Thistellssedtoperformtheeditingcommandonthefirstlineofthefile.Inthisexample,sedwilldeletethefirstlineof/etc/passwordandprinttherestofthefile.

ThesedAddressRanges

So,whatifyouwanttoremovemorethanonelinefromafile?Youcanspecifyan

addressrangewithsedasfollows−$cat/etc/passwd|sed‘1,5d’|more

games:x:5:60:games:/usr/games:/bin/sh

man:x:6:12:man:/var/cache/man:/bin/sh

mail:x:8:8:mail:/var/mail:/bin/sh

news:x:9:9:news:/var/spool/news:/bin/sh

backup:x:34:34:backup:/var/backups:/bin/sh

$

The above commandwill be applied on all the lines starting from 1 through 5.Therefore,itdeletesthefirstfivelines.

Tryoutthefollowingaddressranges–

Range Description

‘4,10d’ Linesstartingfrom4thtill10tharedeleted

‘10,4d’ Only10thlineisdeleted,becauseseddoesnotworkinreversedirection.

‘4,+5d’ Thiswillmatchline4inthefile,deletethatline,continuetodeletethenextfivelines,andthenceaseitsdeletionandprinttherest

‘2,5!d’ Thiswilldeletedeverythingexceptstartingfrom2ndtill5thline.

‘1~3d’ Thisdeletesthefirstline,stepsoverthenextthreelines,andthendeletesthefourthline.Sedcontinuesapplyingthispatternuntiltheendofthefile.

‘2~2d’ Thistellssedtodeletethesecondline,stepoverthenextline,deletethenextline,andrepeatuntiltheendofthefileisreached.

‘4,10p’ Linesstartingfrom4thtill10thareprinted

‘4,d’ Thiswouldgeneratesyntaxerror.

‘,10d’ Thiswouldalsogeneratesyntaxerror.

Note:Whileusingpaction,youshoulduse-noptiontoavoidrepetitionoflineprinting.Checkthedifferencebetweenthesetwocommands−$cat/etc/passwd|sed-n‘1,3p’

Checktheabovecommandwithout-nasfollows−

Flag Description

g Replaceallmatches,notjustthe

firstmatch.

NUMBER ReplaceonlyNUMBERthmatch.

p Ifsubstitutionwasmade,print

patternspace.

w

FILENAME

Ifsubstitutionwasmade,write

resulttoFILENAME.

$cat/etc/passwd|sed‘1,3p’

TheSubstitutionCommand

Thesubstitutioncommand,denotedbys,willsubstituteanystringthatyouspecify with any other string that you specify. To substitute one string withanother,youneedtohaveawayoftellingsedwhereyourfirststringendsandthesubstitutionstringbegins.This is traditionallydonebybookending the twostringswiththeforwardslash(/)character.Thefollowingcommandsubstitutesthefirstoccurrenceonalineofthestringrootwiththestringamrood.$cat/etc/passwd|sed‘s/root/amrood/’

amrood:x:0:0:rootuser:/root:/bin/sh

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

……………………..

It is very important tonote thatsed substitutes only the first occurrence on aline.Ifthestringrootoccursmorethanonceonaline,onlythefirstmatchwillbereplaced.Totellsedtodoaglobalsubstitution,addthelettergtotheendofthecommandasfollows−$cat/etc/passwd|sed‘s/root/amrood/g’

amrood:x:0:0:amrooduser:/amrood:/bin/sh

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

bin:x:2:2:bin:/bin:/bin/sh

sys:x:3:3:sys:/dev:/bin/sh

………………………

SubstitutionFlags

There are a number ofother useful flags that canbe passed in addition tothe g flag, and you canspecifymorethanoneatatime.

UsinganAlternative

StringSeparator

You may find yourselfhavingtodoasubstitutionon a string that includesthe forward slashcharacter.Inthiscase,youcan specify a differentseparatorbyproviding thedesignated character after

Iori Matchinacase-insensitive

manner.

Morm Inadditiontothenormalbehavior

ofthespecialregularexpression

characters^and$,thisflagcauses

^tomatchtheemptystringaftera

newlineand$tomatchtheempty

stringbeforeanewline.

thes.$cat/etc/passwd|sed

‘s:/root:/amrood:g’

amrood:x:0:0:amrood

user:/amrood:/bin/sh

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

In theaboveexampleweused:asdelimiter insteadof slash/becausewewere

tryingtosearch/rootinsteadofsimpleroot.

ReplacingwithEmptySpace

Useanemptysubstitutionstringtodelete therootstring fromthe/etc/passwd

fileentirely−

$cat/etc/passwd|sed‘s/root//g’

:x:0:0::/:/bin/sh

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

AddressSubstitution

Ifyouwanttosubstitutethestring‘sh’withthestring‘quiet’online10,youcan

specifyitasfollows−

$cat/etc/passwd|sed’10s/sh/quiet/g’

root:x:0:0:rootuser:/root:/bin/sh

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

bin:x:2:2:bin:/bin:/bin/sh

sys:x:3:3:sys:/dev:/bin/sh

sync:x:4:65534:sync:/bin:/bin/sync

games:x:5:60:games:/usr/games:/bin/sh

man:x:6:12:man:/var/cache/man:/bin/sh

mail:x:8:8:mail:/var/mail:/bin/sh

news:x:9:9:news:/var/spool/news:/bin/sh

backup:x:34:34:backup:/var/backups:/bin/quiet

Similarly,todoanaddressrangesubstitution,youcoulddosomethinglikethis−$cat/etc/passwd|sed‘1,5s/sh/quiet/g’

root:x:0:0:rootuser:/root:/bin/quiet

daemon:x:1:1:daemon:/usr/sbin:/bin/quiet

bin:x:2:2:bin:/bin:/bin/quiet

sys:x:3:3:sys:/dev:/bin/quiet

sync:x:4:65534:sync:/bin:/bin/sync

games:x:5:60:games:/usr/games:/bin/sh

man:x:6:12:man:/var/cache/man:/bin/sh

mail:x:8:8:mail:/var/mail:/bin/sh

news:x:9:9:news:/var/spool/news:/bin/sh

backup:x:34:34:backup:/var/backups:/bin/sh

Asyoucanseefromtheoutput,thefirstfivelineshadthestring‘sh’changedto‘quiet,’buttherestofthelineswereleftuntouched.

TheMatchingCommand

Youwouldusepoptionalongwith-noptiontoprintall thematching linesasfollows−$cattesting|sed-n‘/root/p’

root:x:0:0:rootuser:/root:/bin/sh

[root@ip-72-167-112-17amrood]#vitesting

root:x:0:0:rootuser:/root:/bin/sh

daemon:x:1:1:daemon:/usr/sbin:/bin/sh

bin:x:2:2:bin:/bin:/bin/sh

sys:x:3:3:sys:/dev:/bin/sh

sync:x:4:65534:sync:/bin:/bin/sync

games:x:5:60:games:/usr/games:/bin/sh

man:x:6:12:man:/var/cache/man:/bin/sh

mail:x:8:8:mail:/var/mail:/bin/sh

news:x:9:9:news:/var/spool/news:/bin/sh

backup:x:34:34:backup:/var/backups:/bin/sh

UsingRegularExpression

Whilematchingpatterns,youcanuseregularexpressions,whichprovidegreaterflexibility. Check the following example, which matches all the lines startingwithdaemonandthendeletesthem−

$cattesting|sed‘/^daemon/d’

root:x:0:0:rootuser:/root:/bin/sh

bin:x:2:2:bin:/bin:/bin/sh

sys:x:3:3:sys:/dev:/bin/sh

sync:x:4:65534:sync:/bin:/bin/sync

games:x:5:60:games:/usr/games:/bin/sh

man:x:6:12:man:/var/cache/man:/bin/sh

mail:x:8:8:mail:/var/mail:/bin/sh

news:x:9:9:news:/var/spool/news:/bin/sh

Expression Description

/a.c/ Matcheslinesthatcontainstringssuchas

a+c,a-c,abc,match,anda3c,whereasthe

pattern

/a*c/ Matchesthesamestringsalongwith

stringssuchasace,yacc,andarctic.

/[tT]he/ MatchesthestringTheandthe:

/^$/ MatchesBlanklines

/^.*$/ Matchesanentirelinewhateveritis.

/*/ Matchesoneormorespaces

/^$/ MatchesBlanklines

backup:x:34:34:backup:/var/backups:/bin/sh

Examplethatdeletesalllinesendingwithsh−$cattesting|sed‘/sh$/d’

sync:x:4:65534:sync:/bin:/bin/sync

The following table lists four special characters that are very useful in regularexpressions.

Character Description

^ Matchesthebeginningoflines.

$ Matchestheendoflines.

. Matchesanysinglecharacter.

* Matcheszeroormoreoccurrencesofthe

previouscharacter

[chars] Matchesanyoneofthecharactersgivenin

chars,wherecharsisasequenceofcharacters.

Youcanusethe-charactertoindicatearange

ofcharacters.

MatchingCharacters

Expressionstodemonstratethe

useofmetacharacters.

The following table showssome frequently used sets ofcharacters−

CharacterClassKeywords

Some special keywords arecommonlyavailabletoregexps,especially GNU utilities thatemployregexps.Theseareveryuseful for sed regularexpressions as they simplifythingsandenhancereadability.

For example, the characters a

Set Description

[a-z] Matchesasinglelowercaseletter

[A-Z] Matchesasingleuppercaseletter

[a-zA-Z] Matchesasingleletter

[0-9] Matchesasinglenumber

[a-zA-Z0-9]

Matchesasingleletterornumber

Character

Class

Description

[[:alnum:]] Alphanumeric[a-zA-Z0-9]

[[:alpha:]] Alphabetic[a-zA-Z]

[[:blank:]] Blankcharacters(spacesortabs)

[[:cntrl:]] Controlcharacters

[[:digit:]] Numbers[0-9]

[[:graph:]] Anyvisiblecharacters(excludes

whitespace)

[[:lower:]] Lowercaseletters[a-z]

[[:print:]] Printablecharacters(noncontrol

characters)

[[:punct:]] Punctuationcharacters

[[:space:]] Whitespace

[[:upper:]] Uppercaseletters[A-Z]

throughzaswellasthecharacters

A through Z constitute one such

class of characters that has the

keyword [[:alpha:]] Using the

alphabetcharacterclasskeyword,

this command prints only those

lines in the /etc/syslog.conf file

that start with a letter of the

alphabet−

$cat/etc/syslog.conf|sed-n‘/^[[:alpha:]]/p’

authpriv.*/var/log/secure

mail.*-/var/log/maillog

cron.*/var/log/cron

uucp,news.crit/var/log/spooler

local7.*/var/log/boot.log

C omplete list of availablecharacter class keywords inGNUsed.

AmpersandReferencing

The sed metacharacter &represents the contents of thepattern that wasmatched. Forinstance,youhavea file calledphone.txt full of phonenumbers−5555551212

5555551213

5555551214

6665551215

6665551216

7775551217

You want to make the area

code (the first three digits)

surroundedbyparentheses for

easier reading.Todo this, you

can use the ampersand

replacement character, like so

[[:xdigit:]] Hexdigits[0-9a-fA-F] −

$sed-e‘s/^[[:digit:]][[:digit:]][[:digit:]]/(&)/g’phone.txt

(555)5551212

(555)5551213

(555)5551214

(666)5551215

(666)5551216

(777)5551217

Hereyouarematchingthefirst3digitsandthenusing&replacingthose3digits

withsurroundingparentheses.

UsingMultiplesedCommands

Youcanusemultiplesedcommandsinasinglesedcommandasfollows−$sed-e‘command1’-e‘command2’…-e‘commandN’files

Here command1 through commandNaresed commands of the typediscussedpreviously.Thesecommandsareappliedtoeachlineinthelistoffilesgivenbyfiles.Usingthesamemechanism,wecanwriteabovephonenumberexampleasfollows–

$sed-e‘s/^[[:digit:]]\{3\}/(&)/g’\

-e‘s/)[[:digit:]]\{3\}/&-/g’phone.txt

(555)555-1212

(555)555-1213

(555)555-1214

(666)555-1215

(666)555-1216

(777)555-1217

Note− In theaboveexample, insteadof repeating thecharacterclasskeyword[[:digit:]] three times, you replaced it with \{3\}, which means to match thepreceding regular expression three times.Here I used \ to give line break youshouldremovethisbeforerunningthiscommand.

BackReferences

The ampersandmetacharacter is useful, but evenmore useful is the ability todefinespecificregionsinaregularexpressionsoyoucanreferencetheminyourreplacement strings.Bydefining specific parts of a regular expression, you canthen refer back to those parts with a special reference character. To do backreferences,youhavetofirstdefinearegionandthenreferbacktothatregion.Todefinearegionyouinsertbackslashparenthesesaroundeachregionofinterest.Thefirstregionthatyousurroundwithbackslashesisthenreferencedby\1,thesecondregionby\2,andsoon.

Assumingphone.txthasthefollowingtext−(555)555-1212

(555)555-1213

(555)555-1214

(666)555-1215

(666)555-1216

(777)555-1217

Nowtrythefollowingcommand−$catphone.txt|sed‘s/\(.*)\)\(.*-\)\(.*$\)/Area\

code:\1Second:\2Third:\3/’

Areacode:(555)Second:555-Third:1212

Areacode:(555)Second:555-Third:1213

Areacode:(555)Second:555-Third:1214

Areacode:(666)Second:555-Third:1215

Areacode:(666)Second:555-Third:1216

Areacode:(777)Second:555-Third:1217

Note:Intheaboveexampleeachregularexpressioninsidetheparenthesiswouldbebackreferencedby\1,\2andsoon.HereIused\togivelinebreakyoushouldremovethisbeforerunningthiscommand.

ChapterEighteen:FILESYSTEMBASICS

Afilesystemisalogicalcollectionoffilesonapartitionordisk.Apartitionisacontainerforinformationandcanspananentireharddriveifdesired.Yourharddrivecanhavevariouspartitionswhichusuallycontainonlyonefilesystem,suchasonefilesystemhousingthe/filesystemoranothercontainingthe/homefilesystem.Onefilesystemperpartitionallowsforthelogicalmaintenanceandmanagement of differing file systems.Everything inUnix is considered to be afile, includingphysicaldevicessuchasDVD-ROMs,USBdevices, floppydrives,andsoforth.

DirectoryStructure

Unix uses a hierarchical file system structure,much like an upside-down tree,withroot(/)atthebaseofthefilesystemandallotherdirectoriesspreadingfromthere. A UNIX file system is a collection of files and directories that have thefollowingproperties−

Ithasarootdirectory(/)thatcontainsotherfilesanddirectories.

Eachfileordirectoryisuniquelyidentifiedbyitsname,thedirectoryinwhichitresides,andauniqueidentifier,typicallycalledaninode.

Byconvention,therootdirectoryhasaninodenumberof2andthelost+founddirectoryhasaninodenumberof3.Inodenumbers0and1arenotused.Fileinodenumberscanbeseenbyspecifyingthe-ioptiontolscommand.

Itisself-contained.Therearenodependenciesbetweenonefilesystemandanyother.

The directories have specific purposes and generally hold the same types ofinformationforeasilylocatingfiles.ThefollowingarethedirectoriesthatexistonthemajorversionsofUnix−

Directory Description

/ Thisistherootdirectory,whichshould

containonlythedirectoriesneededatthe

toplevelofthefilestructure.

/bin Thisiswheretheexecutablefilesare

located.Theyareavailabletoallusers.

/dev Thesearedevicedrivers.

/etc Supervisordirectorycommands,

configurationfiles,diskconfiguration

files,validuserlists,groups,ethernet,

hosts,wheretosendcriticalmessages.

/lib Containssharedlibraryfilesand

sometimesotherkernel-relatedfiles.

/boot Containsfilesforbootingthesystem.

/home Containsthehomedirectoryforusersand

otheraccounts.

/mnt Usedtomountothertemporaryfile

systems,suchascdromandfloppyforthe

CD-ROMdriveandfloppydiskettedrive,

respectively.

/proc Containsallprocessesmarkedasafileby

processnumberorotherinformationthat

isdynamictothesystem.

/tmp Holdstemporaryfilesusedbetween

systemboots.

/usr Usedformiscellaneouspurposes,canbe

usedbymanyusers.Includes

administrativecommands,sharedfiles,

libraryfiles,andothers.

/var Typicallycontainsvariable-lengthfiles

suchaslogandprintfilesandotherfile

typesthatmaycontainavariableamount

ofdata.

/sbin Containsbinary(executable)files,usually

forsystemadministration.For

examplefdiskandifconfigutlities.

/kernel Containskernelfiles

NavigatingtheFileSystem

Nowthatyouunderstandthebasicsofthefilesystem,youcanbeginnavigating

to the files youneed.The followingare commandsyouwilluse tonavigate the

system−

Command Description

cat

filename

Displaysafilename.

cddirname Movesyoutothedirectoryidentified.

cpfile1file2 Copiesonefile/directorytospecified

location.

file

filename

Identifiesthefiletype(binary,text,

etc).

find

filename

dir

Findsafile/directory.

head

filename

Showsthebeginningofafile.

less

filename

Browsesthroughafilefromendor

beginning.

lsdirname Showsthecontentsofthedirectory

specified.

mkdir

dirname

Createsthespecifieddirectory.

more

filename

Browsesthroughafilefrombeginning

toend.

mvfile1

file2

Movesthelocationoforrenamesa

file/directory.

pwd Showsthecurrentdirectorytheuseris

in.

rm

filename

Removesafile.

rmdir

dirname

Removesadirectory.

tail

filename

Showstheendofafile.

touch

filename

Createsablankfileormodifiesan

existingfile.sattributes.

whereis

filename

Showsthelocationofafile.

which

filename

Showsthelocationofafileifitisin

yourPATH.

You can use Manpage Help to check complete syntax for each of these

commands.

ThedfCommand

Thefirstwaytomanageyourpartitionspaceiswiththedf(diskfree)command.Thecommanddf-k (disk free) displays the disk space usage in kilobytes, asshownbelow–

$df-k

Filesystem1K-blocksUsedAvailableUse%Mountedon

/dev/vzfs104857607836644264911675%/

/devices0000%/devices

$

Someofthedirectories,suchas/devices,shows0inthekbytes,used,andavail

columnsaswellas0%forcapacity.Thesearespecial(orvirtual)filesystems,and

althoughtheyresideonthediskunder/,bythemselvestheydonottakeupdisk

space.

The df -k output is generally the same on all Unix systems. Here’s what itusuallyincludes−

Column Description

Filesystem Thephysicalfilesystemname.

Kbytes Totalkilobytesofspaceavailable

onthestoragemedium.

Used Totalkilobytesofspaceused(by

files).

Avail Totalkilobytesavailableforuse.

Capacity Percentageoftotalspaceusedby

files.

Mountedon Whatthefilesystemismounted

on.

Youcanuse the-h (human readable) option to display the output in a formatthatshowsthesizeineasier-to-understandnotation.

TheduCommand

Thedu (disk usage) command enables you to specify directories to show diskspace usage on a particular directory. This command is helpful if you want todetermine how much space a particular directory is using. The followingcommandwilldisplaythenumberofblocksusedbyeachdirectory.Asingleblockmaytakeeither512Bytesor1KiloBytedependingonyoursystem.$du/etc

10/etc/cron.d

126/etc/default

6/etc/dfs

…

$

The-hoptionmakestheoutputeasiertocomprehend−$du-h/etc

5k/etc/cron.d

63k/etc/default

3k/etc/dfs

…

$

MountingtheFileSystem

Afilesystemmustbemountedinordertobeusablebythesystem.Toseewhatis

currentlymounted(availableforuse)onyoursystem,usethiscommand−

$mount

/dev/vzfson/typereiserfs(rw,usrquota,grpquota)

procon/proctypeproc(rw,nodiratime)

devptson/dev/ptstypedevpts(rw)

$

The /mnt directory, by Unix convention, is where temporarymounts (such as

CD-ROMdrives, remote network drives, and floppy drives) are located. If you

needtomountafilesystem,youcanusethemountcommandwiththefollowing

syntax−

mount-tfile_system_typedevice_to_mountdirectory_to_mount_to

Forexample,ifyouwanttomountaCD-ROMtothedirectory/mnt/cdrom,for

example,youcantype−

$mount-tiso9660/dev/cdrom/mnt/cdrom

ThisassumesthatyourCD-ROMdeviceiscalled/dev/cdromandthatyouwantto mount it to /mnt/cdrom. Refer to the mount man page for more specificinformationortypemount-hatthecommandlineforhelpinformation.Aftermounting, you can use the cd command to navigate the newly available filesystemthroughthemountpointyoujustcreated.

UnmountingtheFileSystem

To unmount (remove) the file system from your system, usetheumountcommandbyidentifyingthemountpointordevice.Forexample,tounmountcdrom,usethefollowingcommand−$umount/dev/cdrom

The mount command enables you to access your file systems, but on mostmodernUnixsystems,theautomountfunctionmakesthisprocessinvisibletotheuserandrequiresnointervention.

UserandGroupQuotas

User and groupquotasprovide themechanismsbywhich the amount of spaceusedbyasingleuseroralluserswithinaspecificgroupcanbelimitedtoavaluedefined by the administrator. Quotas operate around two limits that allow theusertotakesomeactioniftheamountofspace,ornumberofdiskblocksstarttoreachtheadministratordefinedlimits−

SoftLimit−Iftheuserexceedsthelimitdefined,thereisagraceperiodthatallowstheusertofreeupsomespace.

HardLimit−Whenthehardlimitisreached,regardlessofthegraceperiod,nofurtherfilesorblockscanbeallocated.

Thereareanumberofcommandstoadministerquotas−

Command Description

quota Displaysdiskusageandlimitsforauserofgroup.

edquota Thisisaquotaeditor.UsersorGroupsquotacanbeeditedusingthiscommand.

quotacheck Scanafilesystemfordiskusage,create,checkandrepairquotafiles

setquota Thisisalsoacommandlinequotaeditor.

quotaon Thisannouncestothesystemthatdiskquotasshouldbeenabledononeormorefilesystems.

quotaoff Thisannouncestothesystemthatdiskquotasshouldbedisabledoffoneormorefilesystems.

repquota Thisprintsasummaryofthediscusageandquotasforthespecifiedfilesystems

ChapterNineteen:UNIX-USERADMINISTRATION

TherearethreetypesofaccountsonUnixsystem−

Rootaccount−alsocalledsuperuserandhascompleteand

unfetteredcontrolofthesystem.Asuperusercanrunanycommands

withoutanyrestriction.Thisusershouldbeassumedasasystem

administrator.

Systemaccounts−Systemaccountsarethoseneededforthe

operationofsystem-specificcomponentsforexamplemailaccounts

andthesshdaccounts.Theseaccountsareusuallyneededforsome

specificfunctiononyoursystem,andanymodificationstothemcould

adverselyaffectthesystem.

Useraccounts−Useraccountsprovideinteractiveaccesstothe

systemforusersandgroupsofusers.Generalusersaretypically

assignedtotheseaccountsandusuallyhavelimitedaccesstocritical

systemfilesanddirectories.

UNIXsupportsaconceptofGroupAccount,whichlogicallygroupsanumberof

accounts.Everyaccountwouldbeapartofanygroupaccount.Unixgroupsplays

importantroleinhandlingfilepermissionsandprocessmanagement.

ManagingUsersandGroups

Therearethreemainuseradministrationfiles−

/etc/passwd:−Keepsuseraccountandpasswordinformation.This

fileholdsthemajorityofinformationaboutaccountsontheUnix

system.

/etc/shadow:−Holdstheencryptedpasswordofthecorresponding

account.Notallsystemssupportthisfile.

/etc/group:−Containsgroupinformationforeachaccount.

/etc/gshadow:−Containssecuregroupaccountinformation.

Checkalltheabovefilesusingcatcommand.

Commands available on the majority of Unix systems to create and manage

accountsandgroups–

Command Description

useradd Addsaccountstothesystem.

usermod Modifiesaccountattributes.

userdel Deletesaccountsfromthesystem.

groupadd Addsgroupstothesystem.

groupmod Modifiesgroupattributes.

groupdel Removesgroupsfromthesystem.

CreateaGroup

Youneedtocreategroupsbeforecreatinganyaccountotherwiseyouwouldhaveto use existing groups on your system. You have all the groups listedin /etc/groups file. All the default groups would be system account specificgroups and it is not recommended to use them for ordinary accounts.Use thefollowingsyntaxtocreateanewgroupaccount−groupadd[-ggid[-o]][-r][-f]groupname

Herearethedetailsoftheparameters:

Option Description

-gGID Thenumericalvalueofthegroup’sID.

-o Thisoptionpermitstoaddgroupwith

non-uniqueGID

-r Thisflaginstructsgroupaddtoadda

systemaccount

-f Thisoptioncausestojustexitwith

successstatusifthespecifiedgroup

alreadyexists.With-g,ifspecifiedGID

alreadyexists,other(unique)GIDis

chosen

groupname Actualgroupnametobecreated.

Ifyoudonotspecifyanyparametersthenthesystemwillusethedefaultvalues.

Thefollowingexamplewillcreateadevelopersgroupwithdefaultvalues,which

isacceptableformostadministrators.

$groupadddevelopers

ModifyaGroup

Tomodifyagroup,usethegroupmodsyntax−$groupmod-nnew_modified_group_nameold_group_name

Tochangethedevelopers_2groupnametodeveloper,type−$groupmod-ndeveloperdeveloper_2

HereishowyouwouldchangethefinancialGIDto545−$groupmod-g545developer

DeleteaGroup:

Todelete an existinggroup, all youneedare thegroupdel commandand thegroupname.Todeletethedevelopergroup,thecommandis−

$groupdeldeveloper

Thisremovesonly thegroup,notany filesassociatedwith thatgroup.The files

arestillaccessiblebytheirowners.

CreateanAccount

LetusseehowtocreateanewaccountonyourUnixsystem.Usethesyntaxto

createauser’saccount−

useradd-dhomedir-ggroupname-m-sshell-uuseridaccountname

AvailableParameters−

Option Description

-dhomedir Specifieshomedirectoryforthe

account.

-g

groupname

Specifiesagroupaccountforthis

account.

-m Createsthehomedirectoryifit

doesn’texist.

-sshell Specifiesthedefaultshellforthis

account.

-uuserid Youcanspecifyauseridforthis

account.

accountname Actualaccountnametobe

created

If youdonot specify a parameter then systemwill use the default values.Theuseraddcommandmodifiesthe/etc/passwd,/etc/shadow,and/etc/groupfilesandcreatesahomedirectory.Thefollowingisanexamplewhichwillcreatean accountmcmohd setting its home directory to /home/mcmohd and groupasdevelopers.ThisuserwouldhaveKornShellassignedtoit.$useradd-d/home/mcmohd-gdevelopers-s/bin/kshmcmohd

Before issuing the above command, make sure you already have

a developers group created using groupadd command. Once an account is

createdyoucansetitspasswordusingthepasswdcommandasfollows−

$passwdmcmohd20

Changingpasswordforusermcmohd20.

NewUNIXpassword:

RetypenewUNIXpassword:

passwd:allauthenticationtokensupdatedsuccessfully.

Whenyoutypepasswdaccountname,itgivesyouoptiontochangethepassword

provided you are superuser otherwise you would be able to change just your

passwordusingthesamecommandbutwithoutspecifyingyouraccountname.

ModifyanAccount

Theusermod command enables you to make changes to an existing account

fromthecommandline.Itusesthesameargumentsastheuseraddcommand,plus the -l argument, which allows you to change the account name. Forexample, to change the account namemcmohd tomcmohd20 and to changehomedirectoryaccordingly,youwouldneedtoissuefollowingcommand−$usermod-d/home/mcmohd20-m-lmcmohdmcmohd20

DeleteanAccount

Theuserdelcommand can be used to delete an existing user. This is a verydangerous command if not used with caution. There is only one argument oroptionavailableforthecommand:-r,forremovingtheaccount’shomedirectoryandmail file. For example, to remove accountmcmohd20, you would need toissuefollowingcommand−$userdel-rmcmohd20

Ifyouwanttokeepthehomedirectoryforbackuppurposes,omitthe-roption.Youcanremovethehomedirectoryasneededatalatertime.

ChapterTwenty:SYSTEMPERFORMANCE

Thepurposeofthistutorialistointroducetheperformanceanalysttosomeof

the free tools available tomonitor andmanageperformanceonUNIXsystems,

andtoprovideaguidelineonhowtodiagnoseandfixperformanceproblemsina

Unix environment. UNIX has following major resource types that need to be

monitoredandtuned−

CPU

Memory

Diskspace

Communicationslines

I/OTime

NetworkTime

Applicationsprograms

PerformanceComponents

Therearefivemajorcomponentswheretotalsystemtimegoes–

Component Description

UserstateCPU TheactualamountoftimetheCPUspendsrunningtheusersprogramintheuserstate.Itincludestimespentexecutinglibrarycalls,butdoesnotincludetimespentinthekernelonitsbehalf.

SystemstateCPU ThisistheamountoftimetheCPUspendsinthesystemstateonbehalfofthisprogram.AllI/Oroutinesrequirekernelservices.TheprogrammercanaffectthisvaluebytheuseofblockingforI/Otransfers.

I/OTimeandNetworkTime

ThesearetheamountoftimespentmovingdataandservicingI/Orequests

Command Description

nice/renice Runaprogramwithmodifiedscheduling

priority

netstat Printnetworkconnections,routing

tables,interfacestatistics,masquerade

connections,andmulticastmemberships

time Timeasimplecommandorgiveresource

usage

uptime SystemLoadAverage

ps Reportasnapshotofthecurrent

processes.

vmstat Reportvirtualmemorystatistics

gprof Displaycallgraphprofiledata

prof ProcessProfiling

top Displaysystemtasks

Term Description

VirtualMemoryPerformance

Thisincludescontextswitchingandswapping.

ApplicationProgram Timespentrunningotherprograms-whenthesystemisnotservicingthisapplicationbecauseanotherapplicationcurrentlyhastheCPU.

PerformanceTools

Unix provides the followingimportanttoolstomeasureandfine-tune Unix systemperformance−

Unix-SystemLogging

UNIXsystemshaveavery

flexible and powerful logging

system, which enables you to

record almost anything and

then manipulate the logs to

retrieve the information you

require. Many versions of

UNIX provide a general-

purpose logging facility

called syslog. Individual

programs that need to have

information logged send the

informationtosyslog.

Unix syslog is a host-configurable, uniform system logging facility. The

system uses a centralized system logging process that runs the

program/etc/syslogdor/etc/syslog.

Theoperationofthesystemloggerisquitestraightforward.Programssend

theirlogentriestosyslogd,whichconsultstheconfigurationfile/etc/syslogd.conf

or/etc/syslogand,whenamatchisfound,writesthelogmessagetothedesired

logfile.

There are four basic syslog

Facility Theidentifierusedtodescribetheapplicationor

processthatsubmittedthelogmessage.Examples

aremail,kernel,andftp.

Priority Anindicatoroftheimportanceofthemessage.

Levelsaredefinedwithinsyslogasguidelines,from

debugginginformationtocriticalevents.

Selector Acombinationofoneormorefacilitiesandlevels.

Whenanincomingeventmatchesaselector,an

actionisperformed.

Action Whathappenstoanincomingmessagethatmatches

aselector.Actionscanwritethemessagetoalog

file,echothemessagetoaconsoleorotherdevice,

writethemessagetoaloggedinuser,orsendthe

messagealongtoanothersyslogserver.

Facility Description

auth Activityrelatedtorequestingnameand

password(getty,su,login).

authpriv Sameasauthbutloggedtoafilethatcan

onlybereadbyselectedusers.

console Usedtocapturemessagesthatwould

generallybedirectedtothesystem

console.

cron Messagesfromthecronsystemscheduler.

daemon Systemdaemoncatchall.

ftp Messagesrelatingtotheftpdaemon.

kern Kernelmessages.

local0.local7 Localfacilitiesdefinedpersite.

lpr Messagesfromthelineprintingsystem.

mail Messagesrelatingtothemailsystem.

mark Pseudo-eventusedtogeneratetimestamps

terms that you should

understand−

SyslogFacilities

Here are the available

facilities for the selector.

Notallfacilitiesarepresent

onallversionsofUNIX.

SyslogPriorities

The syslog priorities aresummarized in thefollowingtable−

The combination of facilities

and levels enables you to be

discerning about what is

logged and where that

information goes. As each

program sends its messages

dutifullytothesystemlogger,

theloggermakesdecisionson

what to keep track of and

what to discardbased on the

levels defined in the selector.

Whenyouspecifya level, the

system will keep track of

everything at that level and

higher.

The/etc/syslog.conffile

The /etc/syslog.conf file

controls where messages are

logged. A typical syslog.conf

filemightlooklikethis−

inlogfiles.

news Messagesrelatingtonetworknews

protocol(nntp).

ntp Messagesrelatingtonetworktime

protocol.

user Regularuserprocesses.

uucp UUCPsubsystem.

Priority Description

emerg Emergencycondition,suchasanimminent

systemcrash,usuallybroadcasttoallusers.

alert Conditionthatshouldbecorrected

immediately,suchasacorruptedsystem

database.

crit Criticalcondition,suchasahardwareerror.

err Ordinaryerror.

warning Warning.

notice Conditionthatisnotanerror,butpossibly

shouldbehandledinaspecialway.

info Informationalmessage.

debug Messagesthatareusedwhendebugging

programs.

none Pseudolevelusedtospecifynottolog

messages.

*.err;kern.debug;auth.notice

/dev/console

daemon,auth.notice

/var/log/messages

lpr.info

/var/log/lpr.log

mail.*

/var/log/mail.log

ftp.*

/var/log/ftp.log

auth.*

@prep.ai.mit.edu

auth.*

root,amrood

netinfo.err

/var/log/netinfo.log

install.*

/var/log/install.log

*.emerg

*

*.alert

|program_name

mark.*

/dev/console

Eachlineofthefilecontainstwoparts−

Amessageselectorthatspecifieswhichkindofmessagestolog.Forexample,allerrormessagesoralldebuggingmessagesfromthekernel.

Anactionfieldthatsayswhatshouldbedonewiththemessage.Forexample,putitinafileorsendthemessagetoauser’sterminal.

Followingarethenotablepointsfortheaboveconfiguration−

Messageselectorshavetwoparts:afacilityandapriority.Forexample,kern.debugselectsalldebugmessages(thepriority)generatedbythekernel(thefacility).

Messageselectorkern.debugselectsallprioritiesthataregreaterthandebug.

Anasteriskinplaceofeitherthefacilityorthepriorityindicates“all.”Forexample,*.debugmeansalldebugmessages,whilekern.*meansallmessagesgeneratedbythekernel.

Youcanalsousecommastospecifymultiplefacilities.Twoormoreselectorscanbegroupedtogetherbyusingasemicolon.

LoggingActions

Theactionfieldspecifiesoneoffiveactions−

Logmessagestoafileoradevice.Forexample,/var/log/lpr.logor/dev/console.

Sendamessagetoauser.Youcanspecifymultipleusernamesbyseparatingthemwithcommas(e.g.,root,amrood).

Sendamessagetoallusers.Inthiscase,theactionfieldconsistsofanasterisk(e.g.,*).

Pipethemessagetoaprogram.Inthiscase,theprogramisspecifiedaftertheUNIXpipesymbol(|).

Sendthemessagetothesyslogonanotherhost.Inthiscase,theactionfieldconsistsofahostname,precededbyanatsign(e.g.,@tutorialspoint.com)

TheloggerCommand

UNIX provides the logger command, which is extremely useful for systemlogging.Theloggercommandsendsloggingmessagestothesyslogddaemon,and consequently provokes system logging. Thismeanswe can check from thecommandlineatanytimeusingthesyslogddaemonanditsconfiguration.Thelogger commandprovidesamethod foraddingone-lineentries to thesystemlogfilefromthecommandline.

Theformatofthecommandis−

logger[-i][-ffile][-ppriority][-ttag][message]…

Hereisthedetailoftheparameters–

Option Description

-f

filename

Usethecontentsoffilefilenameasthemessageto

log.

-i LogtheprocessIDoftheloggerprocesswitheach

Application Directory

httpd /var/log/httpd

samba /var/log/samba

cron /var/log/

mail /var/log/

mysql /var/log/

line.

-p

priority

Enterthemessagewiththespecifiedpriority

(specifiedselectorentry);themessageprioritycan

bespecifiednumerically,orasafacility.priority

pair.Thedefaultpriorityisuser.notice.

-ttag Markeachlineaddedtothelogwiththespecified

tag.

message Thestringargumentswhosecontentsare

concatenatedtogetherinthespecifiedorder,

separatedbythespace

YoucanuseManpageHelptocheckcompletesyntaxforthiscommand.

LogRotation

Logfileshavethepropensitytogrowveryfastandconsumelargeamountsofdiskspace. To enable log rotations, most distributions use tools suchas newsyslog or logrotate. These tools should be called at frequent intervalsusingthecrondaemon.Checkthemanpagesfornewsyslogorlogrotateformoredetails.

ImportantLogLocations

All the system applicationscreate their log filesin /var/log and its sub-directories. Here are fewimportant applications andtheir corresponding logdirectories−

ChapterTwenty-one:UNIX SIGNALS

ANDTRAPS

Signals are software interrupts sent to a program to indicate that an

importanteventhasoccurred.Theeventscanvary fromuserrequests to illegal

memoryaccesserrors.Somesignals,suchastheinterruptsignal,indicatethata

user has asked the program to do something that is not in the usual flow of

control.

The following are someof themore common signals youmight encounter and

wanttouseinyourprograms−

SignalName

SignalNumber

Description

SIGHUP 1 Hangupdetectedoncontrollingterminalordeathofcontrollingprocess

SIGINT 2 Issuediftheusersendsaninterruptsignal(Ctrl+C).

SIGQUIT 3 Issuediftheusersendsaquitsignal(Ctrl+D).

SIGFPE 8 Issuedifanillegalmathematicaloperationisattempted

SIGKILL 9 Ifaprocessgetsthissignalitmustquitimmediatelyandwillnotperformanycleanupoperations

SIGALRM 14 AlarmClocksignal(usedfortimers)

SIGTERM 15 Softwareterminationsignal(sentbykillbydefault).

LISTofSignals

There isaneasywayto listall thesignalssupportedbyyoursystem.Just issuethekill–lcommandanditwilldisplayallthesupportedsignals−$kill-l

1)SIGHUP2)SIGINT3)SIGQUIT4)SIGILL

5)SIGTRAP6)SIGABRT7)SIGBUS8)SIGFPE

9)SIGKILL10)SIGUSR111)SIGSEGV12)SIGUSR2

13)SIGPIPE14)SIGALRM15)SIGTERM16)SIGSTKFLT

17)SIGCHLD18)SIGCONT19)SIGSTOP20)SIGTSTP

21)SIGTTIN22)SIGTTOU23)SIGURG24)SIGXCPU

25)SIGXFSZ26)SIGVTALRM27)SIGPROF28)SIGWINCH

29)SIGIO30)SIGPWR31)SIGSYS34)SIGRTMIN

35)SIGRTMIN+136)SIGRTMIN+237)SIGRTMIN+338)SIGRTMIN+4

39)SIGRTMIN+540)SIGRTMIN+641)SIGRTMIN+742)SIGRTMIN+8

43)SIGRTMIN+944)SIGRTMIN+1045)SIGRTMIN+1146)SIGRTMIN+12

47)SIGRTMIN+1348)SIGRTMIN+1449)SIGRTMIN+1550)SIGRTMAX-14

51)SIGRTMAX-1352)SIGRTMAX-1253)SIGRTMAX-1154)SIGRTMAX-10

55)SIGRTMAX-956)SIGRTMAX-857)SIGRTMAX-758)SIGRTMAX-6

59)SIGRTMAX-560)SIGRTMAX-461)SIGRTMAX-362)SIGRTMAX-2

63)SIGRTMAX-164)SIGRTMAX

TheactuallistofsignalsvariesbetweenSolaris,HP-UX,andLinux.

DefaultActions

Everysignalhasadefaultactionassociatedwithit.Thedefaultactionforasignalistheactionthatascriptorprogramperformswhenitreceivesasignal.

Someofthepossibledefaultactionsare−

Terminatetheprocess.

Ignorethesignal.

Dumpcore.Thiscreatesafilecalledcorecontainingthememoryimageoftheprocesswhenitreceivedthesignal.

Stoptheprocess.

Continueastoppedprocess.

SendingSignals

Thereareseveralmethodsfordeliveringsignalstoaprogramorscript.OneofthemostcommonisforausertotypeCONTROL-CortheINTERRUPTkeywhileascriptisexecuting.

When you press theCtrl+C key a SIGINT is sent to the script and as per thedefineddefaultactionscriptterminates.

The other common method for delivering signals is to use the kill commandwhosesyntaxisasfollows−$kill-signalpid

HeresignaliseitherthenumberornameofthesignaltodeliverandpidistheprocessIDthatthesignalshouldbesentto.ForExample−$kill-11001

SendstheHUPorhang-upsignaltotheprogramthatisrunningwithprocessID

1001.Tosendakillsignaltothesameprocessusethefollowingcommand−

$kill-91001

ThiswouldkilltheprocessrunningwithprocessID1001.

TrappingSignals

WhenyoupresstheCtrl+CorBreakkeyatyourterminalduringexecutionofa

shell program, normally that program is immediately terminated, and your

commandpromptreturned.Thismaynotalwaysbedesirable.Forinstance,you

mayendupleavingabunchoftemporaryfilesthatwillnotgetcleanedup.

Trappingthesesignalsisquiteeasy,thetrapcommandhasthefollowingsyntax−

$trapcommandssignals

HerecommandcanbeanyvalidUnixcommand,orevenauser-definedfunction,

andsignalcanbealistofanynumberofsignalsyouwanttotrap.

Therearethreecommonusesfortrapinshellscripts−

Cleanuptemporaryfiles

Ignoresignals

CleaningUpTemporaryFiles

Asanexampleof the trapcommand, the following showshowyoucan remove

filesandthenexitifsomeonetriestoaborttheprogramfromtheterminal−

$trap“rm-f$WORKDIR/work1$$$WORKDIR/dataout$$;exit”2

From the point in the shell program that this trap is executed, the twofileswork1$$anddataout$$willbeautomaticallyremovedifsignalnumber2isreceived by the program. Therefore, if the user interrupts execution of theprogramafterthistrapisexecuted,youcanbeassuredthatthesetwofileswillbecleanedup.Theexitcommandthatfollowsthermisnecessarybecausewithoutitexecutionwouldcontinueintheprogramatthepointthatit leftoffwhenthesignalwasreceived.

Signalnumber1isgeneratedforhangup:Eithersomeoneintentionallyhangsup

thelineorthelinegetsaccidentallydisconnected.Youcanmodifythepreceding

traptoalsoremovethetwospecifiedfilesinthiscasebyaddingsignalnumber1

tothelistofsignals−$trap“rm$WORKDIR/work1$$$WORKDIR/dataout$$;

exit” 1 2. Now these files will be removed if the line gets hung up or if

theCtrl+Ckeygetspressed.Thecommandsspecifiedtotrapmustbeenclosedin

quotesiftheycontainmorethanonecommand.Also,notethattheshellscansthe

command lineat the time that the trapcommandgets executedandalsowhen

oneofthelistedsignalsisreceived.

Sointheprecedingexample,thevalueofWORKDIRand$$willbesubstitutedat

the time that the trap command is executed. If youwanted this substitution to

occuratthetimethateithersignal1or2wasreceivedyoucanputthecommands

insidesinglequotes−

$trap‘rm$WORKDIR/work1$$$WORKDIR/dataout$$;exit’12

IgnoringSignals

If thecommandlistedfor trap isnull, thespecifiedsignalwillbe ignoredwhenreceived.Forexample,thecommand−$trap”2

Specifies that the interruptsignalbe ignored.Youmightwant to ignorecertainsignalswhenperformingsomeoperationsthatyoudonotwantinterrupted.Youcanspecifymultiplesignalstobeignoredasfollows−$trap”12315

Notethatthefirstargumentmustbespecifiedforasignaltobeignoredandisnotequivalenttowritingthefollowing,whichhasaseparatemeaningofitsown−$trap2

Ifyouignoreasignal,allsubshellsalsoignorethatsignal.However,ifyouspecifyanactiontobetakenonreceiptofasignal,allsubshellswillstilltakethedefaultactiononreceiptofthatsignal.

ResettingTraps

Afteryouhavechangedthedefaultactiontobetakenonreceiptofasignal,youcanchangeitbackagainwithtrapifyousimplyomitthefirstargument;so.$trap12

Resetstheactiontobetakenonreceiptofsignals1or2backtothedefault.

DEDICATION

Thisbookisdedicatedto……MyWifeandSon

SPECIALTHANKSTomyWifeKatherineandmysonAdam