unix structure

5/20/2018 Unix Structure

1/122 Copyright IBM Corporation 2011

IBM Global Business Services IBM

Welcome

Welcome

Unix structure and Commands1


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Copyright IBM Corporation 2011

IBM Global Business Services

IBM

Unix Structure andCommands

Copyright IBM Corporation 2011Unix structure and Commands2




Objectives

By the end of this module on Unix structure and commands, you should be able to:

Discuss the basics of Unix File System

Put into practice file handling commands

Define vi Editor basics

Identify command substitution, filters, and pipes

Illustrate locating files with find

Demonstrate the xargs command





Agenda

This module on Unix structure and commands includes:

Introduction

Unix File System

File Handling Commands

vi Editor Basics

Command substitution, filters and pipes

Locating files with find

xargs command



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Topic 1: Introduction




Sub-topics covered

The sub-topics covered in this module include:

Operating system

History of Unix

Features of Unix

Architecture of Unix





Operating system

The operating system can be defined as follows:

It is the interface between hardware and user.

It is responsible for management and coordination of

activities and sharing of resources of computer.

It acts as host for computing applications that run

on the machine.

It provides applications access OS services throughAPIs or System Calls.

It provides two types of interfaces to the users, namelyCommand Line Interface and Graphical User Interface.





History of Unix

Here is a timeline that shows how Unix developed over time:

In 1969, UNIX first originated in form of Multics at Bell Laboratories.

In 1974, Thompson and Ritchie both published a paper regarding UNIX in

Communications of ACM.

By 1977, several UNIX systems were used in Universities. Between 1977 to 1982,UNIX

System III was released by Bell Laboratories.

By the start of 1984, the use of UNIX systems significantly increased.

Linux is a complete rewrite of Unix, developed by Linus Tourvalds, when he was a

Finnish undergraduate.





Features of Unix

The feature of Unix are listed below:

Portable: Unix OS can be installed on any architecture.

Multi-user: Multiple users can access the system and share its resources.

Multi-tasking: Multiple tasks can be initiated and run simultaneously.

Time-sharing: Server shares CPU time between requesting processes.

Hierarchical file organization: / (root) is at the top of hierarchy and the various other

file systems are below that.





The architecture of Unix includes:

System components

Kernel

Shell

The system components are

shown in the diagram here.

Architecture of Unix

Hardware

Kernel

Shell Shell

sed

ps

grep

lswho

tar

sort

cp

X-Window

cc

Other

Compilers

Various Text

Processors

Spread

Sheets

Browsers

Different

Databases

Other

Softwares

User 2User 1





The architecture of Unix, especially kernel, is definedbelow:

This is the core of Operating System.

It functions as the Hardware interface.

It contains system calls that perform

low-level tasks.

It generates inode-numbers for newly created files andmaintains inode tables.

It generates process-IDs for newly created processesand maintains process control blocks.

Architecture of Unix: Kernel





The architecture of Unix, especially shell, is defined below:

User interface: Shell provides an interface to the user, wherein the user could issue hisor her commands, and shell displays output and error messages to the user.

Command interpreter: Shell accepts command from user and interprets it to the kernel.

Command processor: Shell parses the command line arguments, expands the special

meaning of meta characters, searches for the command, and if the command is found,then transfers control to the command.

Programming language: Shell provides a native programming language.

Architecture of Unix: Shell





Questions and answers





Knowledge check

What is the interface between the hardware and the user?

Who developed Unix?

Enumerate three features of Unix.



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Topic 2: UNIX File System

IBM


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Sub-topics covered

The sub-topics covered in this topic include:

File system

Inode table

Directory structure


IBM


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File system is a way of organizing files in the secondary storage device. The Unix filesystem is partitioned into four partitions:

Boot Block: Programs associated with booting of the system are stored in this block.

Super Block: This stores accounting information about the file system.

Inode Block: This stores inode tables.

Data Block: This stores data.

File system


IBM


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Every file in Unix file system has an inode table, which stores meta data of the file.The Inode table stores the following information about the file:

Inode table

File

Type

Permission

Mode

User

Id

Group

Id

File

SizeBytes

Modification

Time

Access

Time

Inode

UpdationTime

Ptrs

ToDataBlock

Ord. 644 Tom Ken 85 14-Jun-09

09:11:45

14-Jun-09

09:11:45

18-Jun-09

15:12


IBM


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Inode table: Block addressing scheme

Inode table consists of 13 fields, each containing addresses to a block each.The first 10 address fields contains addresses of a data block each. This is direct addressing.Number of data blocks addressed: 10.

The 11th field contains address of an address block, the addresses of which point to a data

block each. This is single indirect addressing. Number of data blocks addressed: 128.

12th field contains address of an address block, the addresses of which point to an address

block each, each of the addresses of which point to data blocks; Number of data blocksaddressed: 128 * 128.

13th field contains address of an address block, the addresses of which points to an

address block each; each of the address of these address blocks point to an address blockeach, through which, data blocks are pointed. Number of data blocks addressed.128 * 128 * 128.


IBM


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Directory structure

Directory structure in Unix is an inverted tree structure, wherein the root (/) directory is atthe top of the hierarchy and the subdirectories are placed as children of the root.

/

etc dev sbinbin usr tmp


IBM


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There are two means of referencing of files, including:

Absolute referencing: The referencing of a file done with reference to the root directory, /

Examples:$ cd /usr/include # changes to /usr/include directory$ ls /dev/tty # lists the file /dev/tty

Relative referencing: The referencing of a file done relative to the working directory.

Current directory and parent to current directory are referred by shortcuts . and ..respectively.

Examples:$ cd cppdir # changes to subdirectory cppdir

Directory structure: Referencing of files


IBM


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IBM


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Knowledge check

What are the four partitions of the Unix file system?

Enumerate three types of information stored in the Inode table.

What is the referencing of a file done relative to the working directory?



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Topic 2: UNIX file system

IBM Gl b l B i S i IBM


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Sub-topics covered


File system

Inode table

Directory structure




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pwd: Knowing your present working directory

$ pwd

/h ome/sac h in




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ls: Listing files and subdirectories in any directory

$ ls

abc.txt s.sh test.c dir1

$ ls /home/sach in

pmode.sh f ibonacci .c prof i le. tx t

$ lsl

-rwxr-xr-x 1 sach in foo tbal l 512 feb 23 12:37 abc .txt

-rwxr-xr-x 1 sach in foo tbal l 20 mar 12 14:16 s.sh

-rwxr-xr-x 1 sachin f ootb al l 134 apr 4 09:11 test.c


IBM Global B siness Ser ices IBM


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ls: Listing files and subdirectories in any directory

$ ls l /hom e/sachin

-rwxr-xr-x 1 sachin foo tbal l 36 mar 3 17:25 pm ode.sh

-rwxr-xr-x 1 sach in foo tbal l 114 jan 24 20:12 fibo nacci.c

-rwxr-xr-x 1 sachin footb al l 50 apr 5 10:20 pro f i le.txt

$ ls -a

$ ls -a /usr /sachin

$ ls -a | mor e

$ ls -lrt




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$ cd

$ pwd

/h ome/sach in

$ cd /usr/ l ib

$ pwd

/u sr/l ib

$ cd ..

$ pwd

/u sr

cd: Changing Directory




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$ cd bin

$ pwd

/u sr/b in

$ cd ../..

$ pwd

/

$ cd -

$ pwd

(Takes you to the p revious directory)

cd: Changing Directory (continued)




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$ cd /home/sachin

$ mkdir playdt

$ cd playdt

$ pwd

/h ome/sac h in /p lay d t

$ mkdir /home/sachin/playdt /mi l lnm

$ cd mar

$ pwd

/h ome/sac h in /p lay d t/m il lnm

mkdir: Creating new directory or subdirectory




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$ mkdi r p thisyr /mar/f i rs tprd

$ cd thisyr /mar/f i rs tprd

$ pwd

/h ome/sac h in /p lay d t/m il lnm / th isy r /m ar /f irs tprd

mkdir: Creating new directory or subdirectory (continued)




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The removing criteria for the directory or subdirectory to be removed is as follows:

It should not be the current directory

It should be vacant

$ cd /hom e/sachin/playdt /mi l lnm /th isyr /mar

$ pwd

/h ome/sach in /p lay d t/m il lnm /th isyr /m ar

$ rmdir f i rs tprd

$ cd ..

$pwd

/h ome/sach in /p lay d t/m il lnm /th isyr

rmdir: Removing existing directory or subdirectory




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$ mk dir /hom e/sachin/playdt /mi l lnm /th isyr /mar

$ cd ..

$ pwd

/h ome/sach in /p lay d t/m il lnm

$ cd ../..

$ pwd

/home/sach in

$ rmd ir p /playdt /mi l lnm

rmdir: Removing existing directory or subdirectory (continued)




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Some file-oriented commands include:

cat

mv

cp

rm

chmod

Some file oriented commands




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$ cat pro f i le.txt

My com pany name is IBM.

My wo rk locat ion is Kolkata.

$ cat /us er/sach in/pmode.sh

echo The working mode is Learning.

$ cat pro f i le.txt pm ode.sh

My com pany name is IBM.

My wo rk locat ion is Kolkata.

echo The working mode is Learning.

cat: Displaying the content of one or more file




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$ mv /home/sach in/f ibonacci.c /usr/bin

$ mv /home/sach in/f ibonacci.c /us r/bin/f ibonacc i.c

$ mv /home/sach in/f ibonacci.c /home/sach in/pmode.sh /us r/bin

$ mv /home/sach in/f ibonacci.c /home/sach in/f ibbo .c

$ cd /hom e/sach in

$ mv f ibo.c f ibonacci .c

mv: Moving file from one directory or subdirectory to another




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$ cp /home/sach in/f ibonacci.c /home/sach in/fb.c

$ cd /hom e/sach in

$ cp pmo de.sh p.sh

cp: Copying of one file to another




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$ cp /hom e/sach in/fb.c /hom e/sachin /p.sh /usr /bin

$ cd /hom e/sach in

$ cp f ibonacci .c pmode.sh /usr

cp: Copying files from source directory to another




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G oba us ess Se ces

$ rm /home/sach in/fb.c

$ rm /hom e/sach in/f ibo.c /home/sach in/p.sh

$ cd /hom e/sach in

$ rm fib bo .c

$ rm f.c pm.sh

$ rm *

(Use the above command with great caution)

rm: Deleting one or more files




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Interactive Mode:

$ rm i fb.c

fb.c: ? y

Force Mode:

$ rmf p.sh

Recursive Mode:

$ rm r /home/sachin

$ rm r * (Recursiv e remov al of f i les )

rm: Several options




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$ date

Mon Ap r 23 11:23:34 IST 2007

date: Displaying system date




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d => Day (for exam ple, 23)

m => Mont h Num ber (for examp le, 10)

y => Rightm ost Two Digits of Year (for examp le, 07 for 2007)

a => Sho rt Name o f Week Day (for examp le, Mon )

h => Short Name o f Month (for examp le, Apr)

H => The Hour in 24 Hou r Form at (for examp le, 20)

M => Minu te (for example, 34)

S => Second (for example, 12)

date: Several format specifiers




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$ date +%a

Mon

$ date +%H %M

11 34

$ date +%H : %M 11 : 34

date: Use of several format specifies




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$ cal 2007

$ cal

$ cal apr

$ cal 2007 | more

cal: Displaying calendar




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$ banner IBM KOLKATA

IBM

KOLKATA

$ banner IBM KOL

IBM KOL

$ banner IBM KOL IT WORK

IBM KOL

IT WORK

banner: Displaying posters for any text

Output will bemuch bigger than

shown here.




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Locking without time specification:

$ lock

passwo rd: ******

Reenter passwo rd: ******

Terminal locked by sachin 0 minu tes ago.

Locking with time specification:

$ lock -20

..

lock: Locking the system without logging out

Locking for 30Minutes, if time not

specified duringcommandinvocation




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Waits for All:

$ wait

Waits for Some Specific One:

$ wait 232

( wait for pr oc ess id 232 )

wait: Waits for finishing of the system background process




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$ echo Delay Invocation; sleep 20; echo Back Again After 20 Sec

Delay Invocat ion Back A gain After 20 Sec

Delay of 20 Second s

sleep: Invoking delay




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$ who

roo t conso le apr 23 15:23

sach in tty01 apr 23 15:24

sh tty02 apr 23 15:25

who: Aiding in being acquainted with all logged-in users




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$ who am I

sachin tty01 apr 23 15:24

who am I: To know current user, who has issued command




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$ uname -n

sachdev

unamen: Knowing computers name in network




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$ tty

/d ev /t ty01

tty: To be acquainted with the name of users terminal




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$ tput cup 15 28

$-

tput cup: Cursor positioning at desired location




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$ tput c lear

$-

tput clear: Monitor screen clearing




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$ tput sm so

echo Tutorial For Highlighting Displayable Text.

$ tput rms o

tput smso and tput rmso: Highlighting displayable text

Tutorial for Highlighting Displayable Text




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$ bc

7+17

24

12/7

1

99 ; 3 3 ; 4 * 5

0

27

20

$_

bc: Performing numeric calculation




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$ bc

ibase =2

1001

9

obase=2

11

1011

scale=3

10/3 3.333

$_

bc: Performing numeric calculation (continued)




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$ bc

r=9 ; s=4 ;

t=r-s

t

5

$_

$ x=3 $ y= echo $x + 4 | bc `

$ echo $y

7

bc: Performing numeric calculation (continued)




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UNIX:

$ spell /home/sachin /prof i le.txt

$ cd /home/sach in

$ spell pro f i le.txt

LINUX:

$ ispell /home/sachin/profile.txt

$ cd /home/sachin

$ ispell profile.txt

spell / ispell: Checking of spellings




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The wildcard characters basics include:

? => Must be One Character, Any character

* => Can be Zero or Any Number of Characters, AnyCharacter

[L] where L is a set of characters placed without separation => One character, anyone

character from L.

Wildcard characters basics




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$ ls *

$ ls l p*.??

$ cat ???? ?.sh

$ ls p[rm ]*

Wildcard characters: Examples




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$ chmod u+x pro f i le.tx t

$ chmo d g+rw prof i le.tx t

$ chmod o-r prof i le.tx t

$ chmod +wx p rof i le.tx t

$ chmod x pro f i le.txt

$ chmod go -w prof i le.tx t

$ chmo d u=rw x, go=rx prof i le.tx t

chmod: Altering file access permissions using symbols

Several Symbols

u => File Owner

g => Group Ownero => Other User

r => Read

w => Write

x => Execute




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$ chmod 741 pro f i le.txt




chmod: Altering file access permissions using numbers

Several Numbers

0 => No Permission Is Present

1 => Execute Only

2 => Write Only

3 (2+1) => Write & Execute

4 => Read Only

5 (4+1) => Read & Execute

6 (4+2) => Read & Write

7 (4+2+1) => Read, Write & Execute

Several Permission WeightsRead => 4

Write => 2

Execute => 1




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Running processes related to current user at current terminal:

$ ps

PID TTY TIME CMD

234 tty 01 00:00:02 sh

684 tty 01 00:00:00 ps

All Running User and System Processes:

UNIX: $ ps -e

LINUX: $ ps -ax

ps: Knowing about running processes of system




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Details of running processes related to current user at current terminal:

UNIX: $ ps -f

LINUX: $ ps -u

ps: Knowing about running processes of system (continued)




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INPUT REDIRECTION:

$ cat < prof i le.txt

$ cat 0< prof i le.txt

OUTPUT REDIRECTION:

$ cat pro f i le.txt >pm ode.sh

$ cat pro f i le.txt >> fibb onac ci.c

ERROR REDIRECTION:

$ cat pl.txt 2> err.txt

Redirection: Altering input, output, or error files for a command



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Topic 4: vi Editor Basics



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Sub-topics covered


vi Editor Basics

Mode commands

Repeat factor




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vi Editor is a powerful full-screen editor for UNIX. Texts, numbers, commands, and more

can be inserted to any file through this. For file creation, editing, and the like, this

is used extensively in UNIX.

vi Editor can be invoked with the following command: $ vi viexmpl.sh

Some of the important modes of vi Editor include:

Input Mode

Command Mode

vi Editor: Introduction




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vi Editor: Toggling between important modes and Shell

Shell

Command

Mode

Input

Mode

Vi filename

i, a, I, A etc.

:wq, :q!, :x etc.




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Several Input Mode Commands in vi Editor

Some input mode commands in vi Editor include:

i: Inputs text at left of current cursor position.

a:Appends text at right of current cursor position.

I:Inputs text at starting of current line.

A:Appends text at the end position of current line.

R:Replaces (overwrites) text from current cursor position to right direction.

S:Replaces the full line in which the cursor is.




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Several essential command mode commands in vi Editor


:x (or :wq): Saves and Exits from vi Editor.

:q!: Quits from vi Editor without Save.

:w: Saves current file and dont exit the vi Editor.

h: Shifts the cursor to one character left.

J:Shifts the cursor to one line down.

K: Shifts the cursor to one line up.

l: Shifts the cursor to one character right.

4h:Shifts the cursor to four characters left.

5j:Shifts the cursor to five lines down.

6k:Shifts the cursor to six lines up.

7l:Shifts the cursor to seven characters right.




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More essential command mode commands in vi Editor


|:Cursor reaches the beginning of current line.

$:Cursor reaches the beginning of current line.

:Scrolls forward one page.

:Scrolls backward one page.

20G:Cursor reaches 20th line of the current file.

15|:Cursor reaches 15th column of current line.

1G:Cursor reaches the Starting of the current file.

G:Cursor reaches the end of the current file.

x: Erases the current character.

4x: Erases current character and three next characters.

d15G: Erases all from current cursor position to 15th line.




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Additional essential command mode commands in vi Editor


dd:Erases full current line.

7dd:Erases full current line and next six lines.

. :Applies the last editing command used.

u:Undoes the last editing operation performed.

J:Joins the current line with the next line.

7yy:Copies the current line and next six lines together.

p:Pastes the copied content after the current cursor position.

~ :Changes current character case to the reverse one.

15~:Changes current and next 14 character case to the reverse one.

1p:Restores latest erase work performed.

3p:Restores latest three erase work performed.




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Repeat factor in vi Editor

In Command Mode:

10i^

or

10i^

Will enter consecutive 10 ^

that is, ^^^^^^^^^^




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Some search commands include:

/IBM:Searches in forward direction for pattern IBM in current file.

?kolkata:Searches in backward direction for pattern kolkata in current file.

Some substitute commands include:

:1,25s/Calcutta/Kolkata/:Replaces first occurrence of Calcutta with Kolkata

between lines 1 to 25 in current file.

:1,25s/Calcutta/Kolkata/g:Replaces all occurrence of Calcutta with Kolkata

between lines 1 to 25 in current file.

:.,$s/Calcutta/Kolkata/gc:Replaces Calcutta with Kolkata interactively between

current line and end of current file.

Commands



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Topic 5: Command Substitution, Filters, and Pipes



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Sub-topics covered


Command substitution

Filters

Pipes




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Command substitution is the technique of passing a commands output as argument to

another command. The command that passes output as argument can be called as innercommand. The command that receives the output of another command as its argument,

can be called as outer command. Here is an example:

$ echo "Today's date is `date`

Today's d ate is Tue Apr 7 15:14:41 IST 200

$ echo "No. of f i les in $PWD is $(ls|wc -l)

No. of f i les in /home/mural i is 45

Command substitution

Explanation:The meta-characters ` `(pair of backticks) and $() are known as command

substitution meta-characters. When a command is issued, shell first parses the command line

arguments; the shell first expands special meaning of these meta-characters; hence, shell first

executes the command specified within `` or $() and places Output of this command as

argument to the main command; then, Shell transfers control to the main command.




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This refers to a command which, by default, expects input from standard input file and

sends processed output to standard output file.

Here is a list of some filters:

uniq

t r

tee pr

cut

paste

bc

Filters




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It translates consecutive identical entries from the input file, into unique entries. These

include:

$ cat dom est ics

dog

goat

goat

goat

horse

$ uniq dom estics

dog

goat

horse

Filters: Unique




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Here is an example of unique filters:

c opt ion

$ cat domest ics

dog

goat

goat

$ uniq -c domest ics

1 dog

2 goat

Filters: Unique (continued)

Explanation of code:

With c option, uniq command displays number

of consecutive occurrences of the identical

entries and also the unique entries.




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It translates all occurrences of a set of characters in the first expression to corresponding

set of characters in second expression, from the input file.

Syntax:

tr exp1 exp2 < file1

Options:

S: This will squeeze multiple consecutive occurrences of a specified set ofcharacters to single occurrence.

D: This deletes the specified set of characters from the string. Cd: This complement deletes the specified set of characters from the string.

Filters: tr




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Here is an example of tr filters:

$ cat > text1

a quick brown fox jump ed over the lazy dog

$ tr '[a-z]' '[A -Z]' < text1

A QUICK BROWN FOX JUMPED OVER THE LAZY DOG

$

Filters: tr (example)


The tr command translates all occurrences of

lower-case alphabets to corresponding

upper-case alphabets in the file text1;

it displays the output.




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Here is another example of tr filters:

$ cat mydir info

tot al 12

-rw-r--r-- 1 murali murali 0 2009-03-25 12:48 ch ap1

-rwxr--r-- 1 mu ral i m ural i 133 2009-03-25 12:48 my fun ction s

$ tr -s ' ' < my dir info

tot al 12

-rw-r--r-- 1 mu rali m urali 0 2009-03-25 12:48 chap1

-rwxr--r-- 1 mu ral i m ural i 133 2009-03-25 12:48 my fun ction s

Filters: tr (example) (continued)


The tr command squeezes consecutive multiple occurrences of space character to single

occurrence in the input file mydirinfo, and displays output.




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Here is another example of tr filters using d option:

$ cat > num fi le

78343hhdfdh434384

834893849&*&*&dfdhfhdj

4839483jhdjfhdjf

hsdjfhdjfhdj4738473

jd f jdh f384738

$ tr -d '[a-z&*] ' < num fi le

78343434384

834893849

4839483

4738473

384738

Filters: tr (example: d option)


The tr command removes lower-case

alphabets, the characters &and *

from the input file numfile, and

displays output.




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Here is another example of tr filters using cd option:

$ cat > num fi le

78343hhdfdh434384

834893849&*&*&dfdhfhdj

4839483jhdjfhdjf

hsdjfhdjfhdj4738473

jd f jdh f384738

$ tr -cd '[0-9\n] ' < num fi le

78343434384

834893849

4839483

4738473

384738

Filters: tr (example: cd option)


The tr command removes all other

characters except digit characters and

newline characters from the input file

numfile, and displays output.




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It examines and counts the number of arguments say, n issued to it, creates n+1 copies of

the input it receives, and writes n copies to the n files specified to it as arguments, and onecopy to the standard output file.

Syntax:

tee file1 file2 file3

Filters: tee




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It paginates or columnates files for printing.

Syntax:

pr [ file1 file2 file3 ]

Options:

D: This will double space the output.

D: This will use format for the header date.

L : This sets the page length.

W: This sets the page width.

Filters: pr




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It extracts specified characters or fields from the input file.

Syntax:

cu t [] [ ]

Options:

c: Used to specify the characters, that have to be extracted from every line of input file

d: Used to specify field delimiter, based on which, cut would understand the fields

f: Used to specify the number of the fields that have to be extracted

Filters: cut




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It expects two files as input files, joins corresponding lines of the two files, and sends the

output to standard output file.

Syntax:

paste [] [] []

Filters: paste




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Performs calculation on the input expression. Takes input for standard input and sends

processed output to standard output.

Syntax:

bc

bc c alcf i le # calcf i le contains expression

Examples:

$ bc # issues input interrupt

5^3 # f inds 5 raised to pow er of 3

125 # and displays outpu t on screen

qui t # terminates bc prog ram

$ # and returns con trol back to shel l

Filters: bc




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A pipe is a communicating process. It receives output of one command and sends it as

input to another command.

comm and1 | comm and2

Example:

ls t | head -15

Output of ls command is passed on to head command as its input, through the pipe.

Pipes

Command1 Command2




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K l d h k


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Knowledge check

What is the command that receives the output of another command as its argument?

What filter extracts specified characters or fields from the input file?

What receives output of one command and sends it as input to another command?



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Topic 6: Locating Files withfind


S b t i d


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Sub-topics covered


find

find example

find example (2)

find example (3)



fi d


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It searches for the files with specified criteria, recursively starting from the specified

directory, and takes action on those files. The default action is print.

Syntax:

f ind

Examples:

$ find $HOME -name "*.kor n" -print

/h ome/mural i /k o rnd ir /n amechange.korn

/h ome/mural i /k o rnd ir /u n t i lDemo.ko rn

/h ome/mural i /k o rnd ir /cmdArgs .ko rn

/h ome/mural i /k o rnd ir /w h i le2Demo.ko rn

find



fi d


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List of operators and their purpose:

find

-name : search for files matching specific names; find supports wild cards

-mtime n : File was last modified n*24 hours ago

-atime n : File was last accessed n*24 hours ago-amin n : File was last accessed n minutes ago

-cmin n : Files status last changed n minutes ago

-mmin n : Files data was last modified n mins ago

-newer rfile : Files that are modified more recently than rfile

-inum n : File has inode number n.

-links n : File has n links

-user uname : File is owned by user uname (numeric user ID allowed).



fi d


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find

-size n[cwbkMG]: File uses n units of space.

The following suffixes can be used:b : for 512 bytes blocks (this is default if no suffix is used)

C : for bytes

w : for two-byte words

k : for kilobytes (units of 1024 bytes)

M : for megabytes (units of 1048576 bytes)

G : for Gigabytes (units of 1073741824 bytes)



find


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find

-type c : file is of type c

b : block special

c : character special

ddirectory

pnamed pipe (FIFO)

fregular file

lsymbolic link

ssocket



find: example (1)


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$ find /tmp -m time +30 -prin t

f ind: /tmp /orbi t -gdm : Permis sion denied

/tmp/m app ing-roo t

f ind: / tmp/gconfd-user1: Permis sion d enied

find: example (1)


find command recursively searches for files under the directory /tmp

which are not modified within past 30 days and prints them.



find


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find

-print: print the full file name on the standard output, followed by

a newline.

-exec: executes a unix command placing files output by find,

one, for each execution

-ok: executes a unix command placing files output by find, one,

for each execution non-interactively



find: example (1)


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$ pwd

/h ome/m ural i

$ f ind . -l inks +1 -type f -print 2> /dev/nul l

. /cppdir/new.cpp

./cppdir/vector1.cpp

find: example (1)


find searches recursively under home directory of user, for regular

files whose link count is more than one, that is, hard linked files.



find: example (2)


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$ find / -size 0c -print 2> /dev/nu l l |xargs ls -l 2> /dev/nul l 1> ZeroBy teFiles &

[1] 30299

find: example (2)


find searches recursively under directory /, whose file size is zero bytes

and pipes output to xargs and xargs places. The list of files as arguments

to ls command; ls command redirects output to the file ZeroByteFiles and

errors are redirected to /dev/null; this command is run in background.



find: example (2) (continued)


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$ find / -perm 777 -type f 2> /dev/nul l | xargs ls -l

-rwx rw xrw x 1 user20 user20 11688 2009-06-25 15:41

/h ome/u ser20/.b as h_h is to ry


/h ome/u ser20 /.bas h_logou t


/h ome/u ser20 /.bas h_pro f i le-rwx rwxrwx 1 user20 user20 124 2009-03-06 15:43 /hom e/user20/.bashr c



The find command recursively lists all regular files under the directory /whose

octal permission mode is 777; errors are discarded; xargs receives list of files

output by find through pipe and places this list as arguments to ls command, and

transfers control to ls command; ls command displays long-listing of these files.



find: example (3)


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$ tou ch -t 07070900 my reff i le

$ find $HOME -newer m yreff i le -prin t 2> /dev/nul l

/h ome/mural i

/h ome/mural i /.lesshs t

/h ome/mural i /ZeroBy teF iles

find: example (3)


The find command recursively lists all files under the home directory of user, files

whose modification timestamp is later than the file, myreffile; find displays output

and sends errors to /dev/null.





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$ find . -m time +365 -type f -exec ls -l {} \; # -exec executes a shell cmd

# on the output of f ind command

-rw-r--r-- 1 murali m urali 658 2007-10-11 19:46 ./.zsh rc

-rw-r--r-- 1 mu rali m urali 33 2007-08-31 19:50 ./.bash_logou t

$ find . -size 0 -typ e f -ok rm {} \; # -ok interact ively confirm s from user< rm ... ./usr s_at_now > ? Y # before executin g shell comm and

< rm ... ./no_access_tmp > ? Y # on every argum ent

< rm ... ./mynewerrf i le > ? n

< rm ... ./users > ? y

< rm ... ./my perlsc ripts /scores_hash .pl > ? n

< rm ... ./my per lscr ipts/mysu bst i tute.p l > ? n

< rm ... ./cobo lpro gs > ? y






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The find command recursively outputs all regular files under working

directory of user, which are not modified since the past 365 days;

exec action of find command places the files one by one as

argument to ls command and executes ls command.





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Knowledge check


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Knowledge check

find / -type fsize +32print

Output of the above command is:

a) Regular files that are greater than 32 bytes in sizeb) Regular files that are greater than 32 MB in sizec) Regular files that are greater than 32 blocks in sized) Regular files that are exactly 32 blocks in size



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Topic 6: Thexargs command


Sub-topics covered


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Sub topics covered


xargs

xargs commands


IBM Global Business ServicesIBM

xargs


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It reads arguments from standard input, place theses as arguments to the shell command,

and runs the command on these arguments.

Syntax:

xargs

Example:

$ xargs grep "cout"

autodemo.c++

mynewprog.c++

autodemo.c++: cout


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Here is another example:

Example:

$ ls *.c++ | xargs tar -cvf cppArchive.tar

autodemo.c++

inheritance.c++

methOverriding.c++

mynewprog.c++

scope.c++

test.c++

virtualFunction.c++

$ ls -l cppArchive.tar

-rw-rw-r-- 1 murali murali 10240 2009-07-07 12:34 cppArchive.tar

xargs



xargs


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Another example can be illustrated as follows:

Example:

$ find . -mtime +180 -type f -name "*.txt" | xargs -I {} -t mv {} {}.old

mv ./logFile.txt ./logFile.txt.old

mv ./links.txt ./links.txt.old

mv ./link.txt ./link.txt.old

xargs



xargs commands


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Some xargs commands include:

-I replace-str: It replaces occurrences of replace-str in the initial-arguments with

names read from standard input.

-t: It prints the command line on the standard error output before executing it.

- diff filename1.txt filename2.txt:It reports the difference between the files

- compress filename.txt: It compresses the filename filename.txt

tailf filename.txt:It lists the last entry of the file filenname.txt run time

mailx -s test email emailid < test.out:It sends an e-mail to emailid with thesubject test email with the content of the file test.out

passwd:It allows the user to change his or her password on the server man command:It shows the manual page for the command

xargs commands





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Q



Knowledge check


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g

User types the command xargs at the $ prompt, and presses key. What is the

response?

User types the following command at the $ prompt; what is the response? $ find / 2>/dev/null | xargs grepl DISPLAY > outfiles 2> /dev/null & tar tf shellprogs.tar | xargs cat |more



Tying the ends


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y g

By the end of this module on Unix Structure and Commands, you are expected to:

Paraphrase the basics of Unix File System

List file handling commands

Summarize vi editor basics

Analyze command substitution, filters, and pipes

Illustrate locating files with find

Interpret xargs command


IBM


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unix structure

Documents

unix os

use of unix systems

basics of unix file

complete rewrite of

unix incommunications

xargs commandunix structure

system calls

hierarchical file organization