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UNIXAdnan Niazi

November 2014

UNIX Lecture Goals

Goal 1: Know basic UNIX commands and their use.

Goal 2: Understand the basic structure of a

common Unix system.

Goal 3: Know how to find information on more

advanced UNIX commands and their use.

New Concepts

Shell A “shell” is an interface to a system, we’ll use

BASH, the Bourne Again Shell.

Recursion Something that repeats in a way similar to

itself. (eg. a mirror reflecting a mirror …)

Variable A symbol representing a non-static value.

Pointer A variable that stores a reference to another

variable.

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UNIX HISTORY

UNIX History

1969 – First Version of UNIX developed at Bell Labs by

AT&T

1975 – UNIX 6, the first to be widely available outside Bell

Labs. The first “Berkeley Software Distribution”

(BSD) is released.

1989 – UNIX System V, the last traditional UNIX version.

1991 – Linus Torvalds begin developing Linux.

“UNIX-like”

Today – UNIX itself, what’s now called “traditional UNIX” is not used, except by enthusiasts.

There are many “UNIX-like” systems (also known as *nix or UN*X) that are similar to UNIX while not conforming to the Single UNIX Specification.

In fact, most operating systems today except windows are “UNIX like”.

UNIX History

*NIX Systems

Mac OS X

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*NIX Command Line

Basics

The command line

Host, tells

you

where you

are!User, tells you who you are!

The prompt! This is where

you write stuff

Command line structure

Format:

$ command [switches] [arguments]

Square brackets mean

“optional”!

The prompt! Tells you your scope.

Switches control the behavior of the command

Arguments are the “target” of the command

Why text?

Scary, complicated and tedious at first, but supercomputing is impossible without it.

Text based commands allow scripting and automation, making work re-usable and repeatable

Well designed commands allow fast and powerful data manipulation that graphical interfaces can’t replicate.

Navigation Commands

List ls

Change Directory cd

Print Working Directory pwd

listing

The Basic command

The command generates a compact list of files and directories

listing

Adding switches:

The ‘l’ switch gives detailed (“long”) output

listing

… and adding arguments

The argument defines which directory or pattern to list.

print working directory

One of the easiest commands, prints your location in the directory tree.

change directory

Self explanatory, changes your position in the directory tree.

Combining all the Navigation commands allow you to explore the file system as efficient as a graphical interface!

TAB COMPLETION!!!

Never let typing slow you down! Pressing <TAB> while typing automatically completes what you are typing as long as the computer can “guess” it!

Tab turns

into

File System Interaction Commands

Copy cp

Move mv

Remove rm

copy

Makes a copy of a file with a new name

Copy always take two arguments; first the file to be copied, and then the name of the new file.

copy

To copy a directory, you need to copy recursively.

The “-r” switch makes the command recursively copy everything within the directory as well.

move

Move behaves exactly the same as copy, but removes the original

Moving does not care about recursion.

move

The move command is also used to rename things!

Moving something into a new name is the same as changing the name after all!

remove

Used to remove files or directories.

There is no trash bin on the command line! If you delete something it’s GONE!

remove

Remove a directory! You need to specify recursion with “-r”.

This is since it affects every file and not just the top one!

File Interaction Commands

less look inside files

head print beginning of file

tail print end of file

cat print entire file

nano basic text editor

less

Light-weight program for looking inside text files

You exit less by pressing “q” and scroll one page with <space>

head

Prints the first rows from a file, defaults to 10 lines but can be asked to print any number of lines.

tail

Prints the last rows from a file, defaults to 10 lines but can be asked to print any number of lines.

cat

Prints every row from a file. Short for concatenate as it can be used to concatenate files.

nano

Light-weight text editor.

Command help is available at the bottom of the screen!( ^ means <ctrl>, so you exit with <ctrl>+x )

The Great Summary

Move mv

List ls

Copy cp

Remove rm

Change Directory cd

Print Working Directorypwd

less look inside file

head print start of file

tail print end of file

cat print entire file

nano edit file

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BASIC LINUX FILE SYSTEM

Basic Linux File Structure

/dev This is where all the hardware is!

/etc This is where important stuff lives

/home This is where user files are

/root This is where the boss hangs out

/tmp This is where the system stores temp files

/usr/local This is where most programs are

/var/log This is where the log files are

Directory Tree

/

homeetc vardev usr

loglocalerikhenrikmartin

Documents

Pictures

notes.txt

script.sh

photo.jpg

Special files: . and ..

Hidden files in UNIX start with a “.”, these can be viewed with the “-a” switch for ls.

There are also the special files “.” and “..” in each directory.

. is a pointer to self, i.e. it references the directory itself

.. is a pointer to parent, i.e. to the directory containing the current directory.

File Permissions

First row is d rwx rwx rwx this is the file permissions!

The first “d” means that the file is a directory, the three triplets following is “read”, “write” and “execute” permissions for “user”, “group” and “other”.

This data is followed by “owner user” (martin) “owner group” (staff), file size, date and name

Changing Permissions

The command for changing permissions is chmod.

ex. $ chmod 750 myscript.sh

The number 755 is derived from the binary representation of three permission bits, “read, write, execute”.

111 = read, write and execute = 1×22+1×21+1×20 = 7

101 = read and execute = 1×22+0×21+1×20 = 5

000 = no permissions = 0×22+0×21+0×20 = 0

Note that sometimes changing permissions requires sudo

Questions?

Tutorial!

There is a tutorial at http://sgbc.slu.se/unix/

The tutorial deals with the things that we have looked at in this lecture as well as some extra bonuses!