The Linux Shell and BASH Scripting

 Identify differrent Linux shell environments Understand the redirection of input  Understand and utilize command substitution  Write and configure BASH script using variables, flow

 Identify differrent Linux shell environments

 Understand the redirection of input

 Understand and utilize command substitution

 Write and configure BASH script using

variables, flow controls interactive input, functions, arithmetic and arrays

 Shells : Bourne (sh), Bourne Again

( bash ), Korn (ksh), C shell (csh, tcsh)

 Programs start from command line have

separate environments : parameters,

variables , functions.

 Shells : Bourne (sh), Bourne Again

( bash ), Korn (ksh), C shell (csh, tcsh)

 Programs start from command line have

separate environments : parameters,

variables , functions.

 bash config files :

~/.profile,

 Default environment variables : PS1, PS2,

HOME, LOGNAME, SHELL, PATH, PAGER, LPDEST, PWD, DISPLAY, MAIL,

 set, unset, export, … commands

 gpm : mouse server deamon

 up and down keys (~/.bash_history )

 Ctrl+Z, Ctrl+C, *, ?, …

 Sometimes the output of a command is a list (ex: ls) and we wish to execute

another command on each of the entries, use xargs

#ls | xargs grep README

Do Not use :

#ls –al | xarg grep README

Note : not SPACES around “=” Ex: # VAR=“Hello World”

 Quotes and Command Substitution

Note: # VAR=“Hello World”

# echo “ $VAR ” Hello World

# echo ‘ $VAR ’ $VAR

# VAR1= ` ls /var/log | wc –l `

# echo $VAR1

65

 Passing Info to Sript

 On the command line, info can be passed to script through pre-set variables called postion parameter.

$0 The name of script

$1-$9 Parameters being passed to script

$* String contains ALL parameters

passed to script separated by the first chacracter in IFS

$@ A list of ALL as separate string

$# Number of parameters on included

the command line

 The shift command will shift the positional

parameters one or more position to the left or right.

 Loops : do something more than one

 Loop commands : for, while, until

until <condition>

do

#list of commands to do

done

echo $count count=$((count +1))

done

Output:

0 1 2 3

 The variable $? contains the return code of the previous executed command or

application

≠0 Failure

 The exit n command will cause the

script to quit and assign the value of n to

the variable $?

 Test : use “[ ]” around expression

# what to do if the exp2 is true

else fi

echo –n “$1 hits the “ case $1 in

read VAR1 VAR2 …

 If there is more input than you are

looking for, all the extras are put in the

last variable.

function_name ()

{ }

 Functions can be called in the main

script by function’s name, parameters are given on the command line.

 It inherits ALL variables in main script

 We can change the return code of

function by using return n command

 More thrilling Examples

for file in $(ls file*) do

mv $file ${file%html}txt done

Step 3 : run it (add script directory to

PATH environment or use absolute path)