The Linux Shell and BASH Scripting

The Saigon CTT
The Linux Shell and
BASH Scripting
The Saigon CTT



Objectives
Objectives



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
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


Example of Script
Example of Script
$ more example_script
#!/bin/bash
/usr/bin/nmbd -D
/usr/bin/smbd -D

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


The Linux Shell
The Linux Shell

Shells : Bourne (sh), Bourne Again
(bash), Korn (ksh), C shell (csh, tcsh)

Programs start from command line have
separate environments : parameters,
variables , functions.
The Saigon CTT



The Linux Shell
The Linux Shell

Shells : Bourne (sh), Bourne Again
(bash), Korn (ksh), C shell (csh, tcsh)

Programs start from command line have
separate environments : parameters,
variables , functions.
The Saigon CTT


Shell Environment Customize
Shell Environment Customize

bash config files :
•
/etc/profile
•
~/.bash_profile, ~/.bash_login,
~/.profile, ..

Default environment variables : PS1, PS2,
HOME, LOGNAME, SHELL, PATH,
PAGER, LPDEST, PWD, DISPLAY,
MAIL, ..

set, unset, export, … commands
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


Using the
Using the
bash
bash


shell
shell

Alt+Fn


gpm : mouse server deamon

up and down keys (~/.bash_history )

Ctrl+Z, Ctrl+C, *, ?, …
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


Redirecting Input and Output
Redirecting Input and Output

Input (<) or (<0)
#mail < file_name

Output (>) or (1>)
# ls –l > file_name
( set –C or set –o noclobber : prevent
overwrite )

Append (>>)

Error (2>)
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


Redirecting Input and Output
Redirecting Input and Output


Pipe (|)
#ls –l *.JPG | tee file_name
#ls –al /root | grep error >error_file

Back ticks (`) or “$()”
# which passwd
/usr/bin/passwd
# ls –l `which passwd`
-r-sr-xr-x 1 root root 13476 Aug 7 /usr/bin/passwd
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


Redirecting Input and Output
Redirecting Input and Output

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
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


Background jobs
Background jobs


Job
#ls –l *.JPG | tee file_name
#ls –al /root | grep error >error_file

Backround jobs :
- Append with (&)
or
- Ctrl+Z and #bg %job_id
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


Variables
Variables

Naming : not begin with a digit

Assigning : VAR=value
VAR=$(command)
VAR=`command`
Note : not SPACES around “=”
Ex: # VAR=“Hello World”