Bash Shell Scripting Linux

8/13/2019 Bash Shell Scripting Linux

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Bash Shell Scripting

Shell is just the platform where your comment gets compiled and get executed, which has thecapacity to convert the binary codes int machinery language and return output. There are somany shell platform like /bin/bash, /bin/tsh, /usr/bin/python, /usr/bin/perl etc..

Shell scripting (Automation): A shell scriptis ascriptwritten for theshell,orcommand lineinterpreter,of anoperating system.It is often considered a simpledomain-specific programminglanguage.Typical operations performed by shell scripts include file manipulation, programexecution, and printing text.

Ok,Shell Scripting is just a text file which contains of sequences of commands put together lineby line to perform a customized task as per your requirement to be executed. They are used toautomate commonly used commands, as System Administration Tools, to develop SimpleProgram and Manipulation of text or files.

Arithmetic Operators

-eq = equals to

-ne = not equal to

-gt = greater than

-ge = greater than or equals to

-lt = less than

-le = less than or equals to

-a = and

Conditional Execution

|| = logical or

&& = logical and

=======================

[root@station1]# vi script1

a=10b=5a=`expr $a7`echo a is equal to $a
http://en.wikipedia.org/wiki/Scripting_languagehttp://en.wikipedia.org/wiki/Scripting_languagehttp://en.wikipedia.org/wiki/Scripting_languagehttp://en.wikipedia.org/wiki/Shell_%28computing%29http://en.wikipedia.org/wiki/Shell_%28computing%29http://en.wikipedia.org/wiki/Shell_%28computing%29http://en.wikipedia.org/wiki/Command_line_interpreterhttp://en.wikipedia.org/wiki/Command_line_interpreterhttp://en.wikipedia.org/wiki/Command_line_interpreterhttp://en.wikipedia.org/wiki/Command_line_interpreterhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Domain-specific_programming_languagehttp://en.wikipedia.org/wiki/Domain-specific_programming_languagehttp://en.wikipedia.org/wiki/Domain-specific_programming_languagehttp://en.wikipedia.org/wiki/Domain-specific_programming_languagehttp://en.wikipedia.org/wiki/Domain-specific_programming_languagehttp://en.wikipedia.org/wiki/Domain-specific_programming_languagehttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Command_line_interpreterhttp://en.wikipedia.org/wiki/Command_line_interpreterhttp://en.wikipedia.org/wiki/Shell_%28computing%29http://en.wikipedia.org/wiki/Scripting_language


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a=èxpr $a \* $bècho a is equal to $aa=èxpr $a / 3ècho a is equal to $a==============

Shift + ; -> :

:wq > Save and Quit

-

Making the script executable:

#chmod +x script1 > you have to save all the script and make executable before runningthem.

Running the shell script. (U can run the script with two ways,)

1) run the script from the current location and like (./script1)

2) make a bin directory inside the users home directory (like #mkdir /home/abhandari/bin,you dont have to worry about the path of the script i:e u can run it from any location just typing# script1 like this)

# ./script1

or

# mkdir /root/bin

# cd /root/bin

# script1

==================

Example2

==================

[root@station1]# vi script2

echo Enter the value for a:

read a


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echo Enter the value for b:

read b

a=èxpr $a7`

echo a is equal to $a

a=èxpr $a \* $b`

echo a is equal to $a

a=èxpr $a / 3`

echo a is eual to $a

:wq

[root@station1]# bash script2

==================

If Construct / Condition

==================

Example3

==================

[root@station1]#vi ifscript1

echon Enter your no.:

read N

if [ $Nge 1a $Nlt 100 ]

then echo Your input No. is between 1 and 100.

else echo Number is greater than 100

fi

:wq


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[root@station1]# bash ifscript1

==================

Example4

==================

[root@station1]# vi ifscript2

echo -n Enter your no.:

read N

if [ $N -lt 50 ]

then echo The No. you entered is less than 50

elif [ $N -ge 50 -a $N -lt 60 ]

then

echo The No. you entered is between 50 and 60

elif [ $N -ge 60 -a $N -le 100 ]

then

echo The No. you entered is between 60 and 100

else

echo The No.you entered wrong entry

fi

:wq

[root@station1]# bash ifscript2

Exit Command

==================

Example5


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==================

[root@station1]# vi exit

echo Do you like to exit..?

read ans

if [ $ans = "y" ]

then exit

fi

:wq

[root@station1]# bash exit

While Construct

==================

Example6

==================

[root@station1]# vi while

while true

do

echon Do you wish to continue..?

read ans

if test $ans = n

then exit

fi

done

:wq


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[root@station1]# bash while

==================

Example7

==================

[root@station1]# vi reply

ans=y

#while test $reply !=n

while test $ans!=n

do

echo -n Enter your desired number:

read N

if [ $N -ge 1 -a $N -lt 100 ]

then echo The number you entered is between 1 and 100

else echo The number you entered is greater than 100

fi

echo -n -e Would you like to continue..? \n\t[Enter to Continue]\n\t [Press Ctrl + C to quit]:

read ans

done

:wq

[root@station1]# bash reply

==================

Example8

==================


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[root@station1]# vi reply1

reply = y

while test $reply ! = n

do

echon Enter the filename:

read filename

cat ${filename}

echon Would you like to enter another filename?

read reply

done

:wq

[root@station1]# bash reply1

==================

Example9

==================

[root@station1]#vi reply3

while:

do

read-p "Enter two numnbers ( - 1 to quit ) : " a b

if[$a -eq -1 ]

then

break

fi

ans=$((a + b ))

echo$ans

done

[root@station1]# bash reply3

For Construct

==================


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Example10

==================

[root@station1]# vi forin

for name in zeshan rabi sandeep

do

echo ${name}

done

:wq

[root@mycentos script]# bash forin

==================

Example11

==================

[root@mycentos script]# vi forloop

#!/bin/bash

for i in {1..5}

do

echo Welcome $i times

done

===

[root@mycentos script]# ./forloop

Welcome 1 times

Welcome 2 times

Welcome 3 times


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Welcome 4 times

Welcome 5 times

==================

Example12

==================

[root@mycentos script]# vi forloopwith_seq

#!/bin/bash

for i in $(seq 1 2 20)

do

echo Welcome $i times

done

[root@mycentos script]# ./forloopwith_seq

Welcome 1 times

Welcome 3 times

Welcome 5 times

Welcome 7 times

Welcome 9 times

Welcome 11 times

Welcome 13 times

Welcome 15 times

Welcome 17 times


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Welcome 19 times

==================

Example13

==================

[root@station1]# vi for2

for NAMEFILE in `ls /home/`

do

echo File listing are ${NAMEFILE}

cat /home/${NAMEFILE}

done

:wq

[root@station1]# bash for2

Case

==================

Example14

==================

[root@station1]# vi case

echo Enter the choice to run command

echo 1) date 2) who

echo 3) ls 4) pwd

read choice

case $choice in

1)


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date;;

2)

who;;

3)

ls;;

4)

pwd;;

*)

echo There is no such choice for this No.

esac

:wq

[root@station1]# bash case

==================

Example15

==================

[root@station1]# vi case2

while true

do

echo Enter the choice to run command.

Echo press q to quit.

echo 1) date 2) who

echo 3) ls 4) pwd

read choice


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case $choice in

1)

date;;

2)

who;;

3)

ls;;

4)

pwd;;

q)

break;;

*)

echo There is no such choice for this No.

esac

done

:wq

==================

Example16

==================

# cat > menuui

## Script to create simple menus and take action according to that selected# menu item#while :doclearecho "-------------------------------------"echo " Main Menu "


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echo "-------------------------------------"echo "[1] Show Todays date/time"echo "[2] Show files in current directory"echo "[3] Show calendar"echo "[4] Start editor to write letters"echo "[5] Exit/Stop"echo "======================="echo -n "Enter your menu choice [1-5]: "read yourchcase $yourch in1) echo "Today is `date` , press a key. . ." ; read ;; 2) echo "Files in `pwd`" ; ls -l ; echo "Press a key. . ." ; read ;; 3) cal ; echo "Press a key. . ." ; read ;; 4) vi ;;5) exit 0 ;;*) echo "Opps!!! Please select choice 1,2,3,4, or 5";echo "Press a key. . ." ; read ;; esacdone

[root@station1]# bash menuui

[root@station1]#

Test command with if

==================

Example17

==================

[root@station1]# vi testwithif

echon Enter your filename

read fname

if testf $fname

then echo $fname is an ordinary file.

elif testd $fname

then echo $fname is a directory.

elif tests $fname

then echo $fname is not an emply file.


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elif testr $fname

then echo $fname exists & is readable.

elif test !r $fname

then echo $fname is a not readable

elif testL $fname

then echo $fname is a symbolic link file.

fi

:wq

[root@station1]# bash testwithif

====================

-dtrue if file is a directory

-ftrue if file exists

-htrue if file is a slymbolic link

-Ltrue if file is a symbolic link

-rtrue if file is readable by you

-strue if file exists and is not empty

-e = check if the file exists or not.

-w = writeable

-x = executable

-b = block device file

-O = owned by current user or not

-G = owned by group of current user or not

String Operators:


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-x stringtrue if string is empty

-n string true if string is not empty

String1 = string2true if the strings are equal

String

Further help of this type run help test

Expression

==================

Example19

==================

[root@station1]# vi expr

A = 1

while test ${A}lt 100

do

echo `expr ${A} \* ${A}`

A = `expr ${A} + 1`

done

:wq

[root@station1]# bash expr

Input from file

==================

Example20

==================

[root@station1]# vi inputfile


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while read infile

do

echo $infile

done < /etc/passwd

:wq

[root@station1]# bash inputfile

==================

Example21

==================

[root@station1]# vi inputfile2

while read finput

do

login = $(echo $finput | cutd : f1)

directory = $(echo $finput | cut d : f6-8)

echo login = $login and details = $directoru

done < /etc/passwd

exit()

:wq

[root@station1]# bash inputfile2

==================

Example22

==================

[root@station1]# vi inputfile3


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lsla > ./result

while read finput

do

filename = $(echo $finput | cut d f9)

permission = $(echo $finput | cut d f1)

echo filename = $filename and permission = $permission

done < ./result

:wq

==================

Example-23

Shell Script to add user and password input from file (need 2 files if best)

==================

Create Users using file containing List of Users/Password/Description with commaseparated===========There are two files with a shell script and users (users.sh ) list.

[root@station1 test2]# vi users.txt

=======================user100,password100,User1_Staffuser200,password200,User2_Staffuser300,password300,User3_Staff=========================

[root@station1 test2]# cat users.sh#!/bin/sh

#for line in `more sortdetails.txt`for line in `more users.txt`# while read linedousername=ècho $line | cut -d, -f1`password=ècho $line | cut -d, -f2`name=ècho $line | cut -d, -f3`#echo $username $password $name


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/usr/sbin/useradd -c $name -p $password $usernameecho $password > pwcat pw | passwdstdin $usernamedoneexit 1

==================root@station1test2]# chmod a+x users.sh[root@vmail01 test2]# sh users.sh

Example 24

==================

Script with argument passing on command line

[root@r6 bin]# cat plus

a=$1b=$2c=$3z=èxpr $b$cècho value $zecho addition $0echo addition $1echo addition $2echo addition $3[root@r6 bin]# ./plus 2 3 5value -2

addition ./plusaddition 2addition 3addition 5[root@r6 bin]#

==================

Example 25

=============

[root@r6 bin]# cat plusa=$1b=$2c=$3z=èxpr $b$cècho Substracted value from second arg to third: $zecho dollor $@
mailto:root@vmail01mailto:root@vmail01mailto:root@vmail01


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echo Total arguments value $#echo Command run successfully or not {zero=successful} $?echo First value is command: $0echo First argument value passed: $1echo Second argument value passed: $2

echo Third argument value passed: $3[root@r6 bin]# ./plus 2 3 5Substracted value from second arg to third: -2dollor 2 3 5Total arguments value 3Command run successfully or not {zero=successful} 0First value is command: ./plusFirst argument value passed: 2Second argument value passed: 3Third argument value passed: 5[root@r6 bin]#

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Automation is a vast topic. This is a tips only. So you guys really got Enjoy with thisi know.Stay tuned this will be further updated as i got the time. Thanks for Visiting this site.

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Bash Shell Scripting Linux