Bash / Example Scripts

Examples of small bash Scripts
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Here is a set of small scripts, which demonstrate some features of bash programming.
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//===================================================================================

// set new prompt

//===================================================================================

PS1=">"

PS1="[${LOGNAME}@$(hostname)] # "

PS1="[${LOGNAME}] # "

PS1='$PWD $ '


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//===================================================================================

// set (and automatically create) shell variable

//===================================================================================

$ test="test"

$ homedir='pwd'

string="The man said \" hello \"."

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//===================================================================================

// To use the variable within the shell, it is preceded by a $

//===================================================================================

homedir=$HOME

cd $homedir

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//===================================================================================

// how to print shell variable

//===================================================================================

echo PS1

echo $PS1

echo $USERNAME

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//===================================================================================

// predefined shell variables

//===================================================================================

HOME    name of users login directory

IFS     internal field separators

PATH    search path used for finding commands

PS1     shell prompt

OSTYPE

USERNAME

SHELL

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//===================================================================================

// The shell supports pattern matching

//===================================================================================

* Match all characters in a string

? Match a single character


ls *.dat

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//===================================================================================

// Command Substitution

//===================================================================================

today=`date`



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//===================================================================================

#---------------------------------------------------

# empty sh script program

#---------------------------------------------------

#!/bin/sh



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#---------------------------------------------------

# comments

#---------------------------------------------------

#!/bin/sh

# this is comment



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#---------------------------------------------------

# printing of string constant

#---------------------------------------------------

#!/bin/sh

echo 'hello'

echo "hello"

echo hello



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#---------------------------------------------------

# declaration and printing of string variable

#---------------------------------------------------

#!/bin/sh



x='Wonderful new World'

echo $x

echo x # just string 'x'





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#---------------------------------------------------

# call of other programs

#---------------------------------------------------

#!/bin/sh

ls



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#---------------------------------------------------

# indirect call of other programs

#---------------------------------------------------

#!/bin/sh



x='pwd'

$x



x='ls -l'

$x



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#---------------------------------------------------

# indirect call with indirect parameters

#---------------------------------------------------

#!/bin/sh

u='-l'



x='ls '



$x $u



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#---------------------------------------------------

# print current shell name ???

#---------------------------------------------------

#!/bin/sh



echo $SHELL



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#---------------------------------------------------

# Anything enclosed in double quotes is passed on exactly

# as presented with the exception that the values of

# shell variables are substituted

#---------------------------------------------------

#!/bin/sh



v1="abc "

v2="$v1 d"

echo $v1 $v2



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#---------------------------------------------------

# Any matter enclosed in single quotes is passed on

# exactly as presented. The values of shell variables

# are not substituted.

#---------------------------------------------------

#!/bin/sh



v1="abc"

v2='$v1 d'

echo $v1 $v2



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#---------------------------------------------------

# Back quotes are used to enclose commands. An item

# enclosed in back quotes is replaced by the standard

# output of the command. Shell variable values

# are substituted within back quotes.

#---------------------------------------------------

#!/bin/sh



date=`date`

echo the date is $date



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#---------------------------------------------------

# escaping

#---------------------------------------------------

#!/bin/sh



msg=`echo Your Current Directory is \`pwd\``



echo $msg



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#---------------------------------------------------

# reading of text line from keyboard

#---------------------------------------------------

#!/bin/sh



read x



echo $x

echo $x



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#---------------------------------------------------

# reading of text line from keyboard with help comment

# echo without new line at the end

#---------------------------------------------------

#!/bin/sh



echo -n "Input text line=? "

read x



echo $x

echo $x



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#---------------------------------------------------

# syntax:  many commands in one line !!!!

#---------------------------------------------------

#!/bin/sh



echo "a"; echo "b"; echo "c"



var=5; echo `expr $var + $var`



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#---------------------------------------------------

# integer variable and its increment

# does not works in sh !!!

#---------------------------------------------------

#!/bin/bash



var=12345

let var=$var+1 # let is important

echo $var



v=12345

v=$v+1 # result "12345+1"



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#---------------------------------------------------

# integer arithmetics - bash only !

#---------------------------------------------------

#!/bin/bash



echo 'number=?' ; read x



let y=$x+$x ; echo 'x+x=' $y



let y=$x*$x ; echo 'square=' $y



let y=$x/3 ; echo 'x/3=' $y



let y=$x%7 ; echo 'x%7=' $y



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#---------------------------------------------------

# integer arithmetics in sh !!! using expr - slow

#---------------------------------------------------

#!/bin/sh



a=123

b=12



c=`expr $a + $b` # addition

echo $c



c=`expr $a \* $b` # multiplication

echo $c



c=`expr $a / $b` # division

echo $c



c=`expr $a % $b` # residual

echo $c



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#---------------------------------------------------

# very simple 'if'

#---------------------------------------------------

#!/bin/sh



echo 'number=?'

read x



if [ $x -eq 5 ]

then

    echo "five"

fi



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#---------------------------------------------------

# if ... else

#---------------------------------------------------

#!/bin/sh



echo 'number=?'

read x



if [ $x -eq 5 ]

then

    echo "five"

else

    echo "not 5"

fi



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#---------------------------------------------------

# if ... elif ... else

#---------------------------------------------------

#!/bin/sh



echo 'number=?'

read x



if [ $x -eq 5 ]

then

    echo "five"

elif [ $x -eq 7 ]

then

    echo "seven"

else

    echo "not 5 and not 7"

fi



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#---------------------------------------------------

# comparison -lt  and  -gt, nested if

#---------------------------------------------------

#!/bin/sh



echo -n 'number=?'

read x



if [ $x -gt 0 ]

then

    if [ $x -lt 10 ]

    then

        echo "0 < x < 10"

    fi

fi



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#---------------------------------------------------

# while loop - print first 10 integers from 0

#---------------------------------------------------

#!/bin/bash



x=0



while  [ $x -lt 10 ]

do

    echo $x

    let x=$x+1

done



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#---------------------------------------------------

# 10 random numbers generation

#---------------------------------------------------

#!/bin/bash



i=0

while [ $i -lt 10 ]

do

    x=$RANDOM

    echo $x

    let i=$i+1

done



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#---------------------------------------------------

# endless loop: interrupting by ctrl-c

#---------------------------------------------------

#!/bin/sh



while [ 1 ]

do

    read x

    echo $x$x

done



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#---------------------------------------------------

# divisors of integer number

#---------------------------------------------------

#!/bin/bash



echo -n 'number=?'

read x



i=2 # possible divisor

k=1

let n=$x/2 # top limit for divisor



while [ $i -le $n ]

do

    let k=$x%$i # residual

    if [ $k -eq 0 ]

    then

        echo -n "Divisor= "

        echo $i

    if

    let i=$i+1

done



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#---------------------------------------------------

# simple use of  for ... in ...

#---------------------------------------------------

#!/bin/sh



for i in "abc" "xyz" 1 2 99

do

    echo $i

done



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#---------------------------------------------------

# use for as in C-programming

# sum of the first n integer numbers

#---------------------------------------------------

#!/bin/bash



echo -n "number=?"

read n



s=0 # here sum



for((i=1; i <=n ; i++))

do

    let s=$s+$i

done



echo "sum= "$s



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#---------------------------------------------------

# operator case for selection of logical branches

# end marker ;; of branch

#---------------------------------------------------

#!/bin/sh



echo "input string=?"

read str



case "$str" in

    abc) echo "string = abc"

        ;;

    xyz) echo "string = xyz"

        ;;

    *)   echo "not abc, not zyz" ;;

esac



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#---------------------------------------------------

# exit operator

#---------------------------------------------------

#!/bin/sh



while [ 1 ]

do

    read x

    echo $x

    if [ $x -eq 0 ] # in $x must be number!

    then

        echo "script done ..."

        exit 0

    fi

done



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#---------------------------------------------------

# string comparing

#---------------------------------------------------

#!/bin/sh



echo "Input string=?"

read str



if [ $str = "abc" ]

then

    echo "You got it!"

else

    echo "Its not 'abc'"

fi



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#---------------------------------------------------

# simple strings concatenation

#---------------------------------------------------

#!/bin/sh



echo "Input string=?"

read str



s2=$str"AAAA"

echo $s2



s3="XXX"$s2

echo $s3



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#---------------------------------------------------

# strings concatenation

#---------------------------------------------------

#!/bin/sh



echo "Input string=?"

read str1



echo "Input second string=?"

read str2



s3=$str1$str2 # it works!

echo $s3



s4=${str1}${str2} # it works too!

echo $s4



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#---------------------------------------------------

# testing whether a string is null

#---------------------------------------------------

#!/bin/sh



echo "Input string=?"

read str



if [ $str ]

then

    echo "Not empty"

else

    echo "Empty"

fi



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#---------------------------------------------------

# length of string

#---------------------------------------------------

#!/bin/sh



echo "Input string=?"

read str



leng=`expr length $str`

echo "length= "$leng



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#---------------------------------------------------

# how to insert string to constant string

#---------------------------------------------------

#!/bin/sh



var="good"



echo "This is $var test"



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#---------------------------------------------------

# simplest function example

#---------------------------------------------------

#!/bin/sh



#---------------------------

func()

{

    echo "Inside function"

}



#---------------------------

echo "Now function call..."

func

echo "end of main"



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#---------------------------------------------------

# function can see variables of main program

#---------------------------------------------------

#!/bin/sh



#--------------------------

func()

{

    echo $var

}

#--------------------------



var="test of global "

func



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#---------------------------------------------------

# pass of parameters to function

#---------------------------------------------------

#!/bin/sh



#---------------------------------

func()

{

    echo "We are in function now"

    echo $0  # shell script name

    echo $1  # first parameter

    echo $2  # second parameter

    echo "We leave function..."

    exit 0

}



#---------------------------------



func  123  "abc"



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#---------------------------------------------------

# passing variable parameters

#---------------------------------------------------

#!/bin/bash



#-------------------------------

func2()

{

    let r=$1*$1

    echo $r

}

#-------------------------------

var=123

func2 $var





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#---------------------------------------------------

# recursive function example

# calculation of factorial

#---------------------------------------------------

#!/bin/sh

#-------------------------------

factorial()

{

    if [ "$1" -gt "1" ]

    then

        i=`expr $1 - 1`

        j=`factorial $i`

        k=`expr $1 \* $j`

        echo $k

    else

        echo 1

    fi

}

#-------------------------------

read x

factorial $x





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#---------------------------------------------------

# using of function library ????????

#---------------------------------------------------



file with name my.lb



func2()

{

    echo $1$1

}

func3()

{

    echo $1$1$1

}



shell program:



#!/bin/sh



./my.lb



var=123



func2 123



func3 123





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#---------------------------------------------------

# floating point numbers

#---------------------------------------------------

#!/bin/sh



# does not support !!!!



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#---------------------------------------------------

# simpiest array : declaration, element access and assignment

#---------------------------------------------------

#!/bin/bash



arr=(aa bb cc dd)



echo ${arr[0]} # curly bracket notation

echo ${arr[1]}

echo ${arr[2]}

echo ${arr[3]}



arr[2]="CCCCCCC"

echo ${arr[2]}



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#---------------------------------------------------

# number of elements in array

#---------------------------------------------------

#!/bin/bash



arr=(aa bb cc dd)



n=${#arr[@]}

echo $n



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#---------------------------------------------------

# array with filenames of current directory

#---------------------------------------------------

#!/bin/sh



arr=(*)  # * is list of all file and dir names



n=${#arr[@]}

echo "number of files and dirs "$n



echo ${arr[0]}

echo ${arr[1]}



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#---------------------------------------------------

# print all array elements -not good

# works then no holes in indexes

#---------------------------------------------------

#!/bin/bash



arr=(aa bb cc dd ee ff gg)

n=${#arr[@]}

i=0

while test $i -lt $n

do

    echo ${arr[$i]}

    let i=$i+1

done



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#---------------------------------------------------

# dynamic expansion of array

# one array element in reality is couple (index, value)

#---------------------------------------------------

#!/bin/bash



arr=()



n=${#arr[@]}

echo "number of array elements "$n



arr[0]=a

n=${#arr[@]}

echo "number of array elements "$n



arr[1]=b

n=${#arr[@]}

echo "number of array elements "$n



arr[2]=c

n=${#arr[@]}

echo "number of array elements "$n



arr[10]=h

n=${#arr[@]}

echo "number of array elements "$n





echo ${arr[10]}



echo ${arr[4]} # empty string

echo ${arr[6]} # empty string



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#---------------------------------------------------

# get all array and print it

#---------------------------------------------------

#!/bin/bash



arr=(aa bb cc dd ee ff gg)



echo ${arr[*]} # all array



echo ${arr[@]:0}   # aa bb cc dd ee ff gg



echo ${arr[@]:1}   # bb cc dd ee ff gg



echo ${arr[@]:2:3} # cc dd ee



for i in ${arr[*]}

do

    echo $i

done



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#---------------------------------------------------

# adding element to array

#---------------------------------------------------

#!/bin/bash



arr=(aa bb cc dd ee ff gg)



echo ${arr[*]}



arr=( "${arr[@]}" "newElem" ) # from right



echo ${arr[*]}



arr=( "newElem" "${arr[@]}" ) # from left



echo ${arr[*]}



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#---------------------------------------------------

# move last element from array

#---------------------------------------------------

#!/bin/bash





arr=(aa bb cc dd ee ff gg)



echo ${arr[*]}



unset arr[${#arr[@]}-1] #  move last element

echo ${arr[*]}



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#---------------------------------------------------

# copying of array

#---------------------------------------------------

#!/bin/bash



arr=(aa bb cc dd ee ff gg)



echo ${arr[*]}



arr2=( "${arr[@]}" )



echo ${arr2[*]}



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#---------------------------------------------------

# get substring from string

#---------------------------------------------------

#!/bin/bash



echo "long string input=?"

read st



st2=${st:2:4}



echo $st2



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#---------------------------------------------------

# substring replacement "abc" to "xyz"

#---------------------------------------------------

#!/bin/bash



echo "string input=?"

read str



st2=${str/abc/xyz} # only ones



echo $st2



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#---------------------------------------------------

# search of character 'a' in a string

#---------------------------------------------------

#!/bin/sh



echo "string input=?"

read str



pos=`expr index $str a`



echo "position of the first 'a' = "$pos



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#---------------------------------------------------

# string list counting

#---------------------------------------------------

#!/bin/sh



for i in aa bb cc dd ee ff gg hh

do

    echo $i

done



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#---------------------------------------------------

# command line arguments

# separated by spaces

#---------------------------------------------------

#!/bin/sh



echo $0  # script file name



echo $1  # first argument

echo $2  # second argument

echo $3  # third argument



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#---------------------------------------------------

# command line arguments without script name number

# all command line without script name

#---------------------------------------------------

#!/bin/sh



echo $#  # argument number



echo $*  # command line



echo $@





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#---------------------------------------------------

# get all files and dir names

#---------------------------------------------------

#!/bin/sh



echo *  # file and dir names of current dir



for i in *

do

    echo $i

done



echo ../* # file and dir names of parent dir



*/ just close comments



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#---------------------------------------------------

# file search from root dir      ???????

# file name - parameter from command line

#---------------------------------------------------

#!/bin/sh



start=$HOME

date

find $start -name $1 -print



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#---------------------------------------------------

# list of all files with extension .txt     !!!!!!

#---------------------------------------------------

#!/bin/sh



echo *.txt



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#---------------------------------------------------

# combine a set of text files in one file use

# script >targetfile.lst , not txt-file !!!

#---------------------------------------------------

#!/bin/sh



lst=*.txt



for i in $lst

do

    echo

    echo "======================================"

    echo "File "$i

    echo "======================================"

    cat <$i

done



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#---------------------------------------------------

# create new file and write string to it

# file name from command string - variable $1

#---------------------------------------------------

#!/bin/sh



echo "String=?"

read str



echo $str >$1



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#---------------------------------------------------

# read textlines from console and add them to file

# file name from command string - variable $1

#---------------------------------------------------

#!/bin/sh



echo "Add strings=?"

str="1"



while [ $str ]

do

    read str

    echo $str >>$1

done





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#---------------------------------------------------

# read first string from text file

#---------------------------------------------------

#!/bin/sh



read str <$1

echo $str





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#---------------------------------------------------

# text file reading

# script res.txt

#---------------------------------------------------

#!/bin/sh



str="1"



while [ $str ]

do

    read str

    echo $str

    echo $str

done



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