Examples of small bash Scripts
Here is a set of small scripts, which demonstrate some features of bash programming.
#--------------------------------------------------- // set new prompt #--------------------------------------------------- PS1=">" PS1="[${LOGNAME}@$(hostname)] # " PS1="[${LOGNAME}] # " PS1='$PWD $ '
#--------------------------------------------------- // set (and automatically create) shell variable #--------------------------------------------------- $ test="test" $ homedir='pwd' string="The man said \" hello \"."
#--------------------------------------------------- // To use the variable within the shell, it is preceded by a $ #--------------------------------------------------- homedir=$HOME cd $homedir
#--------------------------------------------------- // how to print shell variable #--------------------------------------------------- echo PS1 echo $PS1 echo $USERNAME
#--------------------------------------------------- // 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
#--------------------------------------------------- // The shell supports pattern matching #--------------------------------------------------- * Match all characters in a string ? Match a single character ls *.dat
#--------------------------------------------------- // Command Substitution #--------------------------------------------------- today=`date`
#--------------------------------------------------- # empty sh script program #--------------------------------------------------- #!/bin/sh
#--------------------------------------------------- # comments #--------------------------------------------------- #!/bin/sh # this is comment
#--------------------------------------------------- # printing of string constant #--------------------------------------------------- #!/bin/sh echo 'hello' echo "hello" echo hello
#--------------------------------------------------- # declaration and printing of string variable #--------------------------------------------------- #!/bin/sh x='Wonderful new World' echo $x echo x # just string 'x'
#--------------------------------------------------- # call of other programs #--------------------------------------------------- #!/bin/sh ls
#--------------------------------------------------- # indirect call of other programs #--------------------------------------------------- #!/bin/sh x='pwd' $x x='ls -l' $x
#--------------------------------------------------- # indirect call with indirect parameters #--------------------------------------------------- #!/bin/sh u='-l' x='ls ' $x $u
#--------------------------------------------------- # print current shell name ??? #--------------------------------------------------- #!/bin/sh echo $SHELL
#--------------------------------------------------- # Anything enclosed in double quotes is passed on exactly # as presented with the exception that the values of # shell variables are substituted #--------------------------------------------------- #!/bin/sh v1="abc " v2="$v1 d" echo $v1 $v2
#--------------------------------------------------- # Any matter enclosed in single quotes is passed on # exactly as presented. The values of shell variables # are not substituted. #--------------------------------------------------- #!/bin/sh v1="abc" v2='$v1 d' echo $v1 $v2
#--------------------------------------------------- # 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
#--------------------------------------------------- # escaping #--------------------------------------------------- #!/bin/sh msg=`echo Your Current Directory is \`pwd\`` echo $msg
#--------------------------------------------------- # reading of text line from keyboard #--------------------------------------------------- #!/bin/sh read x echo $x echo $x
#--------------------------------------------------- # 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
#--------------------------------------------------- # syntax: many commands in one line !!!! #--------------------------------------------------- #!/bin/sh echo "a"; echo "b"; echo "c" var=5; echo `expr $var + $var`
#--------------------------------------------------- # integer variable and its increment # does not works in sh !!! #--------------------------------------------------- #!/bin/bash var=12345 let var=$var+1 # let is important echo $var v=12345 v=$v+1 # result "12345+1"
#--------------------------------------------------- # 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
#--------------------------------------------------- # 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
#--------------------------------------------------- # very simple 'if' #--------------------------------------------------- #!/bin/sh echo 'number=?' read x if [ $x -eq 5 ] then echo "five" fi
#--------------------------------------------------- # if ... else #--------------------------------------------------- #!/bin/sh echo 'number=?' read x if [ $x -eq 5 ] then echo "five" else echo "not 5" fi
#--------------------------------------------------- # 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
#--------------------------------------------------- # 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
#--------------------------------------------------- # while loop - print first 10 integers from 0 #--------------------------------------------------- #!/bin/bash x=0 while [ $x -lt 10 ] do echo $x let x=$x+1 done
#--------------------------------------------------- # 10 random numbers generation #--------------------------------------------------- #!/bin/bash i=0 while [ $i -lt 10 ] do x=$RANDOM echo $x let i=$i+1 done
#--------------------------------------------------- # endless loop: interrupting by ctrl-c #--------------------------------------------------- #!/bin/sh while [ 1 ] do read x echo $x$x done
#--------------------------------------------------- # 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
#--------------------------------------------------- # simple use of for ... in ... #--------------------------------------------------- #!/bin/sh for i in "abc" "xyz" 1 2 99 do echo $i done
#--------------------------------------------------- # use for as in C-programming # sum of the first n integer numbers #--------------------------------------------------- #!/bin/bash echo -n "number=?" read n s=0 # here sum for((i=1; i <=n ; i++)) do let s=$s+$i done echo "sum= "$s
#--------------------------------------------------- # 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
#--------------------------------------------------- # 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
#--------------------------------------------------- # string comparing #--------------------------------------------------- #!/bin/sh echo "Input string=?" read str if [ $str = "abc" ] then echo "You got it!" else echo "Its not 'abc'" fi
#--------------------------------------------------- # simple strings concatenation #--------------------------------------------------- #!/bin/sh echo "Input string=?" read str s2=$str"AAAA" echo $s2 s3="XXX"$s2 echo $s3
#--------------------------------------------------- # strings concatenation #--------------------------------------------------- #!/bin/sh echo "Input string=?" read str1 echo "Input second string=?" read str2 s3=$str1$str2 # it works! echo $s3 s4=${str1}${str2} # it works too! echo $s4
#--------------------------------------------------- # testing whether a string is null #--------------------------------------------------- #!/bin/sh echo "Input string=?" read str if [ $str ] then echo "Not empty" else echo "Empty" fi
#--------------------------------------------------- # length of string #--------------------------------------------------- #!/bin/sh echo "Input string=?" read str leng=`expr length $str` echo "length= "$leng
#--------------------------------------------------- # how to insert string to constant string #--------------------------------------------------- #!/bin/sh var="good" echo "This is $var test"
#--------------------------------------------------- # simplest function example #--------------------------------------------------- #!/bin/sh #--------------------------- func() { echo "Inside function" } #--------------------------- echo "Now function call..." func echo "end of main"
#--------------------------------------------------- # function can see variables of main program #--------------------------------------------------- #!/bin/sh #-------------------------- func() { echo $var } #-------------------------- var="test of global " func
#--------------------------------------------------- # 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"
#--------------------------------------------------- # passing variable parameters #--------------------------------------------------- #!/bin/bash #------------------------------- func2() { let r=$1*$1 echo $r } #------------------------------- var=123 func2 $var
#--------------------------------------------------- # 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
#--------------------------------------------------- # 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
#--------------------------------------------------- # floating point numbers #--------------------------------------------------- #!/bin/sh # does not support !!!!
#--------------------------------------------------- # 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 ${arr[2]}
#--------------------------------------------------- # number of elements in array #--------------------------------------------------- #!/bin/bash arr=(aa bb cc dd) n=${#arr[@]} echo $n
#--------------------------------------------------- # array with filenames of current directory #--------------------------------------------------- #!/bin/sh arr=(*) # * is list of all file and dir names n=${#arr[@]} echo "number of files and dirs "$n echo ${arr[0]} echo ${arr[1]}
#--------------------------------------------------- # print all array elements -not good # works then no holes in indexes #--------------------------------------------------- #!/bin/bash arr=(aa bb cc dd ee ff gg) n=${#arr[@]} i=0 while test $i -lt $n do echo ${arr[$i]} let i=$i+1 done
#--------------------------------------------------- # dynamic expansion of array # one array element in reality is couple (index, value) #--------------------------------------------------- #!/bin/bash arr=() n=${#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
#--------------------------------------------------- # 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
#--------------------------------------------------- # 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[*]}
#--------------------------------------------------- # 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[*]}
#--------------------------------------------------- # copying of array #--------------------------------------------------- #!/bin/bash arr=(aa bb cc dd ee ff gg) echo ${arr[*]} arr2=( "${arr[@]}" ) echo ${arr2[*]}
#--------------------------------------------------- # get substring from string #--------------------------------------------------- #!/bin/bash echo "long string input=?" read st st2=${st:2:4} echo $st2
#--------------------------------------------------- # substring replacement "abc" to "xyz" #--------------------------------------------------- #!/bin/bash echo "string input=?" read str st2=${str/abc/xyz} # only ones echo $st2
#--------------------------------------------------- # 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
#--------------------------------------------------- # string list counting #--------------------------------------------------- #!/bin/sh for i in aa bb cc dd ee ff gg hh do echo $i done
#--------------------------------------------------- # 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
#--------------------------------------------------- # command line arguments without script name number # all command line without script name #--------------------------------------------------- #!/bin/sh echo $# # argument number echo $* # command line echo $@
#--------------------------------------------------- # get all files and dir names #--------------------------------------------------- #!/bin/sh echo * # file and dir names of current dir for i in * do echo $i done echo ../* # file and dir names of parent dir */ just close comments
#--------------------------------------------------- # file search from root dir ??????? # file name - parameter from command line #--------------------------------------------------- #!/bin/sh start=$HOME date find $start -name $1 -print
#--------------------------------------------------- # list of all files with extension .txt !!!!!! #--------------------------------------------------- #!/bin/sh echo *.txt
#--------------------------------------------------- # 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
#--------------------------------------------------- # create new file and write string to it # file name from command string - variable $1 #--------------------------------------------------- #!/bin/sh echo "String=?" read str echo $str >$1
#--------------------------------------------------- # 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
#--------------------------------------------------- # read first string from text file #--------------------------------------------------- #!/bin/sh read str <$1 echo $str
#--------------------------------------------------- # text file reading # scriptres.txt #--------------------------------------------------- #!/bin/sh str="1" while [ $str ] do read str echo $str echo $str done