Code-Searching: Shell script : Basic exmples

Create variables

test="test"

homedir='pwd'

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

Use the variable (using $)

homedir=$HOME

cd $homedir

Print variable

echo $s1

Pattern matching

* Match all characters in a string

? Match a single character

ls *.dat

Comments

# this is comment

Print string constant

echo 'hello'

echo "hello"

echo hello

Print string variable

x='Wonderful world'

echo $x

Running commands from script

x='pwd'

x='ls -l'

u='-l'

x='ls '

$x $u

Use commands and string together

Back quotes are used to enclose commands.

An item enclosed in back quotes is replaced by the standard output of the command.

date=`date`

echo the date is $date

Read text from keyboard

read x

echo $x

Many commands in one line

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

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

Integer arithmetics + - * / %

#!/bin/bash

let sum=$x+$y

echo 'x+y=' $sum

#!/bin/sh

sum=`expr $x + $y`

echo $sum

if statement

#!/bin/sh

if [ $x -eq 5 ]

then

echo "five"

if / else statement

if [ $x -eq 5 ]

then

echo "five"

else

echo "not 5"

if / elif / else statement

if [ $x -eq 5 ]

then

echo "five"

elif [ $x -eq 7 ]

then

echo "seven"

else

echo "not 5 and not 7"

Comparing numeric using nested if

if [ $x -gt 0 ]

then

if [ $x -lt 10 ]

then

echo "x is greater than 0 but less than 10"

while loop

#!/bin/bash

x=0

while [ $x -lt 10 ]

echo $x

let x=$x+1

done

Example - Generate 10 random numbers

i=0

while [ $i -lt 10 ]

x=$RANDOM

echo $x

let i=$i+1

done

Example - Infinite loop : interrupting by ctrl+c

#!/bin/sh

while [ 1 ]

read x

echo $x

done

for - in loop

#!/bin/sh

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

echo $i

done

for loop

#!/bin/bash

s=0

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

let s=$s+$i

done

echo "sum= "$s

case operator for selection of logical branches

Note: End marker of branch indicated by ;;

#!/bin/sh

case "$str" in

abc) echo "string = abc"

;;

xyz) echo "string = xyz"

;;

*) echo "not abc, not zyz"

;;

esac

exit operator

#!/bin/sh

while [ 1 ]

read x

echo $x

if [ $x -eq 0 ]

then

echo "script done ..."

exit 0

done

String comparison

#!/bin/sh

if [ $str = "abc" ]

Strings concatenation

str1="AAAAA"

str2=$str1"BBBB"

str3=$str1$str2

str4=${str1}${str2}

Check if a string is null

if [ $str ]

then

echo "Not empty"

else

echo "Empty"

Length of string

x=`expr length $str`

echo "length= "$x

Insert string to constant string

var="good"

echo "This is $var test"

Get substring from string

#!/bin/bash

str2=${str:2:4}

echo $str2

Substring replacement "abc" to "xyz"

#!/bin/bash

str2=${str1/abc/xyz} # replaces only ones

echo $str2

Search of character 'a' in a string

#!/bin/sh

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

echo $i

done

Functions in script

#!/bin/sh

func() {

echo "Inside function"

}

echo "Calling function..."

func

echo "end of main"

Using variables of main program in function

#!/bin/sh

func() {

echo $var

}

var="test of using global variable"

func

Passing of parameters to function

#!/bin/sh

func() {

echo "inside function"

echo $0 # shell script name

echo $1 # first parameter

echo $2 # second parameter

echo "End of function..."

exit 0

}

func 123 "abc"

Passing variable parameters

#!/bin/bash

func() {

let r=$1*$1

echo $r

}

var=123

func $var

Recursive function - 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

}

read x

factorial $x

Using the function library

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

Command line arguments

#!/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

#!/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 *

echo $i

done

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

echo "------------------------------------------------------"

echo "File "$i

echo "------------------------------------------------------"

cat <$i

done

Create new file and write string to it

# Get file name from command line - variable $1

#!/bin/sh

echo $str >$1

Read textlines from console and add them to file

# Get file name from command line - variable $1

#!/bin/sh

echo "Add strings=?"

str="1"

while [ $str ]

read str

echo $str >>$1

done

Read first string from text file

#!/bin/sh

read str <$1

echo $str

Text file reading

# script res.txt

#!/bin/sh

str="1"

while [ $str ]

read str

echo $str

done

Using Arrays

#!/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" # Assignment to array element

echo ${arr[2]}

Get 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

#!/bin/bash

arr=(aa bb cc dd ee ff gg)

n=${#arr[@]}

i=0

while test $i -lt $n

echo ${arr[$i]}

let i=$i+1

done

Dynamic expansion of array

# One array element in reality is pair of its index and value

#!/bin/bash

arr=()

n=${#arr[@]}