Linux Shell Script

Shell script• The first line is used to specify shell program• #!/bin/sh• Variables

variable=“text”variable=0variable=`program arguments`

• To use the declared variables=“hello” echo $secho ${s}_123

• System environment variables$ export

Passing argument

• Special variables• Number of arguments $#• 1st, 2nd, .. arguments $1, $2, ...• Each argument $@ = .$1. .$2....• All arguments $* = .$1 $2 ....• Exit status $?

• echo - display text or variable to stdout• echo “hello”• read - read from stdin

read secho “you type: $s”

• expr - evaluate the expressionread ij=`expr $i + 10`echo $j

Shell Arithmetic

• Use to perform arithmetic operations.• Syntax:

expr op1 math-operator op2

Examples: $ expr 1 + 3$ expr 2 - 1$ expr 10 \/ 2$ expr 20 \% 3$ expr 10 \* 3$ echo `expr 6 + 3`

• if .- conditional statementif condition then ... fiif [ “$s” = “abc” ]; then ...fi

• Most conditions can be written by using test or [...]• Test if file size > 0 -s filename• Test if file exists -f filename• Test file permission -r -w -x

filename• String equality string1 =

string2• String inequality string1 != string2

• Test if string length = 0 -z string• Test if string length > 0 -n filename• Equality i1 -eq i2• Inequality i1 -neq i2• Greater than i1 -gt i2• Greater than or equal to i1 -ge i2• Less than i1 -lt i2• Less than or equal to i1 -le i2• Negate !

• Casecase variable in value1) ...;; value2) ...;; *) ...;;esac

case $f in “english”) echo .hello.;; “thai”) echo .sawasdee.;;esac

• While Loopwhile condition do ... done

i=0while [ $i -lt 10]; do

echo “Hello”i=`expr $i + 1`

done

• For Loopfor variable [ in range ] do ... done

for f in *.txt; do cat $fdone

echo command

• \n new line• \a alert (bell)• \b backspace• \c suppress trailing new line• \r carriage return• \t horizontal tab