Unix / Linux - Shell String Operators Example

The following string operators are supported by Bourne Shell.

Assume variable a holds "abc" and variable b holds "efg" then −

Example

Here is an example which uses all the string operators −

#!/bin/sh
a="abc"
b="efg"
if [ $a = $b ]
then
   echo "$a = $b : a is equal to b"
else
   echo "$a = $b: a is not equal to b"
fi
if [ $a != $b ]
then
   echo "$a != $b : a is not equal to b"
else
   echo "$a != $b: a is equal to b"
fi
if [ -z $a ]
then
   echo "-z $a : string length is zero"
else
   echo "-z $a : string length is not zero"
fi
if [ -n $a ]
then
   echo "-n $a : string length is not zero"
else
   echo "-n $a : string length is zero"
fi
if [ $a ]
then
   echo "$a : string is not empty"
else
   echo "$a : string is empty"
fi

The above script will generate the following result −

abc = efg: a is not equal to b
abc != efg : a is not equal to b
-z abc : string length is not zero
-n abc : string length is not zero
abc : string is not empty

The following points need to be considered while using the operator −

• There must be spaces between the operators and the expressions. For example, 2+2 is not correct. It should be written as 2 + 2.

• if...then...else...fi statement is a decision-making statement which has been explained in the next chapter.