Unix / Linux - Shell Boolean Operators Example

The following Boolean operators are supported by the Bourne Shell.

Assume variable a holds 10 and variable b holds 20 then −

Example

Here is an example which uses all the Boolean operators −

#!/bin/sh
a=10
b=20
if [ $a != $b ]
then
   echo "$a != $b : a is not equal to b"
else
   echo "$a != $b: a is equal to b"
fi
if [ $a -lt 100 -a $b -gt 15 ]
then
   echo "$a -lt 100 -a $b -gt 15 : returns true"
else
   echo "$a -lt 100 -a $b -gt 15 : returns false"
fi
if [ $a -lt 100 -o $b -gt 100 ]
then
   echo "$a -lt 100 -o $b -gt 100 : returns true"
else
   echo "$a -lt 100 -o $b -gt 100 : returns false"
fi
if [ $a -lt 5 -o $b -gt 100 ]
then
   echo "$a -lt 100 -o $b -gt 100 : returns true"
else
   echo "$a -lt 100 -o $b -gt 100 : returns false"
fi

The above script will generate the following result −

10 != 20 : a is not equal to b
10 -lt 100 -a 20 -gt 15 : returns true
10 -lt 100 -o 20 -gt 100 : returns true
10 -lt 5 -o 20 -gt 100 : returns false

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

• 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.