Ubuntu Unleashed 2019 Edition: Covering 18.04, 18.10, 19.04

String Comparison

You can use the following operators to compare two string expressions:

=—Compares  whether two strings are equal

!=—Compares whether two strings are not equal

-n—Evaluates    whether the string  length  is  greater than    zero

-z—Evaluates    whether the string  length  is  equal   to  zero

Next are some examples using these operators when comparing two strings,
string1 and string2, in a shell program called compare1:

Click here to view code image
#!/bin/sh
string1="abc"
string2="abd"
if [ $string1 = $string2 ]; then
echo "string1 equal to string2"
else
echo "string1 not equal to string2"
fi

if  [   $string2    !=  string1 ];  then

            echo    "string2    not equal   to  string1"

else

            echo    "string2    equal   to  string2"

fi

if  [   $string1    ];  then

            echo    "string1    is  not empty"

else

            echo    "string1    is  empty"

fi

if  [   -n  $string2    ];  then

            echo    "string2    has a   length  greater than    zero"

else

            echo    "string2    has length  equal   to  zero"

fi

if  [   -z  $string1    ];  then

            echo    "string1    has a   length  equal   to  zero"

else

        echo    "string1    has a   length  greater than    zero"

fi

If you execute compare1, you get the following result:

Click here to view code image