Bourne/bash shell scripts: string comparison | Bourne shell scripting | Tech-Recipes

Bourne/bash shell scripts: string comparison

Contributed by Rex

October 21, 2003

Tagged: Bourne shell scripting

To determine if the value of a variable ($var) is empty (null):

if [ $var == "" ] then echo variable is null fi

To determine if the value of a variable is not empty:

if [ $var != "" ] then echo variable is not null fi

To compare the contents of a variable to a fixed string:

if [ $var == "value" ] then echo is the same fi

To determine if variable’s contents are not equal to a fixed string:

if [ $var != "value" ] then echo not the same fi

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Viewing 4 Comments

Anonymous 4 years ago 1 point
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Wouldn't the following be better?

if [ -z $var ];then
echo null
fi

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Anonymous 1 month ago 1 point
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i believe the $var needs to be in quotes, like so:

if [ -z "$var" ];then
echo null
fi

Best Regards,
Kibokina

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guest 4 years ago 1 point
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the following syntax is wrong

if [ $var == "" ] ......

because if the variable $var is empty the test is
if [ == "" ] and gives an error

you are obliged to quote the var :
if [ "$var" == "" ] ...

Sergio

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BhupinderSingh 3 years ago 1 point
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this can also be used to compare 2 strings

s1 = "as"
s2 = "bs"

if test $s1 == $s2
then
echo s1 and s2 are equal
fi

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