Clever Geek Handbook

Validating Variables in the Script Shell

What is the best way to make sure all the environment variables I need for my script have been set? I currently have a few if statements that are not very neat:

if [ -z "$VAR1" ]
then
    echo VAR1 not set
    exit
fi

if [ -z "$VAR2" ]
then
    echo VAR2 not set
    exit
fi

if [ -z "$VAR3" ]
then
    echo VAR3 not set
    exit
fi

Is there a better way?

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4 answers


You can use indirect actions:



vars="FOO BAR"
for var in $vars
do
    [[ -z ${!var} ]] && 
        echo "Variable ${var} is empty" ||
        echo "The value of variable ${var} is ${!var}"
done
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Use a for in loop (set of variables u want). Will not work?



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you can shorten them significantly:

[ -z "$FOO" ] && echo "FOO is empty"
[ -z "$BAR" ] && echo "BAR is empty"

The best way:

${FOO:?"FOO is null or not set"}
${BAR:?"BAR is null or not set"}

Of course, if the number of variables you intend to test is small, the loop suggested by @Aviator can be helpful to avoid repeating your code.

In response to @Aviator's answer, I would suggest defining a well-commented variable containing a list of variables to check. This way you don't make your code cryptic.

TEST_FOR_IS_SET="FOO BAR BAZ"

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I have this function in my shell library:

# Check that a list of variables are set to non-null values.
# $@: list of names of environment variables. These cannot be variables local
#     to the calling function, because this function cannot see them.
# Returns true if all the variables are non-null, false if any are null or unset
varsSet()
{
        local var
        for var ; do
                eval "[ -n \"\$$var\" ] || return 1"
        done
}

I am using it in code like this:

varsSet VAR1 VAR2 VAR3 || <error handling here>
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