I'm currently writing a bash testing framework, where in a test function, both standard bash tests ([[
) as well as predefined matchers can be used. Matchers are wrappers to '[[' and besides returning a return code, set some meaningful message saying what was expected.
Example:
string_equals() {
if [[ ! $1 = $2 ]]; then
error_message="Expected '$1' to be '$2'."
return 1
fi
}
So, when a matcher is used, and it fails, only then an error_message is set.
Now, at some point later, I test whether the tests succeeded. If it succeeded, I print the expectation in green, if it failed in red.
Furthermore, there may be an error_message set, so I test if a message exists, print it, and then unset it (because the following test may not set an error_message
):
if [[ $error_message ]]; then
printf '%s\n' "$error_message"
unset -v error_message
fi
Now my question is, if it is better to unset the variable, or to just set it to '', like
error_message=''
Which one is better? Does it actually make a difference? Or maybe should I have an additional flag indicating that the message was set?
Mostly you don't see a difference, unless you are using set -u
:
/home/user1> var=""
/home/user1> echo $var
/home/user1> set -u
/home/user1> echo $var
/home/user1> unset var
/home/user1> echo $var
-bash: var: unbound variable
So really, it depends on how you are going to test the variable.
I will add that my preferred way of testing if it is set is:
[[ -n $var ]] # True if the length of $var is non-zero
or
[[ -z $var ]] # True if zero length