Why do I get an “unexpected operator” error for my condition in Bash?

Question

I got the code for monitoring apache. The name of the file is test.sh. I changed the code a bit.

What I was looking for is, when I do:

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Answer 1

One of your variables ( user_arg, warn_req etc ) in the if condition might be empty.

Better way to write that is with quoting the variables as (which may fail in your case if you want to compare as integers):

if [ "${user_arg}" -ge "${warn_req}" -a "${user_arg}" -lt "${crit_req}" ]

Or another way is to specify the default values so that if variable is null or undefined if won't fail as below.

if [ ${user_arg:-0} -ge ${warn_req:-0} -a ${user_arg:-0} -lt ${crit_req:-0} ]

Answer 2

If you don't need POSIX compatibility, you can use bash's arithmetic evaluation command instead:

if (( user_arg >= 0 && user_arg < crit_req )); then

Unset variables will be implicitly treated as 0-valued, so using default value expansion is unnecessary.