I'm trying to test and see whether a variable that is being extracted from a line in a file is numeric or not. I have tried everything that I can think of and I cannot figure out how to get it to work. I am trying to test and see if the string extracted contains 5 numeric digits. This is what I have so far:

case $zipcode in
+([0-9])|+([0-9])|+([0-9])|+([0-9])|+([0-9]))
if [[ $zipcode -lt 1 ]] && [[ $zipcode -gt 99999 ]] || [[ $zipcount -ne 6 ]]
then
echo ${myline}
echo "ZIPCODE WARNING! -> ${zipcode}"
fi
;;
*)
echo ${myline}
echo "ZIPCODE WARNING! -> ${zipcode}"
;;
esac

If it's five digits then it can't be bigger than 99999 or less than 00000, so that check seems superfluous. Also you seem to have a logic error there (it cannot be less than one and bigger than 99999). The check for bigger than 0 still needs to be done but it complicates things a bit so I didn't want to dilute this example with the handling of that.

Sorry it was a little tedious, but I just tried it your way and it still doesnt work...it prints out zipcode warnings for every line in the file. even the ones that are legit...I'm not sure what we are doing wrong, but is there another way to do it?

Do you have spaces around the digits? Is there a trailing newline?

No there aren't any leading or trailing whitespaces or newlines in this variable. I'm not sure why it is giving me warnings for legit zipcodes with 5 digits, but is there another way to check and see if a variable is numeric?

There are ways of course, but it would be better IMHO to understand what's wrong here. Does it pass strict numerical test? Does it pass five-character test?

I was able to get it to work...sorry it had one leading whitespace that was keeping it from recognizing that the variable was numeric and not a string. Thanks for all your help I really appreciate it.