How to warn for the use of unset variables in a KornShell script.
Question
Is there any way to throw errors or warnings in a KornShell (ksh) script to prevent the use of unset variables? Let's assume I have a temporary folder that I want to remove.
TEMP_FILES_DIR='/app/myapp/tmp'
rm -Rf $TEMP_FILE_DIR #notice the misspelling
How to prevent this kind of mistakes before they actually happen?
I know the script should check for file existence and empty string before attempting to remove, this is just a silly example to illustrate a mistake that could have been avoided with some warnings. I don't know if this feature exists in ksh. If it does exist, how do you turn it on?
Solution
The command
set -u
Will cause POSIX sh(1) and its derivatives to grouse when an attempt to expand an unset variable is made.
Example:
$ echo $foo $ set -u $ echo $foo sh: foo: parameter not set
OTHER TIPS
You could check the variable for having content, ie not being '', and print-out a message like "the variable is empty".
However, that's still not going to fix PEBCAK errors like this - all you'd know is that nothing happened.