Shell Programming and Scripting

I am writing script that will act like the 'comm' utility. My
problem is when trying to read whether the user has entered -123 or -1
or -1...etc.

I currently have:

Code:

                if(m/[\-][0-3][0-3]?[0-3]?[^a-z]/g){
                        print "Good.\n";
                }

So, this should check for all -123, -1, -12, -32, etc. But I would like
to output an error message if the user enters something like:
-123333

or

-123abc

Something is wrong with the [^a-z] part. Could someone help me clean
this up? Thanks.

Code:

if ( /^-[0-3]{1,3}$/ ) {
    print "Good.\n";
}