I'll take this a step further too and mention the diagnostics pragma (perldoc diagnostics). I don't think it is practical for production use, but can be helpful for new Perl folks when learning and finding that their code doesn't seem to work with -w all of a sudden :) The diagnostics pragma will give verbose warning messages (more verbose than the normal -w warnings). Here is an example:

#!/usr/bin/perl -w

print "Hello;
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When run, this will produce:

Can't find string terminator '"' anywhere before EOF at ./test.pl line 3.

Ok, this is an easy one to see the error :) I am using it for examples sake! Anyways, now, let's change the script to:

#!/usr/bin/perl -w

use diagnostics;
print "Hello;
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Now, this is what you would see:

Can't find string terminator '"' anywhere before EOF at ./test.pl line 4 (#1)

    (F) Perl strings can stretch over multiple lines.  This message means that
    the closing delimiter was omitted.  Because bracketed quotes count nesting
    levels, the following is missing its final parenthesis:

        print q(The character '(' starts a side comment.);

    If you're getting this error from a here-document, you may have
    included unseen whitespace before or after your closing tag. A good
    programmer's editor will have a way to help you find 
these characters.

Uncaught exception from user code:
        Can't find string terminator '"' anywhere before EOF at ./test.pl line 4.

Just an aside to hopefully help some folks learn