An annoyance to me (I come from a C background) is a variable failing to be defined does NOT return 0 or a 'FALSE' definition, it returns "".

Actually, that's not exactly what is going on. Perl has a special "false" value that is 0 when used in numeric context and "" in a string context, so in Perl if (boolean) and if (!boolean) are actually "explicit" tests for truth and falsehood for functions that return "true" and "false" values (this applies to just about every builtin, of course there are some rare special cases). Have a look at Truth and Falsehood. Once you get used to this, I hope you'll find if (!defined(...)) (or any of its variants like if (not defined(...)) or unless (defined(...))) more natural. At least personally, I was initially confused when I read if ( defined($x = $1) eq "" ), and I thought you might accidentally be misapplying an idiom like if ( (my $x = $1) eq "foo" ) (which does the assignment and then the comparison).

If I do print "$3" from a match on 'var = 10' I do not get the same as print "". Regex DO NOT return "" on failing to match, they return undef. After further testing, it appears the difference is where the quantifier comes in:

Right, which is why I left your $3, that is (])?, out of my explanation, and explicitly referred to your $1 (([@%\$]?)), which you were asking about :-)

... portable ... I already had an issue where a CPAN module I would've liked had some Linux-only make commands.

According to CPAN Testers, Config::Perl runs on Linux, MSWin32, Cygwin, Darwin (Mac OS X), and various *BSD, and from Perl versions 5.8.1 thru 5.26.1.

Update 2019-08-17: Updated the link to "Truth and Falsehood".

In reply to Re^3: Regex result being defined when it shouldn't be(?) by haukex
in thread Regex result being defined when it shouldn't be(?) by chenhonkhonk

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