Determing whether a regexp has capturing matches

Is there a nice way I can figure out whether my regexp has capturing matches in it? My question turned up with some code that (boiled down) needs to differentiate between these two cases:

my @x = ( "1234" =~ m/(\d)/ );  # @x contains a captured match of "1"
my @y = ( "1234" =~ m/34/ );    # @y contains a "1" for a successful m
+atch
print "x=(@x), y=(@y)\n";
# x=(1), y=(1)
[download]

Now I guess I could set $1 to undef before the match and test it afterwards - but this seems so darn inelegant. Am I missing a trick?

Comment on Determing whether a regexp has capturing matches Download Code
Re: Determing whether a regexp has capturing matches by kyle (Abbot) on Feb 27, 2007 at 15:45 UTC
You don't need to set `$1` before the match. In fact, I think you can't. `$ perl -le '$1=undef;' Modification of a read-only value attempted at -e line 1.` [download] `$1` will be set to undef after a match with no parentheses. `"1234"=~/(\d)/; print "$1\n"; "1234"=~/34/; print "$1\n"; print "undef\n" if ! defined $1;` [download] Prints: `1 undef` [download] This doesn't work when a regex had capturing parentheses that didn't match. Just like the "no parentheses" case above, this also prints "`undef`": `"1234"=~/(x)?34/; print "undef" if ! defined $1;` [download]	[reply] [d/l] [select]
Re^2: Determing whether a regexp has capturing matches by adrianh (Chancellor) on Feb 27, 2007 at 15:58 UTC
$1 will be set to undef after a match with no parentheses. Is this documented behaviour? I could have sworn I'd used a perl at some point where $1 persisted unless you made another captured match. I could, of course, be making shit up :-)	[reply]
Re^3: Determing whether a regexp has capturing matches by Limbic~Region (Chancellor) on Feb 27, 2007 at 17:15 UTC
adrianh, See Zen and the Art of Match Variables. In a nutshell, match variables are weird. Cheers - L~R	[reply]
Re: Determing whether a regexp has capturing matches by rhesa (Vicar) on Feb 27, 2007 at 15:52 UTC
See perlvar for `@-` and `@+`.	[reply] [d/l] [select]
Re^2: Determing whether a regexp has capturing matches by adrianh (Chancellor) on Feb 27, 2007 at 16:03 UTC
D'oh. Of course. Thanks. `sub has_captured_matches { return $#+ };` [download]	[reply] [d/l]
Re^3: Determing whether a regexp has capturing matches by kyle (Abbot) on Feb 27, 2007 at 16:08 UTC
Keep in mind that `$#+` is -1 when the pattern does not match, regardless of whether there are captures. `"1234" =~ /(1)34/; print $#+, "\n"; "1234" =~ /134/; print $#+, "\n";` [download] That prints "-1" both times, and -1 is considered a "true" value.	[reply] [d/l] [select]
Re^4: Determing whether a regexp has capturing matches by adrianh (Chancellor) on Feb 27, 2007 at 16:45 UTC


No such thing as a small change
	PerlMonks

Determing whether a regexp has capturing matches

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