update

I don't recommend the following code anymore

rather 

    if ( my (@caps) = ($line =~ $re) ) {
        no warnings 'uninitialized';
        @caps = () if $caps[0] ne $1;           # reset pseudo capture
+s
        $cb->(@caps);
        last;
    }

[download]
/update

This should be backward compatible

    my (@matches) = ($line =~ $re)
    if (defined $&) {
        $cb->(@matches);
        last;
    }

[download]

# tests...

use v5.12;
use warnings;

for my $str ("AB","") {
    say "****** str=<$str>";
    for my $re ( qr/../, qr/(.)(.)/, q/XY/, q/(X)Y/, q// ) {
        say "--- re=<$re>";
        my @captures = $str =~ $re;
        if ( defined $& ) {
            say "matched"
        } else {
            say "no match"
        }
        if (defined $1) {
            say "with captures <@captures>";
        } else {
            say "no captures";
        }
    }
}

[download]


****** str=<AB>
--- re=<(?^u:..)>
matched
no captures
--- re=<(?^u:(.)(.))>
matched
with captures <A B>
--- re=<XY>
no match
no captures
--- re=<(X)Y>
no match
no captures
--- re=<>
matched
no captures
****** str=<>
--- re=<(?^u:..)>
no match
no captures
--- re=<(?^u:(.)(.))>
no match
no captures
--- re=<XY>
no match
no captures
--- re=<(X)Y>
no match
no captures
--- re=<>
matched
no captures

[download]

Cheers Rolf
(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery

In reply to Re^3: How to know that a regexp matched, and get its capture groups? by LanX
in thread How to know that a regexp matched, and get its capture groups? by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.