If you want the number of the backreference and you know in advance the number of possible backreferences, here's a quick hack:

#!/usr/bin/perl -w
use strict;

my $string = 'abcbar';
my $sub = get_backref( $string );

print $sub;

sub get_backref {
    my $string = shift;
    my $regex  = '(foo)|(bar)|(baz)';
    my $backref = 0;
    
    # This is the number of possible backreferences
    # It's easier to set than generate dynamically
    my $limit = 3;
    local ( $1, $2, $3 );

    $string =~ /$regex/;
    for ( 1 .. $limit ) {
        no strict 'refs';
        $backref = $_, last if defined $$_;
    }
    return $backref;
}
[download]

Update: Here's a much more robust example (though with no validation of arguments to the sub). Pass the string, the number of backreferences, and the regex and it will return to you the regex that matched:

#!/usr/bin/perl -w
use strict;

my $string = 'abcbar';
my $sub = get_backref( $string, 3, '(foo)|(bar)|(baz)' );

print $sub;

sub get_backref {
    my ( $string, $num_refs, $regex ) = @_;
    my $backref = 0;

    # This is the number of possible backreferences
    # easier to set than count
    my $local_brefs = '';
    for ( 1 .. $num_refs ) {
        $local_brefs .= "\$$_,";
    }
    chop $local_brefs;
    my $code = <<"    END_OF_CODE";
    local ( $local_brefs );

    \$string =~ /$regex/;
    for ( 1 .. $num_refs ) {
        no strict 'refs';
        \$backref = \$_, last if defined \$\$_;
    }
    END_OF_CODE
    eval $code;
    return $backref;
}
[download]

Of course, it returns the number of the backreference that matched first (i.e., if $2 matched first, it returns 2). It returns zero if no match is found. You'll have to test for this if you're using it as an array index unless $array[0] is a default.

Cheers,
Ovid

Vote for paco!

Join the Perlmonks Setiathome Group or just click on the the link and check out our stats.

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.