You can set pos of the string to continue matching, and then capture the digits to the left and right of the continuation point (\G):

#!/usr/bin/perl

use 5.020;
use experimental 'signatures';
use Test::More;

sub digits( $S, $pos ) {
    pos($S) = $pos;
    return ($S =~ m/\b(\d*\G\d*)\b/c) ? $1 : undef;
}

is digits( 'Hello World 123456 !!! 789 ...', 14 ), '123456', "In middl
+e";
is digits( '12345 World 123456 !!! 789 ...', 14 ), '123456', "No digit
+s before";
is digits( '12345 World 123456 !!! 789 ...', 17 ), '123456', "At end";
is digits( '12345 World 123456 !!! 789 ...', 12 ), '123456', "At start
+";

done_testing;

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In reply to Re: How to capture backwards using regex? by Corion
in thread How to capture backwards using regex? by harangzsolt33

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