Trying to match a pattern which is roughly a-or-b-followed by digits or digits-followed-by-a-or-b.

use strict;
use warnings;
use Data::Dumper;
$Data::Dumper::Indent = 0;

my $string_one = 'foo bar [a21] plus (b23) baz bax';
my @string_one_results = $string_one =~ m { (a|b) (\d+) }gx;
print "RESULTS: " , Dumper(\@string_one_results), $/;
# RESULTS: $VAR1 = ['a','21','b','23'];

[download]

So far so good for the first pattern. Here's the other

my $string_two = 'foo bar [21a] plus (23b) baz bax';
my @string_two_results = $string_two =~ m{ (\d+) (a|b) }gx;
print "RESULTS: " , Dumper(\@string_two_results), $/;
# RESULTS: $VAR1 = ['21','a','23','b'];

[download]

The second regex matches fine for that other format. Here's what I've been struggling over for half an hour or so: what if the two formats are mixed up?

Shouldn't I be able to come up with a regex matching either pattern?

my $string_three = 'foo bar [21a] plus (b23) baz bax';
my @string_three_results = $string_three =~ m{ (\d+) (a|b) | (a|b) (\d
++) }gx;
print "RESULTS: " , Dumper(\@string_three_results), $/;
# RESULTS: $VAR1 = ['21','a',undef,undef,undef,undef,'b','23'];

[download]

Please help me out, Monks. What am I doing wrong and what are the undefs in my @results?

In reply to Complex regex question by Cody Fendant

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