A lowercase eq will be faster than a regex: 
#!/usr/local/bin/perl -slw
use strict;

use Benchmark qw[ cmpthese ];

our  @a = qw/AA12 BB13 CC14 DD15/;
our  @b = qw/aa1 aa2 aa12 bb13/;

sub regex {
  my @match;
  for my $i ( 0 .. $#a ) {
    for my $j ( 0 .. $#b ) {
      if ( $a[$i] =~ m/^$b[$j]$/i ) {
        push @match, "$i -> $j";
      }
    }
  }
  return @match;
}

sub lccmp {
  my @match;
  for my $i ( 0 .. $#a ) {
    for my $j ( 0 .. $#b ) {
      if ( lc($a[$i]) eq lc($b[$j]) ) {
        push @match, "$i -> $j";
      }
    }
  }
  return @match;
}

cmpthese -1, {
    lccmp  => q[ lccmp() ],
    regex  => q[ regex() ],
};

[download]
Retults: 

         Rate regex lccmp
regex  8083/s    --  -82%
lccmp 45997/s  469%    --

[download]

In reply to Re: Comparing strings by jaa
in thread Comparing strings by tanyeun

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