There are several other reasons for prefering unpack to a regex for fixed width data.

1. Strings are typically left-justified and space padded. When used as keys in a hash, 'xxx' won't match 'xxx '.

   The A template will strip the right-padding on the fly.

   Numbers are typically right-justified. Perl will strip leading spaces the first time you use it in a numeric contexr.

2. unpack is usually much faster than using a regex for this.

   For this application of picking out 6/12 fields from 125/250, it is roughly 10 times faster:

   #! perl -slw
   use strict;
   use Math::Random::MT qw[ rand ];
   use Benchmark qw[ cmpthese ];
   
   our $data = join '', map {
       sprintf '%-25s%15d', 'X' x int( rand 25 ) , int( rand 2**32 )
   } 1 .. 125;
   
   ## extract 6 pairs at positions 3rd, 33rd, 50th, 75th, 100th 123rd
   my $pair = 'A25 A15';
   our $tmpl = "x[($pair)2] $pair x[($pair)29] $pair x[($pair)16] $pair"
             . "x[($pair)24] $pair x[($pair)24] $pair x[($pair)22] $pair 
   +";
   
   cmpthese -3, {
       regex => q[
           our $data;
           my @sixPair = ( 
               $data =~ m[(.{25})(.{15})]g 
           )[ 5, 6, 65, 66, 99, 100, 149, 150, 199, 200, 245,246 ];
       ],
       unpack=> q[
           our( $data, $tmpl );
           my @sixPair = unpack $tmpl, $data
       ],
   };
   
   cmpthese 1, {
       regex => q[
           our $data;
           my @sixPair = ( 
              $data =~ m[(.{25})(.{15})]g 
           )[ 4,5, 64,65, 98,99, 148,149, 198,199, 244,245 ];
           print 'regex  ', join '|', @sixPair;
       ],
       unpack=> q[
           our( $data, $tmpl );
           my @sixPair = unpack $tmpl, $data;
           print 'unpack ', join '|', @sixPair;
       ],
   };
   
   __END__
   C:\test>junk4
             Rate  regex unpack
   regex   3311/s     --   -91%
   unpack 38783/s  1071%     --
   
   regex  
   XXXXXXXXXXXXXXXXXXXXXX   |      189677339|
   XXXXXXX                  |      966124187|
   XXXXXXXXXXX              |    -1269554066|
   XXXXX                    |    -1916129141|
   XXXXXXXXXXXXXXX          |     -479254076|
   XXXXXXXXXXXXXXXXX        |      335028423
   
   unpack 
   XXXXXXXXXXXXXXXXXXXXXX|      189677339|
   XXXXXXX|      966124187|
   XXXXXXXXXXX|    -1269554066|
   XXXXX|    -1916129141|
   XXXXXXXXXXXXXXX|     -479254076|
   XXXXXXXXXXXXXXXXX|      335028423
   [download]

   Results wrapped manually for posting.