Re: Modifying pos() from within (?{...})

[tybalt89]

A few tweaks.

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1213595

use strict;
use warnings;
use 5.016;

our $VERSION = 0.1;

# Rebuild PNG image
local $/;
my $input = <DATA>;
chomp $input;
$input = pack "H*", $input;

# Skip PNG Header
$input = substr( $input, 8 );

while (
    $input =~ /\G
          # four byte length
          (....)
          # four byte tag
          (....)
          # variable length data
          ((??{
              # unpack length
              my $length = unpack "N", $1;
              print STDERR "$2 $length\n";
              ".{$length}"}))
          # four byte crc
          (....)/gcsx
  )
{
    my ( $len, $tag, $data, $crc ) = ($1, $2, $3, $4);
    say "Chunk len:",  unpack "N",  $len;
    say "Chunk tag:",  $tag;
    say "Chunk data:", unpack "H*", $data;
    say "Chunk data len:", length $data;
    say "Chunk CRC: ", unpack "H*", $crc;
}


__DATA__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[phone]cb4944415418d3636040005b264b0614e0e7e50c24f595617ccf201e5f3
+706062e16289f8d39b0d83fc09521980bc237737011e6f370b260080fb11390111195
+55b0b6f7f671b7d2658808e3e665176397282e2e766404298de229860173539040226
+f71b18db43848401eac222db9983d9445925385bb584e0a2490915a1c13c9c0c0aac1
+5fccc10612c8e1e74b8806d28682eacc60fb8b84d3536281b4910ea731588043303b3
+30e481ba8ea690b8104720b05b2e2813413879a96124840282fbf2009c4d034615504
+520015a424be37c5c7be0000000049454e44ae426082

[mxb]

Oh! of course! I was returning "(.){$len}", which is $len number of single character capture groups. What I actually wanted was "(.{$len})" - a single capture of length $len.

I also see you added the missing /s modifier, which explains why it was stopping mid way through.

That makes the (??{...}) issue much clearer. Thanks!