Extact initramfs from zImage

mkinitramfs.pl

#!/usr/bin/env perl
use strict;
use warnings;
use Compress::Zlib;

sub get_unpackdata{
  my $infile = $_[0];
  my $code;
  open IN, " < $infile ";
  binmode(IN);
  while(<IN>){
    $code .= unpack("H*",$_);
  }
  close IN;
  return $code;
}

sub writefile{
  my ( $outfile, $data ) = @_;
  open OUT, " > $outfile ";
  print OUT $data;
  close OUT;
}

sub get_kernel{
  my $code = $_[0];
  my $gz = get_gz($code);
  return ( defined $gz ? Compress::Zlib::memGunzip(pack("H*",$gz)) : 1);
}

sub get_gz{
  my $code = $_[0];
  $code =~ /^.+?(1f8b08.+?)$/;
  return $1;
}

sub get_cpio{
  my $code = $_[0];
  my $count = $_[1] ||= 0;
  my $start = unpack("H*","070701");
  my $trailer = unpack("H*","TRAILER!!!");
  $code =~ /^.+?($start.+?$trailer)/;
  if( defined $1 ){
    return pack("H*",$1);
  } else {
    $count++;
    if( $count == 2){
      return 1;
    }
    get_cpio(get_gz($code),$count);
  }
}

my $zImage = $ARGV[0] ||= "";

if( -f $zImage ){
  my $kernel = get_kernel(get_unpackdata($zImage));
  die("Error!: can't find kernel image.\n") if( $kernel eq 1);
  my $cpio = get_cpio(unpack("H*",$kernel));
  die("Error!: can't find initramfs image.\n") if( $cpio eq 1);
  writefile("initramfs.cpio", $cpio);
} else {
  print "Usage: ./mkinitramfs.pl zImage\n";
}

__END__