If you need to parse, write, change and manipulate PDB files you should probably make an effort and consider bioperl. This code is untested and positively wrong, (the docs of BIO::Structure are starting to bite me like a goliath tiger fish), but you can start playing with this..

use strict; use warnings; 
use Bio::Structure::IO;
#use Data::Dumper;

my $in = Bio::Structure::IO->new(-file => "myfile.pdb",
                                 -format => 'PDB');

 while ( my $struc = $in->next_structure() ){ 
       print "Structure: ", $struc->id;
       for my $model ($struc->get_models){
            print "model: ", $model->id;
        for my $chain ($struc->get_chains) {
           if($chain->id eq "A"){ 
                   print "we have an A!";
           foreach my $res ($struc->get_residues($chain)){
            print "Yeah, Honestly, I don't know what I'm doing here";
        foreach my $atom  ($struc->get_atoms($res)){
                     print "This is the ATOM ",$atom->id;}
          }
        }
        last;
        }
    last;
}}
[download]

mmmh, or maybe use Chemistry::File::PDB?