use strict;
use warnings;

while ( <DATA> ) {
  next unless /^ATOM\b/;
  my $chain = substr $_, 21, 1;
  my $position = 0 + substr $_, 23, 3;
  my $Zcoordinate = 0 + substr $_, 47, 7;
  print "$chain, $position, $Zcoordinate\n";
}

__DATA__
ATOM     30  N   HIS A  66       7.514  15.296  11.222  1.00 12.98      A    N  
ATOM     31  CA  HIS A  66       7.318  14.688  12.568  1.00 12.48      A    C  
ATOM     32  C   HIS A  66       8.676  14.309  13.156  1.00 11.62      A    C  
ATOM     33  O   HIS A  66       9.708  14.518  12.545  1.00 11.76      A    O  

##</code><code>##

while ( <DATA> ) {
  next unless /^ATOM\b/;
  my( $chain, $position, $Zcoordinate ) = unpack( 'x21a1xA3x21A7',$_);
  print "$chain, $position, $Zcoordinate\n";
}

__DATA__
ATOM     30  N   HIS A  66       7.514  15.296  11.222  1.00 12.98      A    N  
ATOM     31  CA  HIS A  66       7.318  14.688  12.568  1.00 12.48      A    C  
ATOM     32  C   HIS A  66       8.676  14.309  13.156  1.00 11.62      A    C  
ATOM     33  O   HIS A  66       9.708  14.518  12.545  1.00 11.76      A    O  
ATOM     34  CB  HIS A  66       6.450  13.434  12.442  1.00 12.81      A    C  
ATOM     35  CG  HIS A  66       5.000  13.829  12.378  1.00 13.36      A    C  
ATOM     36  ND1 HIS A  66       4.332  14.002  11.175  1.00 13.57      A    N  
ATOM     37  CD2 HIS A  66       4.073  14.085  13.360  1.00 13.93      A    C  
ATOM     38  CE1 HIS A  66       3.063  14.347  11.461  1.00 14.23      A    C  
ATOM     39  NE2 HIS A  66       2.851  14.410  12.778  1.00 14.47      A    N