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