I wish to parse a file as described below.
I want to select the line which begins by H until the line finishing by `//`.
I wrote this code but it doesn't work and return 1:

```
use strict;
use warnings;
my $nom='';
# Declare and initialize variables
my $annotation = '';
my $dna = '';
my $record = '';
my $filename = 'ess.txt';
my $i=0;
my $save_input_separator = $/;
open(GBFILE, $filename) or die "Error";

# Set input separator to "//\n" and read in a record to a
#scalar
{
  $/="//\n";
  $record = <GBFILE>;
}
$/ = $save_input_separator;
$nom=($record=~ /(.*)\/\/\n/s);
print $nom;
exit;

```

This is the input:

```
H ANDN920101

D alpha-CH chemical shifts (Andersen et al., 1992)

R LIT:1810048b PMID:1575719

A Andersen, N.H., Cao, B. and Chen, C.

T Peptide/protein structure analysis using the chemical shift index method: 

upfield alpha-CH values reveal dynamic helices and aL sites

J Biochem. and Biophys. Res. Comm. 184, 1008-1014 (1992)
C BUNA790102 0.949

I A/L R/K N/M D/F C/P Q/S E/T G/W H/Y I/V

4.35 4.38 4.75 4.76 4.65 4.37 4.29 3.97 4.63 3.95

4.17 4.36 4.52 4.66 4.44 4.50 4.35 4.70 4.60 3.95

//

```