#!/usr/bin/perl
use strict;
use warnings;

my $filename = "record.gb";

open my $fOut, '>', $filename or die "Failed to create $filename: $!\n";
print $fOut <<STR;
LOCUS some guff ORIGIN
Another line of guff
//
STR
close $fOut;

open my $fIn, '<', $filename or die "Failed to open $filename: $!\n";

#use the input seperator //\n to read a entire file to scalar
my $record = do {local $/ = "//\n"; <$fIn>};

#to seperate the annotation from sequence
$record =~ /^(LOCUS.*ORIGIN\s*\n)(.*)\/\/\n/s or die "Malformed record '$record'\n";

my ($annotation, $dna) = ($1, $2);
print "$annotation, $dna\n";