use strict;
use warnings;
use feature 'say';
use Path::Tiny;
use Test::More;

# When not testing, something like this:
# my $in_file = path("/path/to/file");
# my $fh = $in_file->openr;

my $script = path(__FILE__);
my $out_file = path( sprintf('/tmp/%s-%s.log', $script->basename('.pl'), time) );

my %seen;
my ($count_in, $count_out);

{
    # set the line separator locally to a string that matches
    # the break between your "paragraphs".
    local $/ = "\n>sp";

    while ( my $line = <DATA> ) { # <$fh>
        $count_in++;

        if ( $line =~ /GN=(\S*)/ ) {
            next if $seen{$1};

            $count_out++;
            $seen{$1} = 1;
            $out_file->append( $line );
        }
    }
}

say ' Records processed: ' . $count_in;
say 'Duplicates removed: ' . ($count_in - $count_out);

#----------------------------------------------------#
## Test. Always test.

is( $count_in, 5,  'Input read OK');
is( $count_out, 3, 'Correct number of records kept');

my @written = $out_file->lines;

is( (grep { /GN/ } @written), 3,          'File has correct count for "GN"');

for my $value (qw/ TUFA Blorgle Blargle /) {
    is( (grep { /$value/ } @written), 1,  sprintf('File has correct count for "%s"', $value) );
}

done_testing;

__DATA__
>sp|O24310|EFTU_PEA Elongation factor Tu, chloroplastic OS=Pisum sativum OX=3888 GN=TUFA PE=2 SV=1

MALSSTAATTSSKLKLSNPPSLSHTFTASASASVSNSTSFR

>sp|O24310|EFTU_PEA Elongation factor Tu, chloroplastic OS=Pisum sativum OX=3888 GN=Blorgle PE=2 SV=1

MALSSTAATTSSKLKLSNPPSLSHTFTASASASVSNSTSFR

>sp|Q43467|EFTU1_SOYBN Elongation factor Tu, chloroplastic OS=Glycine max OX=3847 GN=TUFA PE=3 SV=1

MAVSSATASSKLILLPHASSSSSLNSTPFRSSTTNTHKLTP

This is a dupe but has extra content

>sp|O24310|EFTU_PEA Elongation factor Tu, chloroplastic OS=Pisum sativum OX=3888 GN=Blargle PE=2 SV=1

MALSSTAATTSSKLKLSNPPSLSHTFTASASASVSNSTSFR

>sp|O24310|EFTU_PEA Elongation factor Tu, chloroplastic OS=Pisum sativum OX=3888 GN=Blorgle PE=2 SV=1

MALSSTAATTSSKLKLSNPPSLSHTFTASASASVSNSTSFR