Perl script to find duplicate FASTA sequences using their header?

In a large file of FASTA sequences, it is nearly impossible to perform some operations manually.

This is a simple Perl script to find out duplicate sequences in a multi-fasta file using a FASTA header.

Let’s say, your multi-fasta file is ‘sequence.fasta’. 

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

my ($infile, $header) = @ARGV;

my $duplicate;
open my $input, '<', $infile or die $!;
while (<$input>) {
    $duplicate = $1 eq $header if /^>(.*)/;
    print if $duplicate;
}

close $input;
exit;