#!/usr/bin/env perl
use strict;
use warnings;
use Getopt::Declare;

# Note the '...' after each tag tells Getopt::Declare to gather arguments into an array reference.
my $spec = <<'EOS';

    -p <INFILE>...	input filename(s)  [required]
                        { defer{process(@INFILE)} }

    -f <INFILE>...	input filename(s)  [required]
                        { defer{process(@INFILE)} }
EOS

my $opts = Getopt::Declare->new($spec);

sub process {
    @ARGV = @_;
    while(<>){
	chomp;
	# do something here...
    }
    print $ARGV . "\n";
}

__END__

$ perl test.pl -p out.txt -f in.txt -p out.txt -f out.txt
out.txt
in.txt
out.txt
out.txt