#!/bin/perl

use strict;
use warnings;


my $input_file = 'input.txt';
my $output_file = 'output.txt';


open(my $in_file,'<', $input_file) or die "Can not open file $input_file for writing: $!.\n";
open(my $out_file,'>', $output_file) or die "Can not open file $output_file for writing: $!.\n";

if (not (grep{/Monday/} <$in_file>) {

	seek $in_file, 0, 0;
	$. = 0;

	while (<$in_file>) {
		print $out_file $_;

		if ($. == 1) {
			print $out_file "Friday\n";
		}
	}
}

close($in_file);
close($out_file);

##</code><code>##

#!/bin/perl

use strict;
use warnings;


my $input_file = 'input.txt';
my $output_file = 'output.txt';


open(my $in_file,'<', $input_file) or die "Can not open file $input_file for writing: $!.\n";
open(my $out_file,'>', $output_file) or die "Can not open file $output_file for writing: $!.\n";

unless (grep{/Monday/} <$in_file>) {

	seek $in_file, 0, 0;
	$. = 0;

	while (<$in_file>) {
		print $out_file $_;

		if ($. == 1) {
			print $out_file "Friday\n";
		}
	}
}

close($in_file);
close($out_file);