for educational purposes

random-replace

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

sub slurp {
  my $file = shift;
  open my $fh, '<', $file or die;
  my @lines = <$fh>;
  close $fh;
  \@lines;
}

sub replace {
  my $seed = shift;
  my $lines = shift;
  $lines->[int(rand(scalar @$lines))] = "$seed\n";
  $lines
}

my $seed = shift;
my $file = shift;
my $lines = replace $seed, slurp($file);
print @$lines;