open(FILE, "file") or die "Cannot open file for reading: $!\n";


##</code><code>##

print FILE $file[$n];


##</code><code>##

foreach (@file) {
  print FILE $_;
}


##</code><code>##

print FILE <<EOT;
add whatever here
to end of txt.
EOT


##</code><code>##

#!/usr/bin/perl -w
use strict;

open(FILE, "file") or die "Can't open file for reading: $!\n";
my @file = <FILE>;
close(FILE);

open(FILE, ">file") or die "Can't open file for writing: $!\n";
foreach (@file) {
  print FILE $_;
}

print <<EOT;
add whatever here
to end of txt.
EOT

close(FILE);