<form action="/cgi-bin/comments.pl" method="post">
<p>Bitte Logfilenamen eingeben: <br>
<input name="Logfilename" size="40"> </p>
<p> <input type="submit" value="Ok"></p>
</form>

#! /usr/bin/perl

use strict;
use warnings;
use CGI;
use CGI::Carp qw(fatalsToBrowser);

my $cgi = CGI->new();
print $cgi->header();

my $file = $cgi->param('Logfilenam');

die "$file doesn't exist" unless(-e $file);

open(my $fh, "<$file") or die $!;
while(<$fh>){
  print;
}
close $fh;