Some suggestions for improvement:

• Use HERE-docs
• Use the available special variables ($. == line number)
• Include the error variable $! in your die statements
• Use a while loop instead of a foreach loop as the latter reads the whole file into memory. This is totally unnecessary here.
• Translate your variable names from German ;-)

Having said this ... here is how I'd do it:

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

sub usage {
  print << "USAGE";
'REMoveREMarks'!

remrem.pl deletes blank lines or lines starting with a '#' from a give
+n file-one and prints it to STDOUT or writes it to file-two

Syntax :

$0 inputfile
# STDOUT, try $0 inputfile | less

$0 inputfile outputfile
#Output to <outputfile>

USAGE

  exit;
}

usage() if (!@ARGV or $ARGV[0] eq '--help');

open(FUN,"<$ARGV[0]") || die "Can't open file $ARGV[0] for reading: $!
+";

if ($ARGV[1]) {
  open(GUN,">>$ARGV[1]") || die "Can't open file $ARGV[1] for writing:
+ $!"
}

while (<FUN>) {
  if (!/^#/ and /\w/) {
    if ($ARGV[1]) {
      print GUN $_;
    }
    else {
      print "$.: $_"
    }
  }
}

if ($ARGV[1]) {
  close(GUN) || die "Can't close file $ARGV[1]: $!"
}
close(FUN) || die "Can't close file $ARGV[0]: $!"
[download]

-- Hofmator