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

my $aktVerz = $ARGV[0] or &PrintUsage();
my $ausgabedat = $ARGV[1] or &PrintUsage();

unless (opendir(DIR, $aktVerz)) {
  die "Error: couldn't open dir '$aktVerz': $!\n";
} # unless

unless (open (OUT, ">", $ausgabedat)) {
  die "Error: couldn't write to '$ausgabedat': $!\n";
} # unless

while (my $file = readdir(DIR)) {
  my $fileName = "$aktVerz/$file";
  next if -d $filename; # ueberspringe verzeichnisse
  next unless $file =~ /\.txt$/; # ueberspringe nicht-txt
  
  unless (open(FILE, "<", $filename)) {
    warn "Error: couldn't open file '$filename': $!\n"; # oder die ...
  } # unless
  else {
    print OUT $_ while <FILE>;
    close (FILE);
  } # else
} # while

closedir(DIR);
close(OUT);
# --------------------------------------------
sub PrintUsage {
  require File::Basename;
  my $bin = File::Basename::basename($0);
  die "Usage: $bin verzeichnis ausgabedatei\n";
} # PrintUsage