#!/usr/bin/perl

use strict;
use warnings;

while(<>) {
	s/\b(\w+)\b/&wortspiel($1)/ge;
	print;
}

sub wortspiel {
  if ($_[0] =~ m/\b(\w)(\w+)(.)\b/) {
    my @letters = split(//, $2);
    shuffle (\@letters);
    return $1.join ('', @letters).$3;
  }
  else {
    return $_[0];
    }
}

sub shuffle {

  # vgl. O'Reilly, Perl-Kochbuch dt., 1. Auflage, 4.17, fisher-yates-shuffle

  my $array = shift;
  my $i;

  for ($i = @$array; --$i; ) {
    my $j = int rand ( $i+1 );
    next if $i == $j;
    @$array[$i, $j] = @$array[$j, $i];
    }
}