#!/usr/bin/perl -w
#
# $Id: shuffle,v 1.4 2003/08/01 02:10:57 jmates Exp $
#
# The author disclaims all copyrights and releases this script into
# the public domain.
#
# Print input data in random order.
#
# TODO FYS algorithm works on in-memory array; way to shuffle while
# streaming over the input, similar to "print random line from file?"

# read from file(s) on command line, or stdin via <>.
my @input = <>;

die "error: no data supplied to shuffle\n" unless @input;

fisher_yates_shuffle(\@input);

print for @input;

# fisher_yates_shuffle( \@array ) : generate a random permutation
# of @array in place
sub 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];
  }
}

=pod SCRIPT CATEGORIES

Utilities

=cut