#!/usr/local/bin/perl
#
# Lutz Prechelt, 1992/05/02
#
# The files given are shuffled into a random order of lines.

die "usage: shuffle filename...
   Shuffles lines into random order. Files are changed!\n" if ($#ARGV == -1);

srand (time + $$);
select (STDOUT); $| = 1;  # make stdout unbuffered
foreach $filename (@ARGV) {
  &shuffle ($filename);
}

sub shuffle {
  $filename = $_[0];
  open (FILE, $filename) || die "can't open '$filename'";
  print $filename, ": ";
  @lines = <FILE>;
  close (FILE);
  print ($#lines+1, " lines ");
  for ($i = 1; $i <= $#lines; $i++) {
    $newpos = int (rand($i) + 0.5);  # random from interval 0..i
    $help = $lines[$i];               # swap (lines[i], lines[newpos])
    $lines[$i] = $lines[$newpos];
    $lines[$newpos] = $help;
  }
  print "shuffled";
  open (FILE, ">".$filename) || die "   can't write '$filename'";
  print (FILE @lines);
  close (FILE);
  print ".\n";
}