enumerate

#!/usr/bin/perl

use strict;
use Getopt::Std;

my $usage = "Usage: cat file | enumerate [-r] [-s N]\n";
$usage .=   "       Puts an monotonically increasing index at the beginning of each line\n";
$usage .=   "       -r Put one index for each line, but randomize them,";
$usage .=   "          without changing the order of the lines.";
$usage .=   "       -s Start numbering at N, default is 0";

my $count = 0;
my $randomize = 0;

my %para = ();
getopts('rs:', \%para);

if (defined($para{'r'})) {
    $randomize = 1;
}
if (defined($para{'s'})) {
    $count = $para{'s'};
}
if (defined($para{'h'})) {
    die ($usage);
}

if ($randomize) {
    my @lines = ();
    my @indexes = ();
    while (my $line = <>) {
	$lines[$#lines+1] = $line;
	$indexes[$#indexes+1] = $count++;
    }

    &fisher_yates_shuffle (\@indexes);

    for (my $i = 0; $i <= $#lines; $i++) {
	print "$indexes[$i] $lines[$i]";
    }

} else {
    # duplicating because this will run slower if input is big and we don't want to randomize
    while (my $line = <>) {
	print "$count $line";
	$count++;
    }
}

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];
    }
}