/usr/share/irssi/scripts/quitrand.pl is in irssi-scripts 20160301.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52  | # If quit message isn't given, quit with a random message
# read from ~/.irssi/irssi.quit
use Irssi;
use Irssi::Irc;
use strict;
use vars qw($VERSION %IRSSI);
$VERSION = "1.00";
%IRSSI = (
    authors     => 'Fernando J. Pereda',
    contact	=> 'ferdy@ferdyx.org',
    name        => 'quitrand',
    description => 'Random quit messages - based on quitmsg (Timo Sirainen)',
    license     => 'GPLv2',
);
my $quitfile = glob "~/.irssi/irssi.quit";
sub cmd_quit {
	my ($data, $server, $channel) = @_;
	
	open(f,"<",$quitfile);
	my @contenido = <f>;
	close(f);
	my $numlines = 0;
	
	foreach my $nada (@contenido) {
		$numlines++;
	}
	my $line = int(rand($numlines))+1;
	my $quitmsg = "[IRSSI] ".$contenido[$line];
	chop($quitmsg);
	print($quitmsg);
	foreach my $sv (Irssi::servers()) {
		foreach my $item ($sv->channels()) {
			$item->command("PART ".$item->{name}." $quitmsg");
		}
	}
	
	foreach my $svr (Irssi::servers()) {
		$svr->command("DISCONNECT ".$svr->{tag}." $quitmsg");
	}
}
Irssi::command_bind('quit', 'cmd_quit');
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