Here's how you can do it with Inline under linux (the only OS I tested). You need the appropriate perms to the console so YMMV (also, most error checking removed for brevity sake).

(original Inline code) 

#!/usr/bin/perl

use Inline C;
use strict;

toggle_lights();

__END__
__C__
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/kd.h>

#define ERROR -1

void toggle_lights() {
        int fd;
        int i = 0;
        long int orig = 0;

        if ((fd = open("/dev/console", O_NOCTTY)) == ERROR) {
                perror("cannot open console");
                exit(ERROR);
        }

        ioctl(fd, KDGETLED, &orig);

        i |= LED_NUM;
        ioctl(fd, KDSETLED, i);
        sleep( 2 );

        i = 0;
        i |= LED_CAP;
        ioctl(fd, KDSETLED, i);
        sleep( 2 );

        i = 0;
        i |= LED_SCR;
        ioctl(fd, KDSETLED, i);
        sleep( 2 );

        ioctl(fd, KDSETLED, orig);
}

[download]

-derby

Update: Whoa! I forgot that ioctl is normally available under pure perl. I hade to steal the KD_* and LED_* constants from the include file but it works fine.

(buggy pure perl code) 

#!/usr/bin/perl

require "sys/ioctl.ph";

open( FH, "/dev/console" ) ||
                die "cannot open console";

$KDSETLED = 0x4B32;
$KDGETLED = 0x4B31;
$LED_SCR  = 0x01;
$LED_NUM  = 0x02;
$LED_CAP  = 0x04;

ioctl(FH, $KDGETLED, $orig);

$i = 0;
$i |= $LED_NUM;
ioctl(FH, $KDSETLED, $i);
sleep( 2 );

$i = 0;
$i |= $LED_CAP;
ioctl(FH, $KDSETLED, $i);
sleep( 2 );

$i = 0;
$i |= $LED_SCR;
ioctl(FH, $KDSETLED, $i);
sleep( 2 );

ioctl(FH, $KDSETLED, $orig);

[download]

Update (again): Noticed a small bug in the above perl code when resetting the lights back to original. Here it is again: 

#!/usr/bin/perl

require "sys/ioctl.ph";

open( FH, "/dev/console" ) ||
                die "cannot open console";

$KDSETLED = 0x4B32;
$KDGETLED = 0x4B31;
$LED_NUM  = 0x02;
$LED_CAP  = 0x04;
$LED_SCR  = 0x01;

ioctl(FH, $KDGETLED, $orig);
@ary = unpack("ccccs",$orig);

foreach $state ( $LED_NUM, $LED_CAP, $LED_SCR, $ary[0] ) {
        $i = 0;
        $i |= $state;
        ioctl(FH, $KDSETLED, $i);
        sleep( 2 );
}

[download]

In reply to Re: manipulating the lights on a keyboard by derby
in thread manipulating the lights on a keyboard by J0hny_Lightning

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