Blink the CAPS LOCK

Question

Most computer keyboards feature a small integrated LED light, indicating the current input mode, as controlled with the CAPS LOCK button.

Your task is to blink it:

• Turn it on;
• Wait for 0.5 (+/-0.1) seconds;
• Turn it off again.

Video footage of the LED blinking is highly appreciated !

Rules

• You can blink a different LED (e.g. Scroll Lock, Num Lock, Wi-Fi status etc), if you wish, but it must be physically located on your keyboard;

• If your language is missing a subsecond sleep command, your program may use a 1 second delay instead, at a penalty of +2 bytes (that's for 0.);

• Your program must blink at least once, what happens afterward is up to you, i.e. it can continue to blink (in which case you must wait for the same delay, before turning it on again), or halt e.t.c.;

• If the chosen LED is ON by default, on your system, you can assume that it has been explicitly switched off (e.g. manually), before the program is run;

• This is code-golf, the shortest answer in bytes wins.

Leaderboard

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Answer 1

Befunge (BEF32), 390 334 305 bytes

This is really silly, but as long as this site accepts the notion that the interpreter defines the language, I might as well abuse the rule. This code only works in Kevin Vigor's Win32 Befunge-93 Implementation, version 1.01 (I think the only version available). You can download the binary here.

p55p99+5p65*5p")"5p"M"3*"I~q"+\3*3445"|"2*"lm"2v
v"y"*3\*2"e/n"4\5"nnIn"*833*2"mn"4\7"nnIn"*833*<
>2*"yO"4"DJG"3*\2*55*3"T"4"DLG"3*\2*55*3"/~M"+\3*4446"~A"+4v
>+00p9p:v:"l'"*2"^D"4"l3"*2"^D"4"l"*54*2"^D"4"l"*2+94*2"^D"<
^1:g00-4_5"u1"*-:1+:1+"@"\0p"%"5*\0p"P"\0p@
Sleep kernel32.dll keybd_event user32.dll

Now normally you wouldn't expect this sort of challenge to be possible in a Befunge, but BEF32 is a Win32 port of a very old version of the reference implementation, and back then there was no bounds checking on the p (put) command. This effectively allows us to write to any location in memory, which ultimately lets us force the interpreter to execute arbitrary machine code.

Now we can't actually alter any of the existing code, since the .text section of the executable won't have write permissions. However, we can trick the system into executing an address in the .data section, by writing that address into the the runtime library's atexit table (at least I suspect that's what it is). The end result is that our code is automatically executed when the interpreter exits.

This relies on the fact that the executable is loaded at a fixed address, so we know exactly where everything is in memory - it assumedly wouldn't work if you overrode the default ASLR settings. It also relies on the .data section being executable, despite not having the executable attribute set, so again it most likely wouldn't work if you overrode the default DEP settings.

The code itself is essentially a copy of Mego's keybd_event technique translated into machine code:

6823B84000         push "keybd_event"
682FB84000         push "user32.dll"
6810B84000         push "Sleep"
6816B84000         push "kernel32.dll"
BB02000000         mov  ebx,2
               initloop:
89C7               mov  edi,eax
FF1594D14000       call LoadLibraryA
50                 push eax
FF1590D14000       call GetProcAddressA
4B                 dec  ebx
75EE               jnz  initloop
89C6               mov  esi,eax
               flashloop:
6A00               push 0
6A01               push 1
6A45               push 69
6A14               push 20
FFD6               call esi
6A00               push 0
6A03               push 3
6A45               push 69
6A14               push 20
FFD6               call esi
68F4010000         push 500
FFD7               call edi
EBE3               jmp  flashloop

This version of the code continues flashing forever (or at least until you kill the process), since that turned out to be easier to golf than a single flash.

And since everyone is posting animations, this is an approximation of what it looks like on my keyboard.

Answer 2

AutoHotkey, 29 26 bytes

_{Thanks to @Dane for saving 3 bytes}

Loop{
Send,{VK14}
Sleep,500
}

I originally chose NumLock because it's one character shorter than CapsLock. The GIF below reflects that condition. It's the same effect as the altered code above. I could have gone with VK90 above to make the GIF still be accurate but aligning with the original challenge felt better.

---

In honor of mbomb007's comment, here's a morse code message in 239 bytes:

s:=000090901009011091100110090111109111901090190110901109091000091001101909101191000911190190109100001090191010919111901091011
Loop,123{
StringMid,c,s,A_Index,1
IfEqual,c,9
{
Sleep,2000
Continue
}
Send,{NumLock}
Sleep,%c%500
Send,{NumLock}
Sleep,500
}

Here are the first 30 seconds of that message:

Answer 3

GFA-Basic 3.51 (Atari ST),  61 56 43  35 bytes

This code will make the floppy drive LED blink forever at the required rate (PAUSE 25 = pause for 25 / 50 second).

This would probably be shorter in assembly, but I don't have the appropriate tools at my fingertips. This is the size of the GFA-Basic listing once saved in .LST format and manually edited to remove useless whitespace, rename instructions to shorter strings and replace each CR+LF with a simple CR. Note that a final CR is required.

DO
i=i XOR2
SP &HFF8802,i
PA 25
LO

Will automatically expand to:

DO
  i=i XOR 2
  SPOKE &HFF8802,i
  PAUSE 25
LOOP

SPOKE is a supercharged POKE that first puts the 68000 in supervisor mode, so that it's allowed to access restricted memory areas (here: the register write address of the YM2149 soundchip, which is also responsible for some other I/O).

And yes: the LED is physically located on the keyboard ... I suppose.

^{I don't have access to a real ST right now, so this is just a mockup.}

Answer 4

fish + ckb, 56 54 bytes

while cd;echo rgb (random)|tee /d*/*/*/c*;sleep .5;end

Blinks my entire keyboard in random colors, though since the number isn't 6 hex digits long it's a bit limited.

And yes, that shell glob is potentially dangerous. Works On My Machine™

Bonus script, 8 months later: This will go through all colors. Not golfed.

#!/usr/bin/fish
while true
        echo rgb (printf '%06x' (random 0 16777215)) | tee /dev/input/ckb*/cmd > /dev/null
        sleep 0.5
end

Answer 5

Bash + amixer, 45 Bytes

a() { amixer set Master toggle
}
a;sleep .5;a

Blinks the mute light on my keyboard.

Answer 6

C (Windows), 79 bytes

#include<windows.h>
k(n){keybd_event(20,69,n,0);}f(){k(1);k(3);Sleep(500);f();}

Explanation

keybd_event is a (deprecated) Windows API function to send a keyboard event (keyup or keydown). 20 is the code for the Caps Lock key, 69 is the hardware scan code (I have no idea what that means), and 1 means keydown and 3 means keyup. A keypress is simulated by sending a keydown event immediately followed by a keyup event. One keypress is sent to turn on Caps Lock, then the program sleeps for 500 milliseconds, and then another keypress is sent to turn Caps Lock back off.

Thanks to Steadybox for a bunch of bytes saved

Answer 7

x86 machine code for PC (e.g. MS-DOS COM file), 27 bytes

This machine code (displayed here with a Unicode rendering of the usual CP437 of PC BIOS) will blink the CAPS LOCK indicator forever on a PC:

j@▼î▐j`Z░φεê╪εÇ≤♦╞♦◙Ç<☺t∩δ∙

The code has been made so it contains no NULL bytes, and can thus be typed with the keyboard (using the Alt+XXX trick for extended characters) to create a COM file (e.g., using the COPY CON blink.com command under MS-DOS, in which case the output file will have to contain a spurious 28^th byte, the ^Z (EOF) character required to stop the copy operation).

The effect is achieved by directly sending commands to the keyboard controller of the PC (port 60h) to set the LED state (as a side-effect, it might set Num Lock and Scroll Lock LEDs to a random non-blinking state). The timing, to minimize the number of instructions, is achieved by using the countdown timer maintained by the BIOS at address 0040:0040 (it decrements every 54.925 ms, with 9 cycles the blinking cycle is 494.3 ms, which is within the allowed margin) — this counter is normally used by the BIOS to stop the floppy disk motor; as the floppy drive is not used by the program and the code is assumed to run in a single-task environment (e.g. DOS), playing with the floppy motor timer is not an issue.

The code runs fine under MS-DOS (tried with VirtualBox, it should also run fine on real hardware, although I didn't have the time yet to make a bootable MS-DOS USB stick to test). As it doesn't rely on any OS functions, it can even run without the operating system (e.g., by placing it in the boot sector of a disk). It requires at least a 80186 processor to run, because of the "immediate push" instructions used to shorten the code of some bytes.

Assembly source code:

  PUSH 0x40               ; pushes 0x0040 (BIOS data segment) on the stack
  POP DS                  ; pops it into DS segment selector
  MOV SI, DS              ; copies DS to SI (timer counter is nicely placed at 40:40)
  PUSH 0x60               ; pushes 0x0060 (kbd controller port) on the stack
  POP DX                  ; pops it to DX
loop:
  MOV AL, 0xED            ; 8042 keyboard controller 'set mode indicators' command
  OUT DX, AL              ; outputs the command to the keyboard contr oller
  MOV AL, BL              ; copy BL register to AL
  OUT DX, AL              ; outputs LED state to keyboard controller
  XOR BL, 4               ; toggles bit 2 (CAPS LOCK) for next iteration
  MOV BYTE PTR[SI], 0x0A  ; sets floppy motor countdown timer to 10
wait:
  CMP BYTE PTR[SI], 0x01  ; checks if timer reached 1
  JE loop                 ; if yes, time for next iteration
  JMP wait                ; if not, checks again

Hexadecimal dump of the assembled code:

6A 40 1F 8C DE 6A 60 5A B0 ED EE 88 D8 EE 80 F3 04 C6 04 0A 80 3C 01 74 EF EB F9

Here is the result running under MS-DOS in VirtualBox (doesn't work with DosBox, presumably because the keyboard controller is not completely emulated):

(sorry for the shaky video).

Answer 8

MATLAB, 146 136 70

Thanks to @Poke for removing 66 bytes!

r=java.awt.Robot;while 1
r.keyPress(20)
r.keyRelease(20)
pause(.5);end

This uses Matlab's ability to call Java classes. The Caps Lock light is blinked in a loop by programmatically pressing and releasing Caps Lock.

Video or it didn't happen.

Answer 9

SmileBASIC, 36 23 bytes

XON MIC
WAIT 30XOFF MIC

Blinks the microphone status light. (video coming soon)

Answer 10

Python2 - 108 bytes

Does the capslock key. Interestingly, this actually turns on just the LED itself without affecting the keyboard or pressing the key. You can change the 4 at the end to 2 to do numlock. 6 does both.

import fcntl,os,time;exec"fcntl.ioctl(os.open('/dev/console',os.O_NOCTTY),19250,%d);time.sleep(.5);"*2%(4,0)

Answer 11

shell+numlockx, 40 35 bytes

[Saved 5 bytes thanks to Ryan.]

Continually blinks the NumLock light on unixish systems.

numlockx toggle;sleep .5;exec sh $0

Single blink, 33 bytes

numlockx on;sleep .5;numlockx off

Answer 12

PowerShell, 71 bytes

for(){(New-Object -c WScript.Shell).SendKeys('{NUMLOCK}');sleep -m 500}

Notes

• Blinks forever
• Uses NUM LOCK to save a byte.

Answer 13

VBS, 75 bytes

do
wscript.sleep 500
Createobject("wscript.shell").sendkeys"{numlock}"
loop

Repeatedly blinks Num Lock key, as numlock is 1 byte shorter than capslock.

Answer 14

C#, 215 202 198 195 185 bytes

Without realising I have done the "same" code as this answer by @Mego, go check it out!.

[System.Runtime.InteropServices.DllImport("user32")]static extern void keybd_event(int v,int s,int f,int e);n=>{for(n=0;;System.Threading.Thread.Sleep(125))keybd_event(20,69,n++&2,0);};

Saved 13 bytes thanks to @Metoniem
Saved 10 bytes thanks to @VisualMelon

Here's a full formatted version showing it working:

class P
{
    [System.Runtime.InteropServices.DllImport("user32")]
    static extern void keybd_event(int v, int s, int f, int e);

    static void Main()
    {
        System.Action<int> a = n =>
        {
            for (n = 0; ; System.Threading.Thread.Sleep(125))
                keybd_event(20, 69, n++ & 2, 0);
        };

        a(0);
    }
}

---

For bonus fun change n++ & 2 to n+=2 & 2 and watch the num lock and caps lock keys alternate in flashing on and off. I have no idea why that happens because it shouldn't but it looks "cool".

Answer 15

Java 7, 121 118 113 bytes

void a()throws Exception{java.awt.Robot r=new java.awt.Robot();r.keyPress(20);r.delay(500);r.keyRelease(20);a();}

A single press and release just triggers the state; it doesn't blink it. Thus we may as well loop it and it looks like recursion is the cheapest manner of doing that.

Answer 16

Linux terminal, 8+11 = 19 bytes

File f = 1B 5B 33 71 1B 5B 30 71

native@shell:~$ pv f -q -L8

WAT?

According to ECMA-48, 1B starts terminal control escape sequence.

Caps on =1B 5B 33 71, then off = 1B 5B 30 71

pv progress view

f file

-q quiet

-L8 8 bytes/s = 0.5 sec delay

Usage

Prepare

#Create file
echo "1B 5B 33 71 1B 5B 30 71"|xxd -r -p > f 

#Install progress view utility
sudo apt install pv

Ctrl+Alt+F6 switch to native console

run pv f -q -L8

Ctrl+Alt+F7 switch back

Answer 17

JavaScript, 82 bytes

Credit goes to @FinW actually, I just changed old function to new ES6 arrow function in order to save some bytes. And becuase I don't have enough points to comment I wrote a new reply.

Edit - deleted brackets to save another 2 bytes.

o=new ActiveXObject("WScript.Shell");setInterval(()=>o.SendKeys("{NUMLOCK}"),500);

His code looked like this

o=new ActiveXObject("WScript.Shell");setInterval(function(){o.SendKeys("{NUMLOCK}")},500);

Answer 18

Scala, 84 83 78 bytes

Edit: Saved 1 byte thanks to @TheLethalCoder,

He suggested using 1>0 in place of true.

Edit 2: Saved 5 bytes thanks to @Corvus_192,

He suggested using infix notation and dropping the parentheses after the constructor

while(1>0){val r=new java.awt.Robot;r keyPress 20;r keyRelease 20;r delay 500}

Ungolfed:

while(1>0) {
    val r=new java.awt.Robot()
    r.keyPress(20)
    r.keyRelease(20)
    r.delay(500)
}

Standard Scala port of @Poke's Java answer. Type it directly into the Scala interpreter prompt.

A video of it blinking both my Caps Lock LED and my OSD to boot!

Answer 19

Bash, 31 bytes

xset led 1;sleep .5;xset -led 1

Works in X, without root access ! (If it does not work for you, see the init function of the code below to make sure xkbcomp is configured correctly)

And a bonus script to send any morse code through caps lock (not golfed) :

unit=0.15
id=1
function init {
        file=/tmp/blink_tmp
        xkbcomp $DISPLAY $file
        sed -i 's/!allowExplicit/allowExplicit/' $file
        xkbcomp $file $DISPLAY &>/dev/null
        rm $file
}
if [[ -z $1 ]]; then
        echo "Usage : blink [message]"
        exit 1
fi
init
function finish {
        off
}

function on {
#su -c 'setleds -L +caps < /dev/console'
xset led $id
}
function off {
#su -c 'setleds -L -caps < /dev/console'
xset -led $id
}
function slp {
        sleep $(echo "$unit*$1" | bc)
}
function dot {
on
slp 1
off
slp 1
}
function dash {
on
slp 3
off
slp 1
}
function gap {
        slp 3
}
function morse {
        msg=$1
        for (( i=0; i<${#msg}; i++ )); do
                char=${msg:$i:1}
                if [[ $char == "-" ]]; then
                dash
                elif [[ $char == "." ]]; then
                dot
                elif [[ $char == "/" ]]; then
                gap
                fi
        done
}
while true; do
        morse $1
done

Exemple : blink "...././.-../.-../---//.--/---/.-./.-../-..///"

Answer 20

Bash + Xdotool, 36 bytes

for((;;)){ xdotool key 66;sleep .5;}

Just execute it in a bash shell. It needs to be in a graphical environment. Infinite loop from here. Changed Num_Lock to 66 to save 6 bytes, and thanks to @Michael Kjörling for 2 bytes.

Answer 21

xdotool, 20 bytes

key -delay=500 66 66

Presses the key 66 aka Caps Lock twice, with a delay of 500 ms between key presses.

Note that xdotool is a scripting language; it can be run from a file and it even supports shebangs. Since its exec command allow running external programs, it is capable of addition and primality testing, so it satisfies our definition of programming language.

Test run

$ cat blink.xdo; echo
key -delay=500 66 66
$ xdotool blink.xdo

Answer 22

Python using pyautogui: 126 143 115 103 bytes

Thanks to @nedla2004 for saving 12 bytes

from pyautogui import*
import time
while 1:keyDown('capslock');time.sleep(.5);keyUp('capslock')pslock')

Answer 23

Bash + setleds, 43 bytes

setleds -D +caps;sleep 0.5;setleds -D -caps

Pretty simple. Uses setleds to toggle the light.

Answer 24

Bash, 103 bytes

cd /sys/class/leds/asus\:\:kbd_backlight;while true;do echo 3;sleep .5;echo 0;sleep .5;done>brightness

Must be run as root.

Does flashing the entire keyboard backlight work? (video to come when I get home)

Answer 25

JavaScript, 90 bytes

o=new ActiveXObject("WScript.Shell");setInterval(function(){o.SendKeys("{NUMLOCK}")},500);

It requires ActiveX meaning it will only run on IE (Edge doesn't support it, though). It flashes the NUMLOCK key because, as with other answers, it is shorter than CAPSLOCK or SCROLLLOCK.

Ungolfed

shell = new ActiveXObject("WScript.Shell");
setInterval(
    function(){
        shell.SendKeys("{NUMLOCK}")
    }
,500);

Answer 26

Bash, 33 Bytes

This assumes Num-Lock to be on before it is run. Switch off and on otherwise. Requires the numlockx package obviously ;)

numlockx off;sleep .5;numlockx on

Edit:

Saw Alex Howansky has already posted this solution, yet not marked it with Bash and I just searched the site for "Bash".

Answer 27

Batch File (With help of vbs), 74+2=76 bytes

echo Createobject("wscript.shell").sendkeys"{numlock}">z.vbs&z&timeout 1&z

Partially based on Trelzevir's answer.

.vbs is automatically included in PATHEXT.

Answer 28

C (msvc) + Win32, 51 bytes

main(i){main(i+keybd_event(20,69,i%4,Sleep(125)));}

Answer 29

Kotlin Script, 72 bytes

While not smallest one, still it's pretty good. I'm loving kotlin's run for some things, and this is one of them ( smaller than val r = java.awt.Robot() because we don't need both r. and val r =. Still, it's longer than MathLab )

java.awt.Robot().run{while(1>0){keyPress(20);keyRelease(20);delay(500)}}

Ungolfed:

java.awt.Robot().run {
    while(1>0) {
        keyPress(20)
        keyRelease(20)
        delay(500)
    }
}

Answer 30

Python3 , 55 49 bytes

Thank you @NoOneIsHere for -4 bytes!

This includes packages: pyautogui and time modules
Code:

while(1):pag.press("capslock");time.sleep(0.5)  

Thank you @NoOneIsHere for -4 bytes!
The key in action: