Custom module is not updating

[fredx100]

I've written a bash script to use within a custom module. I'm trying to use it as an infinite loop but the custom module never updates.

The script should display the alsa volume. It waits on alsactl monitor for an alsa event and then inspects the output of amixer to get the details. I'm very new to waybar so I've probably just got the config wrong or something elementary.

My script (volume.sh) seems fine from the terminal. (for reference:

#!/bin/bash

# Loop forever
while : ; do
    # Mangle the output of amixer into json
    amixer get Master |                                                                                                                                  
        grep 'Mono:' |
        sed --unbuffered -nre 's/.*\[off\].*/\{"text": "  M x", "class": "muted", "percentage": 0\}/p'\
                           -e 's/.*\[(.*)%\].*/\{"text": "\1%  ", "class": "unmuted", "percentage": \1\}/p'

    # Wait until the next alsa event
    /usr/sbin/alsactl monitor | grep -m 0 .

    # Exit if alsactl monitor was interrupted
    if (( ${PIPESTATUS[0]} != 141 )); then
            break;
    fi
done

) and my waybar config is

"custom/alsa": {
    "exec": "~/.config/waybar/volume.sh",
    "return-type": "json",
    "on-click": "amixer set Master toggle",
    "on-scroll-up": "amixer set Master 5+",
    "on-scroll-down": "amixer set Master 5-",
    "tooltip": false
}

On launch of waybar the custom module displays correctly, but it never updates.

From a terminal ./volume.sh outputs a line every time I change the volume or mute/unmute, which is what I want. The output from the terminal appears correct:

$ ./volume.sh
{"text": "43% ", "class": "unmuted", "percentage": 43}
{"text": "50% ", "class": "unmuted", "percentage": 50}
{"text": "  M x ", "class": "muted", "percentage": 0}
{"text": "57% ", "class": "unmuted", "percentage": 57}

(this would be after 4 events) which, I believe is a sensible output for waybar. As such I expect the issue is with what form the output should take (this will be specific to waybar, potentially) or how the module is configured.

If I remove the loop from volume.sh and put an interval into my custom module config then the module updates correctly, but I'm hoping to avoid polling.

I'm aware that some scripts buffer when not outputting to a terminal and so I've tried prefixing the call to volume.sh with stdbuf -oL, which the internet says would force line buffering. I've also tried prefixing the pinelines within the bash script in the same way. Neither helped.

Any ideas about why my custom waybar module's not updating? Thanks!

[ordy]

Why not remove the loop, just have your amixer line in your script and add signal and interval to your config?

#!/bin/bash

amixer get Master | grep 'Mono:' | 
    sed --unbuffered -nre 's/.*\[off\].*/\{"text": "  M x", "class": "muted", "percentage": 0\}/p'\
                           -e 's/.*\[(.*)%\].*/\{"text": "\1%  ", "class": "unmuted", "percentage": \1\}/p'

"custom/alsa": {
    "exec": "~/.config/waybar/volume.sh",
    "return-type": "json",
    "signal": 1,
    "interval": 1,
    "on-click": "amixer set Master toggle",
    "on-scroll-up": "amixer set Master 5+",
    "on-scroll-down": "amixer set Master 5-",
    "tooltip": false
}

[fredx100]

Yes, that would work but relies on polling. As stated in the original post, I'm hoping to avoid this. I appreciate that avoiding polling is a "want" rather than a "need" but I'm confused as to why the elegant solution (waiting on alsactl monitor) doesn't work. Thanks for the suggestion, though.

[ordy]

Oh my bad, completely missed the paragraph where you mentioned your were trying to avoid polling.

There is the option to not use interval and just signal, it would work on scroll events, but the value won't update if you change it from another place (like alsamixer, shortcuts or physical buttons)... So probably not ideal.

[fredx100]

I have a working solution and so can guess at reasons!

The working solution is

#!/bin/bash

set -e

createJson(){
    amixer get Master |
        grep 'Mono:' |
        sed -nre 's/.*\[(.*)%\].*\[off\].*/\{"text": "\1% x", "class": "muted", "percentage": \1\}/p'\
            -e   's/.*\[(.*)%\].*/\{"text": "\1%  ", "class": "unmuted", "percentage": \1\}/p'
}

createJson
while read line; do
    createJson
done < <( /usr/sbin/alsactl monitor )

This reads one line at a time of the output from alsactl, pumping the relevant info from amixer each time (and ignoring the line from alsactl). I also tweaked the sed line so that you could still see the volume when it was muted, but that's just cosmetic.

I expect this works because the pipe containing the output of alsactl is never broken. In the original script grep terminates after each line, breaking the pipeline. Somehow this detatched alsactl (sending a SIGCHLD which showed up in the debug output from waybar) and knackered the script (but only in non-interactive mode). In the newer script alsactl just keeps piping to the while loop until we quit.

[tienbuigia]

I have a similar problem with a script to display dwl's layout. Your mention of stdbuf helps me.

  "custom/dwl-layout": {
    "format": " {}",
    // "exec": "dwlmsg -wl | while read -r layout; do echo $layout | sed 's/.* //'; done"
    // "exec": "dwlmsg -wl"
    // "exec": "dwlmsg -wl | sed 's/.* //'"
    "exec": "dwlmsg -wl | stdbuf -oL sed 's/.* //'"
  },

This is my simple script using dwlmsg, it watches dwl layout (ipc). The while loop works, without sed works, but using sed will not output anything on waybar. It does work on terminal:

❯ dwlmsg -wl | sed 's/.* //'
[]=
[3]
[]=
^C

And then I add stdbuf -oL as you mention and it works nicely now. You may need to try again, this time add stdbuf to the grep.