Here's the new script proto, cleaned it up some too and fixed a backup bug (I think):

#!/bin/sh
# soundswitch – Simple utility to change soundcards, part of AlsaTune.

if [ ! -f ~/.asoundrc ]; then
    yad --error --title="Error" --width=400 --center --text-align=center --window-icon=error \
        --text="\nNo config file (.asoundrc) found in user's home.\n\nChoose okay to install a generic version,\nor choose cancel to abort." \
        --button="Okay:0" --button="Cancel:1"
        
  if [ $? -eq 0 ]; then
    cp /usr/share/mxeq/.asoundrc ~/.asoundrc
  else
    exit 1
  fi
fi

CARDS=$(aplay -l | grep "^card [0-9]")

CHOICE=$(echo "$CARDS" | yad --list --title="Select Sound Card" \
    --column="Choose card/device" --width=550 --height=300 --window-icon=info \
    --button="Apply:0" --button="Cancel:1")

[ $? -ne 0 ] && exit 1

# Extract both card and device number from the selected line
CARD_NUM=$(echo "$CHOICE" | grep -o 'card [0-9]' | cut -d' ' -f2)
DEV_NUM=$(echo "$CHOICE" | grep -o 'device [0-9]' | head -n1 | cut -d' ' -f2)
[ -z "$DEV_NUM" ] && DEV_NUM=0

if [ -z "$CARD_NUM" ]; then
  yad --title="Error" --width=300 --center --text-align=center --window-icon=error \
--text="\nNo card was selected. Exiting..." --no-buttons --timeout=3
  exit 1
fi

cp ~/.asoundrc ~/.asoundrc.bak 2>/dev/null || true

# Replace card/device number(s).
sed -i \
    -e "s/hw:[0-9]*,[0-9]/hw:$CARD_NUM,$DEV_NUM/g" \
    -e "s/plughw:[0-9]*,[0-9]/plughw:$CARD_NUM,$DEV_NUM/g" \
    -e "s/card [0-9]/card $CARD_NUM/g" \
    ~/.asoundrc

yad --title="Sound" --window-icon=info --text-align=center --width=340 --center \
    --text="\nNow using Card $CARD_NUM – Device $DEV_NUM\n\nConfig backed up to ~/.asoundrc.bak" \
    --button=gtk-ok:0

The script as-is isn't what you'd call precision, but there's an elegance to it in brevity of code and taking advantage of simple edits to a config file to completely change behavior.

Philosophy and methodology of use has to be taken into consideration, this little utility does not and should not work for someone with their own custom 500-line .asoundrc, if a user is that far into it then they know how to edit config files. This utility is for the garden-variety user who just wants sound to work and would be put-off by having to manually locate and edit config files that may be complete gibberish to them if they're not a nerd.

Problem is i'm working blind here as I have no machine that has multiple cards with at least one having multiple devices. So I can't fully test.

Also that script I posted above in addition to removing the legacy stuff, can also be swapped to /bin/sh as it's posix compliant, dash is quicker anyway, so that's a win.

Packaging locally here using dpkg-deb is fast and uncomplicated. But again you're right that it might get some more testing if I used git.

This is the first year i've branched out to more complex things than simple scripts, so i'm still trying to get a feel for things.

I have seen someone (fsmithred ?, ralph.ronquist ?) offer someone project space on git.devuan.org.
Your project is quite small (no offence, small is beautiful ) and therefore would not be a resource gobbler, and I am sure of interest to Devuan users even if unlikely to be qualified for packaging.
Uploading to git.devuan.org. you could concentrate on developing and the interested could follow your progress as (in)frequently as they choose.
Testing and bug reports could also be more forthcoming (at least in theory).

So I did some work on this card-switcher script as I mentioned above, enlarged the list window some, and added a check at the start of the script to check for ~/.asoundrc, and if absent it offers to install the generic one included with the package, or you can hit cancel to abort.

The script works great and fast for me and should for the vast majority of simple laptops and desktops. But going forward I want to improve detection and expand a bit, first thing I want to do is deal with sub-devices, that pesky second number, currently this script only swaps the card number.

And thus my dilemma today, should I upload the new AlsaTune as-is so hopefully it can get tested some more, or should I work on the next phase of this script and wait until I have it working before uploading a new AT....*sigh*....

I added an error check to look for ~/.asoundrc right at the start and exit if there isn't one. But now i'm thinking in the error message to also add the ability to copy a simple .asoundrc (to be shipped with the mxeq/AT package) to the users home if there isn't one, and then continuing (or hit cancel to back out of course).

I'll be modding AT a fair bit to add a button for the card-switcher and some other functions including a button to test sound, using aplay to play a .wav file I made, just 3 seconds of a 500hz note, the idea being you can test whatever changes you made with the card-switcher right there in the gui after doing it, without having to cycle audio/video apps on and off.

Thanks for the help, I really appreciate it and at some point i'll take you up on the offer to test the next version.

724 lines in asound.conf? Holy crap, that's epic! Yeah I can see where my little script probably wouldn't be good for that system, but it's a dang fine one for testing the limits of it for sure.

a lot of trial-and-error

With the work you put in for the benefit of others I judge that you are entitled to use the computer science term for that, stepwise refinement

I don't mind throwing it at my workstation on occasion and reporting back, I guarantee it is an edge case, my /etc/asound.conf contains 724 lines.

Basic philosophy/use-case is for Vuu-do as it already has a working alsa system, and is meant for simple everyday garden-variety use, just a quick switch for those machines that have an analog and an HDMI output as most of the time the dual-setups default to HDMI as card 0.

At least at this stage...baby steps...but i'd like to pursue it and figure out all the edge-cases and sub-devices and such so I can package it with AT for general use at some point.

Ummm, GPU?

Outputs are capable of carrying digital sound as well as video, so consequently show up in ALSA as individual sink devices.

ls -ld /proc/asound/card1/pcm*
dr-xr-xr-x 4 root root 0 Nov 18 13:07 /proc/asound/card1/pcm3p
dr-xr-xr-x 4 root root 0 Nov 18 13:07 /proc/asound/card1/pcm7p
dr-xr-xr-x 4 root root 0 Nov 18 13:07 /proc/asound/card1/pcm8p
dr-xr-xr-x 4 root root 0 Nov 18 13:07 /proc/asound/card1/pcm9p

No .asoundrc is a case, at the start of this endeavour I am writing this to be included in AlsaTune/Vuu-do which will already have an .asoundrc in the system, but like other things I want to also make a generic/portable version that can be used anywhere so that's the next target for functionality.

Window-size: How many cards are in your list? I had envisioned entries for just a couple, can you elaborate? Do I need a scroll function?