Mute either USB microphone or internal soundcard, depending on presence.

mute_tool.sh

#!/usr/bin/env bash
USB=false
select_card() {
    USB="false" # assume that usb mic is not attached
    cards="$(arecord -l | grep card)"
    echo "${cards}" | grep -q USB && USB="true" # if a device has USB in the name, usb mic is attached and we probs want to use it
    while read -r card; do
        # loop through cards. if USB, then pick the first card with USB in the name. else, pick the first card w/o
        if [ "${USB}" == "true" ]; then
            echo "${card}" | grep -q USB && echo "true" $(echo "${card}" | awk '{print $2}' | cut -d':' -f1) && return
        else
            echo "${card}" | grep -vq USB && echo "false" $(echo "${card}" | awk '{print $2}' | cut -d':' -f1) && return
        fi
    done <<<"${cards}"
}
SELECT="$(select_card)"
USB="$(echo ${SELECT} | cut -d' ' -f1)"
ALSA_CARD_NO="$(echo ${SELECT} | cut -d' ' -f2)"

general_mute_toggle() {
    if [ "${USB}" == "false" ]; then
        amixer -c "${ALSA_CARD_NO}" set Capture toggle # my internal soundcard's mic mute setting is called "Capture"
    else
        amixer -c "${ALSA_CARD_NO}" set Mic toggle # my usb mic's mute setting is called "Mic"
    fi
    exit 0
}
general_mute_toggle