a script to adjust volume. it will try to use the most recent audio card by default.

adjust_volume.sh

#! /bin/bash

case $1 in
    -c)
        card=$2; shift; shift;;
    *)
        card=$(awk '/digital audio playback/ {c = substr($0, 7, 2)} END {print c}' /proc/asound/devices)
        ;;
esac

if [ $# -eq 2 ]
then
    channel="$1"; shift
else
    # get name of simple mixers with p(layback) volume
    channels=($(amixer -c $card scontents |
                    awk 'BEGIN{RS="Simple mixer control "} /pvolume/ {print $1}' |
                    cut -d, -f1))
    # without an index, an array variable expands to first element
    channel=$channels
fi

if [ $# != 1 ]
then
    cat <<EOF >&2
Usage: $0 [-c CARD] [<channel>] <adjustment>

Examples:
  volume_adjust toggle   -- toggles mute on/off
  volume_adjust 5%+      -- increase volume by 5%

EOF
    printf "Available controls for card %d: %s\n" $card "${channels[*]}"
    exit 64
fi

case $1 in
    [0-9]*)
        amixer -c $card set $channel $1 >/dev/null ;;
    mute|unmute|toggle)
        pasink=($(pacmd list-sinks | awk '/[*] index:/ {i=$3} i && /muted:/ {print i, $2; exit}'))
        case "$1:${pasink[1]}" in
            mute:*)     mute=true ;;
            unmute:*)   mute=false ;;
            toggle:yes) mute=false ;;
            toggle:no)  mute=true ;;
            *)          echo "wha?  [$1] [${pasink[@]}]"; exit 1 ;;
        esac
        pacmd set-sink-mute ${pasink[0]} $mute
esac

pkill -USR1 -x i3status