A shell script to map all Wacom devices to a given monitor, in particular to switch through all available monitors by repeatedly calling it with the parameter NEXT

wacom2monitor.sh

#!/usr/bin/env bash

# exit on error or on use of undeclared variable or pipe error:
set -o errexit -o errtrace -o nounset -o pipefail
# optionally debug output by supplying TRACE=1
[[ "${TRACE:-0}" == "1" ]] && set -o xtrace

shopt -s inherit_errexit
PS4='+\t '
IFS=$'\n\t'

error_handler() {
  echo >&2 "Error: In ${BASH_SOURCE[0]}, Lines $1 and $2, Command $3 exited with Status $4"
  pr -tn "${BASH_SOURCE[0]}" | tail -n+$(($1 - 3)) | head -n7 | sed '4s/^\s*/>> /' >&2
  exit "$4"
}
trap 'error_handler $LINENO "$BASH_LINENO" "$BASH_COMMAND" $?' ERR

usage() {
  cat << EOF
Usage: $0 <Monitor>

Map all Wacom Devices to Monitor <Monitor>.
For example, to map to Monitor VGA-1:

  $0 VGA-1

If <Monitor> is NEXT, then to the next monitor
as listed by xrandr. Useful, for example, to bind, 
say by xbindkeys, a key to
  
  notify-send "\$($0 NEXT)"

EOF
  exit 1
}

next() {
  [ -n "$TMPDIR" ] || TMPDIR=/tmp
  WFILE="$TMPDIR/wacom2mon"

  # Since
  #   xsetwacom --get "Wacom Pad pad" MapToOutput
  # returns
  #   'MapToOutput' is a write-only option.
  # we store the output device in a temp file.
  # This, woefully, cannot detect output device changes;
  # for example, after a reboot.

  if [ -f "$WFILE" ]; then
    current_monitor="$(cat "$WFILE")"
  else
    current_monitor=""
  fi

  if [ -z "$current_monitor" ]; then
    # no mapping known, just use the first monitor
    next_monitor=$(xrandr --listactivemonitors | sed -n 2p | awk '{print $4}')
  else
    # duplicate the output in case the current monitor is the last one, so we automatically cycle
    # through. head after grep takes the first match and sed afterwards drops the match and keeps
    # only the next monitor
    next_monitor=$(xrandr --listactivemonitors | sed 1d | awk '{print $4}' | tee /dev/stdout | grep -A 1 "$current_monitor" | sed -n 2p)
  fi

  echo "$next_monitor" >$WFILE
  echo "$next_monitor"
}

command -v xsetwacom >/dev/null 2>&1 || exit 1
command -v xrandr >/dev/null 2>&1 || exit 1

if [[ $# == 0 ]]; then
  usage
else
  screen="$1"
fi

[ "$screen" = "NEXT" ] && screen="$(next)"

devices="$(xsetwacom --list devices | cut -f 1)"
[ -z "$devices" ] && exit 1

while read -r d; do
  # instead of `while IFS=$' \n\t'`; from https://stackoverflow.com/a/15398846
  d=$(echo $d | xargs echo -n)
  xsetwacom --set "$d" MapToOutput "$screen"
  echo "$d was mapped to:    $screen"
done <<< $devices

Thanks for the script! Here's some suggestions: instead of taking the last two entries from the xrandr output, you can keep them all if you just delete the first line with sed 1d. I also took the liberty of changing the way a current mapping is found, so it's not limited to bash and its arrays

next() {
  [ -n "$TMPDIR" ] || TMPDIR=/tmp
  WFILE="$TMPDIR/wacom2mon"

  # Since
  #   xsetwacom --get "Wacom Pad pad" MapToOutput
  # returns
  #   'MapToOutput' is a write-only option.
  # we store the output device in a temp file.
  # This, woefully, cannot detect output device changes;
  # for example, after a reboot.

  if [ -f "$WFILE" ]; then
    current_monitor="$(cat "$WFILE")"
  else
    current_monitor=""
  fi

  if [ -z current_monitor ]; then
    # no mapping known, just use the first monitor
    next_monitor=$(xrandr --listactivemonitors | sed -n 2p | awk '{print $4}')
  else
    # duplicate the output in case the current monitor is the last one, so we automatically cycle
    # through. head after grep takes the first match and sed afterwards drops the match and keeps
    # only the next monitor
    next_monitor=$(xrandr --listactivemonitors | sed 1d | awk '{print $4}' | tee /dev/stdout | grep -A 1 "$current_monitor" | sed -n 2p)
  fi

  echo "$next_monitor" >$WFILE
  echo "$next_monitor"
}

this still fails if the stored monitor is not found anymore though

Glad to have been of help. Thank you for your improvements as well, which have just been added where [ -z current_monitor ] was replaced by [ -z $current_monitor ].