this script uses v4l2-ctl to set the zoom level of a webcam

camera-zoom.sh

#!/usr/bin/env bash
#
# this script uses v4l2-ctl to set the zoom level of a webcam
#

set -e

# you may have multiple cameras but usual video0 is the right one
camera=/dev/video0

# you may need to tweak these values
# v4l2-ctl --list-ctrls-menus may return values between 1 and 5
# or values between 100 and 500 like in my case, but
# the max zoom is 200
max_zoom=200
min_zoom=100
zoom_step=10

set_zoom() {
    v4l2-ctl -d $camera --set-ctrl zoom_absolute="${1}"
}

get_zoom() {
    v4l2-ctl -d $camera --list-ctrls-menus --list-ctrls-menus | grep zoom_absolute | grep -E -o value=\[0-9\]+
}

increase_zoom() {
  # shellcheck disable=SC2004
  new_zoom=$(($(get_zoom) + $zoom_step))
  # shellcheck disable=SC2046
  if [ $new_zoom -le $max_zoom ]; then
    set_zoom $new_zoom
  fi
}

decrease_zoom() {
  # shellcheck disable=SC2004
  new_zoom=$(($(get_zoom) - $zoom_step))
  # shellcheck disable=SC2046
  if [ $new_zoom -ge $min_zoom ]; then
    set_zoom $new_zoom
  fi
}

# if no argument
if [ -z "$1" ]; then
    echo "Usage: $0 {max|min|increase|decrease}"
    exit 1
fi

case "$1" in
    "min")
        set_zoom $min_zoom
        ;;
    "max")
        set_zoom $max_zoom
        ;;
    "decrease")
        decrease_zoom
        ;;
    "increase")
        increase_zoom
        ;;
    *)
        echo "Usage: $0 {away|close|middle}"
        exit 1
esac