Changing the UID/GID of a docker user before starting the process

change_uid_www.sh

#!/bin/bash
set -e
set -u

DEFAULT_UID=33
DEFAULT_GID=33

usage(){
  printf "Usage: ./%s -u NEW_UID [-f Force, needed if NEW_UID = 0 ]\n" "$0"
}

while getopts ":u:g:f" opt
do
  case $opt in
    u) WWW_UID=${OPTARG}
    ;;  
    g) WWW_GID=${OPTARG}
    ;;  
    f) FORCE=1
    ;;  
    *) usage
    ;;  
  esac
done
shift $((OPTIND-1))

WWW_UID=${WWW_UID:-${DEFAULT_UID}}
WWW_GID=${WWW_GID:-${DEFAULT_GID}}
FORCE=${FORCE:-0}

if [ ${WWW_UID} -eq ${DEFAULT_UID} ] && [ ${WWW_GID} -eq ${DEFAULT_GID} ]
then
  # printf "Not changing anything.\n"
  :
elif [ ${WWW_UID} -eq 0 ] || [ ${WWW_GID} -eq 0 ] && [ ${FORCE} -ne 1 ] 
then
  printf "ID 0 without -f. Won't change anything.\n"
elif [ `id -u` -ne 0 ] 
then
  printf "Need root permissions for this script.\n"
else
  if [ "${WWW_UID}" -ne ${DEFAULT_UID} ]
  then
    # printf "Changing UID to %s\n" "${WWW_UID}"
    usermod -u "${WWW_UID}" www-data
    chown -R --from="33" ${WWW_UID} `find /* -maxdepth 0 -path /proc -prune -o -print`
  fi  
  if [ "${WWW_GID}" -ne ${DEFAULT_GID} ]
  then
    # printf "Changing GID to %s\n" "${WWW_GID}"
    groupmod -g "${WWW_GID}" www-data
    chown -R --from=":33" :${WWW_GID} `find /* -maxdepth 0 -path /proc -prune -o -print`
  fi  
fi
exec "$@"