switch_user

#!/usr/bin/env sh
set -e

DYNAMIC_USER='docker_alias_dyn_user'

switchToDynamicUser() {
    userExists() {
        id "$1" > /dev/null 2>&1
    }
    if [ "$UID_HOST" = "" ]; then
        print "UID_HOST not present!"
    fi
    USERNAME="$1"
    if userExists "$UID_HOST"; then
        modifyUser "$(id -nu "$UID_HOST")" 978654321 978654321
        modifyUser "$USERNAME" "$UID_HOST" "$UID_HOST"
    else
      HOME="/home/$DYNAMIC_USER"
      mkdir "$HOME"
      useradd "$USERNAME" -d "$HOME" --no-log-init -u "$UID_HOST"
      chown -R $USERNAME:$USERNAME $HOME
    fi
}

modifyUser() {
    _USERNAME=$1
    _NEWUID=$2
    _NEWGID=$3

    if ! userExists "$_USERNAME"; then
      echo "User does not exist: '$_USERNAME'"
      exit 1
    fi
    _GROUPNAME=$(id -gn "$_USERNAME")
    _OLD_UID=$(id -u "$_USERNAME")
    _OLD_GID=$(id -g "$_USERNAME")
    _HOME="$(eval echo ~_USERNAME)"

    userdel "$_USERNAME"
    useradd "$_USERNAME" -d "$_HOME" --no-log-init -u "$_NEWUID"
    groupmod -g "$_NEWGID" "$_GROUPNAME"
    find "$_HOME" -ignore_readdir_race -user "$_OLDUID" -exec chown -h "$_NEWUID" {} \;
    find "$_HOME" -ignore_readdir_race -group "$_OLDGID" -exec chgrp -h "$_NEWGID" {} \;
    usermod -g "$_NEWGID" "$_USERNAME"
}

switchToDynamicUser $DYNAMIC_USER
runuser -u "$DYNAMIC_USER" -- $@