Change User/Primary Group UID and GID

change_user_uid_gid.sh

#!/usr/bin/env bash

usage() {
  cat <<-EOF
  usage: ${0} -l <login> -u <new uid> [-g <new gid>]
    -h            this help screen
    -l login      account login account name
    -p            primary group for account login
    -u uid        new UID to assign to account
    -g            new GID to assign to account group

  returns status code of 0 for success, otherwise, failure
EOF
exit -2
}

# Reference Commands
cmd_list='usermod groupmod find chgrp getent id awk tr wc'

# Function to check if referenced command exists
cmd_exists() {
  if [ $# -eq 0 ]; then
    echo 'WARNING: No command argument was passed to verify exists'
  fi

  cmd=${1}
  hash "${cmd}" >&/dev/null # portable 'which'
  rc=$?
  if [ "${rc}" != "0" ]; then
    echo "${cmd} command not found"
    exit 1
  #else
  #  echo "Found: ${cmd} at ${cmd_fullpath}"
  fi
}

# Verify that referenced commands exist on the system
for cmd in ${cmd_list}; do
  cmd_exists "$cmd"/
done

#Parse command line flags
#If an option should be followed by an argument, it should be followed by a ":".
#Notice there is no ":" after "h". The leading ":" suppresses error messages from
#getopts.
while getopts ":l:u:g:p:h" opt; do
  case $opt in
    g)
      newgid="$OPTARG"
      ;;
    h)
      usage
      ;;
    l)
      login="$OPTARG"
      ;;
    p)
      prigroup="$OPTARG"
      ;;
    u)
      newuid="$OPTARG"
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      usage
      ;;
  esac
done

if [ -z "${login}" ]; then
  echo -e "Error: You must specify a login\n"
  usage
elif [ -z "${prigroup}" ]; then
  #verify that login and primary   
  echo -e "Info: Setting the primaray group to ${login}\n"
  prigroup="${login}"
  membercount=$(getent group "${prigroup}" | awk -F: '{ print $4 }' | tr -cd , | wc -c)
  if [ "${membercount}" != "0" ]; then
    echo -e "Warning: The primary group for account ${login} contains other accounts\n"
    echo -e "Would you like to continue to update the GID for ${prigroup} ? [Y/n] " input
    if [[ ! $input =~ ^[Yy]$ ]]; then
      echo -e "\nWarning: Aborting on user prompt"
      exit 2
    fi
  fi
fi

if [ -z "${newuid}" ]; then
  echo -e "Error: You must specify a new UID\n"
  usage
elif [ -z "${newgid}" ]; then
  echo -e "Warning: Setting the new GID to ${newuid}\n"
  read -r -n 1 -p " Would you like to continue with these settings ? [Y/n] " input
  if [[ ! $input =~ ^[Yy]$ ]]; then
    echo -e "\nWarning: Aborting on user prompt"
    exit 2
  fi
  newgid="${newuid}"
fi

# Capture old UID and GID
olduid=$(getent passwd "${login}" | awk -F: '{ print $3 }')
oldgid=$(getent group "${login}" | awk -F: '{ print $3 }')

if [ -z "${olduid}" ]; then
  echo -e "Error: Couldn't determine current UID for ${login}\n"
  exit 1
elif [ -z "${oldgid}" ]; then
  echo -e "Error: Couldn't determine current GID for ${login}\n"
  exit 1
fi

check_uid() {
  check_uid=$1
  local status
  status=$(getent passwd "${check_uid}" | awk -F: '{ print $1 }')
  rc=$?
  if [ "${rc}" -ne "0" ]; then
    echo "Error: ${check_uid} is already assigned to login [ ${status} ]"
    exit 1
  fi
}

check_gid() {
  check_gid=$1
  local status
  status=$(getent group "${check_gid}" | awk -F: '{ print $1 }')
  rc=$?
  if [ "${rc}" -ne "0" ]; then
    echo "Error: ${check_gid} is already assigned to group  [ ${status} ]"
    exit 1
  fi
}

check_uid "${newuid}"
check_gid "${newgid}"

echo -e "\n Updating User UID and Primary Group GID\n"

sudo usermod -u "${newuid}" "${login}"
sudo groupmod -g "${newgid}" "${prigroup}"
sudo find / -path /sys -prune -o -path /proc -prune -o \
-user "${olduid}" -exec chown -h "${newuid}" {} \;
sudo find / -path /sys -prune -o -path /proc -prune -o \
-group "${oldgid}" -exec chgrp -h "${newgid}" {} \;
sudo usermod -g "${newgid}" "${login}"