A Plex Media Server update script for Linux. Checks local PMS if update is available, then attempts to download and install the update is one exists.

update-plexmediaserver

#!/usr/bin/env bash

scriptSudo() {
  local SUDO_IS_ACTIVE
  SUDO_IS_ACTIVE=$(sudo -n uptime 2>&1|grep "load"|wc -l)
  if [[ ${SUDO_IS_ACTIVE} -le 0 ]]; then
    # Ask for the administrator password upfront
    sudo -v

    # Keep-alive: update existing `sudo` time stamp until `.osx` has finished
    while true; do sudo -n true; sleep 60; kill -0 "$$" || exit; done 2>/dev/null &
  fi
  
  sudo "$@"
}

install () {
  local INSTALL_STATUS
  if [ -z "${PACAPT:+x}" ]; then
    if ! [ -x "$(command -v pacapt)" ]; then
      PACAPT="/tmp/pacapt"
      if ! [ -f $PACAPT ]; then
        LATEST_TAG=$(curl -s https://api.github.com/repos/icy/pacapt/tags | grep sha | head -n 1 | cut -d '"' -f 4)
        curl -Lso "$PACAPT" "https://raw.githubusercontent.com/icy/pacapt/$LATEST_TAG/pacapt"; INSTALL_STATUS=$?
        if [[ $INSTALL_STATUS -ne 0 ]]; then
          die "Error installing ${@:$#}" $INSTALL_STATUS
        fi
      fi
      if ! [ -x "$PACAPT" ]; then
        chmod 755 $PACAPT
      fi
    else
      PACAPT=pacapt
    fi
  fi
  
  info "Installing ${@:$#}..."
  scriptSudo $PACAPT $@; INSTALL_STATUS=$?
  if [[ $INSTALL_STATUS -ne 0 ]]; then
    die "Error installing ${@:$#}" $INSTALL_STATUS
  fi
}

getXPath () {
  echo "$1" | xmllint --recover --xpath "$2" -
}

getXPathFromFile () {
  xmllint --recover --xpath "$2" "$1"
}

################################################################################
# Resolve Dependencies
################################################################################

requireBashfulLibrary () {
  local UPPER
  UPPER=$(echo "$1" | tr '[:lower:]' '[:upper:]')
  local LOWER
  LOWER=$(echo "$1" | tr '[:upper:]' '[:lower:]')
  
  local IS_LOADED
  eval IS_LOADED=\$"BASHFUL_${UPPER}_LOADED"
  
  if [[ "$IS_LOADED" -lt 1 ]]; then
    BASHFUL_INSTALL_DIR="/tmp/bashful-master"
    if ! [ -d $BASHFUL_INSTALL_DIR ]; then
      mkdir $BASHFUL_INSTALL_DIR
    fi
  fi
  
  BASHFUL_LIB_PATH="$BASHFUL_INSTALL_DIR/bin/bashful-${LOWER}"
  if ! [ -r "$BASHFUL_LIB_PATH" ]; then
    curl -Lso "/tmp/bashful.tar.gz" "https://github.com/jmcantrell/bashful/tarball/master"
    tar -xzf /tmp/bashful.tar.gz -C $BASHFUL_INSTALL_DIR --strip-components=1
  fi
  
  local WD
  WD=$(pwd)
  LIB_DIR=$(dirname "$BASHFUL_LIB_PATH")
  cd "$LIB_DIR"
  source "$BASHFUL_LIB_PATH"
  cd "$WD"
}

requireBashfulLibrary messages
requireBashfulLibrary input
requireBashfulLibrary utils

if ! [ -x "$(command -v xmllint)" ]; then
  warn "$(basename $0) requires the utility 'xmllint'. Included in 'libxml2-utils'"
  question -p  "Would you like to Install 'libxml2-utils'?" -d1 || exit 0
  install -S libxml2-utils
fi

################################################################################
# Check Plex Media Server for Available Updates
################################################################################

getPlexOnlineToken() {
  [ -f /etc/default/plexmediaserver ] && . /etc/default/plexmediaserver
  local pmsApplicationSupportDir="${PLEX_MEDIA_SERVER_APPLICATION_SUPPORT_DIR:-${HOME}/Library/Application Support}"
  local prefFile="${pmsApplicationSupportDir}/Plex Media Server/Preferences.xml"
  local PlexOnlineToken
  eval $(getXPathFromFile "$prefFile" "Preferences/@PlexOnlineToken")
  
  echo "$PlexOnlineToken"
}

queryPMS() {
  X_PLEX_TOKEN=${X_PLEX_TOKEN:-$(getPlexOnlineToken)}
  
  info $1
  query="https://localhost:32400/"$(echo "$1" | trim "/")
  curl -skL --header "X-Plex-Token: $X_PLEX_TOKEN" "$query"
}

PMS_UPDATER_STATUS=$(queryPMS "updater/status")

info "$PMS_UPDATER_STATUS"

# Get the size attribute, and assign to a 'size' variable
#   It just so happens that the format returned by `xmllint` for an Entity's
#   attribute, feeds perfectly into an `eval` assignment.
let size
eval $(getXPath "$PMS_UPDATER_STATUS" "MediaContainer/@size")
if [[ $size -eq 0 ]]; then
  info "No Update Available."
  exit 0
fi

let state
eval $(getXPath "$PMS_UPDATER_STATUS" "MediaContainer/Release[1]/@state")
case $state in
none|checking)
  info "No Response from Update Server"
  exit 0
  ;;
"done")
  info "Plex Media Server is already Up to Date."
  exit 0
  ;;
downloaded|downloading|available)
  info "Update available, and your server should be downloading/installing as per it's capabilities" | fmt -s -
  exit 0
  ;;
error)
  die "Encountered an Error. Aborting" 1
  ;;
esac

# If we've reached this far, the state must be "notify", and therefore we need to do some more work.

# Gather remaining attributes needed from the PMS_UPDATER_STATUS xml
let downloadURL
eval $(getXPath "$PMS_UPDATER_STATUS" "MediaContainer/@downloadURL")
let version
eval $(getXPath "$PMS_UPDATER_STATUS" "MediaContainer/Release[1]/@version")
let added
eval $(getXPath "$PMS_UPDATER_STATUS" "MediaContainer/Release[1]/@added")
let fixed
eval $(getXPath "$PMS_UPDATER_STATUS" "MediaContainer/Release[1]/@fixed")

# Decode HTML Entities back into their normal characters for printing to screen
added=$(echo "$added" | php -R 'echo html_entity_decode($argn, ENT_QUOTES|ENT_XML1);')
fixed=$(echo "$fixed" | php -R 'echo html_entity_decode($argn, ENT_QUOTES|ENT_XML1);')

info "Update Available!\n"
info "Plex Media Server version $version"
if [[ -n $added || -n $fixed ]]; then
  info "Change Log:"
  if [[ -n $added ]]; then
    echo "  Added:"
    echo "$added" | sed 's/^/    * /g' | fmt -s -
  fi
  if [[ -n $fixed ]]; then
    echo "  Fixed:"
    echo "$fixed" | sed 's/^/    * /g' | fmt -s -
  fi
fi

PMS_STATUS_SESSIONS=$(queryPMS "status/sessions")
let CURRENT_STREAMS
eval $(getXPath "$PMS_STATUS_SESSIONS" "MediaContainer/@size" | sed "s/^\(.*\)\(=.*\)/CURRENT_STREAMS\2/")
if [[ $CURRENT_STREAMS -gt 0 ]]; then
  if [[ $CURRENT_STREAMS -eq 1 ]]; then
    info "There is $CURRENT_STREAMS user currently streaming from the server."
  else 
    info "There are $CURRENT_STREAMS users currently streaming from the server."
  fi
  question -p  "Upgrading will kick out all users. Would you like to continue?" -d1 || exit 0
fi

# Manually follow URL redirect so that the download's filename is accurate
REDIRECT_URL=$(echo "$downloadURL" | xargs curl -sI | sed -e 's/^Location: \(.*\)/\1/' -e 'tx' -e 'd' -e ':x')
if ! [ -z "$REDIRECT_URL" ]; then
  downloadURL=$REDIRECT_URL
fi

info "Downloading..."
# Get file name, and remove any exraneous new line characters
FILE_NAME=$(basename "$downloadURL" | sed 's/[\n\r]$//')

# Encode HTML Entities so that the URL passes through cURL properly
echo "$downloadURL" | php -R 'echo htmlentities($argn, ENT_QUOTES|ENT_HTML401);' | xargs curl -o "/tmp/$FILE_NAME" ; EXIT_STATUS=$?
if [ $EXIT_STATUS -eq 0 ]; then
  info "Installing..."
  install -U "/tmp/$FILE_NAME"
else
  echo ""
  die "Error with curl download. Aborting" $EXIT_STATUS
fi

Updated script to fall back on the Server's token if it exists.

Honestly though, you probably want to use the following script instead though, it has a lot more options and more fleshed out.
https://github.com/mrworf/plexupdate

I submitted a similar server auth fallback to that project as a PR here: mrworf/plexupdate#158