docker-plex/root/etc/cont-init.d/50-plex-update

#!/usr/bin/with-contenv bash

# copy config on first run, regardless of update status
[[ ! -e /etc/default/plexmediaserver ]] && \
	cp /defaults/plexmediaserver /etc/default/plexmediaserver

# set no update message
[[ -e /tmp/no-version.nfo ]] && \
	rm /tmp/no-version.nfo
NOVERSION_SET='/tmp/no-version.nfo'
cat > "${NOVERSION_SET}" <<-EOFVERSION
#######################################################
# Update routine will not run because you havent set  #
# the VERSION variable or you opted out of updates.   #
#          For more information checkout :-           #
#    https://github.com/linuxserver/docker-plex       #
#######################################################
EOFVERSION

# set update failed message
[[ -e /tmp/update_fail.nfo ]] && \
	rm /tmp/update_fail.nfo
UPGRADE_FAIL='/tmp/update_fail.nfo'
cat > "${UPGRADE_FAIL}" <<-EOFFAIL
########################################################
# Upgrade attempt failed, this could be because either #
# plex update site is down, local network issues, or   #
# you were trying to get a version that simply doesn't #
# exist, check over the VERSION variable thoroughly &  #
# correct it or try again later.                       #
########################################################
EOFFAIL

# test for no version set or opt out for autoupdates
if [[ -z "$VERSION" ]] || [[ "$VERSION" == "0" ]] || [[ ! -z "$ADVANCED_DISABLEUPDATES" ]]; then
printf "\n\n\n%s\n\n\n" "$(</tmp/no-version.nfo)"
exit 0
fi

# set header for no preferences/token message
[[ -e /tmp/no-token.nfo ]] && \
	rm /tmp/no-token.nfo
NOTOKEN_SET='/tmp/no-token.nfo'
cat > "${NOTOKEN_SET}" <<-EOFTOKEN
#####################################################
#   Login via the webui at http://<ip>:32400/web    #
#   and restart the docker, because there was no    #
EOFTOKEN

# if preferences files doesn't exist, exit out
if [ ! -e "/config/Library/Application Support/Plex Media Server/Preferences.xml" ]; then
cat >> "${NOTOKEN_SET}" <<-EOFTOKEN
#   preference file found, possibly first startup.  #
#####################################################
EOFTOKEN
printf "\n\n\n%s\n\n\n" "$(</tmp/no-token.nfo)"
exit 0
fi

# attempt to read plex token
PLEX_TOKEN=$( sed -n 's/.*PlexOnlineToken="//p' \
	"/config/Library/Application Support/Plex Media Server/Preferences.xml" \
	| sed "s/\".*//")

# if plex token isn't found, exit out
if [ -z "$PLEX_TOKEN" ]; then
cat >> "${NOTOKEN_SET}" <<-EOFTOKEN
#      plex token found in the preference file      #
#####################################################
EOFTOKEN
printf "\n\n\n%s\n\n\n" "$(</tmp/no-token.nfo)"
exit 0
fi

# determine installed version of plex
INSTALLED_VERSION=$(dpkg-query -W -f='${Version}' plexmediaserver)

# start update routine
if [[ "$VERSION" = latest ]] || [[ "$VERSION" = plexpass ]] || [[ "$PLEXPASS" == "1" ]]; then
REMOTE_VERSION=$(curl -s "${PLEX_WWW}"| cut -d "/" -f 5 )
elif [[ "$VERSION" = public ]]; then
PLEX_TOKEN=""
REMOTE_VERSION=$(curl -s "${PLEX_WWW}"| cut -d "/" -f 5 )
else
REMOTE_VERSION="${VERSION}"
fi

if [[ "$REMOTE_VERSION" == "$INSTALLED_VERSION" ]]; then
echo "No update required"
exit 0
fi

echo "Atempting to upgrade to: $REMOTE_VERSION"
last=130
down_tries=3
if curl --output /dev/null --silent --head --fail "${PLEX_URL}/plex-media-server/$REMOTE_VERSION/plexmediaserver_${REMOTE_VERSION}_amd64.deb"; then
while [[ $last -ne "0" ]] || [[ down_tries -gt 0 ]]; do
	rm -f /tmp/plexmediaserver_*.deb
	curl -o /tmp/plexmediaserver_"${REMOTE_VERSION}"_amd64.deb -L \
		"${PLEX_URL}/plex-media-server/$REMOTE_VERSION/plexmediaserver_${REMOTE_VERSION}_amd64.deb"
	down_tries=$((down_tries-1))
last=$?
done
 apt-get remove --purge -y \
	plexmediaserver
dpkg -i /tmp/plexmediaserver_"${REMOTE_VERSION}"_amd64.deb
rm -f /tmp/plexmediaserver_*.deb
else
printf "\n\n\n%s\n\n\n" "$(</tmp/update_fail.nfo)"
exit 0
fi

# recopy config file in case update overwrites our copy
cp -v /defaults/plexmediaserver /etc/default/plexmediaserver