#!/usr/bin/env bash
################################################################
# copy this script to /etc/snmp/ and make it executable:       #
# chmod +x /etc/snmp/osupdate                                  #
# ------------------------------------------------------------ #
# edit your snmpd.conf and include:                            #
# extend osupdate /etc/snmp/osupdate                           #
#--------------------------------------------------------------#
# restart snmpd and activate the app for desired host          #
#--------------------------------------------------------------#
# please make sure you have the path/binaries below            #
################################################################
BIN_WC='/usr/bin/env wc'
BIN_GREP='/usr/bin/env grep'
CMD_GREP='-c'
CMD_WC='-l'
BIN_ZYPPER='/usr/bin/env zypper'
CMD_ZYPPER='-q lu'
BIN_YUM='/usr/bin/env yum'
CMD_YUM='-q check-update'
BIN_DNF='/usr/bin/env dnf'
CMD_DNF='-q check-update'
BIN_TDNF='/usr/bin/env tdnf'
CMD_TDNF='-q check-update'
BIN_APT='/usr/bin/env apt-get'
CMD_APT='-qq -s upgrade'
BIN_PACMAN='/usr/bin/env pacman'
CMD_PACMAN='-Sup'
BIN_CHECKUPDATES='/usr/bin/env checkupdates'
BIN_PKG='/usr/sbin/pkg'
CMD_PKG=' audit -q -F'
BIN_APK='/sbin/apk'
CMD_APK=' version'

# If using this as a agent and not a extend, uncomment the line below.
#echo '<<<app-os-updates>>>'

################################################################
# Don't change anything unless you know what are you doing     #
################################################################
if command -v zypper &>/dev/null ; then
    # OpenSUSE
    # shellcheck disable=SC2086
    UPDATES=$($BIN_ZYPPER $CMD_ZYPPER | $BIN_WC $CMD_WC)
    if [ "$UPDATES" -ge 2 ]; then
        echo $(($UPDATES-2));
    else
        echo "0";
    fi
elif command -v dnf &>/dev/null ; then
    # Fedora
    # shellcheck disable=SC2086
    UPDATES=$($BIN_DNF $CMD_DNF | $BIN_WC $CMD_WC)
    if [ "$UPDATES" -ge 1 ]; then
        echo $(($UPDATES-1));
    else
        echo "0";
    fi
elif command -v tdnf &>/dev/null ; then
    # PhotonOS
    # shellcheck disable=SC2086
    UPDATES=$($BIN_TDNF $CMD_TDNF | $BIN_WC $CMD_WC)
    if [ "$UPDATES" -ge 1 ]; then
        echo "$UPDATES";
    else
        echo "0";
    fi
elif command -v pacman &>/dev/null ; then
      # Arch
      # calling pacman -Sup does not refresh the package list from the mirrors,
      # thus it is not useful to find out if there are updates. Keep the pacman call
      # to accomodate users that do not have it. checkupdates is in pacman-contrib.
      # also enables snmpd to collect this information if it's not run as root
      if command -v checkupdates &>/dev/null ; then
          # shellcheck disable=SC2086
          UPDATES=$($BIN_CHECKUPDATES | $BIN_WC $CMD_WC)
      else
          # shellcheck disable=SC2086
          UPDATES=$($BIN_PACMAN $CMD_PACMAN | $BIN_WC $CMD_WC)
      fi
      if [ "$UPDATES" -ge 1 ]; then
          echo $(($UPDATES-1));
      else
          echo "0";
      fi
elif command -v yum &>/dev/null ; then
      # CentOS / Redhat
      # shellcheck disable=SC2086
      UPDATES=$($BIN_YUM $CMD_YUM | $BIN_WC $CMD_WC)
      if [ "$UPDATES" -ge 1 ]; then
          echo $(($UPDATES-1));
      else
          echo "0";
      fi
elif command -v apt-get &>/dev/null ; then
      # Debian / Devuan / Ubuntu
      # shellcheck disable=SC2086
      UPDATES=$($BIN_APT $CMD_APT | $BIN_GREP $CMD_GREP 'Inst')
      if [ "$UPDATES" -ge 1 ]; then
          echo "$UPDATES";
      else
          echo "0";
      fi
elif command -v pkg &>/dev/null ; then
      # FreeBSD
      # shellcheck disable=SC2086
      UPDATES=$($BIN_PKG $CMD_PKG | $BIN_WC $CMD_WC)
      if [ "$UPDATES" -ge 1 ]; then
          echo "$UPDATES";
      else
          echo "0";
      fi
elif command -v apk &>/dev/null ; then
      # Alpine
      # shellcheck disable=SC2086
      UPDATES=$($BIN_APK $CMD_APK | $BIN_WC $CMD_WC)
      if [ "$UPDATES" -ge 2 ]; then
          echo $(($UPDATES-1));
      else
          echo "0";
      fi
else
      echo "0";
fi