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

################################################################
# Don't change anything unless you know what are you doing     #
################################################################
if [ -f "$BIN_ZYPPER" ]; then
    # OpenSUSE
    # shellcheck disable=SC2086 # CMD_* are intentionally-split option strings
    UPDATES=$("$BIN_ZYPPER" $CMD_ZYPPER | "$BIN_WC" $CMD_WC)
    if [ "$UPDATES" -ge 2 ]; then
        echo $((UPDATES-2));
    else
        echo "0";
    fi
elif [ -f "$BIN_DNF" ]; then
    # Fedora
    # shellcheck disable=SC2086 # CMD_* are intentionally-split option strings
    UPDATES=$("$BIN_DNF" $CMD_DNF | "$BIN_WC" $CMD_WC)
    if [ "$UPDATES" -ge 1 ]; then
        echo $((UPDATES-1));
    else
        echo "0";
    fi
elif [ -f "$BIN_PACMAN" ]; then
    # Arch
    # shellcheck disable=SC2086 # CMD_* are intentionally-split option strings
    UPDATES=$("$BIN_PACMAN" $CMD_PACMAN | "$BIN_WC" $CMD_WC)
    if [ "$UPDATES" -ge 1 ]; then
        echo $((UPDATES-1));
    else
        echo "0";
    fi
elif [ -f "$BIN_YUM" ]; then
    # CentOS / Redhat
    # shellcheck disable=SC2086 # CMD_* are intentionally-split option strings
    UPDATES=$("$BIN_YUM" $CMD_YUM | "$BIN_WC" $CMD_WC)
    if [ "$UPDATES" -ge 1 ]; then
        echo $((UPDATES-1));
    else
        echo "0";
    fi
elif [ -f "$BIN_APT" ]; then
    # Debian / Devuan / Ubuntu
    # shellcheck disable=SC2086 # CMD_* are intentionally-split option strings
    UPDATES=$("$BIN_APT" $CMD_APT | "$BIN_GREP" $CMD_GREP 'Inst')
    if [ "$UPDATES" -ge 1 ]; then
        echo "$UPDATES";
    else
        echo "0";
    fi
else
    echo "0";
fi