#!/bin/bash

varName="servicedesc"
varDefault=""
myDelim="[ :-]"
myField=""
myHost=""
myService=""
myContact=""
doUpper=""

do_help() {
cat << HELP_EOF
This utility is designed to be called by the ARGx parameters of a Nagios configuration as follows:

  \$\$(\$USER1\$/env [-n <var>] [-t <default>] [-f <field>] [-d <delim>] [-u] [-H|-S|-C <suffix>]

Where:

  var     the name of a case-insensitive NAGIOS_variable (defaults to "servicedesc")
  default a default value if \$NAGIOS_var\$ is blank (case sensitive)
  field   an awk-compatible field number (potentially to use with <delim>)
  delim   an awk-compatible field delimiter (defaults to space, dash, and colon)
  -u      Convert the output to uppercase (useful for further levels of indirection)
  suffix  Take var result and use the it to get NAGIOS__[HOST|SERVICE|CONTACT]<result><suffix>

The value will always be trimmed of leading and/or trailing spaces/tabs.

If -f is used, then the result will be as if the request were as follows, unless the field starts with a negative, in which case it will read from the last word forward:

  eche \$NAGIOS_var\$ | awk -F <delim> '{print $<field>}'

Examples (service_description is assumed to be "MySQL Check: myDatabase performance"):

  .../env -n servicedesc		Return: "MySQL Check: myDatabase performance"
  .../env -n hostName			Return: "localhost" (or whatever the name of the host is that ran the check)
  .../env -n SERVICESTATE -t 0		Return: current state of the service (0, 1, 2) or 0 if the state is not defined
  .../env -n servicedesc -f 2		Return: "Check" (watch out for defaults!)
  .../env -n servicedesc -f 4		Return: "myDatabase" (watch out for defaults!)
  .../env -n servicedesc -d : -f 2	Return: "myDatabase performance"
  .../env -n servicedesc -d : -f -2 	Return: "MySQL Check" (2nd field from right, split by :)*
  .../env -n servicedesc -f -2 -H pass	Return: the value of \$NAGIOS__HOSTNAGIOSXIPASS\$

see https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/4/en/macrolist.html for possible macro names.
*0 for this field will print the entire line
HELP_EOF
  exit
}

while [ -n "$1" ]; do
  case "$1" in
    -h|--help) do_help;;
    -n) varName="$2"; shift 2;;
    -t) varDefault="$2"; shift 2;;
    -d) myDelim="$2"; shift 2;;
    -f) myField="$2"; shift 2;;
    -H) myHost="$2"; shift 2;;
    -S) myService="$2"; shift 2;;
    -C) myContact="$2"; shift 2;;
    -u) doUpper="true"; shift 1;;
    *) shift 1;;
  esac
done

varName=`echo "NAGIOS_$varName" | tr "a-z" "A-Z"`
varValue="${!varName}"
if [ -n "$myField" ]; then
  if [ "$myField" -lt 0 ]; then
    varValue=`echo "$varValue" | rev | awk -F "$myDelim" -v f="${myField:1}" '{print $f}' | rev`
  else
    varValue=`echo "$varValue" | awk -F "$myDelim" -v f="$myField" '{print $(f)}'`
  fi
fi
varValue=`echo $varValue | sed -e "s/^[ \t]*//" -e "s/[ \t]*$//"`

[ -n "$doUpper" ] && varValue=`echo "$varValue" | tr "a-z" "A-Z"`

# Check for myHost
if [ -n "$myHost" ]; then
  myHost=`echo "NAGIOS__HOST${varValue}${myHost}" | tr "a-z" "A-Z"`
  varValue=${!myHost}
fi

# Check for myService
if [ -n "$myService" ]; then
  myService=`echo "NAGIOS__SERVICE${varValue}${myService}" | tr "a-z" "A-Z"`
  varValue=${!myService}
fi

# Check for myContact
if [ -n "$myContact" ]; then
  myContact=`echo "NAGIOS__CONTACT${varValue}${myContact}" | tr "a-z" "A-Z"`
  varValue=${!myContact}
fi

[ -z "$varValue" ] && varValue="$varDefault"
echo "$varValue"

exit 0