#!/bin/ksh
#Trace the ancestry of the given PID: Handout 6, pp. 2-3.

if [[ $# -ne 1 ]]
then
	echo $0: arg must be PID 1>&2
	exit 1
fi

ps -Af |
awk '
	NR == 1 {print}

	NR > 1 {
		line[$2] = $0		#$2 is PID
		parent[$2] = $3		#$3 is PPID
	}

	END {
		for (pid = '$1';; pid = parent[pid]) {
			if (line[pid] == "") {
				print "'$0': PID " pid " not found"
				exit 2
			}
			print line[pid]
			if (pid == parent[pid]) {   #reached the top
				exit 0
			}
		}
	}
'