How to get parent PID of a given process in GNU/Linux from command line?

Question

Resolved before asked: cat /proc/1111/status | grep PPid

Answer 1

Command line:

ps -p 1111 -o ppid=

Function:

ppid () { ps -p ${1:-$$} -o ppid=; }

Script:

#!/bin/sh
pid=$1
if [ -z $pid ]
then
    read -p "PID: " pid
fi
ps -p ${pid:-$$} -o ppid=

If no PID is supplied to the function or the script, they default to show the PPID of the current process.

Answer 2

Read /proc/$PID/status. Can be easily scripted:

#!/bin/sh
P=$1
if [ -z "$P" ]; then
    read P
fi
cat /proc/"$P"/status | grep PPid: | grep -o "[0-9]*"