Bash: Evitando multiplas instâncias de um script

Alguns scripts não podem rodar multiplas instâncias, um caso clássico é o apt-get, caso ele rodasse mais de uma vez certamente teriamos quebra dos pacotes, para evitar isto usamos um script para evitar multiplas instâncias.

	#!/bin/bash
	# ------------------------------------------------------------
	# File : AmIRunning
	# Author : Jonathan Franzone
	# Company : http://www.franzone.com
	# Date : 09/23/2007
	# Description : Test script for creating lock files
	# source: http://www.franzone.com/2007/09/23/how-can-i-tell-if-my-bash-script-is-already-running/
	# ------------------------------------------------------------
	# ------------------------------------------------------------
	# Setup Environment
	# ------------------------------------------------------------
	PDIR=${0%`basename $0`}
	LCK_FILE=`basename $0`.lck
	# ------------------------------------------------------------
	# Am I Running
	# ------------------------------------------------------------
	if [ -f "${LCK_FILE}" ]; then
	# The file exists so read the PID
	# to see if it is still running
	MYPID=`head -n 1 "${LCK_FILE}"`
	TEST_RUNNING=`ps -p ${MYPID} | grep ${MYPID}`
	if [ -z "${TEST_RUNNING}" ]; then
	# The process is not running
	# Echo current PID into lock file
	echo "Not running"
	echo $$ > "${LCK_FILE}"
	else
	echo "`basename $0` is already running [${MYPID}]"
	exit 0
	fi
	else
	echo "Not running"
	echo $$ > "${LCK_FILE}"
	fi
	# ------------------------------------------------------------
	# Do Something
	# ------------------------------------------------------------
	while true
	do
	clear
	echo
	ls -F
	echo
	date
	echo
	sleep 5
	done
	# ------------------------------------------------------------
	# Cleanup
	# ------------------------------------------------------------
	rm -f "${LCK_FILE}"
	# ------------------------------------------------------------
	# Done
	# ------------------------------------------------------------
	exit 0

view raw lock_file.sh hosted with ❤ by GitHub

O artigo original que me inspirou foi este.