lockscript - Shell script locking template

lockscript

#! /bin/sh

# lockscript - Shell script locking template
# Copyright (C) 2012-2014 Matous J. Fialka, <http://mjf.cz/>
# Released under the terms of The MIT License

# USAGE
# =====
#
# Rename, link or source this file to your desired script.
#
# ENVIRONMENT
# ===========
#
# Name		Description
# -----------	-----------------------------------------------------
# LOCKTIME	Time to stay locked (-1 means to never unlock)
# LOCKFILE	Path to lockfile
# PIDFILE	Path to file to write process ID (PID) to
# CONFIGFILE	List of paths to configuration (separated by collons)
# SCRIPTFILE	Path to file to include as main script
# -------------------------------------------------------------------
#
# DESCRIPTION
# ===========
#
# The script first tries to read CONFIGFILE in order, then it writes
# PIDFILE and LOCKFILE. If everything went OK it sources SCRIPTFILE.
# It also does signal trapping so that you do not have to handle it.
# The SCRIPTFILE or main part wouldn't get run again unless LOCKTIME
# expires (to reset lock use LOCKTIME=0 which means to ignore lock).

#
# <<>> BASIC INFORMATION <<>>
#
PROGRAM=`basename "$0"`

if [ "$PROGRAM" = "$__PROGRAM" ]
then
	echo "Source loop detected for $__PROGRAM" 1>&2
	exit 1
fi
__PROGRAM="$PROGRAM"


#
# <<>> CONFIGFILE <<>>
#
if [ "${#CONFIGFILE}" -eq 0 ]
then
	CONFIGFILE="/etc/${PROGRAM}.conf:$HOME/.${PROGRAM}rc":"./.${PROGRAM}rc"
else
	CONFIGFILE="/etc/${PROGRAM}.conf:$HOME/.${PROGRAM}rc":"./.${PROGRAM}rc":"$CONFIGFILE"
fi

__OFS="$IFS"
IFS=:

for __CONFIGFILE in $CONFIGFILE
do
	if [ -e "$__CONFIGFILE" ]
	then
		if ! [ -r "$__CONFIGFILE" ]
		then
			echo "Could not source $__CONFIGFILE" 1>&2
			exit 1
		fi

		source "$__CONFIGFILE"
	fi

	unset __CONFIGFILE
done

IFS="$__OFS"


#
# <<>> PIDFILE <<>>
#
if [ "${#PIDFILE}" -eq 0 ]
then
	if [ "$USER" = 'root' ]
	then
		PIDFILE="/var/run/$PROGRAM.pid"
	else
		PIDFILE="/tmp/$PROGRAM.pid"
	fi
fi

if [ -e "$PIDFILE" ]
then
	echo "Concurent session is running. PID file is $PIDFILE" 1>&2
	exit 1
fi

__PIDFILE_DIRNAME=`dirname "$PIDFILE"`

if [ -w "$__PIDFILE_DIRNAME" ]
then
	echo "$$" > "$PIDFILE"
else
	echo "Path to write PID file $PIDFILE is not writable" 1>&2
	exit 1
fi

unset __PIDFILE_DIRNAME


#
# <<>> SIGNALS <<>>
#
signal_handler_general()
{
	EXIT=${EXIT:-$?}

	if [ -r "$PIDFILE" ]
	then
		if [ $(< $PIDFILE) -eq $$ ]
		then
			rm -f "$PIDFILE"
		fi
	fi

	trap - 0 1 2 3 13 15
	kill -2 $$
}

signal_handler_exit()
{
	EXIT=${EXIT:-$?}

	if [ $EXIT -eq 0 ]
	then
		rm -f "$LOCKFILE"
	fi

	signal_handler_general
}

trap signal_handler_exit 0
trap signal_handler_general 1 2 3 13 15


#
# <<>> LOCKFILE <<>>
#
if [ "${#LOCKFILE}" -eq 0 ]
then
	if [ "$USER" = 'root' ]
	then
		LOCKFILE="/var/lock/$PROGRAM.lock"
	else
		LOCKFILE="/tmp/$PROGRAM.lock"
	fi
fi

__LOCKFILE_DIRNAME=`dirname "$LOCKFILE"`

if [ ! -w "$__LOCKFILE_DIRNAME" ]
then
	echo "Path to write lock file $LOCKFILE is not writable" 1>&2
	exit 1
fi

unset __LOCKFILE_DIRNAME

LOCKTIME="${LOCKTIME:--1}"

if [ "$LOCKTIME" -lt -1 ]
then
	echo 'Invalid LOCKTIME value (must be in range -1..N)' 1>&2
	exit 1
fi

if [ -e "$LOCKFILE" ]
then
	if [ "$LOCKTIME" -eq -1 ]
	then
		echo "Session is permanently locked. Lockfile is $LOCKFILE" 1>&2
		exit 1
	fi

	if ! [ `stat -c %Z "$LOCKFILE"` -lt $((`date +%s` - $LOCKTIME + 1)) ]
	then
		echo "Session is temporarily locked. Lockfile is $LOCKFILE" 1>&2
		exit 1
	fi
fi

touch "$LOCKFILE"


#
# <<>> SCRIPTFILE <<>>
#
if [ "${#SCRIPTFILE}" -ne 0 ]
then
	if [ -e "$SCRIPTFILE" ]
	then
		if [ -r "$SCRIPTFILE" ]
		then
			source "$SCRIPTFILE"
		else
			echo "Unable to read script file $SCRIPTFILE" 1>&2
			exit 1
		fi
	else
		echo "Unable to find script file $SCRIPTFILE" 1>&2
		exit 1
	fi
fi


#
# <<>> MAIN <<>>
#

USAGE

Create a demo script somewhere in the $PATH:

$ cat > /usr/local/bin/lockscript-demo
#! /bin/sh

echo -n 'Press Ctrl-C (OK) or Ctr-D (failure) or enter something (OK): '
read
echo "You have entered: '$REPLY'"

Run it via lockscript:

$ SCRIPTFILE=`which lockscript-demo` LOCKTIME=5 lockscript

If the lockscript-demo script specified in the SCRIPTFILE variable
fails then it can not be run again using the lockscript program for
at least 5 seconds specified in then LOCKTIME variable.

In case you would like to enjoy the lockscript configuration files
link it to you desired name, say test.sh:

$ ln -s `which lockscript` /usr/local/bin/test

Now you can place your configuration in CONFIGFILE paths, in order:

1. /etc/test.conf
2. $HOME/testrc
3. ./testrc
4. $CONFIGFILE

And run lockscript as test like this:

$ SCRIPTFILE=`which lockscript-demo` LOCKTIME=5 test

You can place configuration variables for the lockscript-demo in any of the
configuration files as listed above.

You can also copy the lockscript program with another name and use the last MAIN
part of the script to either place SCRIPTFILE post-run code or you can use
it to implement standalone script as well.

Of course, feel free to source this file at the beginning of any script you like.