#!/bin/bash
IAm=${0##*/}
LockFile="/tmp/$IAm.lock"

# Set lock and verify that no other copy of this code is already running...
set -C	# set no clobber option

# Create the lock file...  This will fail if the lock file already exists.
if ! echo "PID $$ holds the lock." > "$LockFile"
then	echo "$IAm: Another $IAm is already running." >&2
	cat "$LockFile" >&2
	echo "$IAm: Aborting!" >&2
	exit 1
fi

# We now hold an exclusive lock to the lock file (as long as other processes
# wanting to create this lock file also use set -C when trying to create this
# lock file).
set +C	# clear no clobber option

# Set up to remove the lock file when we're done.
trap 'rm -f "$LockFile"' EXIT

echo "$IAm: $$ running."
sleep 60
echo "$IAm: $$ quitting."