Using temporary files

• use traps to clean up the system after exit
  Useful signals are:
  0 = ?? (FIXME)
  1 = HUP
  2 = INT
  3 = QUIT
  15 = TERM
  
• be sure not to use the same temporary file if two instances of the same program are running
  • use mktemp or
  • use the pid of the program $$

#!/bin/sh

lockfile=/var/lock/foo.lock
tempfile=/tmp/foo-$$

#handle command line arguments here

if [ -f $lockfile ]; then
    exit 0;
fi

trap "rm -f $lockfile $tempfile" 0 1 2 3 15
touch $lockfile $tempfile || exit 1

#user program here