#!/bin/sh
  #
  # This script takes at minimum one argument: the time that the alarm should go off
  # using the format hh:mm, it does only rudimentary checks that the format is 
  # specified is correct. An optional second argument specifies what should be done 
  # when the alarm goes off. If no second argument is supplied, a simple shell bell 
  # is used.
  #
  # Be sure this bell works before you go to sleep!
  #
  # If the second argument is included and the alarm method is more than one command,
  # it will need to be enclosed in quotes.
  
  # First check that the required minimum arguments have been supplied, and that
  # the time is of the format hh:mm. If not exit with the proper usage.
  
  if [ $\#\; -eq\; 0\; ]\; then\; echo\; "Usage:\; \$0\; hh:mm\; [alarm-method]"\; echo\; "eg.\; \$0\; 13:30\; \backslash "mplayer\; /media/music/dr\_octagon/01.mp3\backslash "\; "\; exit\; 1\; else\; alarm\_time="\$1"\; \#\; Check\; that\; the\; format\; for\; the\; alarm\; time\; is\; correct,\; the\; first\; digit\; \#\; should\; be\; a\; number\; between\; 0-2,\; followed\; by\; a\; colon,\; and\; ending\; with\; a\; \#\; number\; between\; zero\; and\; 60.\; NB:\; This\; check\; is\; not\; perfect.\; if\; [\; !\; `echo\; "$alarm_time" | sed -n '/[0-2][[:digit:]]:[0-60]/p'` ]
          then
                  echo "Incorrect time specified, please use format hh:mm"
                  exit 1
          fi
  
  fi
  
  # Set the number of seconds in a minute
  seconds=1
  
  # Test to see if a second argument is supplied, if it is not then set the
  # bell to a shell bell. The -e argument to echo specifies that echo should
  # enable interpretation of the backslash character, and \a is defined in
  # the echo(1) man page as a bell.
  
  if [ ! $2 ]
  then
          bell="echo -e \a"
  else
  
          bell=$2
  fi
  
  # The wait_between_checks function sleeps for the specified number of
  # seconds and then calls the check_time function when it is done sleeping.
  # This makes the script only check the time once a minute, instead of constantly.
  
  wait_between_checks ()
  {
          sleep $seconds\; check\_time\; \}\; \#\; The\; check\_time\; function\; looks\; at\; the\; current\; time\; (in\; hh:mm\; format)\; and\; \#\; compares\; it\; to\; the$alarm_time, if they match, then it calls the wakeup function
  # otherwise it goes back to sleep by calling the wait_between_checks function 
  again.
  
  check_time ()
  {
          current_time=`date +\%H:\%M`
  
          if [ "$current\_time"\; =\; "$alarm_time" ]
          then
                  wakeup
          else
                  wait_between_checks
          fi
  
  }
  
  # The wakeup function simply rings the bell over and over until the script
  # is interrupted.
  
  wakeup ()
  {
          echo -n "Wake up! Hit control-c to stop the madness"
          $bell\; sleep\; 1\; wakeup\; \}\; \#\; Finally\; the\; main\; body\; of\; the\; script\; simply\; starts\; things\; up\; by\; calling\; the\; \#\; wait\_between\_checks\; function\; wait\_between\_checks$