[Gllug] Automatic shutdown script

[Dylan]

Hi all,

I'm taking my first serious plunge into bash. I want to make the server and 
gateway machines on my home LAN shutdown when they are not needed. I figure I 
can do this:

Set up a cron job on the server which executes a script to do (roughly) the 
following:

Check for lock file
  if file exists then
    exit
  otherwise
    create it
loop through a set of defined hosts
  if one or more responds to a ping
    record an active response
if there was an active host
  check if there was an active host on the last run
if there was no active host on this run and no active host on the last run
  record state
  tidy up
  shutdown
if there was no active host this time but there was one last time
  record state
  tidy up
  exit
if there was an active host this run and last run
  record state
  tidy up
  exit

Clearly this is still at the conceptual stage. My questions are:

How should I discover the hosts to ping? The server's /etc/hosts file is kept 
current (for sharing over NIS) so I figure that's the best place to get the 
info. I can easily define a numerical IP range to cover the hosts in the 
script (any one between 192.168.0.2 and 192.168.0.200 inclusive) or add 
comments to the hosts file to tell the script what to do. Or maybe I could 
create a set of aliases (say pingtest1, pingtest2) which the script could 
then just use somehow.

I figure recording the result of the ping test can be stored in a variable - 
but I'm not clear on the difference between 'shell variable' and 'local 
variable'.

Recording the final state (i.e. whether the run resulted in no response or 
not) needs to persist from one run to the next, so is that best recorded in a 
state file or as an environment variable?

Any other comments...?

TIA

Dylan

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