#!/usr/bin/perl

open(PIPE, "/bin/df -h|")
  or die "error spawning df thingy! $!\n";

$alert=0;

while(<PIPE>) {
  next unless /%/o;                      # skip header
  $l=$_;                                 # preserve $_ 
  chomp;
  s/%//go;
  split;
  $alert=1
    if($_[4]>90);
}

&sendmail
  if($alert);

close(PIPE) 
  or warn "error closing pipe: $!\n";

0;

sub sendmail {

  open(MAIL, "|/usr/sbin/sendmail admins")
    or warn "error spawning sendmail! $!\n";

  print MAIL<<EOF;
Subject: disk space alert!

Howdo,

The disk space watcher has noticed that one or more partitions are >90%
full. Have a quick check:

`/bin/df`

~Tim

EOF

close(MAIL)
  or warn "Error closing mail: $!\n";
}