use strict;
use Mail::Send;
use Sys::Hostname;

my $MAX = 50;

my $dir = shift || '/usr';
my $to  = 'foo@bar.com';
my $body;

open(DF, "df -k $dir | ") or die;
$body .= $_ while <DF>;
my ($perc) = $body =~  /(\d+)%/;
close DF;

exit if $perc < $MAX;

my $msg = new Mail::Send Subject => 'df alarm', To => $to;
my $fh  = $msg->open;

print $fh "Disk uskagage for $dir on ", hostname(), "\n";
print $fh $body;
$fh->close;