Check disk space and report on

check_disk_space.pl

#!/usr/bin/perl

use FileHandle; 

$mailfrom = "sender\@example.com";
$mailto = "recipient\@example.com";
@check=`df -k`;

@warn = grep { m/(\d+\%)/ and $1 >=90} @check;

$mail = new FileHandle; 
$mail->open("| /usr/sbin/sendmail -t") || die "Cannot open: $!";
$mail->print("From: $mailfrom\n");
$mail->print("To: $mailto\n");
$mail->print("Subject: Disk space is low!\n\n");

foreach (@warn)
{
    $mail->print($_, "\n");
}
$mail->close();