Something

sub unix_fsmon {
        my $hostname = shift;
        my $df = shift;
        open DF, "$df | tail +2 |";
        while (<DF>) {
                if ( m!^//! ) {
                        $filesystem = undef;
                        next;
                }
                if ( /^\S+$/ ) {
                        $filesystem = $_;
                        next;
                }
                if ( s/^\s+// ) {
                        ($kbytes, $used, $avail, $util, $filesys) = split /\s+/, $_;
                } else 
                        ($filesystem, $kbytes, $used, $avail, $util, $filesys) = split /\s+/, $_;
                }
                $util =~ s/%//;
                $avail = int($avail / 1024);
                send_msg($avail, $filesys);
        }
}