while (<FILE>) {
    my $boxname;
    if ( ! ( /^Filesystem/ ) ) {
        $boxname = $_;
    } else {
        while (<FILE>) {
            my ( $title, $blocks, $used, $avail, $percent, $mounted ) 
+= split /\s+/;
            last if ( !defined( $title ) );
            my $number = ( $percent =~ /(\d*)\%/ );
            if ( $number > 88 ) {
                print "$boxname's $title is at $percent!\n";
            }
        }
    }
}
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Update Should be split \/s+\ rather than \/s*\