@lines = map {
    /(\/\w+\/\w+)\s+\w+\s+\d+\s+\d+\s+(\d+)\s+(\d+)%/;
    {
        volume => $1,
        available => $2,
        free => 100 - $3,
    }
} split /\n/, $space{ $host };

# This is the sorting line!
@lines = sort { $a->{available} <=> $b->{available} } @lines;

push @out, "$host:$_->{volume}    $_->{available}    $_->{free}%" for @lines;