I'll add that assigning a new IO::File to $handle before calling open probably doesn't do what you'd expect:

If FILEHANDLE is an undefined scalar variable (or array or hash element) the variable is assigned a reference to a new anonymous filehandle, otherwise if FILEHANDLE is an expression, its value is used as the name of the real filehandle wanted. (This is considered a symbolic reference, so "use strict ’refs’" should not be in effect.)

So a declared $handle is all you need. It can even be written as open my $handle, "$command |".

Combining with moritz's advice,

my @handles;
foreach my $f ( 0 .. 9 )
{
    open $handles[$f], "$command |";
}
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Of course, this is assuming that you actually want to read the standard output of $command. If all you want to do is fire and forget the process, there are lighter alternatives (system).