print $_ foreach(@open);
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You don't really need the loop there:

print @open;
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And it might be better if you used strings instead of arrays:

use strict;
use warnings;

my $zero = "\nZero Active Processors:\n\n";
my $one  = "\nOne Active Processor:\n\n";

foreach ( `ganglia proc_run` )
{
    $zero .= $_ if /\s0\s+$/;
    $one  .= $_ if /\s1\s+$/;
}

print "$zero$one\n";
[download]