RegExp Search/Replace is a better match for this kind of job. But I also would like to show how to do this via split/join. This might come in handy if you want to skip certain fields or need an array representation later on.

The split pattern

I see you're using the pattern 'a single space' / /, but since you want to fold whitespace anyway a better solution is to use 'multiple spaces' / +/ or 'any whitespace' /\s+/, the effect is this:

my $CPU = 'Intel(R) Xeon(R) CPU          X5660  2.80GHz ';
# field:    0        1       2  3..11     12  13 14       # using / /
# field:    0        1       2            3      4        # using / +/
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Usage of join

There are multiple ways to feed the generated array into join. In order to get the expected result you can either feed each field separately, use an array slice or just feed the whole array:

my @CPU_SPLIT = split / +/, 'Intel(R) Xeon(R) CPU          X5660  2.80
+GHz ';

# 1 - feed each field explicitly
print join ' ', $CPU_SPLIT[0], $CPU_SPLIT[1], $CPU_SPLIT[2], $CPU_SPLI
+T[3], $CPU_SPLIT[4]; print "\n";

# 2a - use an array slice - explicitly
print join ' ', @CPU_SPLIT[0,1,2,3,4]; print ">n";

# 2b - use an array slice - via a range
print join ' ', @CPU_SPLIT[0..4]; print "\n";

# 3 - feed the whole array
print join ' ', @CPU_SPLIT; print "\n";
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