The parentheses indicate list context. For example:

my @fred = qw(42 43 44 45);
my ($q, $x, $y, $z) = grep /\d+/, @fred;
print "$q $x $y $z\n";
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I don't think you would be surprised at the result:

42 43 44 45
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So $q is 42. Now remove $z:

($q, $x, $y) = grep /\d+/, @fred;
print "$q $x $y\n";
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Now we get just 42 43 44That is $q has not changed. Now remove $y:

($q, $x) = grep /\d+/, @fred;
print "$x\n";
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and we get

42 43
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$q still is unchanged. Finally remove $x:

($q) = grep /\d+/, @fred;
print "$q\n";
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and $q is still:

42
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