N. B. Perl 6 has been renamed to Raku.
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In October 2019, Perl 6 has been renamed to Raku. Its grammar, syntax, sigils, and everything remain the same, but when reading this article, please read Perl 6 as Raku.
You are reading the article written before the rename. What is said here, most likely still works, but you may want considering to review the differences after the rename. The texts published on this site prior to the rename will stay unchanged for reflecting the historical truth.
gcd calculates the greatest common denominator of the two integer operands.