Question

From the documentation, I see

$rex = qr/my.STRING/is;
print $rex; # prints (?si-xm:my.STRING)

But I am not sure how to understand (?si-xm:...). If I do a print on qr/quick|lazy/, I got (?-xism:quick|lazy). What does it mean here (?-xism:...) too?

Thanks!

Answer 1

As explained in the perlre man-page:

Any letters between ? and : act as flags modifiers […]

The letters before the - are positive modifiers; those after it are negative modifiers. So, for example, (?-xism:quick|lazy) means that whitespace and comments are not allowed inside the parentheses, the parenthesized part is not case-sensitive, a dot . does not match newlines, and ^ and $ do not match line-start and line-end.