Understanding strange Perl multiline comment mechanism

Question

EDIT: Note to new Perl programmers: This mechanism should NOT be used for multiline comments! It has a flaw decreases readability.

In this PerlMonks

Answer 1

Abigail's answer is partly humorous. There is in fact no << >> operator (not in versions of Perl before 5.22), but there is a (not that well-known, I guess) << operator. Not the binary shift operator, but the unary here-document (heredoc for short). A simple form of it is:

$long_string = <

This is, in fact, the “multiline comment” feature underlying Abigail's answer — a multiline string literal. The rest is a bit of somewhat obfuscated Perl.

The bareword or quoted string after << ends the string literal. You can use q as a bareword:

<

To understand the rest of Abigail's snippet, it helps to rewrite the here-document into a simple string literal:

"This is a multiline comment.\n" =~ q>>;

Ok, now q>> is the q quote-like operator with > as the delimiter character. q>> is equivalent to '' (a non-interpolated literal, which happens to be empty). So the string literal is matched against an empty pattern. The result of that matching is ignored anyway, but this clobbers the match result variables ($1, $&, etc).