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perlop:

PATTERN may contain variables, which will be interpolated every time the pattern search is evaluated, except for when the delimiter is a single quote.

Parens aren't the only thing you have to look out for. '.' (dot) will be treated as a meta-character that matches anything except for newline. [] square brackets will be treated like character classes, and so on through the entire list of regexp pattern tokens. quotemeta or \Q and \E are not just quirks providing a lucky solution, this sort of situation is on the short list of reasons for quotemeta and \Q\E to exist.

In perldoc -f quotemeta you'll read, "quotemeta (and \Q ... \E ) are useful when interpolating strings into regular expressions, because by default an interpolated variable will be considered a mini-regular expression. I wouldn't call it an anomaly, it's just how Perl is designed.

perlop contains a good crash course on how interpolation works. The sections to look for start with Quote and Quote-like Operators, and continue through the end of "Gory details of parsing quoted constructs".


Dave


In reply to Re: Parens mess up regex substitute by davido
in thread Parens mess up regex substitute by BenHopkins

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