When using /m with a regexp, $ becomes particularly ambiguous; it means both 'end of line' and 'interpolate a variable'. (Although this is true without /m, it causes me grief much less often in that case.) I've never seen the rules documented for how Perl disambiguates. I've looked. What I find is that they're explained as "magic'; 'Perl usually does what you mean.'

What are the rules? And what's the best idiom for influencing the outcome?

For example, consider /foo$.*^bar/ms - is this $. (the variable) or EOL followed by random stuff?

I find myself introducing non-capturing parens, as it seems that if a paren can be matched it won't be used as a variable name.

A more realistic example:
$QQ->get_private_key_string =~ /(^-----BEGIN (?:(RSA) )?PRIVATE KEY-----$(?:.*)^-----END (?:RSA )?PRIVATE KEY-----$(?:\s*))/ms;

This gets quite entertaining, considering that $. $( and $) are variables.

It would be nice to have a deterministic way to code these cases. And may I suggest that this should be documented?

Thanks.

This communication may not represent my employer's views, if any, on the matters discussed.

In reply to Disambuating $ in (especially /m) regexps by tlhackque

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