in reply to qr delimiter question

Can anybody explain why it does work if you make it: qr(\s+execution\s+time\s+[(]\s+millis\s+[)]\s+\:\s+) It seems inconsistent, somehow. It seems to me that either the above should require backslashes on the () to compile at all or the backslashes in the original example should make them match literal () characters.

can somebody point out my point of confusion on this point?

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Re:* qr delimiter question
by Roy Johnson (Monsignor) on Nov 17, 2003 at 18:21 UTC
    Paired delimiters can nest. Hence: my $exp = qr(x(capture)y); is valid. Perl recognizes the parens inside the expression as being inside the expression. In the example you gave, there is a ( inside the expression before the ) inside the expression, so Perl understood it as a nested pair.

    You can see how perl is parsing the regex by printing it:

    >perl -e "print qr(a(b)c)"
(?-xism:a(b)c)
>perl -e "print qr(a\(b\)c)"
(?-xism:a(b)c)
>perl -e "print qr(a\\(b\\)c)"
(?-xism:a\\(b\\)c)

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    As you see, a single backslash is interpreted as escaping the parens from the qr(), rather than as part of the regex. A double-backslash escapes the backslash in the regex, so there's no backslashy way to match a literal paren. You have to use a character class, plus a backslash, unless you're going to have a balancing paren in the expression, in which case, perl will notice the balanced parens and Do The Right Thing. 
    >perl -e "print qr(a\(bc)"
Unmatched ( in regex; marked by <-- HERE in m/a( <-- HERE bc/ at -e li
+ne 1.
>perl -e "print qr(a[(]bc)"
Search pattern not terminated at -e line 1.
>perl -e "print qr(a[\(]bc)"
(?-xism:a[(]bc)

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