Hello monks,

Following is the excerpt from "Programming perl". I am having trouble wrapping my head around this regular expression and there is not much explanation to it in the book, can someone shed some light please? Just an fyi I tried my best to understand this but I am still not clear, sorry if I am asking a question that isn't supposed be asked here.

"You can do recursive patterns, too. One way is to have a compiled pattern that uses (??{ CODE }) to refer to itself. Recursive matching is pretty irregular, as regular expressions go. Any text on regular expressions will tell you that a standard regex can’t match nested parentheses correctly. And that’s correct. It’s also correct that Perl’s regexes aren’t standard. The following pattern matches a set of nested parentheses, however deep they go:

$np = qr{
\(
(?:
(?> [^()]+ ) # Non–parens without backtracking
|
(??{ $np }) # Group with matching parens
)*
\)
}x;

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You could use it like this to match a function call:

$funpat = qr/\w+$np/;<br>
"myfunfun(1,(2*(3+4)),5)" =~ /^$funpat$/; #Matches!"

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Jr. Monk

In reply to Recursive regex by raghuprasad241

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