regex-recursion | 易学教程

Regex Recursion: Nth Subpatterns

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问题 I'm trying to learn about Recursion in Regular Expressions, and have a basic understanding of the concepts in the PCRE flavour. I want to break a string: Geese (Flock) Dogs (Pack) into: Full Match: Geese (Flock) Dogs (Pack) Group 1: Geese (Flock) Group 2: Geese Group 3: (Flock) Group 4: Dogs (Pack) Group 5: Dogs Group 6: (Pack) I know neither regex quite does this, but I was more curious as to the reason why the the first pattern works, but the second one doesn't. Pattern 1: ((.*?)($\w{1,}$

How exactly does this recursive regex work?

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问题 This is a followup to this question. Have a look at this pattern: (o(?1)?o) It matches any sequence of o with a length of 2 n , with n ≥ 1. It works, see regex101.com (word boundaries added for better demonstration). The question is: Why? In the following, the description of a string (match or not) will simply be a bolded number or a bolded term that describes the length, like 2 n . Broken down (with added whitespaces): ( o (?1)? o ) ( ) # Capture group 1 o o # Matches an o each at the start

Capturing text before and after a C-style code block with a Perl regular expression

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问题 I am trying to capture some text before and after a C-style code block using a Perl regular expression. So far this is what I have: use strict; use warnings; my $text = << "END"; int max(int x, int y) { if (x > y) { return x; } else { return y; } } // more stuff to capture END # Regex to match a code block my $code_block = qr/(?&block) (?(DEFINE) (?<block> \{ # Match opening brace (?: # Start non-capturing group [^{}]++ # Match non-brace characters without backtracking | # or (?&block) #

How exactly does this recursive regex work?

阅读更多关于 How exactly does this recursive regex work?

This is a followup to this question . Have a look at this pattern: (o(?1)?o) It matches any sequence of o with a length of 2 n , with n ≥ 1. It works, see regex101.com (word boundaries added for better demonstration). The question is: Why? In the following, the description of a string (match or not) will simply be a bolded number or a bolded term that describes the length, like 2 n . Broken down (with added whitespaces): ( o (?1)? o ) ( ) # Capture group 1 o o # Matches an o each at the start and the end of the group # -> the pattern matches from the outside to the inside. (?1)? # Again the

Capturing text before and after a C-style code block with a Perl regular expression

阅读更多关于 Capturing text before and after a C-style code block with a Perl regular expression

I am trying to capture some text before and after a C-style code block using a Perl regular expression. So far this is what I have: use strict; use warnings; my $text = << "END"; int max(int x, int y) { if (x > y) { return x; } else { return y; } } // more stuff to capture END # Regex to match a code block my $code_block = qr/(?&block) (?(DEFINE) (?<block> \{ # Match opening brace (?: # Start non-capturing group [^{}]++ # Match non-brace characters without backtracking | # or (?&block) # Recursively match the last captured group )* # Match 0 or more times \} # Match closing brace ) )/x; # $2