How to get all captures of subgroup matches with preg_match_all()?
- by hakre
Update/Note:
I think what I'm probably looking for is to get the captures of a group in PHP.
Referenced: PCRE regular expressions using named pattern subroutines.
(Read carefully:)
I have a string that contains a variable number of segments (simplified):
$subject = 'AA BB DD '; // could be 'AA BB DD CC EE ' as well
I would like now to match the segments and return them via the matches array:
$pattern = '/^(([a-z]+) )+$/i';
$result = preg_match_all($pattern, $subject, $matches);
This will only return the last match for the capture group 2: DD.
Is there a way that I can retrieve all subpattern captures (AA, BB, DD) with one regex execution? Isn't preg_match_all suitable for this?
This question is a generalization.
Both the $subject and $pattern are simplified. Naturally with such the general list of AA, BB, .. is much more easy to extract with other functions (e.g. explode) or with a variation of the $pattern.
But I'm specifically asking how to return all of the subgroup matches with the preg_...-family of functions.
For a real life case imagine you have multiple (nested) level of a variant amount of subpattern matches.
Example
This is an example in pseudo code to describe a bit of the background. Imagine the following:
Regular definitions of tokens:
CHARS := [a-z]+
PUNCT := [.,!?]
WS := [ ]
$subject get's tokenized based on these. The tokenization is stored inside an array of tokens (type, offset, ...).
That array is then transformed into a string, containing one character per token:
CHARS -> "c"
PUNCT -> "p"
WS -> "s"
So that it's now possible to run regular expressions based on tokens (and not character classes etc.) on the token stream string index. E.g.
regex: (cs)?cp
to express one or more group of chars followed by a punctuation.
As I now can express self-defined tokens as regex, the next step was to build the grammar. This is only an example, this is sort of ABNF style:
words = word | (word space)+ word
word = CHARS+
space = WS
punctuation = PUNCT
If I now compile the grammar for words into a (token) regex I would like to have naturally all subgroup matches of each word.
words = (CHARS+) | ( (CHARS+) WS )+ (CHARS+) # words resolved to tokens
words = (c+)|((c+)s)+c+ # words resolved to regex
I could code until this point. Then I ran into the problem that the sub-group matches did only contain their last match.
So I have the option to either create an automata for the grammar on my own (which I would like to prevent to keep the grammar expressions generic) or to somewhat make preg_match working for me somehow so I can spare that.
That's basically all. Probably now it's understandable why I simplified the question.
Related:
pcrepattern man page
Get repeated matches with preg_match_all()
