How do I create a dynamic capturing group in regex?

Question

I have a string like this:

$str ="
- group1
- group2
- group3
";

Also I have this regex:

/(\-\s\w+)\n(\-\s\w+)\n(\-\s\w+)/

As you know, there is three capturing groups: $1, $2 and $3. I made those group manually. I mean if I append this to the string above:

- group4 
- group5

Then that regex doesn't matches them.

Well, I have a constant pattern: (\-\s\w+), And I want to create a separated capturing group on the number of matches items in the string. Hare is a few examples:

Example1:

$str="
- group 1
";

I need a regex to give me all the string by $1.

Example2:

$str="
- group 1
- group 2
";

I need a regex to give me first line of string (- group 1) by $1 and second line (- group 2) by $2

Ok well, as you see in the examples above, string is dynamic but it is according to a constant pattern ... Now I want to know how can I create a dynamic capturing group according to the string?

Why capture groups? `preg_match_all('/- .*/', $str, $matches);` — AbraCadaver, Feb 19 '16 at 18:48
Once in a while this question pops up. There is no stack for each capture group in PHP PCRE regex. Use multiple matching as shown above. There are always ways to work around this limitation. — Wiktor Stribiżew, Feb 19 '16 at 18:51
@AbraCadaver Yeah ... `:-)` However using `preg_match_all()` would be useful greatly ..! I will work on it. tnx — Shafizadeh, Feb 19 '16 at 18:52
@AbraCadaver All I can express as a example is [this comment](http://stackoverflow.com/questions/35505957/regex-match-double-curly-braces-nested/35506502#comment-58715130) — Shafizadeh, Feb 19 '16 at 19:00
If you want an answer, please define the requirements. I guess the first part should appear at least once. Then, what should be replaced with what? The first part should be put into `[ ]` and each part should be separated with a comma ("replace" the newlines with `,`)? — Wiktor Stribiżew, Feb 19 '16 at 19:42
See if [this demo would be of any help](https://eval.in/522045). — bobble bubble, Feb 19 '16 at 21:52

score 3 · Accepted Answer · edited May 23 '17 at 12:31

The impossibility to capture repeating groups is a well known limitation.

If you know the max repeating pattern, you can set your regex as (i.e. max=5):

/(\-\s\w+)\n(\-\s\w+)?\n?(\-\s\w+)?\n?(\-\s\w+)?\n?(\-\s\w+)?\n?/

and you will find from one to five matches in the groups from 1 to 5.
Substantially, you have to repeat (\-\s\w+)?\n? for the max possible number of repeating pattern.

Otherwise, if your max possible number is undefined, I don't know other way than construct a dynamic pattern, as:

$regex = '(\-\s\w+)\n';
$regex = '/'.( str_repeat( $regex, preg_match_all( "/$regex/", $str, $matches ) ) ).'/';

The above pattern will works, but I don't know your exactly replace condition, so it can be unusable for your purpose.

Very nice idea this `str_repeat` with return value of `preg_match_all` (not knowing, what OP actually exactly wants to achieve). [Played around with it a bit](https://eval.in/522066) :) — bobble bubble, Feb 19 '16 at 22:10

score 2 · Answer 2 · edited Feb 19 '16 at 19:42

2

Using the m-modifier (multi-line): that will let the match on each line.

Try using below regex:

 preg_match_all('/(\-\s\w+)/m', $str, $matches);
 print_r($matches);

edited Feb 19 '16 at 19:42

fusion3k

11,568
4
25
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answered Feb 19 '16 at 19:00

Sandeep

51
3

Good answer, but missing a `'`. – elixenide Feb 19 '16 at 19:04
Good but not helpful. Read the comments to understand what OP wants to do. – Wiktor Stribiżew Feb 19 '16 at 19:08

How do I create a dynamic capturing group in regex?

2 Answers2