I want a regex pattern to grab text within a pattern that excludes matches followed by a particular string

Question

I'm using preg_match_all() like this:

preg_match_all('/("user":"(.*?)".*?-->)/', $input_lines, $output_array);

On a string, the idea is that I want it to get whatever comes after "user" in a commented out block (it's a long story). So let's say $input_lines is something like:

<!-- block {"user":"josh-hart", 1234566 ,"hide":false} /-->
<!-- block {"user":"jalen-brunson", 7744633 ,"hide":true} /-->
<!-- block {"user":"julius-randle", 333333,"hide":false} /-->
<!-- block {"user":"obi-toppin", 4hh3n33n33n, /-->
<!-- block {"user":"rj-barrett", nmremxxx!! ,"hide":true} /-->
<!-- block {"user":"mitch-robinson",yahaoao /-->

I want it to match the user. But here's the the thing, I only want the user if "hide":true does not appear before the /-->. So for this string I would want the matches to be:

josh-hart, julius-randle, obi-toppin, mitch-robinson

What is this called in regex terms and how do i do it?

The term you are looking for is "lookahead", https://www.regular-expressions.info/lookaround.html — CBroe, Jun 21 '23 at 06:14
Here's an example: [`"user":"([^"]*?)"(?!(?:(?!\/-->).)*"hide"\s*:\s*true)`](https://regex101.com/r/BuF2Dk/1) — Hao Wu, Jun 21 '23 at 06:52
You can also use [`(*SKIP)(*F)`](https://stackoverflow.com/questions/24534782/how-do-skip-or-f-work-on-regex) to skip something. Further [`\K` to reset](http://www.rexegg.com/regex-php.html#K) Something like e.g. [`"user":"\K[^"]+(?:[^>]*?"hide":true(*SKIP)(*F))?`](https://regex101.com/r/Q0wGeS/1) might suffice for your data. — bobble bubble, Jun 21 '23 at 07:58

Mustofa Rizwan · Answer 1 · 2023-06-21T08:49:15.227

2

You may try that:

user":"([^"]+)"(?!.*"hide":true(?=.*\/-->))

Explanation:

user":"([^"]+)" - after matching user":" it looks for characters inside " until it reaches a ".
() ensures 1st capture group.
(?!.*"hide":true negative lookahead to figure there is no "hide":true after that.
(?=.*\/-->) positive lookahead to ensure that /--> is not preceded by "hide":true

Demo

edited Jun 21 '23 at 08:49

answered Jun 21 '23 at 08:27

Mustofa Rizwan

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score 2 · Answer 2 · answered Jun 21 '23 at 08:48

As suggested by @bobblebubble, you can use the (*SKIP)(*FAIL) combo to skip whatever you don't want to match:

^                     # Match at the start of a line
.*                    # anything
"hide"\s*:\s*true     # followed by '"hide":true'
.*                    # then anything until the end of the line
                      # (i.e. a line that contains '"hide":true')
(*SKIP)(*FAIL)        # which we tell the engine to skip entirely
|                     # or
"user"\s*:\s*"\K      # '"user":"', which we forfeit,
[^"]+                 # followed by 1 or more non-quote characters.

Try it on regex101.com.

score 2 · Accepted Answer · answered Jun 21 '23 at 10:43

Assuming that opening and closing a comment is from  and there is no other use of these in between, you can first get the matches out of the way that contain  without crossing the opening or closing of a comment.

Then you can get a single match of the username, still in between the comment markers and independent of the order of appearance.

<!--(?:(?!-->|"hide":).)*+"hide":true\b(?:(?!-->).)*/-->(*SKIP)(*F)|<!--(?:(?!-->|"user":).)*"user":"\K[^"]+(?="(?:(?!-->).)*-->)

The pattern matches:

<!-- Match literaly
(?:(?!-->|"hide":).)*+ Optionally repeat matching any character not directly followed by either --> or "hide": using a Tempered greedy token
"hide":true\b Match "hide":true followed by a word boundary to prevent a partial word match
(?:(?!-->).)*/--> Match until the closing -->
(*SKIP)(*F) Skip the current match
| Or
<!-- Match literally
(?:(?!-->|"user").)* Optionally repeat matching any character not directly followed by either --> or "user:
"user":"\K Match "user":" and forget what is matched so far
[^"]+ Match 1+ chars other than " (the username that you want to match)
(?="(?:(?!-->).)*-->) Assert --> to the right

Note that you can make the matching of the username more specific, as for now it matches 1 or more characters other than a double quote with [^"]+ which can also be a space or a newline. If you want to match only non whitespace characters except for a double quote, than you can change it to [^\s"]+

See a regex demo.

I want a regex pattern to grab text within a pattern that excludes matches followed by a particular string

3 Answers3