使用 REGEX 'Lookbehind' 作为可选将长字符串拆分为块

Question

I'm working on a regex that lets me split into chunks a long text that could have #variables# inside. The rules to do the splitting basically are:

1. Split by each #photo# or #childphoto# variable and look behind or ahead for text to don't cut the sentence.
2. Each chunk should have only one #photo# or #childphoto# variable, or not have any of these variables
3. Also, the chunk should be less than 350 characters
4. The chunk should not have to cut words or sentences
5. The chunk should not have to cut any of the possible text variables into the text #anyOtherVariables#

Currently, I have this Regex

/^.*[\S\s]{0,350}[\s\S](?<=(#photo#|#childphoto#)).*/

That currently is working with the .match() JavaScript method to extract the chunks of text that have the variables using the 'look behind' approach, but is not working with the other chunks that do not match the 'look behind' condition, is there a way to include the other parts?

There are the regexp and the study test case. https://regex101.com/r/kdKHkQ/1

I will really appreciate any help with that.

Answer 1

Here is a single JavaScript regex that does what you have specified:

^\\b(?=([^]*))[^]{0,350}$(?<=(?![^]{1,}\\1$)(?:#(photo|childphoto)#)?[^]*?)(?<!(?=\\1$)(?:[^]*?#(photo|childphoto)#){2}[^]*?)

Demo on regex101

It enforces the 350 character limit by taking a snapshot (using lookahead) at the beginning, consuming and capturing up to 350 characters, and then using a lookbehind to look no further back than the snapshotted beginning, to assert that one of the variables in question is inside the just-captured string. Then it uses a negative lookbehind to enforce that there are not two or more of the variables in question in the just-captured string.

I did not understand your rule "The chunk should not have to cut any of the possible text variables into the text #anyOtherVariables#". If by that you mean that the lines containing variables other than #photo# or #childphoto# should be skipped over (not matched), then this regex does not do that, but it could be easily modified to do so.

Now, practically speaking, it would probably be better to implement this in code, or a combination of code and regex, but this demonstrates that exactly what you asked is possible with a pure regex.

I would like to point out that calling this "splitting by each #photo# or #childphoto# variable" is disingenous, and if I actually took that literally, it would be breaking your other rule, that the chunk should not cut sentences. That is probably why you got downvoted.

I'm posting my answer here, despite the fact that you got downvoted, because I already answered this on reddit and you disappeared without commenting.