Regex for stripping specific characters from string

Question

Please consider the following examples.

The next line is **

_This line surrounded with emphasis mark_

`hey this is crazy`

**bold**

Now, I want to figure out a regex that identifies the special characters. Basically I want to use string.replaceAll(regex,"")so that I can replace only these special characters **,_,` from the string. Consider each line to be 1 string.

I can identify that each special character is preceded by either space or a new line, followed by the a string, followed by the special character I am trying to remove.

Also please explain the regex.

@WiktorStribiżew Currently, the regex that I thought is like this. `^(\\s|\\n)(\\**|_|`) ` — Nayanjyoti Deka, May 22 '16 at 14:30
Possible duplicate of [Learning Regular Expressions](http://stackoverflow.com/questions/4736/learning-regular-expressions) — Biffen, May 22 '16 at 14:32
Well, sorry, it is either rather broad or unclear. Removing symbols is as easy as using `.replaceAll("[_*\`]+","")`. BTW, `\s` matches `\n`. — Wiktor Stribiżew, May 22 '16 at 14:36
@WiktorStribiżew I want to replace only when it is preceded by space/new line. Basically not when it is part of an word. eg. `unicode_snob` Now with the above regex, it will replace the underscore here as well. — Nayanjyoti Deka, May 22 '16 at 14:40
Like `.replaceAll("(?<!\\S)[_*\`]++|[_*\`]++(?!\\S)","")`? See, without exact requirements it is difficult to help. — Wiktor Stribiżew, May 22 '16 at 14:41
@WiktorStribiżew slightly closer, also the regex has to replace only when there are 2 asterisk and not one. the string might have 1 asterisk which is valid case. also i think this won't remove the trailing special characters. Or maybe need to do another regex pass to remove trailing ones? — Nayanjyoti Deka, May 22 '16 at 14:45
Ok, I can only suggest `"(?<!\\S)(\\*{2}|[_\`])|(\\*{2}|[_\`])(?!\\S)"`. — Wiktor Stribiżew, May 22 '16 at 14:47
@WiktorStribiżew Bingo!!! Thanks a lot!! Could you please explain as well how you figured it ? `(?<!\\S)` this looks for space at beginning. `(\\*{2}|[_`])` this is where you say asterisk to be twice and underscore and tilde char. I am unable to understand why this `|(\\*{2}|[_`])` after that? The last `(?!\\S)` is again for space i believe. Could you please explain to me how it works? That would be really helpful. — Nayanjyoti Deka, May 22 '16 at 14:52

score 1 · Accepted Answer · answered May 22 '16 at 14:56

You may use

"(?<!\\S)(\\*{2}|[_`])|(\\*{2}|[_`])(?!\\S)"

See the regex demo

The regex matches any **, or _ or ` (with (\*{2}|[_`])) NOT preceded with a non-whitespace symbol (see (?<!\\S)), or any **, _, or ` that is not followed by a non-whitespace symbol.

Regex for stripping specific characters from string

1 Answers1