如何检测没有其他换行符的换行符？

Question

Here is my patter :

/\r\n|\r|\n/

And will be replaced with \\n\\n . All I'm trying to do is replacing all single-newlines with double-newlines.

So the input:

something
something else

The expected result:

something

something else

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The problem is, I want to avoid matching new-lines that are followed by another (or more) new lines. So I want to just select the single-newlines. So this shouldn't have any matches:

something

something else

Any idea how can I do that?

Answer 1

Use ([^\\r\\n])\\n([^\\r\\n]) and replace it with $1\\n\\n$2 . This means

( = start group 1

[^ = start negated set (NOT)

\\n\\r = the characters not to match

] = end negated set

) = end set 1

\\n = match newline

Set 2 is a repeat of set 1.

---

Replaces with

$1 = first set

\\n\\n = your characters

$2 = second set

Answer 2

Use regex ([^\\r\\n])[\\r\\n](?![\\r\\n]+) and replace with $1\\n\\n . It uses a capture group to capture the symbol in front of newline that is not newline itself, and a negative lookahead that makes sure that newline is not followed by another newline without capturing the next symbol.

Unfortunately, JS currently doesn't fully support negative lookbehind (it was accepted in ECMAScript 2018), otherwise it could be possible to use (?<![\\r\\n])[\\r\\n](?![\\r\\n]) – no capture groups at all, so replacing string would be just \\n\\n .