Regex to find and fix LF lineEndings to CRLF

Question

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I mostly work in .NET stack, where we want (almost) all our files to be CRLF.

In my opinion, git should never be editing the contents of a file, so my and my projects' and my colleagues' git settings are autocrlf=false (i.e as-is, as-is), feel free to have that debate on some other question :)

Occasionally someone will have bad git settings, or in some other way accidentally introduce LFs into some files in the git repo, and I want to grep the whole repository for files with LF line-endings, and then fix them to be CRLFs, on a file-by-file basis (in case there are, e.g. bash files which should regrettably be LF).

Every time I need to do this, I can't find the relevant Regex and have to work it out from scratch again.

So this question exists to document the correct regex.

Answer 1

Regex to find any LF that is not part of a CRLF:

(?<!\r)\n

Regex to find any CR that is not part of a CRLF:

\r(?!\n)

Thus Regex to find any non-CRLF lineEnding:

((?<!\r)\n|\r(?!\n))

You can simply replace that with \r\n to fix them all to be CRLFs.

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This is using the "Negative Lookbehind" functionality:

(?<\!a)b matches a "b" that was not preceded by an "a".

and the "Negative Lookahead" functionality:

a(?\!b) matches an "a" that is not followed by a "b".

Further documentation here: https://www.regular-expressions.info/lookaround.html