newline - How line ending conversions work with git core.autocrlf between different operating systems

Question

I've read a lot of different questions and answers on Stack Overflow as well as git documentation on how the core.autocrlf setting works.

This is my understanding from what I've read:

Unix and Mac OSX (pre-OSX uses CR) clients use LF line endings.
Windows clients use CRLF line endings.

When core.autocrlf is set to true on the client, the git repository always stores files in LF line ending format and line endings in files on the client are converted back and forth on check out / commit for clients (i.e. Windows) that use non-LF line endings, no matter what format the line endings files are on the client (this disagrees with Tim Clem's definition - see update below).

Here is a matrix that tries to document the same for the 'input' and 'false' settings of core.autocrlf with question marks where I'm not sure of line ending conversion behavior.

My questions are:

1. What should the question marks be?
2. Is this matrix correct for the "non-question marks"?

I'll update the question marks from the answers as consensus appears to be formed.

                       core.autocrlf value
            true            input              false
----------------------------------------------------------
commit   |  convert           ?                  ?
new      |  to LF      (convert to LF?)   (no conversion?)

commit   |  convert to        ?                 no 
existing |  LF         (convert to LF?)     conversion

checkout |  convert to        ?                 no
existing |  CRLF       (no conversion?)     conversion

I'm not really looking for opinions on the pros and cons of the various settings. I'm just looking for data which makes it clear how to expect git to operate with each of the three settings.

--

Update 04/17/2012: After reading the article by Tim Clem linked by JJD in the comments, I have modified some of the values in the "unknown" values in the table above, as well as changing "checkout existing | true to convert to CRLF instead of convert to client". Here are the definitions he gives, which are more clear than anything I've seen elsewhere:

core.autocrlf = false

This is the default, but most people are encouraged to change this immediately. The result of using false is that Git doesn’t ever mess with line endings on your file. You can check in files with LF or CRLF or CR or some random mix of those three and Git does not care. This can make diffs harder to read and merges more difficult. Most people working in a Unix/Linux world use this value because they don’t have CRLF problems and they don’t need Git to be doing extra work whenever files are written to the object database or written out into the working directory.

core.autocrlf = true

This means that Git will process all text files and make sure that CRLF is replaced with LF when writing that file to the object database and turn all LF back into CRLF when writing out into the working directory. This is the recommended setting on Windows because it ensures that your repository can be used on other platforms while retaining CRLF in your working directory.

core.autocrlf = input

This means that Git will process all text files and make sure that CRLF is replaced with LF when writing that file to the object database. It will not, however, do the reverse. When you read files back out of the object database and write them into the working directory they will still have LFs to denote the end of line. This setting is generally used on Unix/Linux/OS X to prevent CRLFs from getting written into the repository. The idea being that if you pasted code from a web browser and accidentally got CRLFs into one of your files, Git would make sure they were replaced with LFs when you wrote to the object database.

Tim's article is excellent, the only thing I can think of that is missing is that he assumes the repository is in LF format, which is not necessarily true, especially for Windows only projects.

Comparing Tim's article to the highest voted answer to date by jmlane shows perfect agreement on the true and input settings and disagreement on the false setting.

Answer 1

The best explanation of how core.autocrlf works is found on the gitattributes man page, in the text attribute section.

This is how core.autocrlf appears to work currently (or at least since v1.7.2 from what I am aware):

• core.autocrlf = true

1. Text files checked-out from the repository that have only LF characters are normalized to CRLF in your working tree; files that contain CRLF in the repository will not be touched
2. Text files that have only LF characters in the repository, are normalized from CRLF to LF when committed back to the repository. Files that contain CRLF in the repository will be committed untouched.

• core.autocrlf = input

1. Text files checked-out from the repository will keep original EOL characters in your working tree.
2. Text files in your working tree with CRLF characters are normalized to LF when committed back to the repository.

• core.autocrlf = false

1. core.eol dictates EOL characters in the text files of your working tree.
2. core.eol = native by default, which means working tree EOLs will depend on where git is running: CRLF on a Windows machine, or LF in *nix.
3. Repository gitattributes settings determines EOL character normalization for commits to the repository (default is normalization to LF characters).

I've only just recently researched this issue and I also find the situation to be very convoluted. The core.eol setting definitely helped clarify how EOL characters are handled by git.