git replacing LF with CRLF

Running git on a Windows XP machine, using bash. I exported my project from SVN, and then cloned a bare repository.

I then pasted the export into the bare repositories directory, and did a:

git add -A

I then got a list of messages saying:

LF will be replaced by CRLF

What are the ramifications of this conversion? This is a .NET solution in Visual Studio.

These messages are due to incorrect default value of core.autocrlf on Windows.

The concept of autocrlf is to handle line endings conversions transparently. And it does!

Bad news: value needs to be configured manually.
Good news: it should only be done ONE time per git installation (per project setting is also possible).

How autocrlf works:

core.autocrlf=true:      core.autocrlf=input:     core.autocrlf=false:
                                             
        repo                     repo                     repo
      ^      V                 ^      V                 ^      V
     /        \               /        \               /        \
crlf->lf    lf->crlf     crlf->lf       \             /          \      
   /            \           /            \           /            \

Here crlf = win-style end-of-line marker, lf = unix-style (and mac osx).

(pre-osx cr in not affected for any of three options above)

When does this warning show up (under Windows)

    – autocrlf = true if you have unix-style lf in one of your files (= RARELY),
    – autocrlf = input if you have win-style crlf in one of your files (= almost ALWAYS),
    – autocrlf = false – NEVER!

What does this warning mean

The warning "LF will be replaced by CRLF" says that you (having autocrlf=true) will lose your unix-style LF after commit-checkout cycle (it will be replaced by windows-style CRLF). Git doesn't expect you to use unix-style LF under windows.

The warning "CRLF will be replaced by LF" says that you (having autocrlf=input) will lose your windows-style CRLF after a commit-checkout cycle (it will be replaced by unix-style LF). Don't use input under windows.

Yet another way to show how autocrlf works

1) true:             x -> LF -> CRLF
2) input:            x -> LF -> LF
3) false:            x -> x -> x

where x is either CRLF (windows-style) or LF (unix-style) and arrows stand for

file to commit -> repository -> checked out file

How to fix

Default value for core.autocrlf is selected during git installation and stored in system-wide gitconfig (%ProgramFiles(x86)%\git\etc\gitconfig on windows, /etc/gitconfig on linux). Also there're (cascading in the following order):

   – "global" (per-user) gitconfig located at ~/.gitconfig, yet another
   – "global" (per-user) gitconfig at $XDG_CONFIG_HOME/git/config or $HOME/.config/git/config and
   – "local" (per-repo) gitconfig at .git/config in the working dir.

So, write git config core.autocrlf in the working dir to check the currently used value and

   – git config --system core.autocrlf false            # per-system solution
   – git config --global core.autocrlf false            # per-user solution
   – git config --local core.autocrlf false              # per-project solution

Warnings
– git config settings can be overridden by gitattributes settings.
– crlf -> lf conversion only happens when adding new files, crlf files already existing in the repo aren't affected.

Moral (for Windows):
    - use core.autocrlf = true if you plan to use this project under Unix as well (and unwilling to configure your editor/IDE to use unix line endings),
    - use core.autocrlf = false if you plan to use this project under Windows only (or you have configured your editor/IDE to use unix line endings),
    - never use core.autocrlf = input unless you have a good reason to (eg if you're using unix utilities under windows or if you run into makefiles issues),

PS What to choose when installing git for Windows?
If you're not going to use any of your projects under Unix, don't agree with the default first option. Choose the third one (Checkout as-is, commit as-is). You won't see this message. Ever.

PPS My personal preference is configuring the editor/IDE to use Unix-style endings, and setting core.autocrlf to false.

Git has three modes of how it treats line endings:

$ git config core.autocrlf
# that command will print "true" or "false" or "input"

You can set the mode to use by adding an additional parameter of true or false to the above command line.

If core.autocrlf is set to true, that means that any time you add a file to the git repo that git thinks is a text file, it will turn all CRLF line endings to just LF before it stores it in the commit. Whenever you git checkout something, all text files automatically will have their LF line endings converted to CRLF endings. This allows development of a project across platforms that use different line-ending styles without commits being very noisy because each editor changes the line ending style as the line ending style is always consistently LF.

The side-effect of this convenient conversion, and this is what the warning you're seeing is about, is that if a text file you authored originally had LF endings instead of CRLF, it will be stored with LF as usual, but when checked out later it will have CRLF endings. For normal text files this is usually just fine. The warning is a "for your information" in this case, but in case git incorrectly assesses a binary file to be a text file, it is an important warning because git would then be corrupting your binary file.

If core.autocrlf is set to false, no line-ending conversion is ever performed, so text files are checked in as-is. This usually works ok, as long as all your developers are either on Linux or all on Windows. But in my experience I still tend to get text files with mixed line endings that end up causing problems.

My personal preference is to leave the setting turned ON, as a Windows developer.

See http://kernel.org/pub/software/scm/git/docs/git-config.html for updated info that includes the "input" value.