`git checkout branch —.`，不覆盖现有文件

Question

Context

I have a repository containing the development history for an application. The application is compiled on the fly from its source code to be used right after the repository has been cloned.

The application uses a couple of configuration files, which are declined in several configuration archetypes. For ease of deployment, I would like to store each archetype on a separate branch, and obtain both the application from master and the configuration from the selected branch after cloning.

The plain solution would be to base the configuration branches on master , but this requires regularly rebasing them all when master advances. I'm therefore trying out a solution with two separate git histories:

• The master branch contains the application's source code;
• All config/<archetype> stem from a separate root (created through git checkout --orphan ), and only contain the build script and their respective configurations.

The build script must now retrieve all source code from master before building it, taking care not to overwrite the archetype configuration files with the default ones from master . Therefore...

Question

I need a variant of git checkout <branch> --. that does not touch existing files, whatever their state (changed, unchanged, ignored, untracked...).

Leads

I have found this identical question which does have an answer ( git archive mybranch | tar x --skip-old-files ), however I'm encountering some issues:

• I'm using Powershell on Windows, which apparently provide a native tar command that does not have --skip-old-files ;
• Git's version of tar accepts the flag, but fails due to what I assume is a quirk in how Powershell's pipeline works (the same command run from Git Bash works):

PS> &"C:\Program Files\Git\bin\git.exe" archive master | &"C:\Program Files\Git\usr\bin\tar.exe" x --skip-old-files
/usr/bin/tar: Malformed extended header: missing newline
/usr/bin/tar: Substituting `.' for empty member name
/usr/bin/tar: Substituting `.' for empty member name
/usr/bin/tar: Skipping to next header
/usr/bin/tar: Exiting with failure status due to previous errors

In this environment, I would much prefer a solution which only uses Git.

Answer 1

I am not sure this is exactly what you need but instead of a partial checkout you may want to use a merge , which is the standard way to resolve conflicting commits.

Considering that you are on an orphaned branch, you cannot use a simple git merge but you have to specify the option --allow-unrelated-histories . Since you want to script this, there cannot be any conflict: this should be straightforward with the right merging strategy, which could be ours given that you are in config/<archetype> . You also want your orphaned branch to remain untouched, still possible with --no-commit and a following git reset --hard HEAD . In the end, the merge command from config/<archetype> could be something like this (untested):

git merge --allow-unrelated-histories -s recursive -Xours --no-commit master

Answer 2

Personally, I'd favor the git archive... | tar -x --skip-old-files git archive... | tar -x --skip-old-files solution here, but consider the following:

• You're on some orphan branch B right now. You have some set of files occupying your working tree. You want these same files to appear in your working tree after extracting all the files that appear in the tip commit of master .

• Therefore, there are just two ways to achieve this:

  1. Extract files from master but don't touch any existing files: that's the solution that can be done with the pipe, which isn't working from PowerShell. You could also construct a rather fancy "list all files and directories in the top level of the commit; for each such name, test whether it exists here; if not; extract that name from the commit; done" loop. Or
  2. Save these files somewhere: copy or move them away, extract all files from master, then put these files back .

  Method 2 is relatively simple. It's easy to achieve in the absence of subdirectories. The presence of subdirectories makes both methods questionable: what if the working tree currently has a directory d and a file f , but the tip commit on master has a file named d and/or a directory named f ? What result would you like for this case? (The tar method says preserve whatever is here now so you'll end up saving d/* and f , which you can choose to do manually with method 2.)

Once you decide on what to do about directory/file conflicts—these are a hard case for git checkout too, by the way—you can write the rest in some scripting language to implement method 2. Use mktemp -d or equivalent to make a place to hide all the existing files for the duration of the git checkout .