Change file name case using git filter-branch

Question

I've got a git repo where some files differ in name by case only across branches. As a simplified example, in master, there's a file `alpha/beta/foo.cpp` and in branch `bar`, there's a `file alpha/beta/Foo.cpp`. The problem is that when I attempt to switch branches, git won't allow me to do it. There's an error that I don't have handy at the moment, but it basically looks like changes to file alpha/beta/Foo.cpp would be overwritten -- aborting even though a subsequent `git status` shows the working directory is clean. Since this repo is not yet shared (it's actually a mirror of a large Perforce depot that I'm working on migrating), I see no problem with using `git filter-branch` to rewrite the history, but when I do so, any case-sensitive changes I make are lost. When I use ``` git filter-branch -f -d /tmp/tmpfs/filter-it \ --tree-filter path/to/script \ --tag-name-filter cat --prune-empty -- --all ``` with the script looking like this ``` #!/bin/bash if [ -e alpha/beta/foo.cpp ] ; th…

Accepted Answer

The Short Answer

The following solution was modified from multiple sources:

filter-branch --index-filter always failing with "fatal: bad source".

Renaming The Past With Git.

Here is a filter-branch invocation that uses an index-filter to rewrite the commits without a working copy, so it should run really fast. Note that, as an example, I'm renaming the file `alpha/beta/foo.cpp` to `alpha/beta/Foo.cpp`.

As with any potentially destructive Git operation, it is highly recommended that you make a backup clone of your repo before you use this:

```
git filter-branch --index-filter '
git ls-files --stage | \
sed "s:alpha/beta/foo.cpp:alpha/beta/Foo.cpp:" | \
GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
git update-index --index-info && \
mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"
' HEAD
```

Note that `HEAD` is optional, because it should be the default for `filter-branch`. It will rewrite all commits from the root commit to the commit pointed to by HEAD. If you want to increase the speed of the filter-branch even more, you can pass a range of commits instead of `HEAD`, such as

```
HEAD~20..HEAD
```

to rewrite just the last 20 commits. The beginning of the range is exclusive, i.e. it's not rewritten, only its children are, and the ending `HEAD` is again optional, since its a default.

Verification

It's a good idea to do some quick sanity-checks to verify that the filter-branch did what you expected it to do. First, compare the current history with the previous history:

```
git diff --name-status refs/original/refs/heads/master
D       foo.cpp
A       Foo.cpp
```

Notice that when the previous history is compared relative to the current one, the current history no longer has `foo.cpp` (it's deleted), while `Foo.cpp` was added to it.

Now confirm that `foo.cpp` contains the exact same content as `Foo.cpp`:

```
git diff refs/original/refs/heads/master:foo.cpp Foo.cpp
```

The output should be empty, meaning that there are no differences between the two versions.

Detailed Explanation

The following breakdown is also available in more detail from the blog post "Renaming The Past With Git". I am summarizing it here. The basic idea of the script is to create a new index file that contains the new name for the file `foo` (i.e. `foo` becomes `Foo`), and then replace the old index with the new one.

Step 1: Get the Index File Contents

First, the current index file contents are output in a form that can then be fed into `git update-index`, using the `--stage` option:

```
git ls-files --stage
100644 195ff081f7d0d37a60181de790ae1c6b9f177be8 0       alpha/beta/foo.cpp
100644 0504de8997941bf10bcfb5af9a0bf472d6c061d3 0       LICENSE
100644 6293167f0eb7389b2f6f6b73e838d3a547787cbf 0       README.md
...etc...
```

Step 2: Rename the File

Since we want to rename `foo.cpp` to `Foo.cpp`, we use `sed` with a regular expression to replace the string `foo` with `Foo`:

```
"s:alpha/beta/foo.cpp:alpha/beta/Foo.cpp:"
```

In the above command, I'm using a colon `:` to delimit the regexes in the `sed` command, but you can use other characters as delimiters too, such as pipe `|`. I chose a colon instead of the more standard forward-slash `/` as a delimeter so that it wasn't necessary to escape the forward-slashes used in the file paths.

After piping `git ls-files --stage` through `sed`, you should get the following:

```
git ls-files --stage | sed "s:alpha/beta/foo.cpp:alpha/beta/Foo.cpp:"
100644 195ff081f7d0d37a60181de790ae1c6b9f177be8 0       alpha/beta/Foo.cpp
100644 0504de8997941bf10bcfb5af9a0bf472d6c061d3 0       LICENSE
100644 6293167f0eb7389b2f6f6b73e838d3a547787cbf 0       README.md
...etc...
```

Step 3: Create a New Index with the Renamed File

Now the modified output of `git ls-files --stage` can be piped into `git update-index --index-info` to rename the file in the index. Because we want to create an entirely new index to replace the old one, some environment variables for the path to the index file need to be set first, before invoking the `git update-index` command:

```
GIT_INDEX_FILE=$GIT_INDEX_FILE.new git update-index --index-info
```

Step 4: Replace the Old Index

Now we just replace the old index with the new one, which effectively "renames" the file:

```
mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"
```

Summary

Here's the whole command again, when everything is put together:

```
git filter-branch --index-filter '
git ls-files --stage | \
sed "s:alpha/beta/foo.cpp:alpha/beta/Foo.cpp:" | \
GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
git update-index --index-info && \
mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"
' HEAD
```

Documentation

`git filter-branch`.

`git ls-files`.

`git update-index`.

Git environment variables.

Change file name case using git filter-branch

Solution

Problem

Related problems