1. As we need to modify a file when rewriting the history of this repository, we'll use the tree-filter option to filter the branch. The .credentials file looks as follows:

username = foobar
password = verysecret 

2. All we need to do is remove everything after the equals sign on each line of the file. We can use the following sed command to do this:

sed -i '' -e 's/^(.*=).*$/1/' 

3. We can now run the filter branch with the following command:

$ git filter-branch --prune-empty  --tree-filter "test -f .credentials && sed -i '' -e 's/^(.*=).*$/1/' .credentials || true" -- --all 

4. If we look at the file now, we can see that the username and password are gone:

$ cat .credentials 
username = 
password = 

5. As we saw in the previous example, we still need to clean up after  filter-branch, by deleting original references, expiring the reflog, and triggering garbage collection. But, at this point, you can compare the content and commit history of the repository.