How to do git tricks

Find last commit where line existed

blame --reverse START

Comparing files

From https://stackoverflow.com/questions/8131135/git-how-to-diff-two-different-files-in-different-branches

git diff branch1:full/path/to/foo.txt branch2:full/path/to/foo-another.txt

How to link to such comparison view on github?

Compare and copy files from other branches

https://stackoverflow.com/questions/2364147/how-to-get-just-one-file-from-another-branch

Include branches from an unrelated repository

git remote add rep2-git url_to_unrelated_repository
git fetch rep2-git
git checkout remotes/rep2-git/branch2
git checkout -b rep2/branch2
git push -u origin rep2/branch2:rep2/branch2

The resulting repository has another unrelated history. There is no need for the two repositories to have a common initial commit or anything. The commit hashes are preserved. You can even git cherry-pick commit from the other repostory and git will do pretty good job finding files to apply the commits to, even if the files have somewhat different names and are in somewhat different locations in the file two file trees.

Using git cherry pick

Across unrelated histories

After importing branches from another unrelated repository as an unrelated history, git cherry pick can apply a commit from the unrelated history, but:

Sometimes git cherry-pick will work across files having different paths and sometimes just creates copies on new paths, which is not helpful. Not sure why. The same cherry-pick on different computers will do different things.
Be sure to do

git diff HEAD^

to review what changes are being made and to minimize them. git diff seems to produce misleading results.

Undesirable changes from other commits

Often git cherry pick will make more changes including those from other commits. That's why it is important to review carefully all changes to the file and edit as needed. Here is why: Git goes back in the history until the cherry pick source matches the target and creates the patch based on this revision. That's why more changes might appear ...

Patch

Instead of cherry-pick

alternatively one can use patch

git log -p -1 <sha1-of-your-commit>

then

git log -p -1 <sha1> | git apply --3way -

But this can pull more changes too. And without --3way it fails.

To modify only one file

Create a patch file for that individual file:

git show [commit hash] -- path/to/old/file > patchfile

Manually edit the newly created patchfile and replace all occurrences of the old path with the new path.
Apply the patch via

git apply --3way patchfile