Competing line change merge conflicts

To resolve a merge conflict caused by competing line changes, you must choose which changes to incorporate from the different branches in a new commit.

For example, if you and another person both edited the file styleguide.md on the same lines in different branches of the same Git repository, you'll get a merge conflict error when you try to merge these branches. You must resolve this merge conflict with a new commit before you can merge these branches.

1. Open Terminal.

2. Navigate into the local Git repository that has the merge conflict.

   cd REPOSITORY-NAME

3. Generate a list of the files affected by the merge conflict. In this example, the file styleguide.md has a merge conflict.

   $ git status
   > # On branch branch-b
   > # You have unmerged paths.
   > #   (fix conflicts and run "git commit")
   > #
   > # Unmerged paths:
   > #   (use "git add ..." to mark resolution)
   > #
   > # both modified:      styleguide.md
   > #
   > no changes added to commit (use "git add" and/or "git commit -a")

4. Open your favorite text editor, such as Atom, and navigate to the file that has merge conflicts. Atom is easy to use when merge confilit. It has "use me" prompt.

5. To see the beginning of the merge conflict in your file, search the file for the conflict marker <<<<<<<. When you open the file in your text editor, you'll see the changes from the HEAD or base branch after the line <<<<<<< HEAD. Next, you'll see =======, which divides your changes from the changes in the other branch, followed by >>>>>>> BRANCH-NAME. In this example, one person wrote "open an issue" in the base or HEAD branch and another person wrote "ask your question in IRC" in the compare branch or branch-a.

   If you have questions, please
   <<<<<<< HEAD
   open an issue
   =======
   ask your question in IRC.
   >>>>>>> branch-a
   

6. Decide if you want to keep only your branch's changes, keep only the other branch's changes, or make a brand new change, which may incorporate changes from both branches. Delete the conflict markers <<<<<<<, =======, >>>>>>> and make the changes you want in the final merge. In this example, both changes are incorporated into the final merge:

   If you have questions, please open an issue or ask in our IRC channel if it's more urgent.
   

7. Add or stage your changes.

   $ git add .

8. Commit your changes with a comment.

   $ git commit -m "Resolved merge conflict by incorporating both suggestions."

use git diff one file, use

git diff <revision> <path>

example: 

$ git diff 105eda3039f9d928cacf119f0faf59a1f136f12b  Part.1.E.1.entrance.ipynb

git diff <branch>:<dir>/<filename> <branch>:<div>/<filename> 

revision is diff current commit vision.

example:

$ git diff master:Part.1.E.1.entrance.ipynb study:Part.1.E.1.entrance.ipynb

More info please see below references.

references:

1. https://help.github.com/en/articles/resolving-a-merge-conflict-using-the-command-line

2. https://stackoverflow.com/questions/5586383/how-to-diff-one-file-to-an-arbitrary-version-in-git