Merging only certain changes from one git branch to another

Question

Say I have a git repository with two branches - main and custom . Say that I'm working in custom and I make two changes to the file print.php :

/* begin custom only change */
echo "I'm only printed in the custom branch version";
/* end custom only change */

echo "I want this printed in both branches";

Say also that meanwhile, I've pulled a new main branch copy, and it has the following change to print.php :

echo "This should also be printed in both branches";

What should I do -- either with the command-line or with a git program like Tower (or even suggestions for making a custom script) -- in order to have the following resulting files?

print.php in main branch

...
echo "I want this printed in both branches";
echo "This should also be printed in both branches";
...

print.php in custom branch

...
/* begin custom only change */
echo "I'm only printed in the custom branch version";
/* end custom only change */

echo "I want this printed in both branches";
echo "This should also be printed in both branches";
...

Obviously the order of the echo "I want this..." and echo "This should also..." is not something that Git can figure out, so there's going to be some manual decision-making here. But I want to know how to do it in the most "Git" way possible and involving the least number of error messages from a program like Tower.

Answer 1

So the way I understand it, you have 2 changes in custom , only one of which needs to be merged into main , and one change in main that needs to be merged into custom . You can solve your issue this way:

• rewind custom to before the 2 changes
• add the one change to custom that you will want to merge into main
• stash the second change
• merge the one commit from custom into main , resolving merge conflicts
• merge the changes from main into custom
• pop the stashed change in custom , and commit it

If you've already committed the 2 changes in custom, you'll need to first do git reset --soft [hash-of-the-commit-before-new-changes] (you can find the hash for the correct commit with git log ). Otherwise, just proceed as below.

You can do line by line commits in interactive git add mode:

git add -p print.php

In this mode, stage this change first, by itself:

echo "I want this printed in both branches";

(Once in interactive mode, if you hit "s" git will attempt to split commit hunks into smaller hunks for you. "y" will stage a hunk for commit, "n" will skip it. If "s" doesn't work it's magic, hit "e" and manually edit the hunk. More info )

Once that's staged,

git commit
git stash            # stash unstaged, uncommitted change in custom for later

Then,

git checkout main    # get in main branch
git merge custom     # merge custom, you'll probably get a merge conflict

If/when you get a merge conflict:

git mergetool

I am able to tell git to keep lines from both versions of the file and choose either left or right to appear first in the file.

git commit           # commit this change to main
git checkout custom  # get in custom branch
git merge main       # merge main

Then,

git stash pop        # pop that other change to custom out of the stash
git add print.php    # stage it for commit
git commit           # commit that second change to custom

It's ugly... but it works.

Answer 2

You could do a

git checkout -p master -- print.php

from you custom branch and you can patch certain parts of your file.

Read more..

Answer 3

If I understand your question correctly, you should be able to simply do:

git checkout custom
git merge master

This actually creates an automatic merge. I made a repo (with one minor typo) at https://gist.github.com/jordansamuels/8cb8ade97fdaf232d26c .