How to use git mergetool
to resolve conflicts
Skip to the relevant sections if needed.
Git conflicts
git mergetool
mergetool
simple code example for vimdiff
Git conflicts
For using mergetool
in git
, we need to understand the following terminology to understand what is being merged:
LOCAL
- the head
for the file(s) from the current branch on the machine that you are using.REMOTE
- the head
for files(s) from a remote location that you are trying to merge into your LOCAL
branch.BASE
- the common ancestor(s) of LOCAL
and BASE
.MERGED
- the tag / HEAD
object after the merge - this is saved as a new commit.Common mergetool
from editors will display both LOCAL
and REMOTE
so you can decide which changes to keep.
Please read this tutorial explaining the HEAD objects if you do not know what it is. It will help your understanding of Git tremendously.
git mergetool
We have to change the git config
to set a default mergetool.
In this example, we will use vimdiff
:
$ git config merge.tool vimdiff
We can also set the editor to display the common ancestor BASE
while we examine what changes are in LOCAL
and REMOTE
with the following setting:
$ git config merge.conflictstyle diff3
mergetool
editors are supported$ git mergetool --tool-help
And we list a few of them:
mergetool
editorsmergetool
editorsgvimdiff
- almost identical to vimdiff
but uses the Linux GUI for Vim
, please refer to vimdiff
if you still use the keyboard commands for GVim
.kdiff3
meld
tortoisemerge
Or consult the community of your favorite editor to see how to do the equivalent operations for your editor.
mergetool
settingsDo not prompt before launching the merge resolution tool
$ git config mergetool.prompt false
mergetool
simple code example$ mkdir galaxyZoo
$ cd galaxyZoo
$ git init
$ vim astrophy_obj.txt
Add some galaxy types into astrophy_obj.txt
then save the file.
# content of astrophy_obj.txt
spiral
ellipitcal
bar
irregular
save then commit the file.
$ git add astrophy_obj.txt
$ git commit -m 'Initial commit'
$ git branch astrophy_objects # create a new branch
$ git checkout astrophy_objects # change to new branch
$ vim astrophy_obj.txt # make changes to file
Change bar
to barred
in the file.
$ git commit -am 'changed bar to barred'
$ git checkout master # change back to master branch
$ vim astrophy_obj.txt
# add the word `galaxy` to the end of each line using Vim REGEX
# type `:%s/$/ galaxy/g` in Vim then press enter and save `:wq`
$ git commit -am 'added galaxy to each line'
# merge from the astrophy_objects branch to current branch, i.e. master
$ git merge astrophy_objects
Then you will see some error messages:
Auto-merging astrophy_obj.txt
CONFLICT (content): Merge conflict in astrophy_obj.txt
Automatic merge failed; fix conflicts and then commit the result.
We can bring up the mergetool
:
$ git mergetool
Then it will bring up the different versions of the file in different Vim splits
panels.
+--------------------------------+
| LOCAL | BASE | REMOTE |
+--------------------------------+
| MERGED |
+--------------------------------+
The top left split panel is the LOCAL
, top middle split is BASE
and top right split is REMOTE
.
The bottom split refers to the MERGED
version.
You can find this info in the bottom bar of each split (I have put 3 yellow rectangles to highlight that info).
As you can see form the below image, my Vim
has highlighted the differences in red for me.
Now if your terminal has any GUI capability and you have compiled Vim
correctly with GUI support, you can use your mouse to click on the bottom split to edit it.
Or if you are a Vim
ninja, you can use the keyboard shortcut to move to different splits.
Ctrl w + h # move to the split on the left
Ctrl w + j # move to the split below
Ctrl w + k # move to the split on top
Ctrl w + l # move to the split on the right
You can either incorporate the changes by manually editing the MERGED
split,
or use Vim
shortcuts pull from one of the LOCAL
, BASE
ad REMOTE
versions.
:diffg RE # get from REMOTE
:diffg BA # get from BASE
:diffg LO # get from LOCAL
save the changes then quit with :wqa
to close all the splits.
Remember to commit the merge.
$ git commit -am 'merged from several branches'
git pull
If you were trying to do a git pull
when you ran into merge
conflicts,
follow all steps in the previous section for using the mergetool
, then do:
$ git rebase –continue
This command will
Forward-port local commits to the updated upstream HEAD.
according to the documentation, meaning your local commits will be pushed to the upstream remote branch
as a new forward commit that doesn't interfere with previous commits.
Hooray now you can claim that you can collaborate with others with Git without messing up with your collaborators' commits.
vimdiff
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