How to re-merge a file in the git?

Question

I have 10 files which have conflicts when merging branches. I've resolved all conflicts of the 10 files(took long time). Unfortunately before the commit, I find out that one file has been merged wrong and need start again for this file. :(

in the Git, How to mark the file which has been merged unmerged, in other word, how to re-merge that one file?

Answer 1

git checkout -m <filename> 

This will remove it from the index, and revert back to a "conflicted" file that has all of the markers required to then do a merge.

From the git help checkout man page:

-m, --merge     When switching branches, if you have local modifications to     one or more files that are different between the current     branch and the branch to which you are switching, the command     refuses to switch branches in order to preserve your     modifications in context. However, with this option, a     three-way merge between the current branch, your working tree     contents, and the new branch is done, and you will be on the     new branch.      When a merge conflict happens, the index entries for     conflicting paths are left unmerged, and you need to resolve     the conflicts and mark the resolved paths with git add (or git     rm if the merge should result in deletion of the path).      When checking out paths from the index, this option lets you     recreate the conflicted merge in the specified paths. 

(The last sentence is the most important one).

Here is a blog post that describes why it was added and how it is not possible with older versions of git: http://gitster.livejournal.com/43665.html