Simple tool to 'accept theirs' or 'accept mine' on a whole file using git

I don't want a visual merge tool, and I also don't want to have to vi the conflicted file and manually choose the between HEAD (mine) and the imported change (theirs). Most of the time I either want all of their changes or all of mine. Commonly this is because my change made it upsteam and is coming back to me through a pull, but may be slightly modified in various places.

Is there a command line tool which will get rid of the conflict markers and choose all one way or another based on my choice? Or a set of git commands which I can alias myself to do each one.

# accept mine
alias am="some_sequence;of;commands"
alias at="some_other_sequence;of;commands"

Doing this is rather annoying. For 'accept mine' I have tried:

randy@sabotage ~/linus $ git merge test-branch
Auto-merging Makefile
CONFLICT (content): Merge conflict in Makefile
Automatic merge failed; fix conflicts and then commit the result.

randy@sabotage ~/linus $ git checkout Makefile 
error: path 'Makefile' is unmerged

andy@sabotage ~/linus $ git reset --hard HEAD Makefile 
fatal: Cannot do hard reset with paths.

How am I supposed to get rid of these change markers?

I can do:

git reset HEAD Makefile; rm Makefile; git checkout Makefile

But this seems rather round about, there must be a better way. And at this point, I'm not sure if git even thinks the merge happened, so I don't think this necessarily even works.

Going the other way, doing 'accept theirs' is equally messy. The only way I can figure it out is do:

git show test-branch:Makefile > Makefile; git add Makefile;

This also gives me a messed up commit message, which has Conflicts: Makefile in it twice.

Can someone please point out how to do the above two actions in a simpler way? Thanks

The solution is very simple. git checkout <filename> tries to check out file from the index, and therefore fails on merge.

What you need to do is (i.e. checkout a commit):

To checkout your own version you can use one of:

git checkout HEAD -- <filename>

or

git checkout --ours -- <filename>

(Warning!: If you are rebasing --ours and --theirs are swapped.)

or

git show :2:<filename> > <filename> # (stage 2 is ours)

To checkout the other version you can use one of:

git checkout test-branch -- <filename>

or

git checkout --theirs -- <filename>

or

git show :3:<filename> > <filename> # (stage 3 is theirs)

You would also need to run 'add' to mark it as resolved:

git add <filename>

Try this:

To accept theirs changes: git merge --strategy-option theirs

To accept yours: git merge --strategy-option ours

Based on Jakub's answer you can configure the following git aliases for convenience:

accept-ours = "!f() { git checkout --ours -- \"${@:-.}\"; git add -u \"${@:-.}\"; }; f"
accept-theirs = "!f() { git checkout --theirs -- \"${@:-.}\"; git add -u \"${@:-.}\"; }; f"

They optionally take one or several paths of files to resolve and default to resolving everything under the current directory if none are given.

Add them to the [alias] section of your ~/.gitconfig or run

git config --global alias.accept-ours '!f() { git checkout --ours -- "${@:-.}"; git add -u "${@:-.}"; }; f'
git config --global alias.accept-theirs '!f() { git checkout --theirs -- "${@:-.}"; git add -u "${@:-.}"; }; f'