http://jasonrudolph.com/blog/2009/02/25/git-tip-how-to-merge-specific-files-from-another-branch/

00. Git Help

Git Useful Commands

01. Git Typical Commands

## force checkout a new branch and discard non-committed changes on current branch
$ git checkout -f 

## discard any changes on current branch and reset it to the latest version/head on local repo
$ git reset --hard

## merge current branch with another / master branch
$ git merge origin/master [-- no-commit]

## remove all untracked files in current branch
$ git clean -fd

Git Merge Files From Another Branch

git checkout source_branch <paths>...

$ git branch
* master
  twitter_integration
$ git checkout twitter_integration app/models/avatar.rb db/migrate/20090223104419_create_avatars.rb test/unit/models/avatar_test.rb test/functional/models/avatar_test.rb
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   app/models/avatar.rb
#   new file:   db/migrate/20090223104419_create_avatars.rb
#   new file:   test/functional/models/avatar_test.rb
#   new file:   test/unit/models/avatar_test.rb
#
$ git commit -m "'Merge' avatar code from 'twitter_integration' branch"
[master]: created 4d3e37b: "'Merge' avatar code from 'twitter_integration' branch"
4 files changed, 72 insertions(+), 0 deletions(-)
create mode 100644 app/models/avatar.rb
create mode 100644 db/migrate/20090223104419_create_avatars.rb
create mode 100644 test/functional/models/avatar_test.rb
create mode 100644 test/unit/models/avatar_test.rb