##  Git  ###############################

  * add submodule
  +------------------------------------------+
  | $ git submodule add <src_url> <dst_path> |
  +------------------------------------------+

  * rm submodule

    edit <git_dir>/.gitmodules
    edit <git_dir>/.git/config
  +------------------------------------------+
  | $ rm <git_dir>/.git/modules/<dst_module> |
  +------------------------------------------+

  * update submodule
  +-------------------------------------+
  | $ git submodule update ^-i (--init)^|
  +-------------------------------------+
  * replace submodule
  +------------------------------------+
  | $ rm -rf <dst_module>              |
  | $ rm -rf .git/modules/<dst_module> |
  | $ git rm --cached <dst_module>     |
  +------------------------------------+
    edit .git/config


  * change submodule position

    edit these files

    .gitmodules
    .git/config
    .git/modules/<dst module>/config
    <dst module>/.git


  * add new repository on GitHub

    create new repository in WEB
  +--------------------------------------------------------------+
  | $ git remote add origin git@github.com:ekawa/<repo_name>.git |
  | $ git push -u origin master                                  |
  +--------------------------------------------------------------+

  * clone new repository from GitHub
  +-------------------------------------------------------------+
  | $ git clone git@github.com:ekawa/<repo_name>.git <dst_path> |
  +-------------------------------------------------------------+

  * conflict error

    when  conflict:merge error

    then
  +-------------------------------------+
  | $ git reset --hard master; git pull |
  +-------------------------------------+
      at /usr/local


  * do not open editor at merge

    set environment variable
    export GIT_MERGE_AUTOEDIT=no


  * install git under home
  +-------------------------------------------------------------+
  | $ ./configure --prefix=/home/ekawa/local                    |
  | $ PYTHON_PATH=/home/ekawa/local/bin/python3.0@ make         |
  | $ PYTHON_PATH=/home/ekawa/local/bin/python3.0@ make install |
  +-------------------------------------------------------------+
    NOTE : in git 1.8.4 case python3 is necessary


  * check tracked files
  +----------------+
  | $ git ls-files |
  +----------------+

  * recover removed file
  +----------------------------------------+
  | $ git checkout <hash> -- <file>        |
  |                e.g. HEAD\^, ce36818a3a |
  +----------------------------------------+

  * rebase brew Formula
  +-----------------------------------+
  | $ cd /usr/local                   |
  | $ git pull --rebase origin master |
  +-----------------------------------+

  * add new repository to private git server

    make repository dir on git server
  +------------------------------------------+
  | $ mkdir ~/git_repository/<repo name>.git |
  | $ cd ~/git_repository/<repo name>.git    |
  | $ git --bare init                        |
  +------------------------------------------+

    remote add on local machine
  +-----------------------------------------------------------------+
  | $ cd <dst repo>                                                 |
  | $ git remote add origin ssh://ekawa@yang.scphys.kyoto-u.ac.jp:\ |
  |   <port>/home/ekawa/git_repository/<repo name>.git              |
  | $ git push -u origin master                                     |
  +-----------------------------------------------------------------+

    if you want to use this repository on anotner machine, use git clone
  +--------------------------------------------------------+
  | $ git clone ssh://ekawa@yang.scphys.kyoto-u.ac.jp:\    |
  |   <ip>/home/ekawa/git_repository/<repo name>.git <dst> |
  +--------------------------------------------------------+

  * remove file from all history
  +-------------------------------------------------------------------------------------+
  | $ git filter-branch --index-filter 'git rm -r --cached --ignore-unmatch <dst>' HEAD |
  | $ git push -u origin master --force                                                 |
  +-------------------------------------------------------------------------------------+

  * download tag from remote repository
  +-------------------+
  | $ git pull --tags |
  +-------------------+


  * change remote repository URL
  +-------------------------------------+
  | $ git remote set-url <branch> <URL> |
  +-------------------------------------+
    % example
      git remote set-url origin ssh://<usr>@example.jp:22/home/<***.git>