Debian

$ sudo $apt_pref update
$ sudo $apt_pref install git-extras

Mac

$ brew install git-extras

Clone / Tarball:

$ git clone https://github.com/tj/git-extras.git
$ cd git-extras
# checkout the latest tag
$ git checkout $(git describe --tags $(git rev-list --tags --max-count=1))
$ [sudo] make install

One-liner:

curl -sSL http://git.io/git-extras-setup | sudo bash /dev/stdin

Windows (use it at your own risk)

First, please install Git for Windows 2.x from 'https://github.com/git-for-windows/git/releases' and the basic msys2. Second, clone the git-extras repo into any folder you like.

git clone https://github.com/tj/git-extras.git

After that, open the script install.cmd in the folder with any text editor you like. Modify the PREFIX variable to where your Git for Windows 2.x is installed. For example, I install it in the folder called C:\SCM\PortableGit and the PREFIX should be C:\SCM\PortableGit\mingw64 (for 64-bit release) or C:\SCM\PortableGit\mingw32 (for 32-bit release). Third, execute the install.cmd directly or in the command prompt. Last, please copy colrm.exe and column.exe from folder-your-msys2-installed/usr/bin to folder-your-git-installed/usr/bin. Enjoy git-extras!