No gitk in your OSX?

There's no gitk in your OSX. Bottom line: Your git version is too low, and GITK is installed with Git.

Workaround: Just re-use brew to install Git.

First look at the git version:

andy@andymacbookpro:~$ git--version
git version 1.9.5 (Apple Git-50.3)

You can use brew to reinstall GIT:

First Upgrade Brew:

Brew Update

Then install git:

andy@andymacbookpro:/usr/local/webdata/chrome_ext/fanlihelper$ Brew Install git
==> downloading https:// homebrew.bintray.com/bottles/git-2.6.2.mavericks.bottle.tar.gz
########################################### ############################# 100.0%
==> pouring git-2.6.2.mavericks.bottle.tar.gz
==> Caveats
The OS X Keychain Credential Helper has been installed to:
  /usr/local/bin/git-credential-osxkeychain

the " Contrib "Directory have been installed to:
  /usr/local/share/git-core/contrib

Bash completion have been installed To:
  /USR/LOCAL/ETC/BASH_COMPLETION.D

zsh completion have been installed to:
  /usr/local/share/zsh/ Site-functions
==> Summary
/usr/local/cellar/git/2.6.2:1398 files, 33M

The git version is not changed after installation:

andy@andymacbookpro:/usr/local/webdata/chrome_ext/fanlihelper$ git--version
git version 1.9.5 (Apple Git-50.3)

We use which git, found git directory or/usr/bin/git, supposedly git should be located in/usr/local/bin/git, is the directory is not set in profile, so we first upgrade brew:

Brew Upate

Finally, we found this tip:

Consider setting your PATH so that/usr/local/bin
occurs before/usr/bin. Here is a one-liner:
    echo ' Export path= '/usr/local/bin: $PATH ' >> ~/.bash_profile

Then we follow the prompts to execute:

echo ' Export path= '/usr/local/bin: $PATH ' >> ~/.bash_profile

Reference () Here, so to speak:

If you already has git installed via homebrew, you can just do upgrade:

In other words, we have just brew install git, and now we have imported the path, we can directly:

Brew upgrade Git is available with the following effects:

$ which git
/usr/bin/git
$ brew upgrade git
$ which git
/usr/local/bin/git

Then we see that the git version is correct:

andy@andymacbookpro:/usr/local/cellar/git/2.6.2$ git version
git version 2.6.2

And then we can execute GITK in the shell.

Finally, let's look at the situation in the system:

andy@andymacbookpro:/usr/local/cellar/git/2.6.2$/usr/bin/git version
git version 1.9.5 (Apple Git-50.3)
andy@andymacbookpro:/usr/local/cellar/git/2.6.2$ git version
git version 2.6.2
andy@andymacbookpro:/usr/ local/cellar/git/2.6.2$ which git
/usr/local/bin/git
andy@andymacbookpro:/usr/local/cellar/git/2.6.2$ Which gitk
/usr/local/bin/gitk
andy@andymacbookpro:/usr/local/cellar/git/2.6.2$

You can see that we currently have two git in OSX, and GITK is in the/usr/local/bin/directory.

Reference:
Http://stackoverflow.com/questions/17582685/install-gitk-on-mac