How to replace Mac OS X utilities with GNU core utilities?
This adds symlinks for GNU utilities with g prefix to /usr/local/bin/:

brew install coreutils findutils gnu-tar gnu-sed gawk gnutls gnu-indent gnu-getopt grep


See brew search gnu for other packages. If you want to use the commands without a g prefix add for example /usr/local/opt/coreutils/libexec/gnubin before other directories on your PATH.

$ brew info coreutils
coreutils: stable 8.21
http://www.gnu.org/software/coreutils
Depends on: xz
/usr/local/Cellar/coreutils/8.20 (208 files, 9.4M)
/usr/local/Cellar/coreutils/8.21 (210 files, 9.6M) *
https://github.com/mxcl/homebrew/commits/master/Library/Formula/coreutils.rb
==&gt; Caveats
All commands have been installed with the prefix 'g'.

If you really need to use these commands with their normal names, you
can add a "gnubin" directory to your PATH from your bashrc like:

    PATH="/usr/local/opt/coreutils/libexec/gnubin:$PATH"

Additionally, you can access their man pages with normal names if you add
the "gnuman" directory to your MANPATH from your bashrc as well:

    MANPATH="/usr/local/opt/coreutils/libexec/gnuman:$MANPATH"