The following tip is taken directly from: hivelogic 

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Using /usr/local is easy. There are only three things one needs to do:

Compile Using –prefix

When compiling command line utilities, programs, and system tools, tell the system to install things into /usr/local. Just append –prefix=/usr/local to the ./configure command in the build process.

Set The Path

By default, tell the system to look in /usr/local for files first by editing your path. On Mac OS X, either create or edit a file called .bash_login in your home folder (note the ”.”, it’s a hidden file) and add the following line to it:

export PATH=”/usr/local/bin:/usr/local/sbin:$PATH”

Specify the /usr/local Prefix in Scripts

When writing scripts, specify the full path to the executable you’ve installed in the first line of the script. So to specify a Ruby binary in /usr/local/bin, one would use a line like this:

#!/usr/local/bin/ruby

That’s all there is to it.

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