This post will help you get PEAR installed and up and running on your machine, there are two options to below, one describes an OXS Lion specific setup and the other is more generic.
Installing on OSX 10.7 Lion
OSX Lion already has the PEAR install bundle so there is no need to download it, open up a terminal window and enter the following commands:
cd /usr/lib/php sudo php install-pear-nozlib.phar
Downloading and installing
Do not follow this part if you have just done the above steps. Otherwise enter the below into a terminal window:
curl http://pear.php.net/go-pear.phar > go-pear.php sudo php -q go-pear.php
It will ask you to enter a new installation base ($prefix). I recommend you use /usr/local
Configuring PHP include path
Edit /etc/php.ini and find the line: ;include_path = ".:/php/includes". Uncomment it (remove the ; at the beginning) and add the PEAR path to it. It should end up looking similar to the below:
include_path = ".:/usr/lib/php/pear"
Update PEAR
Now to update the install enter the 3 commands below into the terminal window:
sudo pear channel-update pear.php.net sudo pecl channel-update pecl.php.net sudo pear upgrade-all
Install PHPUnit
Just for good measure you will probably also want to install PHPUnit, if you do then execute the below command and your ready to go.
sudo pear channel-discover pear.phpunit.de sudo pear channel-discover pear.symfony-project.com sudo pear install pear.phpunit.de/PHPUnit sudo pear install phpunit/DbUnit --alldeps