PEAR_Size consists of several core classes plus some ancillary ones. Most important is the PEAR_Size class itself. This performs the data-gathering process and then initiates the generation of the output report (using the analyse() and generateReport() methods respectively). The format of the report is set using the setOutputDriver() method.
If writing a command-line script that will utilise the power of PEAR_Size it is best to use the PEAR_Size_CLI class and run() for parsing the details and options set at the command prompt. The usage() method is for displaying either a usage screen or some error message. This method uses the application name as defined with the setAppName() method in those screens. If you intend to embed PEAR_Size into your own application or script you can set its name with the aforementioned method and retrieve it with appName().