Two interesting bits of software to work with proxy auto-config (PAC) files: pacparser is

a library to parse proxy auto-config (PAC) files. Proxy auto-config files are a vastly used proxy configuration method these days.

pactester is

tool to test Proxy Auto Configuration (PAC) files. PAC files are used by browsers to determine the ‘right’ proxy for a URL. Since the PAC file evaluation mechanism is generated inside the browser and cannot be accessed from outside, the only way to tell which proxy your browser will use for a specific URL is manual inspection of the PAC file. But manual inspection doesn’t really scale very well. Pactester resolves this problem. It makes use of JavaScript interpreter and Netscape/Mozilla APIs to evaluate the PAC files and automates the whole process