CLI vs. 'normal' environment differences?

What differences do I need to consider when running a function from command line (CLI) vs. calling it from a browser?
I'm trying get a function running from cron (it's a website scrape using Goutte/Symfony libraries) - it works when called from a browser, but fails (at 338 iterations every time) when attempted via php index.php.
Might there be something missing that I could add to the CLI environment to enable it to not fail?
Thanks.