This link post is quite irrelevant should you never be using PHP. Therefore, I categorized it.
Published in 2010, Unix manual pages for PHP functions is still a useful tip.
A decade of using Python, and you don’t ask yourself where the argument goes in a function you use daily. Experienced PHP developers look at the php.net website quite a lot. Print cheatsheets (but never look at them, since the php.net website exists).
pear channel-discover doc.php.net
pear channel-update doc.php.net
pear install doc.php.net/pman
or, if your setup forces you to use sudo (for your copy-and-pasting pleasure):
sudo pear channel-discover doc.php.net
sudo pear channel-update doc.php.net
sudo pear install doc.php.net/pman
This downloads five megabytes of PHP documentation, and a small command-line utility that fires up your text viewer.
Result: any PHP function can be looked up locally, in your viewer: