Concatenate PDF files on OSX

It turns out that from Tiger onwards, OSX ships with a Python script that does exactly what you need. The script is already executable, and Python is pre-installed on OS X, so all you need to do to run it is opening the Terminal and typing

"/System/Library/Automator/Combine PDF Pages.action/Contents/Resources/join.py" -o PATH/TO/YOUR/MERGED/FILE.pdf /PATH/TO/ORIGINAL/1.pdf /PATH/TO/ANOTHER/2.pdf /PATH/TO/A/WHOLE/DIR/*.pdf