How to get the PID of a process by giving the process name in Mac OS X ?

The answer above was mostly correct, just needed some tweaking for the different parameters in Mac OSX.

ps -A | grep [f]irefox | awk '{print $1}'

macos bash shell process pid

You can use the pgrep command like in the following example

$ pgrep Keychain\ Access44186

macos bash shell process pid

You can install pidof with Homebrew:

brew install pidofpidof <process_name>

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