How to find where an environment variable is set

Question

Say I have some environment variable PROJECT_HOME. I want to find out which file it is set in. How do I do this?

Answer 1

grep -r PROJECT_HOME /etc $HOME

will probably find it.

Answer 2

find $HOME -type f -exec grep -Hn 'PROJECT_HOME' {} \;

Answer 3

I like using ack! in these kind of situations. I would change into the likely super directory and do an ack PROJECT_HOME.