How to print the local variables used in a PHP generated page

Hello,

I am still a beginner of PHP, and while I found out the way to print
all the variables passed as a POST, I was wondering (for debugging
purposes) if there is a simple way to tell the PHP interpreter to print
out all the variables that have been used during that session, without
storing anything anywhere, and without buying a commercial tool.

Any hints?

Thank you

.

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