How do you check if a variable has NOT been set in PHP?

Question

I am trying to pass a "PHP variable" from Apache (2.2.15) to Tomcat (7.0.27) but without success. The apache is used as front-end server of tomcat using mod_proxy_ajp.

I verified that I can pass only variable set by Apache (e.g. using SetEnv directive); How I can pass a variable set by PHP to Tomcat?

Answer 1

You can use check for isset() but i would rather check also for not blank character with != ''

bool isset ( mixed $var [, mixed $... ] )

Determine if a variable is set and is not NULL.

If a variable has been unset with unset(), it will no longer be set. isset() will return FALSE if testing a variable that has been set to NULL. Also note that a NULL byte ("\0") is not equivalent to the PHP NULL constant.

If multiple parameters are supplied then isset() will return TRUE only if all of the parameters are set. Evaluation goes from left to right and stops as soon as an unset variable is encountered.