I want to understand how environment variables are set and reset (overridden). I'm running Apache/2.2.24 (Unix) PHP/5.4.14 on a mac . My theory is this: Environment vars can be set in bash, then they can be overwritten with httpd.conf preceding a VirtualHost directive that precedes php.ini, which can then be overwritten by .htaccess (if allowable) and finally by PHP I tried the following: setting environment variable in bash: I added export ENVIRONMENT='local' to my ~/.bashrc file, restarted apache and did not get any output from print_r($_ENV); (in a simple index.php file at the root of my webserver). I also tried putting ENVIRONMENT='local' into /etc/environment, and restarting apache, nothing, as well as /etc/bashrc, restart apache. still nothing. setting environment variable in httpd.conf: I added SetEnv ENVIRONMENT 'local-httpd to the end of my /etc/apache2/httpd.conf file (but before I load other conf files, such as virtual host [Include /private/etc/apache2/other/*.conf]). I now see the variable in the array print_r($_SERVER); but not print_r($_ENV);. setting environment variable in httpd-vhosts.conf: I added SetEnv ENVIRONMENT 'local-vhost to my /etc/apache2/extra/httpd-vhosts.conf file in my generic directive that points to my default document root. I now see the variable has been overwritten (to local-vhost from local-httpd, so I know where the variable is getting set). setting environment variable in php.ini: while searching for a proper place to put my environment variable, I noticed that variables_order = "GPCS" was set to the production value rather than EGPCS. I changed it, restarted my server and found that I was now getting output for print_r($_ENV); but not my expected custom variable. It also appears that I am not able to set a custom variable in this file. Please tell me if I am wrong setting environment variable in .htaccess: I added SetEnv ENVIRONMENT 'local-htaccess'. This worked as expected, overwriting all other values that were set. setting / overwriting environment variable in PHP: if (...) { putenv('ENVIRONMENT=local'); } I'm asking this question because I have a lot of local and remote testing servers, some of which may or may not allow me access to modify httpd, httpd-vhost, php.ini or environment variables. I want to understand what is best for those difference scenarios (shared hosting, heroku, local servers, etc) I obviously don't know how to properly set the environment variable in bash in a way that php can use it, I'd like to know how to do that (as I think Heroku does something similar with heroku config set...)