How to check with PHP if the script is being run from the console or browser request?

I tried things like $_ENV['CLIENTNAME'] == 'Console' but that seems to work on only certain OS's (worked in windows, not linux).

I tried !empty($_ENV['SHELL']) but that doesn't work always either...

Is there a way to check this that will work in all OS's/environments?

Use php_sapi_name()

Returns a lowercase string that describes the type of interface (the Server API, SAPI) that PHP is using. For example, in CLI PHP this string will be "cli" whereas with Apache it may have several different values depending on the exact SAPI used.

For example:

$isCLI = (php_sapi_name() == 'cli');

You can also use the constant PHP_SAPI

Check on http://php.net/manual/en/features.commandline.php#105568 "PHP_SAPI" Constant

<?php
if (PHP_SAPI === 'cli')
{
   // ...
}
?> 

I know this is an old question, but for the record, I see HTTP requests coming in without a User-Agent header and PHP does not automatically define HTTP_USER_AGENT in this case.

if ($argc > 0) {
    // Command line was used
} else {
    // Browser was used
}

$argc coounts the amount of arguments passed to the command line. Simply using php page.php, $argc will return 1

Calling page.php with a browser, $argc will return NULL