(Backstory: My PHP script is executing another PHP script through the command line (PHP's "exec()" command) so that the cURL session the target script creates doesn't cause the original PHP script to hang. I'm doing this so that I can send transactional email without slow page loads for my user if the email provider's servers are laggy.)
I'm calling a PHP script like this:
exec("[php] [target script] [querystring]"), where [querystring] is a typical HTTP GET querystring (variable=value&variable2=value2). The reason I'm passing the email data to the target script via a querystring is that my PHP host has a flag disabled in the PHP.ini that disallows PHP scripts from detecting the $argv's they're called with via the command line. (For whatever reason, appending a querytring works though.)
So, the question is: What would be the character limit on this querystring? Would there even be one? There is no HTTP or web browser in the mix -- would this mean Apache's and browsers' GET character limits wouldn't be a constraint? Would there naturally be a command line constraint, though?
I don't think there is any character limit, if it is, it's probably determined by the operating system that you use or the language which in this case would translate to your memory.
I hope that answers your question.
Please note that PHP setups with the suhosin patch installed will have a default limit of 512 characters for get parameters. Although bad practice, most browsers (including IE) supports URLs up to around 2000 characters, while Apache has a default of 8000. To add support for long parameters with suhosin, add suhosin.get.max_value_length = in php.ini