Basic all-cap/all-lower case question on Environment variables

I have a basic question on environment variables, that with some 
documentation I have seen in the security modules like Tomoyo I'm hoping 
this could be the right list to ask the following question.

System environment variables, like PATH, LD_LIBRARY_PATH, HOME, etc.  
Can they ever default to all lower-case in a Linux Distro, i.e., path, 
ld_library_path, home, etc?  If so, is there a mode bit, kernel 
configuration setting or sysfs file to check for this setting?

I swear I have worked on Linux systems years ago that had 'path' and 
'ld_library_path' default to lower-case, but maybe I mis-recall.

Thanks for the info in advance, regards,
Jay

On 2019/02/02 6:19, J Freyensee wrote:

System environment variables, like PATH, LD_LIBRARY_PATH, HOME, etc.  Can they ever
default to all lower-case in a Linux Distro, i.e., path, ld_library_path, home, etc?

There is no rule for environment variables, except environment variable name can't
contain '=' because '=' is used as a separator for environment variable value.

If so, is there a mode bit, kernel configuration setting or sysfs file to check for this setting?

No such settings. Just a convention. Even mixed name like OPENSSL_ia32cap is permitted.