You can tell if mod_perl is in use by the setting of the MOD_PERL environment variable. There are other things about the environment an admin really needs to be able to find out when TWiki is live, so I propose this:

ENV{"varname"} -- inspect the value of an environment variable

Returns the current value of the environment variable varname. For security reasons, only those variables listed in {AccessibleENV} in the Security Settings/Miscellaneous section of configure can be displayed. Any other variable will just be shown as the emtpy string, irrespective of its real value.

If a variable is not set (as against being set to the empty string) it will be returned as not set.

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Also took the opportunity to move the HTTP_HOST, REMOTE_* env var eccessors into TWiki variables for deprecation.

CC