Description

   In certain situations, the getenv function attempts to perform a
   logical name translation on the user-specified argument:

   1. If the argument to getenv does not match any of the
      environment strings present in your environment array, getenv
      attempts to translate your argument as a logical name by
      searching the logical name tables indicated by the LNM$FILE_
      DEV logical, as is done for file processing.

      getenv first does a case-sensitive lookup. If that fails, it
      does a case-insensitive lookup. In most instances, logical
      names are defined in uppercase, but getenv can also find
      logical names that include lowercase letters.

      getenv does not perform iterative logical name translation.

   2. If the logical name is a search list with multiple equivalence
      values, the returned value points to the first equivalence
      value. For example:

      $ DEFINE A B,C

      ptr = getenv("A");

      A returns a pointer to "B".

   3. If no logical name exists, getenv attempts to translate the
      argument string as a CLI symbol. If it succeeds, it returns
      the translated symbol text. If it fails, the return value is
      NULL.

      getenv does not perform iterative CLI translation.

   If your CLI is the DEC/Shell, the function does not attempt a
   logical name translation since Shell environment symbols are
   implemented as DCL symbols.

                                 NOTES

      o  In OpenVMS Version 7.1, a cache of OpenVMS environment
         variables (that is, logical names and DCL symbols)
         was added to the getenv function to avoid the library
         making repeated calls to translate a logical name or
         to obtain the value of a DCL symbol. By default, the
         cache is disabled. If your application does not need to
         track changes in OpenVMS environment variables that can
         occur during its execution, the cache can be enabled
         by enabling the DECC$ENABLE_GETENV_CACHE logical before
         invoking the application.

      o  Do not use the setenv, getenv, and putenv functions
         to manipulate symbols and logicals. Instead use the
         OpenVMS library calls lib$set_logical, lib$get_logical,
         lib$set_symbol, and lib$get_symbol. The *env functions
         deliberately provide UNIX behavior, and are not a
         substitute for these OpenVMS runtime library calls.

         OpenVMS DCL symbols, not logical names, are the closest
         analog to environment variables on UNIX systems. While
         getenv is a mechanism to retrieve either a logical name
         or a symbol, it maintains an internal cache of values for
         use with setenv and subsequent getenv calls. The setenv
         function does not write or create DCL symbols or OpenVMS
         logical names.

         This is consistent with UNIX behavior. On UNIX systems,
         setenv does not change or create any symbols that will be
         visible in the shell after the program exits.