Environment Variables

USS Considerations

The POSIX standards implemented by USS make certain requirements on the C library that are not compatible with the SAS/C environment variable implementation defined in the previous section. These requirements are

POSIX.1 requires that environment variable names be case sensitive. For compatibility with CMS, SAS/C treats environment variable names as case insensitive. This problem is handled in two ways:
- For programs called by the shell (or more generally by any exec function), program-scope environment variables are considered case sensitive. For all other programs, these names remain case insensitive for compatibility with CMS and previous releases.
- For non- exec -linkage programs, the original form of the variable is preserved even though the case of an environment variable is not considered significant. (That is, the variable MyName is stored as MyName , not as myname or MYNAME even though these are all names for the same variable.) If a program calls exec to pass control to an exec -linkage program, the called program receives the environment variables with their original case information intact.
POSIX.1 requires that all environment variables be accessible by the external variable environ . SAS/C now makes the program-scope environment variables accessible by environ for all programs. However, variables of other scopes are never accessible by environ . Similarly, when an exec function is called, only the program-scope environment variables are passed to the called program.
POSIX.1 requires that it be possible to modify the environment variable list by manipulating environ and the list it addresses. SAS/C supports this modification but does not recommend it. The POSIX.1a function setenv should be used to update the environment whenever possible. In particular, you should not use both setenv and update environ simultaneously. This is a restriction stated by the POSIX.1a draft standard.
The POSIX use of the environ variable is not strictly ISO/ANSI conforming because environ is in the name space reserved by ISO/ANSI for users. For this reason, the name environ is accessible only to programs compiled with the posix option. Additionally, the name environ is valid only in the main load module of a program. To access environ from another load module, declare
```
extern char ***_environ;
```
and use *_environ in place of environ . This produces correct results in any load module but is not portable. _environ can be used in programs that are not compiled with the posix option.
SAS/C supports the POSIX.1a clearenv function, which removes all environment variables. It has an effect only on program-scope variables. That is, external- and permanent-scope variables are unaffected.

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