z/OS UNIX System Services Command Reference, in its c89 section, assumes that the current level of the z/OS XL C/C++ compiler and Language Environment® runtime library will be used. If you must use a previous level of the compiler, then you must customize other environment variables, which are only documented here.

The environment variables used by the cc command have the same names as the ones used by c89, except that the prefix is _CC instead of _C89. Likewise, for the c++ (cxx) command, the prefix is _CXX instead of _C89. Normally, you do not need to explicitly export the environment variables for all three commands; the "for loop" at the bottom of the c89 customization section can be used. This "for loop" sets the variables for all the c89/cc/c++ (cxx) commands.

By putting any customization statements for c89 into /etc/profile for the z/OS shell (or /etc/csh.login for the tcsh shell) and commenting out those lines, the environment variables are automatically exported for c89, cc, and c++ (cxx). See Customizing /etc/profile and Customizing /etc/csh.login for more information.

After you customize the profile, you probably will not need to change it again. However, you can change the variables at any time; the next time a user logs into the shell, they will get the new settings.