To avoid the limitations of operating-system-specific statements, use the OPSYS function to determine the appropriate operating system. The OPSYS function allows you to build one application that can run on more than one operating system. The OPSYS function identifies the operating system being used so that a single version of a procedure can work differently on different operating systems.

For example, the following procedure produces a listing of the files in your current directory. The OPSYS function determines the operating system you are running OpenEdge on and uses the appropriate operating system command to produce the directory listing:

CASE OPSYS:
  WHEN "unix" THEN OS-COMMAND ls.
  WHEN "win32" THEN OS-COMMAND dir.
  OTHERWISE MESSAGE OPSYS "is an unsupported operating system".
END CASE.

To use operating system commands from within OpenEdge, use either the operating system statement for the operating system you are running on or the OS-COMMAND statement. For example, use the OS-COMMAND statement on a Windows system and on a UNIX system. If you include the operating system statement in a procedure on a system other than the one named, the procedure compiles but does not run if the flow of control passes through that operating system statement. OpenEdge might report an error when it tries to process an operating system statement on a system other than the one named. For more information, see OPSYS function.

You can also use the built-in preprocessor directive, {&OPSYS}, which expands to a character string that contains the name of the operating system that the file is being compiled on.

The preprocessor is a component of the OpenEdge Compiler. You control the preprocessor by placing preprocessor directives throughout your source code.

The {&OPSYS} preprocessor directive allows you to write code that is conditionally compiled, while the OPSYS function is a run-time function. For more information on preprocessor names, see the "Preprocessor" topics in Manage ABL Applications.