12.6 Accessing the Operating System

REDUCE provides limited access to the operating system via the operator system, which takes one argument that must evaluate to a string. It passes the content of this string to the default shell and returns a number, which will be 0 if it succeeds and non-zero if it fails. The output from the shell is displayed on the default output device, which is normally the terminal. There is no straightforward way to process this output within REDUCE. The operator system can be useful for operations such as copying, moving, renaming and deleting files, or for listing a directory interactively. It is used within a few of the REDUCE packages, such as GNUPLOT.

The correct shell syntax to use with system depends on your operating system. On Microsoft Windows, system invokes the cmd.exe shell (not PowerShell); on other operating systems it probably invokes bash. Note that backslash (\) is not an escape character in REDUCE and so can be included in the argument to system without any special precautions. However, to include a double-quote character (") within a REDUCE string it must be doubled.

For example, on Windows, you could use the following to delete a file called “C:\long dir name\file.red”

  system "del ""C:\long dir name\file.red""";

whereas, on most other platforms, you could use the following to delete a file called “/long dir name/file.red”

  system "rm ’/long dir name/file.red’";

More sophisticated use of system is possible, but requires symbolic-mode programming. See the REDUCE source code for examples.

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