Invoking shell commands from within R

In S-Plus, one can invoke a shell command by prepending it with a "!",
e.g.:

    > !ls

Is something similar available in R?  Is it possible to execute shell
commands from within R?

The code to support this is present in main.c.  To compile this in,
place the line

	#define SHELL_ESCAPE

at the top of src/main/main.c.

Using "!" in this way is syntactically ugly and it was a general decision
to not make this a standard R feature (but I left the code in because I
"knew" someone would ask ...).

	Ross

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