[R] Capturing output from external executables, in windows

[Duncan Murdoch]

On 1/24/2007 8:22 AM, Darren Obbard wrote:
> Hi,
> 
> Any help on the following would be much appreciated
> 
> I wish to capture the output (currently going to console) from an 
> external executable.
> 
> The executable is successfully run using
> 
>      system("program -switch ")
> 
> and the output printed to the DOS console.
> 
> How do I capture this output? I have tried redirecting the output to a 
> text file, and then reading this in
>     
>      system("program -switch > textfile.txt")
>      data<-scan("textfile.txt")
> 
> But this does not seem to work (the textfile.txt is not written). 

The redirection character ">" is normally handled by the shell.  The 
system() function is low level, so it will pass it directly to your program.
 >
It
> does however work if I invoke the console to be permanent 
> 
>      system("cmd /K program -switch > textfile.txt")
>      data<-scan("textfile.txt")
> 
> Unfortunately, this leaves me with an open console window I have to 
> close manually.

Use the /C option instead of /K; it executes and then terminates.  Or 
use the "intern" or "show.output.on.console" arg to system().

Duncan Murdoch

> 
> Is there a way of doing this (under windows) using system( ) or some 
> other command? It appears that pipe( ) may do it, but I cannot 
> understand the documentation.
> 
> An example of the appropriate syntax would be an enormous help.
> 
> Thanks in advance,
> 
> Darren
> 
> Darren.Obbard at ed.ac.uk
>