[R] system() and system2() functions

[Uwe Ligges]

On 02.11.2010 15:16, Ralph Olsson wrote:
> Hello,
>
> I help to maintain a moderate library of R code. In this code we have a number
> of calls to the system function along the lines of:
>
>      exe_output = system("./executable.exe",intern=T)
>
> We tend to prefer system() over shell() because, provided the executable has
> been compiled and the working directory set, the command works under both linux
> and windows.
>
> We've never had a problem with this code using R 2.9 and lower, but I've
> recently started testing code in R 2.12 and have been getting "CreateProcess
> failed to run..." error messages.
>
> I've not found much info on this in the change logs/release notes, but from what
> I have found I am under the impression that system() no longer "shell quotes"
> the command passed to it (if I "shQuote()" the command the code runs fine). I
> also see from the help files that a new function "system2()" has been introduced
> which takes a different set of arguments and appears to be under development
> (from the help page: "system2is the beginnings of a more portable interface than
> system").
>
> Since I assume there to be good reasons for this change to system I'm happy to
> spend the time updating our library to work under R 2.12, but before I commence
> on this task I wanted to try to get a better understanding of what changes have
> been made to system().
>
> My questions are:
>
> 1) What is the nature of and motivation for the changes to the system()
> function?

Many, one of them is that system() had different behaviour under Linux 
vs. Windows.


>
> 2) What does system2() offer that system does not?

Portability.


> 3) Can anyone recommend the "best" (in particular most future-proof) way of
> updating our system calls, preferably, and this may be a big ask, such that they
> work in both R 2.9 and R2.12 under both linux and windows?

If it should work for R < 2.12.0, then use system() and add, at least 
for Windows, a shell command (such as "cmd") that allows the executable 
to run under the Windows command shell. Or better, use shell() right 
away, you need to special case for Windows anyway.

Best,
Uwe Ligges


> If any of these questions have previously been answered and I've simply failed
> in my googling, links would be appreciated.
>
> Many thanks for your time,
>
> Ralph
> 	[[alternative HTML version deleted]]
>
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