R help - Nov 2010 - system() and system2() functions

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?

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

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 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]]

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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