[Rd] R's parsing of command line arguments using commandArgs()

[Marc Schwartz (via MN)]

On Fri, 2005-09-23 at 15:37 -0500, Marc Schwartz (via MN) wrote:
> Hi all,
> 
> I am setting up some R program files for use by our DB programmers to
> enable them to utilize some R functions which will be called from within
> TCL code. R has been installed on an RHEL server and R will process the
> results of SQL queries against an Oracle database.
> 
> In some cases, they will generate a data file to be read in and
> processed by R, in others they will simply make the tabulated results
> available.
> 
> I know that I could do the SQL queries from within R, however, this is
> the approach that has been defined for now for various reasons.
> 
> I wanted to provide some flexibility for them, by passing some of the
> tabulated results via command line arguments to R functions, rather than
> via environment variables, which is easier for them to do in TCL it
> would seem. They would create these values at run time, based upon specs
> that I give them.
> 
> Using the following as an example:
> 
> $ R --slave --vanilla --args "c(5,5)" "c(.5,.5)" < RScript.R
> 
> I can then process "c(5,5)" and "c(.5,.5)" as two arguments, via:
> 
> Args <- commandArgs()
> 
> where the two arguments are Args[5] and Args[6], respectively. I can
> then of course pass these as "eval(parse(text = Args[5]))" to other R
> functions.
> 
> 
> However, if there is any whitespace in the two arguments, such as:
> 
> R --slave --vanilla --args "c(5, 5)" "c(.5, .5)" < RScript.R
> 
> even though surrounded by double quotes (or single quotes or
> backquotes), the two arguments are parsed as four.
> 
> Is this behavior expected? I was under the impression, from other C
> based programs and bash shell scripts for example, that the use of the
> double quotes would wrap such text and thus be parsed as a single
> argument.
> 
> This is using:
> 
> Version 2.1.1 Patched (2005-09-22) on FC4.


Apologies for replying to my own post here, but I wanted to follow up
with a solution provided by Robert McGehee, which works here.

The solution is as follows:

echo "a <- c(5, 5); b <- c(0.5, 0.5)" | cat - RScript.R | R --slave \
--vanilla


This uses echo and cat to pre-pend the 'a' and 'b' vector assignments to
the R program file, before passing the whole thing to R.

This then allows for arguments with embedded whitespace to be passed as
required at run time.

Thanks Robert!

Marc