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

[Marc Schwartz (via MN)]

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.

Thanks for any guidance.

Marc Schwartz