[R] Command line and R

[Prof Brian Ripley]

On Thu, 10 Nov 2005, paul sorenson wrote:

> Angelo Secchi wrote:
>>
>> On Wed, 09 Nov 2005 12:25:37 -0000 (GMT)
>> (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk> wrote:
>>
>>
>>> On 09-Nov-05 Roger Bivand wrote:
>>>
>>>> On Wed, 9 Nov 2005, Angelo Secchi wrote:
>>>>
>>>>> Hi,
>>>>> I wrote a small R script (delta.R) using commandArgs(). The script
>>>>> works from the shell in usual way
>>>>>
>>>>> R --no-save arg1 < delta2.R
>>>>>
>>>>> Suppose arg1 is the output of another shell command (e.g. gawk,
>>>>> sed ...). Is there a way to tell R to read arg1 from the
>>>>> output of the previous command? Any other workaround?
>>>>
>>>> Use shell variables, possibly also Sys.getenv() within R as well as or
>>>> instead of commandArgs().
>>>
>>> If it's a fairly simple shell comand (and even if it isn't, though
>>> it could get tricky for complicated ones) you can use the "backquote"
>>> trick (called, in well-spoken circles, "command substitution"):
>>>
>>>  R --no-save `shellcmd` < delta2.R
>>>
>>> As in all shell command lines, wherever you have a command (including
>>> arguments etc.) between backquotes, as exemplified by "`shellcmd`" above,
>>> the output of the command (as sent to stdout) replaces "`shellcmd`" in
>>> the command-line. This could be a lot of stuff (depending on what
>>> "shellcmd" is), or just one value, or whatever.
>
> ... and this behaviour is OS (or at least command shell specific) for
> anyone trying this on Windows and wondering why it doesn't work.

But it does work on Windows if you have a reasonable shell.  Cmd.exe is 
and (especially) command.com are not shells in the usually accepted sense.
Better to use Rterm than incur the additional overhead of R, though.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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