[Rd] R --interactive and readline() creates infinite loop

[Peter Dalgaard]

One canonical way of doing it is:

(echo 'print(readline("Input:"))'; cat -) | R --interactive --no-save

(you don't want to leave out --no-save ....)


John Chambers wrote:
> For an alternative approach to your original goal, take a look at
> demoSource() in the SoDA package from CRAN.  It's a bit tedious to set
> up (see the Details section of the help file) but uses standard R
> sessions to mix lines from a demo file and interactive input.
>
> John
>
> Jon Clayden wrote:
>> Dear all,
>>
>> I have asked before, in R-help [1], about a way to create an
>> interactive session in which commands are taken from a file or
>> standard input - like R CMD BATCH but additionally allowing user
>> input - but there was no response to that question, and the
>> workarounds that I have found (using "expect", creating a temporary
>> .Rprofile) are ugly and problematic.
>>
>> With the appearance of the --interactive flag in R 2.7.0 I thought
>> this might become possible, but it not only does not behave as I
>> would expect, it appears to go into an infinite loop, and uses 100%
>> CPU until killed.
>>
>> $ echo 'print(readline("Input:"))' | R --no-save --quiet
>> > print(readline("Input:"))
>> Input:[1] ""
>> >
>> [no interactivity]
>>
>> $ echo 'print(readline("Input:"))' | R --no-save --quiet --interactive
>> [no response at all]
>>
>> This behaviour remains in the latest alphas of R 2.8.0. My platform
>> is Mac OS X.5.5 on Intel Core 2 Duo.
>>
>> I assume, given this outcome, that this is not the intended use of
>> --interactive, but I still wonder if there is any way to achieve an
>> interactive session based on a predefined set of commands without
>> writing a completely new front-end (overkill, surely?).
>>
>> Any guidance would be appreciated.
>>
>> Regards,
>> Jon
>>
>> [1] http://finzi.psych.upenn.edu/R/Rhelp02a/archive/117412.html
>>
>>
>> -- 
>> Jonathan D. Clayden, Ph.D.
>> Research Fellow
>> Radiology and Physics Unit
>> UCL Institute of Child Health
>> 30 Guilford Street
>> LONDON  WC1N 1EH
>> United Kingdom
>>
>> t | +44 (0)20 7905 2708
>> f | +44 (0)20 7905 2358
>> w | www.homepages.ucl.ac.uk/~sejjjd2/
>>
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>>
>
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-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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