Wait for user input with readline()
On Dec 7, 2010, at 12:19 PM, Petr Savicky wrote:
On Mon, Dec 06, 2010 at 08:25:39AM -0800, Alexandre wrote:
Hi, I have a similar problem as the one of Nate. The point is that I want to design an interactive script that need the value of two variables (x and y). So my script as designed for the moment is : x <- as.numeric (readline(prompt="What is the value of x? ")) y <- as.numeric (readline(prompt="What is the value of y? ")) x y But the problem is that if I run this script, values returned for x and y will be "NA" like you can see below :
How do you call your code? Function readline() does not wait for user input in a non-interactive session, for example R CMD BATCH or Rscript. Another situation, when readline() does not wait is, when you copy a block of code and paste it to a running session, even if it is interactive. If readline() is not the last line of the code, then the next line of code is used instead of the user input.
You can't tell R code and input apart in cases like
R < myScript.R
but you can if you use source() or Rscript -- and you can treat them differently.
I assume what Alexandre wants is something like:
input=file("stdin")
print(readLines(input,1))
which works both in interactive and non-interactive setting and expects input in both cases (if you use Rscript or R -e 'source("...")' ).
Cheers,
Simon