[Rd] readLines function with R >= 3.5.0

[Martin Maechler]

>>>>> Ralf Stubner 
>>>>>     on Fri, 25 May 2018 19:18:58 +0200 writes:

    > Dear all, I would like to draw you attention to this
    > question on SO:
    > https://stackoverflow.com/questions/50372043/readlines-function-with-new-version-of-r


    > Based on the OP's code I used the script

    > #######################################
    > create_matrix <- function() {
    > cat("Write the numbers of vertices: ")
    > user_input <- readLines("stdin", n=1)
    > user_input <- as.numeric(user_input)
    > print(user_input)
    > }
    > create_matrix()
    > #######################################

    > and called it with "R -f <filename>" from the command line.

    > With 'R version 3.4.4 (2018-03-15) -- "Someone to Lean On"' the script
    > prints the inputed number as expected. With both 'R version 3.5.0
    > (2018-04-23) -- "Joy in Playing"' and 'R Under development (unstable)
    > (2018-05-19 r74746) -- "Unsuffered Consequences"' the script does not
    > continue after inputing a number.

I can confirm.
It "works" if you additionally (the [Enter], i.e., EOL) you also
"send" an EOF -- in Unix alikes via  <Ctrl>-D

The same happens if you use  'Rscript <filename>'

I'm not the expert here, but am close to sure that we (R core)
did not intend this change, when fixing other somewhat subtle
bugs in Rscript / 'R -f'

Martin Maechler


    > All these tests where done using docker images from the rocker project,
    > i.e. effectively using Debian Linux.

    > Is this an error in the script or in R?

    > Thanks
    > Ralf

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