R devel - May 2018 - readLines function with R >= 3.5.0

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 ..." 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.

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

-- 
Ralf Stubner
Senior Software Engineer / Trainer

daqana GmbH
Dortustra?e 48
14467 Potsdam

T: +49 331 23 61 93 11
F: +49 331 23 61 93 90
M: +49 162 20 91 196
Mail: ralf.stubner at daqana.com

Sitz: Potsdam
Register: AG Potsdam HRB 27966 P
Ust.-IdNr.: DE300072622
Gesch?ftsf?hrer: Prof. Dr. Dr. Karl-Kuno Kunze

>>>>> 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

    > -- 
    > Ralf Stubner
    > Senior Software Engineer / Trainer

    > daqana GmbH
    > Dortustra?e 48
    > 14467 Potsdam

    > T: +49 331 23 61 93 11
    > F: +49 331 23 61 93 90
    > M: +49 162 20 91 196
    > Mail: ralf.stubner at daqana.com

    > Sitz: Potsdam
    > Register: AG Potsdam HRB 27966 P
    > Ust.-IdNr.: DE300072622
    > Gesch?ftsf?hrer: Prof. Dr. Dr. Karl-Kuno Kunze

    > ______________________________________________
    > R-devel at r-project.org mailing list
    > https://stat.ethz.ch/mailman/listinfo/r-devel

>>>>> Martin Maechler 
>>>>>     on Mon, 28 May 2018 10:28:01 +0200 writes:
>>>>> 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

The same behavior in regular R , no need for a script etc.
> str(readLines("stdin", n=1))
then in addition to the input  you need to "give" an EOF (Ctrl D) in R
>= 3.5.0

Interestingly, everything works fine if you use  stdin() instead
of "stdin" :
> rr <- readLines(stdin(), n=1)
foo
> rr
[1] "foo"
> 
----------

So, for now use  stdin()  which is much clearer than the string
"stdin" anyway

Martin Maechler