[Rd] Option to preserve whitespace in readline()

[Martin Maechler]

>>>>> Viechtbauer, Wolfgang \(NP\) via R-devel 
>>>>>     on Mon, 7 Sep 2026 10:38:15 +0000 writes:

    > Dear R-Core Team,

    > I would like to suggest adding an argument to readline() that allows leading and trailing whitespace to be preserved.

    > Currently, readline() strips leading and trailing spaces and tabs. For example,

    > x <- readline("Input: ")

    > cannot be used when such whitespace is part of the intended input. As far as I can tell, there is currently no way to disable this behavior.

    > Would there be interest in adding an argument along the lines of:

    > readline(prompt = "", trim = TRUE)

    > where the default would retain the current behavior, while trim = FALSE would return the input unchanged (apart from the line ending)?

    > Looking at do_readln() in src/main/scan.c, this appears to require only a fairly small change, since the removal of leading and trailing spaces/tabs is done explicitly there. In particular, when trim = FALSE, the initial loop that skips spaces/tabs and the subsequent removal of spaces/tabs at the end could simply be bypassed. Looking at the sources, do_readln() appears to be used exclusively for readline(), so this seems to be a fairly localized change.

    > The change would also be fully backwards compatible with trim = TRUE as the default. It would also be useful because reproducing this behavior in a package is not straightforward: readLines(stdin(), n = 1) preserves whitespace but does not necessarily have the same console/frontend behavior as readline().

    > Would such an addition be considered?

I haven't seen the use myself, but as you see the usefulness of
this, and I agree the change is relatively small, I'd consider.

As it is really your wish, I'm asking you to use R's bugzilla
and provide a patch for at least these 4 files
    src/library/base/R/New-Internal.R
    src/library/base/man/readline.Rd
    src/main/names.c
    src/main/scan.c

  (yes, names.c needs a small change, too ...)

Best regards,
Martin

    > Best,
    > Wolfgang