[Rd] Option to preserve whitespace in readline()

[Viechtbauer, Wolfgang (NP)]

Dear Martin,

Thanks for responding. I've submitted a patch via bugzilla.

Best,
Wolfgang

> -----Original Message-----
> From: Martin Maechler <maechler using stat.math.ethz.ch>
> Sent: Tuesday, September 8, 2026 11:37
> To: Viechtbauer, Wolfgang (NP) <wolfgang.viechtbauer using maastrichtuniversity.nl>
> Cc: r-devel using r-project.org
> Subject: Re: [Rd] Option to preserve whitespace in readline()
> 
> >>>>> 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