Re: How to read characters from stdin?

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On Tuesday, May 5th, 2026 at 1:55 AM, Mark J. Reed <[email protected]> w=
rote:

> =


> =


> On Mon, May 4, 2026 at 11:53=E2=80=AFAM jlyonm <jlyonm-g/[email protected]> w=
rote:
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> > I wanted to write a simple program that reads input from stdin, and wr=
ites it out to stdout doing a little translation.
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> =


> Ok, so does your program need to respond to each individual key press, o=
r can it read a whole line and then process that all at once?

I'm reading one character at a time.


> > At first I thought I could make use of key and key?, but I see the doc=
umentation indicates this can't be used on stdin.
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> =


> I'm confused - don't those words work exclusively on stdin?

In the Gforth info document, section 2.6 it says, "If you pipe into Gforth=
, your program should read with `read-file' or `read-line' from `stdin'. `=
Key' does not recognize the end of input." This is exactly what I am seein=
g with my little program. It never exits.


> > So, I tried read-line. This works mostly. I can read characters one at=
 a time, and the main program's begin ... while loop will terminate at EOF=
. But, as one would expect by something called read-line, it consumes retu=
rns on its own. I'd like to receive those.
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> =


> Well, you can safely assume that there's a return at the end of the line=
. Can even append one to the string if you need to..

I guess I could have assumed, if I read one character and get zero back, t=
hat it must have been a return, but it still felt a little clunky.


> > =


> > Then I tried a combination of read-file and read-line with:
> > =


> > chr 0 stdin read-line
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> =


> What's chr?

Sorry, I did not elaborate. As the documentation for read-line explains, t=
he first item (third one on the stack) is the memory address into which it=
 puts what's been read. I was trying to indicate that I wanted to use the =
read-line for its side-effect of setting flag, hoping that reading zero ch=
aracters would still set that while not eating the return.


> > hoping to get the flag to know whether the end of the input has been r=
eached (which read-file doesn't provide), but this doesn't work either, an=
d the program hangs indefinitely.
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> =


> Just use stdin file-eof? ?

Thanks a lot, this is exactly what I needed, and makes it work. How does o=
ne find that word? It is not in the info docs, nor can I find it online. I=
 wonder what else I am unaware of.


> > =


> > In case it matters, I'm actually running this on a phone running Linea=
ge OS (ostensibly Android) under termux. I don't think it effects the beha=
vior.
> > =


> > I did find something on rosettacode:
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> > https://rosettacode.org/wiki/Copy_stdin_to_stdout#Forth
> > =


> > So I am currently using slurp-fid to dump all of stdin into memory, an=
d then reading a character out and updating the address pointer as I go.
> > =


> > But I was wondering if it is possible to do this from just reading cha=
racters directly from the file descriptor. Is there some other check for E=
OF I missed in the documentation?
> > =


> > Thanks for reading.
> =


> =


> =


> --
> Mark J. Reed <[email protected]>
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