Re: How to read characters from stdin?

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From: Bernd Paysan <[email protected]>
To: "Mark J. Reed" <[email protected]>, gforth-mXXj517/[email protected]
Cc: "gforth-mXXj517/[email protected]" <gforth-mXXj517/[email protected]>, jlyonm <jlyonm-g/[email protected]>
Subject: Re: How to read characters from stdin?
Date: Tue, 05 May 2026 18:07:39 +0200
Message-ID: <[email protected]>
MIME-Version: 1.0

Am Dienstag, 5. Mai 2026, 17:31:53 Mitteleurop=C3=A4ische Sommerzeit schrie=
b jlyonm=20
via Gforth discussion and announcements:
> On Tuesday, May 5th, 2026 at 1:55 AM, Mark J. Reed <[email protected]>=
=20
wrote:
> > On Mon, May 4, 2026 at 11:53=E2=80=AFAM jlyonm <jlyonm-g/[email protected]> =
wrote:
> > > I wanted to write a simple program that reads input from stdin, and
> > > writes it out to stdout doing a little translation.>=20
> > Ok, so does your program need to respond to each individual key press, =
or
> > can it read a whole line and then process that all at once?
> I'm reading one character at a time.
>=20
> > > At first I thought I could make use of key and key?, but I see the
> > > documentation indicates this can't be used on stdin.>=20
> > I'm confused - don't those words work exclusively on stdin?
>=20
> In the Gforth info document, section 2.6 it says, "If you pipe into Gfort=
h,
> 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
> seeing with my little program. It never exits.

KEY does recognize end of file, but it throws an exception instead of passi=
ng a=20
flag.

=46or that purpose, there is now (in the development snapshot) KEY-IOR, whi=
ch=20
returns a negative value for end of file or other exceptions.

$ echo "check this" | gforth -e ": test begin key-ior dup 0>=3D while h. re=
peat=20
drop ; test cr bye"
$63 $68 $65 $63 $6B $20 $74 $68 $69 $73 $A

End of file is error code -512 (which translates into =E2=80=9Csuccess=E2=
=80=9D if thrown, as=20
there is no errno assigned to EOF).

> > Just use stdin file-eof? ?
>=20
> Thanks a lot, this is exactly what I needed, and makes it work. How does =
one
> find that word? It is not in the info docs, nor can I find it online. I
> wonder what else I am unaware of.

=46ILE-EOF? is documented in the current development manual.

https://net2o.de/gforth/

Go to the index, search for EOF, and second hit is it.

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

The termux version is likely 0.7.3, and the development documentation can b=
e=20
significantly ahead of the functions available there.

=2D-=20
Bernd Paysan
"If you want it done right, you have to do it yourself"
net2o id: kQusJzA;7*?t=3Duy@X}1GWr!+0qqp_Cn176t4(dQ*
https://net2o.de/

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