GNU bug report logs - #34123
A patch to fix reading EOF characters in non-interactive mode

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From: Shawn Presser <shawnpresser <at> gmail.com>
To: 34123 <at> debbugs.gnu.org
Subject: bug#34123: A patch to fix reading EOF characters in non-interactive mode
Date: Fri, 18 Jan 2019 04:35:34 -0600

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Hello,

Here is a patch to allow batch mode scripts to handle EOF characters. This
solves the following problem:

$ git clone https://github.com/shawwn/y
$ cd y
$ bin/y
> (read t)
Lisp expression: 42
42
> (read t)
Lisp expression: ^Derror: Error reading from stdin
> Error reading from stdin
$

Notice that it’s currently impossible for non-interactive scripts to
recover from EOF when reading from tty. After the user sends an EOF
character by pressing C-d, calling read-from-minibuffer will always result
in an error.

This patch solves this by clearing stdin of errors and returning nil when
an EOF character is detected.

Here is the patch:

From 685452ca4a098bbd7c1062a35064755c1d09512a Mon Sep 17 00:00:00 2001
From: Shawn Presser <shawnpresser <at> gmail.com>
Date: Fri, 18 Jan 2019 03:57:37 -0600
Subject: [PATCH] Fix reading EOF characters in batch mode.

* src/minibuf.c (read_minibuf_noninteractive): Handle EOF characters by
clearing stdin and returning Qnil.
---
 src/minibuf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/minibuf.c b/src/minibuf.c
index 321fda1ba8..8c88a316a7 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -250,7 +250,8 @@ read_minibuf_noninteractive (Lisp_Object prompt, bool
expflag,
   else
     {
       xfree (line);
-      error ("Error reading from stdin");
+      clearerr(stdin);
+      return Qnil;
     }

   /* If Lisp form desired instead of string, parse it.  */
-- 
2.19.1

Thanks!
— shawn

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