When the shell is set to interactive (i.e. "-interactive"), the output
(stdout) is flushed with every prompt (shell.c:422) but stderr is not.
In some situations this leads to no error messages being displayed until
the stderr buffer fills.
This happens when running the official sqlite3 binary as subprocess of
Emacs under Windows 7. The error messages do not appear in a timely
fashion. I was unable to trigger the misbehavior in a plain shell so my
only demo is a bit of Emacs Lisp. When this Elisp code below is run, a
buffer will pop up that *should* contain the output of .help. Under
Windows it does not. The same occurs even when it's launched via a shell
subprocess using "2>&1", so it's not simply an issue with Emacs not
reading from the subprocess's stderr output fast enough.
(let* ((buffer (generate-new-buffer "sqlite"))
(proc (start-process "sqlite" buffer "sqlite3" "-interactive")))
(process-send-string proc ".help\n")
(pop-to-buffer buffer))
I suspect it has to do with being compiled without readline, which is
why it behaves better elsewhere. I couldn't figure out how to link with
libreadline on Windows, though, so I couldn't test this.
With the following change to the amalgamation release I got the behavior
I was looking for: timely error messages from the SQLite command line
shell. I understand this is probably not the Right Way to do this, but
it's just a demonstation of a possible fix.
--- a/shell.c
+++ b/shell.c
@@ -418,6 +418,7 @@ static char *one_input_line(FILE *in, char *zPrior, int
isCont
zResult = readline(zPrompt);
if( zResult && *zResult ) add_history(zResult);
#else
+ fflush(stderr);
printf("%s", zPrompt);
fflush(stdout);
zResult = local_getline(zPrior, stdin);
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