How does Emacs launch your program? I was under the impression that it launches programs under debug by redirecting its STDIN and STDOUT to a "console" buffer managed by Emacs and that interactive input/output simply work?

Maybe if you can tell us how Emacs does this we can find out how to hook up interactive input/output to the Perl program...

> I was under the impression that it launches programs under debug by redirecting its STDIN and STDOUT to a "console" buffer

You are describing the debugger API via M-x perldb.

It runs the debugger in a terminal emulation in an extra buffer and is in parallel scrolling the current point in the original source buffer.

And it kind of works after typing c for continue (debugger command) I can input stuff. It actually looks exactly like when run with perl -d

Tho it doesn't seem to have auto linking of Perl's error messages.

I will update my OP later with an SSCCE explaining the output.

> I was under the impression that it launches programs under debug by redirecting its STDIN and STDOUT to a "console" buffer

Well I'm using mode-compile but emacs is more TIMTOWTDI than Perl. I think mode-compile was originally designed for make that's why interactive input isn't that important.

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}

How do you run those programs inside emacs? I guess this is on Windows? Are you using Powershell as your shell-file-name?

One annoying effect I see on Windows is that STDOUT is buffered. So, if you're expecting a prompt, then you won't see it in time, but you can still enter your input line when the program seems to "hang". The w32 FAQ has a workaround for "Perl script buffering".

I could run the following program under M-x perldb and M-x eshell, and it behaves as I would expect:

use 5.028;

# Turn all buffering off.
select((select(STDOUT), $| = 1)[0]);
select((select(STDERR), $| = 1)[0]);
select((select(STDIN), $| = 1)[0]);

print "Give me a cookie: ";
my $thing = readline(STDIN);
$thing =~ /^(a )?cookie$/ or die "That was no cookie.\n";
say "Thanks and goodbye!";
[download]

> How do you run those programs inside emacs? I guess this is on Windows?

With mode-compile, which is not core, but nevertheless the default in cperl-mode.

You may want to look into the perl menu in the top-bar after activating cperl-mode.

<menu-bar> <Perl> <Run> runs the command mode-compile, which is an
interactive autoloaded compiled Lisp function in `mode-compile.el'.
[download]

Auto flush was helpful yes, but input is still ignored.

Actually all input is considered compilation or error navigation commands, which makes sense in a buffer with start

Now I'm thinking about making my script automatically redirecting stdout and stdin to a spawned console /or buffer. This while still keeping stder in the compilation buffer...

I did this before in order to debug Term::ReadLine apps, have to dig that out again. I'm weak on tty Channel foo ...

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}

With mode-compile, which is no not core but the default in cperl-mode.

That would have been helpful to know. That entry is disabled in my Emacs because I don't have mode-compile. Heck, that thing is pretty stale and can't be byte-compiled nor M-x eval-buffered in Emacs 27...

Anyway, mode-compile is the culprit. Contrary to its name, it runs the program, using a mechanism which does not make STDIN of the Perl process available to you.

What you could do is wrap the following lisp snippet into a command which suits you:

(compile "perl your_script.pl" t)

Replacing the program name perl and script name your_script.pl by variables is left as an exercise to the reader. The t parameter does the trick to give you what Emacs calls a "comint" environment. So, you end up in a buffer *compilation* in compilation-mode with "clickable" error messages, but the buffer is not read-only, you can just enter text after the prompt.

I use Komodo IDE which is now free to use and has a very good Perl debug environment including a "terminal" window for managing stdio. For various other languages and target systems I use VSCode which has Perl debugging support available, although I've not used it.

Thanks, we even have a company license for Komodo :)

I'll have a look at it.

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}

SSCCE

use v5.12;
use warnings;

STDOUT->autoflush;
STDERR->autoflush;
STDIN->autoflush;

say "Give me a cookie: ";
my $thing = readline(STDIN);
$thing =~ /^(a )?cookie$/ or warn "That was no cookie.";

say "Thanks and goodbye!";

die "exiting here";
[download]

expected output in pre/tt

Give me a cookie:                                               # waits for input
croock                                                          # manual input             
That was no cookie. at emacs_input.pl line 10, <STDIN> line 1.  # jumps to line 10
Thanks and goodbye!
exiting here at emacs_input.pl line 14, <STDIN> line 1.         # jumps to line 14

For better understanding I manually added meta info

• STDOUT in black
• STDIN in red
• STDERR resp. clickable cross-refs as hrefs
• additional comments in grey

FWIW

I've stumbled over a SO discussion which made this (half) work.

> C-u M-x compile and ... compilation buffer will be in comint mode, i.e. interactive.

(the C-u means prefix arg, a very e-lisp-ish annoyance)

I still have to find a way to make this work inside mode-compile

> I still have to find a way to make this work inside mode-compile

patching this in mode-compile.el seems to work

    
(defun mc--compile (compile-command)
  ;; Call compile with the compile command
  ;; but append the remote-command before
  (if (null mc--remote-command)
      ;; local compile
      (mc--compile-sav compile-command t)                        ; <--
+-- "t" added to list
    ;; remote compile
    (let ((thisdir (expand-file-name (or default-directory "~"))))
      (mc--compile-sav
       (concat
        ;; The command to lauch remote commands
        mc--remote-command
        ;; Change to this buffer directory ...
        "'( cd " thisdir " ; "
        ;; then run the compile command
        compile-command " )'")))))
[download]

But I'm not too sure, only using emacs for 30 years now...

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}

Thanks!

Well ... yes and no.

The first module is actually addressing exactly this, but the solution is extremely magic.

STDIN is tied inside Perl to trigger elisp-code inside emacs to prompt in the minibuffer.

This might work, but I prefer a more robust approach which doesn't diverge too much from production.

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}