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Re: Fwd: Don't set $?=130 when discarding the current command line (not

From: Robert Elz
Subject: Re: Fwd: Don't set $?=130 when discarding the current command line (not run yet) with CTRL-C?
Date: Sat, 23 Nov 2019 16:50:00 +0700

    Date:        Fri, 22 Nov 2019 16:16:58 +0800
    From:        Clark Wang <address@hidden>
    Message-ID:  <CADv8-ogRv-atdWkiRNWdVA=V03XKpq4AF1-pDTmc=address@hidden>

  | Curious why people care about this?

For some people it seems to be related to wanting to see $? in their
prompt, and either have it explicit that a SIGINT interrupted command
entry, or continue with previous $? ..

For me it is partly just because of what $? is.  From posix:

        ? Expands to the decimal exit status of the most recent pipeline
          (see Section 2.9.2).

nothing about being altered by anything other than (at least attempted)
execution of a pipeline (ie: some command or other).

More practically, the times when I want it are when I have run a command,
then start typing the next one, and realise that I really meant to check
the exit status of the last one before running another.   If I finish typing
my next command I just mentally curse my forgetfulness, and take whatever
action I can (often re-running the previous command, if that makes sense).
But if I catch it before I have finished the next command, I have the
opportunity to abort what I'm doing, and check $? before it is lost.

If that happens while still on the first (or only) line of the new command,
then a line kill char (^U often) is OK, deletes whatever I typed, and I
can replace that with "echo $?" or whatever.

But if it happens after a \n has been entered, that no longer works,
whereas SIGINT (^C usually) does:

Compare bash...

jinx$ false
jinx$ while sleep 3
jinx$ echo $?

(in bash my PS2 is set to be (become really) invisible so I can cut/paste
whole command sequences)

to the NetBSD sh (where editline doesn't handle my PS2 "properly")

[jinx]{2}$ false
[jinx]{2}$ while sleep 3
> do
[jinx]{2}$ echo $?
[jinx]{2}$ true
[jinx]{2}$ while sleep 3
> do
[jinx]{2}$ echo $?

(there was a ^C, not echoed explicitly, after the PS2 prompt on the line
after each "do" ... the lack of the echo another difference between editline
and readline I assume, the ^C is echoed if I disable editline and just
use the tty driver, my PS2 also works as planned then).

[jinx]{2}$ set +V
[jinx]{2}$ true
[jinx]{2}$ while sleep 3
[jinx]{2}$ echo $?


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