Re: command negation in modern hush parser

[Anshul Dalal <anshuld@ti.com>]

On Wed Mar 11, 2026 at 5:31 PM IST, Rasmus Villemoes wrote:
> Hi
>
> Today, I was bitten by u-boot shell not supporting the negating
> operator, as in
>
>   if ! some_command args ... ; then ... ; fi
>
> So at first I thought about implementing a simple '!' command which,
> similar to the the 'time' command, would just run the rest of the
> arguments, but then negate the return code.
>
> But then I looked at the modern hush parser code, which did seem to have
> support for that in the shell itself. At least the "! command ..." gets
> parsed, and there is code for rejecting "! ! command" which does seem to
> be active, but unfortunately, the "! command" form doesn't actually work
> as expected:
>
> => cli set modern
>
> => ! false
> => echo $?
> 1
> => ! true
> => echo $?
> 0
> => if ! false ; then echo "This should be printed" ; fi
> => if ! true ; then echo "This should _not_ be printed" ; fi
> This should _not_ be printed
> => if ! echo "echoing always succeeds, so... " ; then echo "this should _not_ be printed" ; fi
> echoing always succeeds, so... 
> this should _not_ be printed
> => version
> U-Boot 2026.04-rc3-00079-gb008b86fd180-dirty (Mar 11 2026 - 12:44:08 +0100)
>
> gcc (GCC) 15.2.1 20260209
> GNU ld (GNU Binutils) 2.46
>
> I don't really grok the whole parser code, but just injecting a simple
> printf at the start of done_pipe, it seems that that gets called twice
> for each command, and the flag indicating inversion gets reset on the
> first call, after which it doesn't affect the actual return code of the
> command:
>
> => ! echo hi
> done_pipe entered, followup 0, ctx->inverted = 1
> done_pipe entered, followup 0, ctx->inverted = 0
> hi
>
> Any ideas?

Hi Rasmus,

I was able to reproduce the issue and it looks like we might have missed
reverting the return code based on pi->pi_inverted inside run_pipe in
the one of the cases. The following diff fixes the issue for me:

	diff --git a/common/cli_hush_upstream.c b/common/cli_hush_upstream.c
	index 748ef60ac90..c01ba00e475 100644
	--- a/common/cli_hush_upstream.c
	+++ b/common/cli_hush_upstream.c
	@@ -10377,6 +10377,7 @@ static NOINLINE int run_pipe(struct pipe *pi)
		debug_printf_exec("run_pipe return -1 (%u children started)\n", pi->alive_cmds);
		return -1;
	 #else /* __U_BOOT__ */
	+       IF_HAS_KEYWORDS(if (pi->pi_inverted) rcode = !rcode;)
		debug_printf_exec("run_pipe return %d\n", rcode);
		return rcode;
	 #endif /* __U_BOOT__ */

Regards,
Anshul


>
> Rasmus