[RFC PATCH v1 17/21] cli: hush_2021: Enable using \< and \> as string compare operators.

[Francis Laniel]

Le mercredi 12 janvier 2022, 21:03:40 CET Simon Glass a écrit :
> Hi Francis,
> 
> On Fri, 31 Dec 2021 at 09:14, Francis Laniel
> 
> <francis.laniel at amarulasolutions.com> wrote:
> > In Busybox hush, '<' and '>' are used as redirection operators.
> > For example, cat foo > bar will write content of file foo inside file bar.
> > In U-Boot, we do not have file system, so we can hardly redirect command
> > output inside a file.
> > 
> > But, in actual U-Boot hush, these operators ('<' and '>') are used as
> > string compare operators.
> > For example, test aaa < bbb returns 0 as aaa is before bbb in the
> > dictionary. Busybox hush also permits this, but operators need to be
> > escaped ('\<' and '\>'), so we stick here to this behavior.
> > Also, if escaping is needed it permits the developer to think about its
> > code, as in a lot of case, we want to compare integers (using '-lt' or
> > '-gt') rather than strings.
> > 
> > Signed-off-by: Francis Laniel <francis.laniel at amarulasolutions.com>
> > ---
> > 
> >  common/cli_hush_2021_upstream.c | 28 +++++++++++++++++++++++++++-
> >  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> Reviewed-by: Simon Glass <sjg at chromium.org>
> 
> We should add a file interface to U-Boot. Is that the only impediment
> to implementing redirection? I thought the problem was lack of fork()
> ?

From my understanding of Busybox hush code dealing with I/O redirection 
(mainly parse_redirect() and struct redir_struct), it seems fork is never used 
here.
So, if we add something to emulate file descriptor it should be OK to add this 
feature to U-Boot.

> Regards,
> Simon