Re: [PATCH 01/11] cmd: test: add support for =~ operator

[Tom Rini <trini@konsulko.com>]

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On Tue, May 06, 2025 at 09:07:05PM +0200, Rasmus Villemoes wrote:
> On Tue, May 06 2025, Tom Rini <trini@konsulko.com> wrote:
> 
> > On Tue, May 06, 2025 at 10:49:31AM -0600, Tom Rini wrote:
> >> On Tue, May 06, 2025 at 04:10:25PM +0200, Rasmus Villemoes wrote:
> >> 
> >> > Currently, the only way to make use of regex matching in the shell is
> >> > by using "setexpr [g]sub" command. That's rather awkward for asking
> >> > whether a string matches a regex. At the very least, it requires
> >> > providing setexpr with a dummy target variable, but also, the return
> >> > value of setexpr doesn't say whether any substitutions were done, so
> >> > one would have to do some roundabout thing like
> >> > 
> >> >   env set dummy "${string_to_test}"
> >> >   setexpr sub dummy '<some regex>' ''
> >> >   if test "${dummy}" != "${string_to_test}" ; then ...
> >> > 
> >> > When CONFIG_REGEX is set, teach the test command a new operator, =~,
> >> > which will allow one to more naturally write
> >> > 
> >> >   if test "${string_to_test}" =~ '<some regex>' ; then ...
> >> > 
> >> > Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
> >> 
> >> We should also mention here (and then in docs) that this the same as the
> >> =~ operator in bash, which I only learned about now as part of answering
> >> my own question of "Are people going to expect =~ to do something
> >> else?".
> >> 
> >> With that,
> >> 
> >> Reviewed-by: Tom Rini <trini@konsulko.com>
> >
> > Oh, and we should update doc/usage/cmd/setexpr.rst at least and we
> > should have one for test as well, but don't, yet.
> 
> Yes, if test.rst had already existed I would have updated it, but I
> didn't feel like writing the whole thing from scratch until I had a
> sense of whether these were going anywhere. I'll take a stab at it,
> including the bash ref, but I'm not sure what you want to put in
> setexpr.rst? Perhaps a reference to test.rst for an overview of what
> regex features are available so they don't need to be repeated?

Yeah, for setexpr.rst I would go for (a) making sure it's correct and
without subtle bugs (as you just fixed a number of them) and then (b)
noting that the =~ operator exists and link to the new test.rst

> Another thing I considered was to have the 'test foo =~ ...' thing
> populate shell variables $1, $2, ... with the capture groups, if any;
> and possibly even $0 with "what matched the whole thing", as U-Boot
> doesn't really have anything sensible for that.

I would ask what bash does here first (are things saved anywhere?) as I
assume you use this feature there. And then a second of how useful the
captured output is likely to be outside of debugging a script you're
writing.

-- 
Tom

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