[PATCH] hush: Fix assignments being misinterpreted as commands

[Tom Rini <trini@konsulko.com>]

On Sun, Feb 28, 2021 at 06:51:53PM -0500, Sean Anderson wrote:
> On 2/28/21 6:40 PM, Heinrich Schuchardt wrote:
> > Am 28. Februar 2021 22:29:51 MEZ schrieb Sean Anderson <seanga2@gmail.com>:
> > > If there were no variable substitutions in a command, then initial
> > > assignments would be misinterpreted as commands, instead of being
> > > skipped
> > > over. This is demonstrated by the following example:
> > > 
> > > 	=> foo=bar echo baz
> > 
> > The commit message does not explain why this patch is needed.
> 
> This is a bug I noticed while writing some tests of hush.
> 
> > What shall be the value off foo after this line?
> 
> It should be bar. This is an existing difference when compared with
> bash. For example, without this patch, we have
> 
> 	=> foo=bar echo $foo
> 	bar
> 	=> echo $foo
> 	bar
> 
> > 
> > What will be the output of
> > 
> > foo=bar echo ${foo}
> > 
> > with and without yor patch?
> 
> It is the same.

bash works as you describe.  dash and busybox-sh both function like
this:
$ foo=bar echo $foo

$ echo $foo

$

That we error out entirely is different from everyone.  Is that a good
thing?  Maybe.  I know I've caught myself making thinkos due to that
logic.  It does also violate the principal of least surprise, that we
don't act like anything else.  But I would suggest the behavior of
busybox-sh (what we forked long long ago) is what we should model here
rather than be more bash-like.  I'm not all that firm on this opinion
frankly, especially given the one-line nature of the change to bring us
that behavior and I assume dash/busybox are acting like pure sh would in
this case, which we aren't anyhow.

-- 
Tom
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