Re: grammar triviality with '&&'

[Ray Andrews <rayandrews@eastlink.ca>]

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On 03/01/2015 09:22 PM, Kurtis Rader wrote:
>
> One obvious cost is that anyone reading a script that uses the feature 
> will naturally assume the author made a mistake and the script is 
> invalid.

So don't use it if, when or where tradition trumps practicality--which 
is almost everywhere.
> The reason this restriction exists is not arbitrary.

That may very well be the case, which is why I raised the question, but 
it seems that it might not be the case after all (Lawrence). I'm over 
fascinated by this sort of minutia.
> It is a an obvious and natural consequence of how the grammar was 
> interpreted by the person(s) who wrote the code for the Bourne-shell, 
> Bash, Zsh, etcetera. Why is it simpler for the code to "just grab the 
> errorlevel of the previous command"  when it sees a leading "&&" or "||"?

But is that not what it already does?  The question is whether a line 
break or a semi *necessarily* prevents that.  IOW, what ambiguity would 
this cause:

[ -e file1 ]
&& [ -e file2 ]
> Also, it is not just a matter of changing the zsh implementation. Unit 
> tests need to be added and existing tests likely updated. 
> Documentation needs to be changed. Whether the change might break 
> existing uses has to be carefully considered.

Absolutely, and that is probably reason enough why it won't happen. It 
would have to be nothing more than a relaxation of an arbitrary rule ( 
**if** it is arbitrary)--maybe there is a very good reason why 
errorlevel can't be passed beyond a newline or semi.  If there is such a 
good reason, I'd be educated to learn what it is.  But since "[[ $? -eq 
0 ]]" works past the newline, at this point I can't see what the 
linewrap would *necessarily* break.
>
> You say "I'd use it for sure". Please provide a non-contrived example, 
> preferably two or three, where this would be useful.

if [ -e 'shelly.txt' ]
&& [ -n "$ozymandias" ]
&& [ grep "I met a traveler" ]
then
   echo "Look on my works, ye mighty"
fi


... I have a trivial preference for that form, I find it neater. It is 
very unimportant.

> How hard is it to be explicit and include the "[[ $? -eq 0 ]]" in a 
> script? If this feature were truly useful for interactive use I might 
> agree with you. But I see no evidence and my 30+ years experience that 
> it has no use outside of making a tiny percentage of scripts a few 
> characters shorter.

Exactly so.  Whereas I'd like it for saving me the line continuation 
backslash, that is monumentally trivial, I'm interested in the theory of 
the thing.  I like Lawrence's thinking on the matter, however.

Don't take this more seriously than I take it.