Re: grammar triviality with '&&'

[Vincent Lefevre <vincent@vinc17.net>]

On 2015-03-01 19:53:28 -0800, Kurtis Rader wrote:
> On Sun, Mar 1, 2015 at 6:27 PM, Vincent Lefevre <vincent@vinc17.net> wrote:
> 
> > However "&& [ -e file2 ]" could constitute a list too. There is
> > currently a parse error, but zsh could have an extension to accept
> > it as being equivalent to: "[[ $? -eq 0 ]] && [ -e file2 ]". Would
> > there be anything wrong with such an extension?
> >
> > Similarly, "|| X" could be regarded as equivalent to
> > "[[ $? -ne 0 ]] || X" by zsh.
> >
> 
> How often would such a feature be useful? Very infrequently in my opinion.

I'm not so sure. It's probably useless in a script (except for
the style as in the original post, but this may not be a good
idea to use such a feature here). But I can see an interesting
use in an interactive shell when using the history. For instance,
one may want to run 3 (long) commands from time to time, by using
the history and accept-line-and-down-history:

cmd1
cmd2
cmd3

Now, assume that as soon as some command fails, you don't want
to execute the following ones, but you still want to have the
3 commands in the history when invoking the latest cmd1 by a
history search (something I often do). Currently, the only way
to do that is, AFAIK:

cmd1
[[ $? -eq 0 ]] && cmd2
[[ $? -eq 0 ]] && cmd3

But having

cmd1
&& cmd2
&& cmd3

could be nicer (I would also like the fact that one can easier see
that these 3 commands are related).

Of course, one could also do:

  cmd1 && cmd2 && cmd3

but if the commands produce output, one may prefer to run them
separately to analyze the output first (which is the main goal
of interactive use vs writing a script).

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)