Re: [Help-bash] && precedence

[Russell Shaw]

On 09/08/17 22:10, Pierre Gaston wrote:
> On Wed, Aug 9, 2017 at 2:35 PM, Russell Shaw <address@hidden> wrote:
>
> > Hi,
> > When i do:
> >
> >    true || echo hi
> >
> > there is no "hi" as expected
> >
> >
> > when i do:
> >
> >    true || true && echo hi
> >
> > i get "hi" echoed. Why does "true && echo hi" get evaluated?
> The manual says:
> "Of these list operators, && and ││ have equal precedence"
>
> Take care that you also have && and || inside [[  ]] where they do not

From the horses mouth:

<http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html>

2.9.3 Lists

An AND-OR list is a sequence of one or more pipelines separated by the operators 
"&&" and "||" .

A list is a sequence of one or more AND-OR lists separated by the operators ';' 
and '&' and optionally terminated by ';', '&', or <newline>.

The operators "&&" and "||" shall have equal precedence and shall be evaluated 
with left associativity. For example, both of the following commands write 
solely bar to standard output:

    false && echo foo || echo bar
    true || echo foo && echo bar

--------------

I think what happens is this.

With equal precedence and left associativity, the parser shifts in a Simple 
command and evaluates it only if it is the first command, or the previous op was 
|| and the "running" shell status is "fail", or if the previous op was && and 
the "running" shell status is "success". It shifts all the and-or list Simple 
commands through to the end.