On 10/10/14, 5:26 AM, Andreas Grünbacher wrote:
> 2014-10-10 3:29 GMT+02:00 Chet Ramey <chet.ra...@case.edu>:
>> What does logically composable mean in this context?
>
> I would like the hypothetical errfail option to:
>
> * Behave like errexit at the top level (outside of functions).
>
> * Be inherited by functions, subshells, and command substitution.
>
> * Inside functions, it should trigger like errexit would outside of
> functions, no matter how the function is called.
> It should return instead of exiting, though.
So you want executing shell functions -- and only executing functions --
to change the entire scope of errexit. For example, you want functions to
return on an error, presumably with a non-zero return status. However,
this is not compatible with your first point, which says that at the top
level, it would behave like errexit. Since functions are simple commands,
a function returning a non-zero status would ordinarily cause the `top
level' to behave as if any other simple command failed.
>
> With errexit, you get vastly different results from functions depending
> on how the functions are called, for example,
Sure, because functions are simple commands. They are subject to the same
conditions as any other simple command.
>
> foo() {
> echo "foo: top"
> false
> echo "foo: bottom"
> }
>
> set -o errexit
>
> # bottom of foo reached:
> if foo; then
> echo "success" # reached
> fi
>
> # bottom of foo not reached:
> foo
>
> With errfail, "foo:bottom" and "success" would not be reached.
>
> Command substitutions would continue to behave as basic commands
> do with respect to control flow: inside functions, a failure would cause
> the function to return; outside of functions, the script would exit.
Hmm...but command substitutions are not themselves commands: they are a
word expansion. The fact that an assignment statement returns the status
of a command substitution in the absence of a command is a very special
case. Given that special case, though, there is already a way to do
what you want, unless you want
some-command with some $(arguments) here
to exit the shell if $(arguments) ends up returning a non-zero status.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
