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Re: -e does not work inside subscript when using || or && operator outsi

From: Archimerged Ark Submedes
Subject: Re: -e does not work inside subscript when using || or && operator outside
Date: Thu, 7 Aug 2008 12:54:39 -0400

On Wed, Aug 6, 2008 at 7:13 AM, Christian Jaeger
<address@hidden> wrote:
>        $ bash -c '( set -e ; false; echo "hu?" ) || echo "false"'
>        hu?
>        # expecting "false"
>        $ bash -c '( set -e ; false; echo "hu?" ); if [ $? -ne 0 ]; then echo 
> "false"; fi'
>        false
>        # Also:
>        $ bash -c '( set -e ; false; echo "hu?" ) && echo "false"'
>        hu?
>        false
>        # expecting no output

On Wed, Aug 6, 2008 at 10:42 AM, Christian Jaeger
<address@hidden> wrote:
> http://www.opengroup.org/onlinepubs/009695399/utilities/set.html

This is bad documentation and ambiguous standardization.

The linked opengroup standard includes the wording

>   When this option is on, if a simple command [fails or exits with status >0],
>   and is not ... and is not ... and is not ..., then the shell shall 
> immediately exit.

What is not specified is whether the scope of the "and is not"
conditions extends outside the subshell created by a fork or not.

Does the meaning of a script enclosed in parenthesis depend on what
appears outside parenthesis?  The behavior of bash clearly shows the
answer is "yes", at least in this case.  Is this documented?

Thus, in the above definition for set -e, assume the simple command
("false" in the example) meets all of the "and is not" conditions"
locally within the parenthesis.

Then if the parenthesis enclosed fragment taken as a simple command
also meets all of the "and is not" conditions, then

  "the shell shall immediately exit"


  "the subshell shall immediately exit and the shell shall not exit".

That is, the child process shall exit and the parent process shall
resume execution at the close parenthesis.  Thus, "exit" is taken
relative to the subshell, but the conditions are taken relative to the
whole script.


  "the shell shall immediately exit"

actually means

  "the subshell shall not exit."

That is, the child process, upon finding that the simple command has
failed, looks in the forked memory image at the state inherited from
all its ancestors and notes that one of them has registered a failure
handler, and therefore decides to ignore the failure without even
looking at the set -e flag.

The semantics of "set -e; false; echo unreachable" depends on the
state of the interpreter when the script fragment is executed, and
cannot be determined without reference to inherited state.  This also
applies when the fragment appears within a function:  the semantics
varies from call to call.

I think the standard needs to refer to the state of the interpreter in
defining the semantics of set -e, rather than pretending that the
meaning is context free.

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