Re: 'wait' in command group in pipeline fails to recognize child process

[Martin Jambon]

On 6/22/21 6:11 PM, Lawrence Velázquez wrote:
> On Tue, Jun 22, 2021, at 8:52 PM, Martin Jambon wrote:
> > It's better. However, the reader is still left wondering what "the
> > shell" is referring to in first sentence.
>
> Subshells aside, I have a hard time believing that "the process ID
> of the shell" confuses anybody in practice.  Even POSIX doesn't
> overcomplicate this:
>
>      $
>          Expands to the decimal process ID of the invoked shell.  In
>          a subshell (see Shell Execution Environment), '$' shall
>          expand to the same value as that of the current shell.
>
> (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_05_02)

This language implies that a subshell is part of the shell but not a 
shell in itself. This is what I pointed out earlier but I received a 
conflicting answer.

This is confirmed by this definition from posix:

A subshell environment shall be created as a duplicate of the shell 
environment, except that signal traps that are not being ignored shall 
be set to the default action. Changes made to the subshell environment 
shall not affect the shell environment. Command substitution, commands 
that are grouped with parentheses, and asynchronous lists shall be 
executed in a subshell environment. Additionally, each command of a 
multi-command pipeline is in a subshell environment; as an extension, 
however, any or all commands in a pipeline may be executed in the 
current environment. All other commands shall be executed in the current 
shell environment.

(https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_12)

In the posix definition, a subshell
- is not necessarily implemented as a separate process
- belongs to a unique shell
- is not a shell

This makes the term "the shell" unambiguous to a reader who's aware of 
this - but it's obvious to me that "subshell" should be clarified in the 
context of '$$'.

A subset is a set, a subgroup is a group, a subtype is a type, a subtree 
is a tree, a subprocess is a process.
However a submarine is not a marine, and a subshell is not a shell (sea 
stuff!).

Anyway, I left a suggestion to revise the documentation for '$$' in my 
previous email. That's the best I can produce at this time.

Martin