Very Computer

by **era eriksso** » Wed, 12 Nov 1997 04:00:00

comp.unix.shell:
> $ echo $$ ; (echo $$)
> 11290
> 11290

$$ is being expanded by the parent before the subshell is started.
If you really need to do this from the command line, try something
like

$ echo $$ ; /bin/sh -c 'echo $$'
13447
13433

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by **J. Wakeley Purp** » Wed, 12 Nov 1997 04:00:00

>$ echo $$ ; (echo $$)
>11290
>11290
>$

>How to refer to the pid of the subshell?

As I remember reading in Bolsky & Korn, it's not guaranteed that
the (commands) construct will generate a separate shell, only that
'commands' will be executed atomically.

If you really _have_ to have a separate shell, do

(ksh echo $$)

Of course I haven't tried it 8)
--

by **David Boyc** » Thu, 13 Nov 1997 04:00:00

> comp.unix.shell:
> > $ echo $$ ; (echo $$)
> > 11290
> > 11290

> $$ is being expanded by the parent before the subshell is started.
> If you really need to do this from the command line, try something
> like

> $ echo $$ ; /bin/sh -c 'echo $$'
> 13447
> 13433

The original poster is correct; ksh (and maybe the posix shell, I don't
remember) deliberately retain the same value for $$ within subshells,
and it's even documented to do so. Getting the pid of the child process
from within the child process is in fact a problem with these shells. I
wish I could provide an answer but cannot; maybe you could use some form
of shell IPC to send the value of $! from the parent to the child, but I
haven't tried this myself.

-David

by **J. Kan** » Thu, 13 Nov 1997 04:00:00

|> >$ echo $$ ; (echo $$)
|> >11290
|> >11290
|> >$
|> >
|> >How to refer to the pid of the subshell?
|> >
|>
|> As I remember reading in Bolsky & Korn, it's not guaranteed that
|> the (commands) construct will generate a separate shell, only that
|> 'commands' will be executed atomically.
|>
|> If you really _have_ to have a separate shell, do
|>
|> (ksh echo $$)
|>
|> Of course I haven't tried it 8)

It really doesn't matter whether the command is executed in a separate
shell or not -- what counts is where the command line is evaluted, which
in this case IS always the calling shell.

I don't understand the alternative suggestion -- as far as I can see,
you are looking for a file named echo, and executing the commands in it.

About the only way I can think of of doing it is sh -c 'echo $$', which
works.

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