On Thu, 14 Jul 2005, Dave Anderson wrote:
> It also, at least under OpenBSD, has the serious problem that "$$"
> isn't the PID of the shell running the script but rather the PID of the
> "original" shell (whatever exactly that means; some testing suggests
> that it's the last process on the PPID chain which is still in this
> process group) and I haven't yet found any straightforward way of
> getting the PID of the "bottom-level" shell, which is what is needed
> for the stale-lock testing to work at all when the exclusion needed is
> among scripts run in subshells of the same shell. (I realize that I
> could create a trivial program which writes its PPID to stdout, or hack
> /bin/sh to add a new variable which contains the PID I want -- but I'd
> prefer to use the tools which come as part of the base system. This
> has also left me rather curious as to *why* the PID and PPID of the
> "original" shell are easily accessible in scripts but those of the
> subshell actually running the script aren't.)
I did not check your script, but POSIX says 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.
There's a similar phrase in the man page,
-Otto
