I have problem with Bash, and I don't know why.
Under shell, I enter:
echo $$ ## print 2433
(echo $$) ## also print 2433
(./getpid) ## print 2602
"getpid" is a C program to get current pid, like:
int main() { printf("%d", (int)getpid()); return 0; }
What confuses me is that:
Can you help me?
$$
is defined to return the process ID of the parent in a subshell; from the man page under "Special Parameters":
$ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell.
In bash
4, you can get the process ID of the child with BASHPID
.
~ $ echo $$
17601
~ $ ( echo $$; echo $BASHPID )
17601
17634