$$ in a script vs $$ in a subshell

Question

$$ gives process id of the script process when used in a script, like this:

Example 1

#!/bin/bash
# processid.sh
# print process ids

ps         


        

Answer 1

I tried and escaping (to pass the $$ to the subshell) does not work as the subshell inherits the $$ value from the parent bash. The solution to this is to use $BASHPID.

(echo $$; echo $BASHPID)

prints the PID from the parent shell and from the subshell.

Answer 2

The replacement takes place in the parent shell; the subshell hasn't been started by the time the substitution takes place.

Answer 3

A more portable way, linux-only, but also compatible with dash:

read -r my_pid _ < /proc/self/stat
echo $my_pid

Answer 4

From the bash manpage:

   $      Expands  to  the  process ID of the shell.  In a () subshell, it
          expands to the process ID of the current  shell,  not  the  sub-
          shell.