echo $$

vinaytp · 11-20-2009, 08:27 AM

Dear all....

I have a file named new.sh which has executable permission, contents of the file is

Code:

echo $$

./new.sh will give the PID of the shell in which new.sh executes....
. new.sh will be executed in current shell so it displays PID of current shell

But if i execute following on command prompt

Code:

echo $$
(echo $$)

First will display current shell's PID, its fine
Why second command will displays current shell's PID eventhough it executes in subshell ????

David the H. · 11-20-2009, 09:55 AM

Note #5 here says that $$ in a subshell gives the PID of the script, not the subshell.

http://www.tldp.org/LDP/abs/html/int...s.html#PROCCID

catkin · 11-20-2009, 10:18 AM

Quote:

Originally Posted by David the H.

Note #5 here says that $$ in a subshell gives the PID of the script, not the subshell.

http://www.tldp.org/LDP/abs/html/int...s.html#PROCCID

And so it does. My gast is flabbered

Code:

c:~$ echo $$
4128
c:~$ (eval echo '$$')
4128

vinaytp · 11-23-2009, 01:54 AM

Dear all...

My doubt is not clear...

why

Code:

(echo $$ )

should give current shell's PID why not subshell's PID, as it executes in subshell

catkin · 11-23-2009, 03:03 AM

Quote:

Originally Posted by vinaytp

Dear all...

My doubt is not clear...

why

Code:

(echo $$ )

should give current shell's PID why not subshell's PID, as it executes in subshell

Because that is how bash is designed, as described in the link given by David the H. Surprised me.

David the H. · 11-23-2009, 04:19 AM

In other words, we don't know why exactly...only that the behavior is intentional. On another section of that page it says that $$ returns the PID of the parent process. Perhaps it's part of the posix specification or something.

Apparently Bash v.4 has a new $BASHPID builtin variable that can give you the subshell's PID.

chrism01 · 11-23-2009, 05:35 PM

My ghast hasn't been so flabbered in ages