How does a Linux/Unix Bash script know its own PID?

Question

I have a script in Bash called Script.sh, and it needs to know its own PID (i.e. I need to get PID inside the Script.sh )

Any idea how to do this ?

Answer 1

The variable $$ contains the PID.

Answer 2

use $BASHPID or $$

See the [manual][1] for more information, including differences between the two.

TL;DRTFM

• $$ Expands to the process ID of the shell.
  • In a () subshell, it expands to the process ID of the invoking shell, not the subshell.
• $BASHPID Expands to the process ID of the current Bash process (new to bash 4).
  • In a () subshell, it expands to the process ID of the subshell [1]: http://www.gnu.org/software/bash/manual/bashref.html#Bash-Variables

Answer 3

In addition to the example given in the Advanced Bash Scripting Guide referenced by Jefromi, these examples show how pipes create subshells:

$ echo $$ $BASHPID | cat -
11656 31528
$ echo $$ $BASHPID
11656 11656
$ echo $$ | while read line; do echo $line $$ $BASHPID; done
11656 11656 31497
$ while read line; do echo $line $$ $BASHPID; done <<< $$
11656 11656 11656

Answer 4

The PID is stored in $$.

Example: kill -9 $$ will kill the shell instance it is called from.

Answer 5

You can use the $$ variable.

Answer 6

If the process is a child process and $BASHPID is not set, it is possible to query the ppid of a created child process of the running process. It might be a bit ugly, but it works. Example:

sleep 1 &
mypid=$(ps -o ppid= -p "$!")