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 ?

Solution 1

The variable $$ contains the PID.

Solution 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

Solution 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

Solution 4

The PID is stored in $$.

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

Solution 5

You can use the $$ variable.

View more solutions

Comments

[Sopalajo de Arrierez]

could you please explain what does "<<<" mean? Thanks.

[SourceSeeker]

It redirects a string into the loop (or anything that reads stdin). The string is referred to as a "here string".

[Willem Van Onsem]

kill -9 (with -9 flag) is considered to be harmful and only to be used if it is absolutely necessary).

[Bruno Bronosky]

It's considered "dangerous" because the process does not get a chance to respond to the signal (and possibly clean up after itself). Doing kill -9 $$ does exactly 1 thing. It kills the current shell process. This is useful if you have done something in the shell session that you do not want written to .bash_history Like: docker run -e PASSWORD=hunter2 ircbot

[Murtaza Haji]

How can i get the pid from outside the script , i use top but it shows a lot of random processes