What starts new subshell in Bash?

A开发者_如何学运维re there actions in Bash other than pipes and command substitution that start a new subshell?

Putting a command chain in parens (( ... )) also starts a new subshell.

( cd /tmp ; pwd ) ; pwd

Each shell script running is, in effect, a subprocess (child process) of the parent shell.

A shell script can itself launch subprocesses. These subshells let the script do parallel processing, in effect executing multiple subtasks simultaneously.

say you have script test.sh. After you run it if you run the command

ps -ef|grep -i test.sh

you will see the it runs with different PID

In general, an external command in a script forks off a subprocess/subshell