I saw this video which explains that when running a command in parentheses it actually runs the command in a subshell, which is a child process of the original shell. Running the following experiment:
// one shell with PID 5344 ~$ (find /) // another shell ~$ ps l F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND ... 0 1000 5344 5333 20 0 10888 5220 do_wai Ss pts/0 0:00 bash 0 1000 5384 5333 20 0 10888 5140 do_wai Ss pts/1 0:00 bash 0 1000 7239 5344 20 0 10860 3444 - R+ pts/0 0:00 find / 4 1000 7240 5384 20 0 11400 3224 - R+ pts/1 0:00 ps l We can see that find / is a child of 5344, with no other shell in between. Wheres running:
// one shell with PID 5344 (cd /; find /) // second shell ~$ ps l F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND ... 0 1000 5344 5333 20 0 10888 5220 do_wai Ss pts/0 0:00 bash 0 1000 5384 5333 20 0 10888 5140 do_wai Ss pts/1 0:00 bash 1 1000 7379 5344 20 0 10888 3036 do_wai S+ pts/0 0:00 bash 4 1000 7380 7379 20 0 10864 3536 - R+ pts/0 0:01 find / 4 1000 7381 5384 20 0 11400 3184 - R+ pts/1 0:00 ps l Now we can see that other shell in between. My guess is that it is some optimization of bash: In the first case, it doesn't really have to spawn another shell, so it just doesn't do it. In the second case, since the commands include cd /, which will have affect on the current shell, it has to spawn another process. Is that so?
