Question

$cat t.sh  
grep "12" test | wc -c  

I want to know how many processes will be created when it runs.
I used

./t.sh;ps -aux | grep "t.sh"    

but it didn’t work because “./t.sh” had run over when ps was working.

How can I reach this goal?

Answer 1

Depends on the system you are running on. If you have strace you can trace all the fork system calls. problem is though that somesystems use fork, some vfork and some clone, you will have to experiment. On linux:

strace -c -f -evfork ./t.sh

should give you a summary. -c gives a count, -f means “follow” child processes, and -evfork means trace the vfork kernel call. The output goes to stderr, but you can redirect it to a file using the -o option (there are some neat tricks you can do if you specify a named pipe here).