Linux shell running programming simultaneuosly

I need to run a programmme, let say ./a for 10 times in the linux shell. What is the command to do that?

Also, how could I differentiate the output from different pr开发者_StackOverflow中文版ocesses?

Besides, my ./a is a continual process. How could I terminate it?

Thanks.

---

In bash you can do:

for ((i=1;i<=10;i++)); do

  # run the command ./a and redirect its output to a file named after
  # its sequence number...like out1.txt, out2.txt...
  ./a > out$i.txt &   

done

The key here is the & which runs the command in the background. Without the & the 2nd ./a will be started after the fist got completed, effectively making it serial execution. But with &, we don't wait for one invocation of ./a to complete before we launch another one and that is how we achieve parallelism.

---

Make a loop that starts the program 10 times in the background:

for i in $(seq 1 10) ; do
 ./a &
done

Also, how could I differentiate the output from different processes?

You can't easily do that, the output can be interwined. Redirect the output of each process to a different file rather, e.g.

for i in $(seq 1 10) ; do
 ./a >output.$i  &
done

As a oneliner, you'd run

for i in $(seq 1 10) ; do ./a >output.$i  & done

to kill those processes later:

for i in $(seq 1 10) ; do kill %$i ; done

---

for i in {1..10}
do
  ./a > "out_${i}.txt" &
done

to terminate a, you can use pkill a

---

Assuming you use Bash or compatible shell, the special variable $! holds the process ID of the last process you made asynchronous. Augumenting nos' answer, I'd suggest using

for i in $(seq 1 10) ; do
    ./a 1> stdout.$i 2> stderr.$i &
    echo $! > pid.$i
done

Now you have error output in stdout.X, error output in stderr.X and the process ID in pid.X so you can kill it with

kill `cat pid.X`

or even kill all processes with

for i in $(seq 1 10) ; do
    kill `cat pid.$i`
done

---

All of the other answers are fine so far, but you amy also want to try repeat, if supported by your system:

repeat 10 ./a

Here to differentiate outputs, unfortunately, you won't be able to use a counter variable. You can however use a timestamp:

repeat 10 ./a  >> output_`date +%N`

That being said, the behavior of date for anything below the second mark is unspecified, so that's not the most reliable way. A bit easier than to write a for loop though.