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Is there a way to create say 10 instances of a process (for example yes) with a single command?

$instantiate 10 yes
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2 Answers 2

up vote 3 down vote

Would something like the following be OK? This assumes bash (for brace expansion) and GNU parallel.

parallel -N0 -j0 -u yes ::: {1..10}

The -j0 setting is there to make sure as many processes as parameters get started, and -u (ungroup) is there so that the output of each process is printed as soon as it is available (this matters in the case of yes, since its output is infinite). -N0 prevents arguments from being inserted into the command line.

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The \; : {} can be avoided by using -N0. If you want to run as many in parallel as possible -j0 is a better choise: It will automatically adjust if it cannot spawn new processes. –  Ole Tange May 5 at 5:53
    
Good point, I integrated your comment into my answer. –  dhag May 6 at 18:26
up vote 2 down vote

@dhag certainly has a one-line answer, but the syntax makes my eyes hurt. :)

Since you asked for a single command, and since the shell considers for-do-done a single (compound) command, I feel justified with this much more readable version:

for i in {1..10}; do yes &; done

Note that some shells automatically nice(2) background jobs, so if that's an issue then this isn't the best solution.

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GNU parallel does have a strange syntax, but once you go through its tutorial for one hour, you'll thank yourself for the rest of your life for the powers it will arm you with :) –  shivams May 5 at 5:05

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