Is there a better way to run a command N times in bash?

Question

I occasionally run a bash command line like this:

n=0; while [[ $n -lt 10 ]]; do some_command; n=$((n+1)); done

To run some_command

Answer 1

for _ in {1..10}; do command; done   

Note the underscore instead of using a variable.

Answer 2

Using a constant:

for ((n=0;n<10;n++)); do some_command; done

Using a variable (can include math expressions):

x=10; for ((n=0; n < (x / 2); n++)); do some_command; done

Answer 3

For loops are probably the right way to do it, but here is a fun alternative:

echo -e {1..10}"\n" |xargs -n1 some_command

If you need the iteration number as a parameter for your invocation, use:

echo -e {1..10}"\n" |xargs -I@ echo now I am running iteration @

Edit: It was rightly commented that the solution given above would work smoothly only with simple command runs (no pipes, etc.). you can always use a sh -c to do more complicated stuff, but not worth it.

Another method I use typically is the following function:

rep() { s=$1;shift;e=$1;shift; for x in `seq $s $e`; do c=${@//@/$x};sh -c "$c"; done;}

now you can call it as:

rep 3 10 echo iteration @

The first two numbers give the range. The @ will get translated to the iteration number. Now you can use this with pipes too:

rep 1 10 "ls R@/|wc -l"

with give you the number of files in directories R1 .. R10.

Answer 4

Using GNU Parallel you can do:

parallel some_command ::: {1..1000}

If you do not want the number as argument and only run a single job at a time:

parallel -j1 -N0 some_command ::: {1..1000}

Watch the intro video for a quick introduction: https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1

Walk through the tutorial (http://www.gnu.org/software/parallel/parallel_tutorial.html). You command line with love you for it.

Answer 5

The script file

bash-3.2$ cat test.sh 
#!/bin/bash

echo "The argument is  arg: $1"

for ((n=0;n<$1;n++));
do
  echo "Hi"
done

and the output below

bash-3.2$  ./test.sh 3
The argument is  arg: 3
Hi
Hi
Hi
bash-3.2$

Answer 6

Another simple way to hack it:

seq 20 | xargs -Iz echo "Hi there"

run echo 20 times.

---

Notice that seq 20 | xargs -Iz echo "Hi there z" would output:

Hi there 1
Hi there 2
...