Linux / UNIX: Run Command a Number of Times In a Row

Linux / UNIX: Run Command a Number of Times In a Row

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How do I run “foo” command 10 times (or n times) under Linux or UNIX like operating systems?

You can use bash shell loop (run code or command repeatedly) to run a command 10 times as follows.
How to run a command N times in bash
there are many ways to run a command N times in bash/ksh/zsh. Use syntax as per your shell.

 

 

 

Syntax

The syntax is:

## run command 10 times 
for i in {1..10}; do commandNameHere; done
 
## run script 20 times
for i in {1..10}; do /path/to/cache.script.sh; done

For example, run UNIX date command five times, enter:

for i in {1..5}; do date; done

You can also use c like bash for loop syntax:

for ((n=0;n<5;n++))
do
 command1
 command2
done

The for loop syntax for tcsh / csh / ksh and other shell may changes from version to version.

Using while loop

Use the bash/sh/ksh posix based while loop as follows:

## define end value ##
END=5
## print date five times ##
x=$END 
while [ $x -gt 0 ]; 
do 
  date
  x=$(($x-1))
done

repeat for zsh users

If you are using the Z shell (zsh)

repeat N { command }
repeat N { /path/to/script }
## print date five times on screen ##
repeat 5 { date }

Say hello to seq command

To print a sequence of numbers one can use the seq command too. The syntax is:
seq LAST
seq FIRST LAST
seq FIRST INCREMENT LASE
seq LAST | xargs command
seq FIRST LAST | xargs command
seq FIRST INCREMENT LASE | xargs command

To just print five number, run:
$ seq 1 5
OR
$ seq 5
Sample outputs:

1
2
3
4
5

Use the xargs command to run the date command five times:
$ seq 1 5 | xargs -I{} date
Sample outputs:

Tue Nov 28 00:32:52 IST 2017
Tue Nov 28 00:32:52 IST 2017
Tue Nov 28 00:32:52 IST 2017
Tue Nov 28 00:32:52 IST 2017
Tue Nov 28 00:32:52 IST 2017

You can use xargs with multiple commands line argument as follows:
$ seq 1 5 | xargs -I{} sh -c "date && sleep 1"
It is also possible to use the parallel command:
$ seq 5 | parallel 'echo {}'
$ seq 5 | parallel 'echo Hello $USER, {} times.'

See man page of the following command for more info:
$ man parallel
$ man xargs
$ man seq

A note about using Perl or Python

You can use python or Perl as follows to run date command 5 times:

#!/usr/bin/perl
for $i (1 .. 5) {
   system("date");
}

Python example:

#!/usr/bin/python
# Run unix date command 3 times 
import os;
for x in range(0,3):
    os.system("date")
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