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Pandya
Asked: 2014-07-07 21:03:49 +0800 CST

How do I get randomness in command-line?

  • 772

How to randomly execute one command within specified list of command? Helpful for randomly choosing startup sound, wallpaper or executing commands.

In General, if I have commands for execution as follows then How do I get randomness:?

#!/bin/bash
<command_1>
<command_2>
<command_3>
.
.
.
<command_n>

Then I want to execute randomly only one command from above possibilities when script is run!

How to do that?

command-line

4 Answers

  1. Best Answer

    The variable $RANDOM (actually a bash function) returns a random number from 0 to 32767 inclusive.

    You would typically want to limit its range by dividing it by some number and take its remainder, eg.

    # output a random number 0 to 3
echo $((RANDOM % 4))

    In this simplistic example it'll be very slightly biased for any divisor that doesn't divide equally into 32768 (eg, anything that isn't a power of two), but in your scenario I don't think you'd be troubled by a slight bias.

    To pick a random file, you'd name your files something like:

    file0.jpg
file1.jpg
file2.jpg
file3.jpg

    And then you can pick a random one with

    # output a random file from file0.jpg to file3.jpg
echo "file$((RANDOM % 4)).jpg"
    • 22

  2. According to @neon_overload answer (using RANDOM),
    I can put RANDOM in example script as follows (for 4 commands):

    #!/bin/bash
random_selection=$((RANDOM % 4))

case $random_selection in

  0)
  <command_1>
  ;;

  1)
  <command_2>
  ;;

  2)
  <command_3>
  ;;

  3)
  <command_4>
  ;;

esac
    • 8

  3. If you want randomness through an external site rather than one generated by your computer, you can use this script:

    curl "http://www.random.org/integers/?num=1&min=$1&max=$2&col=1&base=10&format=plain&rnd=new"

    Run as rand (MIN) (MAX) (assuming you save as /usr/bin/rand)

    You might have to install curl first (sudo apt-get install curl) if it is not already installed.

    • 3

  4. You can use shuf command from GNU coreutils.

    NAME
       shuf - generate random permutations

SYNOPSIS
       shuf [OPTION]... [FILE]
       shuf -e [OPTION]... [ARG]...
       shuf -i LO-HI [OPTION]...

DESCRIPTION
       Write a random permutation of the input lines to standard output

    Example:

    $ shuf -i 1-5
4
1
2
5
3


    $ shuf -e Debian Ubuntu Trisquel 
Trisquel
Debian
Ubuntu

    Now, For getting one random entry you can use -n 1 which outputs first line.

    Example for printing random number from 1-100:

    $ shuf -i 1-100 -n 1
37

    If you've file with following contents:

    $ cat file
command-1
command-2
command-3
command-4
command-5

    You can also do something like:

    $ shuf file -n 1
command-3
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