Creating a sequence of distinct random numbers within a certain range in bash script

Question

I have a file which contains entries numbered 0 to 149. I am writing a bash script which randomly selects 15 out of these 150 entries and create another file from them.
I tried using random number generator:

var=$RANDOM
var=$[ $var % 150 ]

Using var I picked those 15 entries. But I want all of these entries to be different. Sometimes same entry is getting picked up twice. Is there a way to create a sequence of random numbers within a certain range, (in my example, 0-149) ?

John Kugelman · Accepted Answer · 2014-02-08 20:24:45Z

21

Use shuf -i to generate a random list of numbers.

$ entries=($(shuf -i 0-149 -n 15))
$ echo "${entries[@]}"
55 96 80 109 46 58 135 29 64 97 93 26 28 116 0

If you want them in order then add sort -n to the mix.

$ entries=($(shuf -i 0-149 -n 15 | sort -n))
$ echo "${entries[@]}"
12 22 45 49 54 66 78 79 83 93 118 119 124 140 147

To loop over the values, do:

for entry in "${entries[@]}"; do
    echo "$entry"
done

edited Feb 8, 2014 at 20:24

answered Feb 8, 2014 at 19:54

John Kugelman

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4 Comments

nishantsingh Over a year ago

What does the [@] mean in ${entries[@]? Say I wanted to run a loop on these values , can i do : for i in $entries do ... done ?

mklement0 Over a year ago

OSX users: installable via Homebrew: brew install coreutils; invoke as gshuf.

bryn Over a year ago

@user3286661 [@] expands to 'all items in array' - if you do 'echo $entries' you will get the first item. If you do 'echo ${entries[@]}' it will echo all items.

abalter Over a year ago

I can't get it to provide any more than 1001 numbers. CentOS 64 bit. Is that expected?

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