How to pick a random element from the output of a command?

Question

If I have something like:

echo 1 2 3 4 5 6

or

echo man woman child

what do I have to put behind the pipe to pick out one element of 1 2 3 4 5 6 or man woman child?

echo 1 2 3 4 5 6 | command
3

Answer 1

If your system has the shuf command

echo 1 2 3 4 5 | xargs shuf -n1 -e

If the input doesn't really need to be echoed via standard input, then it would be better to use

shuf -n1 -e 1 2 3 4 5

Answer 2

If you don't have shuf (which is a great tool), but you do have bash, here's a bash-only version:

function ref { # Random Element From
  declare -a array=("$@")
  r=$((RANDOM % ${#array[@]}))
  printf "%s\n" "${array[$r]}"
}

You'd have to reverse the sense of your call -- use ref man woman child instead of echo man woman child | command. Note that $RANDOM may not be "strongly" random -- see Stephane's comments on: https://unix.stackexchange.com/a/140752/117549

Here's sample usage, and a random (!) sampling (the leading $ are the shell prompt; do not type them):

$ ref man woman child
child
$ ref man woman child
man
$ ref man woman child
woman
$ ref man woman child
man
$ ref man woman child
man

$ ref 'a b' c 'd e f'
c
$ ref 'a b' c 'd e f'
a b
$ ref 'a b' c 'd e f'
d e f
$ ref 'a b' c 'd e f'
a b


# showing the distribution that $RANDOM resulted in
$ for loop in $(seq 1 1000); do ref $(seq 0 9); done | sort | uniq -c
  93 0
  98 1
  98 2
 101 3
 118 4
 104 5
  79 6
 100 7
  94 8
 115 9