Best way to choose a random file from a directory in a shell script

Question

What is the best way to choose a random file from a directory in a shell script?

Here is my solution in Bash but I would be very interested for a more portable (non-

Answer 1

files=(/my/dir/*)
printf "%s\n" "${files[RANDOM % ${#files[@]}]}"

And don't parse ls. Read http://mywiki.wooledge.org/ParsingLs

Edit: Good luck finding a non-bash solution that's reliable. Most will break for certain types of filenames, such as filenames with spaces or newlines or dashes (it's pretty much impossible in pure sh). To do it right without bash, you'd need to fully migrate to awk/perl/python/... without piping that output for further processing or such.

Answer 2

I think Awk is a good tool to get a random number. According to the Advanced Bash Guide, Awk is a good random number replacement for $RANDOM.

Here's a version of your script that avoids Bash-isms and GNU tools.

#! /bin/sh

dir='some/directory'
n_files=`/bin/ls -1 "$dir" | wc -l | cut -f1`
rand_num=`awk "BEGIN{srand();print int($n_files * rand()) + 1;}"`
file=`/bin/ls -1 "$dir" | sed -ne "${rand_num}p"`
path=`cd $dir && echo "$PWD/$file"` # Converts to full path.  
echo "The randomly-selected file is: $path"

It inherits the problems other answers have mentioned should files contain newlines.

Answer 3

# ******************************************************************
# ******************************************************************
function randomFile {
  tmpFile=$(mktemp)

  files=$(find . -type f > $tmpFile)
  total=$(cat "$tmpFile"|wc -l)
  randomNumber=$(($RANDOM%$total))

  i=0
  while read line;  do
    if [ "$i" -eq "$randomNumber" ];then
      # Do stuff with file
      amarok $line
      break
    fi
    i=$[$i+1]
  done < $tmpFile
  rm $tmpFile
}

Answer 4

Something like:

let x="$RANDOM % ${#file}"
echo "The randomly-selected file is ${path[$x]}"

$RANDOM in bash is a special variable that returns a random number, then I use modulus division to get a valid index, then reference that index in the array.

Answer 5

BusyBox (used on embedded devices) is usually configured to support $RANDOM but it doesn't have bash-style arrays or sort --random-sort or shuf. Hence the following:

#!/bin/sh
FILES="/usr/bin/*"
for f in $FILES; do  echo "$RANDOM $f" ; done | sort -n | head -n1 | cut -d' ' -f2-

Note trailing "-" in cut -f2-; this is required to avoid truncating files that contain spaces (or whatever separator you want to use).

It won't handle filenames with embedded newlines correctly.