#!/bin/bash

# If no directory given, use the current one.
dir=""
if [[ "$1" == "" ]]; then
  dir="."
else
  dir="$1"
fi

# arrn = number of files in directory + 1 (header line)
arrn=$(ls "$dir" | wc -l)
# Add one for sed:
#  sed 11q will print the first 10 lines, but I want the 11th
# Add one for % modulous:
#  10 mod 10 == 0, but I need 10 to be a valid random number
((arrn += 2))
rand=$(($RANDOM % $arrn))
# Add to rand until it is at least two:
#  0 will fail, and 1 will print the header line of ls -l
while [[ "$rand" -lt 2 ]]; do
  ((rand += 1))
done
# List the dir again, get the $rand line, grab the tail of that,
#  then print the 9th element of the line (the file/dir name).
ls -l "$dir" | sed "${rand}q" | tail -n1 | awk '{print $9}'