Open a random file selected from a specified directory and its subdirectories.

randopen.bash

#!/bin/bash
#
# randopen.bash [-n] [DIR]
#
# Choose a random file selected from the directory DIR, or the current
# directory if it is not given, and its subdirectories.  Output the
# selected file's name, and open it unless the `-n` option is given.
#
# Requires at least bash 3.1.  `open` is specific to OS X and should be
# replaced on other platforms (e.g., `xdg-open`).

search_recursive() {
    local i
    for i in "$1"/*; do
        [[ -d "$i" ]] && search_recursive "$i"
        [[ -f "$i" ]] && echo -ne "$i\0"
    done
}

if [[ $1 == "-n" ]]; then
    dry_run=1
    shift
fi
# Use the current directory if no argument is specified.
dir=${1:-.}
# Does the directory exist?
[[ -d "$dir" ]] || exit 1
while read -d '' -r; do
    files+=("$REPLY")
done < <(search_recursive "$dir")
# Are there any files in the directory?
[[ ${#files[@]} -gt 0 ]] || exit 1
file="${files[$((RANDOM % ${#files[@]}))]}"
echo "$file"
[[ -z $dry_run ]] && open "$file"