Choose between 2^n choices with the help of a binary tree.

bin-tree-chooser.sh

#!/usr/bin/env bash

# A shell script that helps a user to choose between 2^n possible choices by
# simulating a tournament through a perfect binary tree with randomly disposed
# nodes. It accepts input from /dev/stdin, i.e. through pipes or redirection.
#
# The power-of-2 input size restriction could be relaxed, but then choices
# would be probably less fair without repetitions of the classification process
# to make up for the generated tree prioritizing rightmost nodes.

CONTENTS="$(shuf < /dev/stdin)"
NUM_LINES="$(echo "$CONTENTS" | wc -l)"
NODES="$((NUM_LINES - 1))"
if ! (( NUM_LINES > 0 && (NUM_LINES & NODES) == 0 )) ; then
  echo "Length of input must be a power of 2!"
  exit 1
fi

ITERATIONS=0
while read -r OPT1 ; read -r OPT2 ; do
  ITERATIONS="$((ITERATIONS + 1))"
  ANSWER=0
  until [ "$ANSWER" = "1" ] || [ "$ANSWER" = "2" ] ; do
    printf "[%3d / %3d] " "$ITERATIONS" "$NODES"
    read -p "Choose 1 ($OPT1) or 2 ($OPT2): " -r -N1 ANSWER < /dev/tty
    [ "$ANSWER" = $'\n' ] && printf "\033[1A"
    printf "\r\033[2K"
  done
  CHOICE="OPT$ANSWER"
  echo "${!CHOICE}" > /dev/stdin
done <<< "$CONTENTS"

echo "Final choice is \"$OPT1\"!"