subset.sh

#!/usr/bin/env bash

# Copy specific characters from a string to the clipboard
# Enter empty character index to exit

# Read password
echo -n "Password: "
read -s password
echo

# Until enough characters have been copied..
while true; do
  # Read character index
  echo -n "Index: "
  read index

  if [[ -z $index ]]; then # Empty input
    echo "Bye"
    exit
  elif ! [[ $index =~ ^[0-9]+$ ]]; then # Non numeric input
    echo "Enter a number"
    echo
  elif [[ $index < 1 ]]; then # Zero input
    echo "Enter a number 1-${#password}"
    echo
  # elif [[ ${index} > ${#password} ]]; then # Index doesn't exist: doesn't work!
  #   echo "Enter a number 1-${#password}"
  #   echo
  else # Copy character
    echo "${password:$index-1:1}" | pbcopy
    echo "Copied!"
    echo
  fi
done