Bash killring visualizer - Script to view the killring in Bash

bash-killring-viewer.sh

# All my gist code is licensed under the terms of the MIT license.

# Video demo: https://www.youtube.com/watch?v=Yat95AAV5k4

# from https://unix.stackexchange.com/a/217390/569343
# write provided text to the terminal input
# (does not work in subshells)
# - There are some weird errors when I remove the 2>/dev/nulls, but I don't
#   even know how to begin to fix them.
function write_to_input () {
  bind '"\e[0n": "'"$*"'"'

  saved_settings=$(stty -g 2>/dev/null)
  stty -echo -icanon min 1 time 0 2>/dev/null
  printf '\e[5n'
  until read -r -t0; do
    sleep 0.02
  done
  stty "$saved_settings" 2>/dev/null
}

# Killring internal function
# - this function performs the actual job of calculating and printing the
#   killring
# - the strange name is because, due to the ungodly hack required for this
#   thing to work, there is an edge case when the kill ring is empty, in which
#   this function will be typed into the Readline input line but the user still
#   needs to press enter. Therefore the function itself acts as the
#   user-friendly message.
# - It works like this:
#   - It guesses the content of the keyring after 10 rotations, and prints it.
#   - It calculates how many times it must rotate to return to the original
#     position, and performs the rotation by editing the Readline input line.
#   - Then it preses delete 500 times, in the hope of returning the input line
#     in pristine condition.
function __Killring_is_empty__Press_enter_to_continue () {
  local array;
  readarray -t array

  # if array is empty, killring is empty
  if [[ ${#array[@]} == 0 ]]; then
    return
  fi

  # the last yanked thing
  local current_position=$((${#array[@]} - 1))

  # find index of element that matches the first, or -1 if none
  # Note: this script assumns that there are no repeated elements in the
  #       killring. If that's not the case, the ring will rotate from the
  #       original position.
  #       A better algorithm to detect repeated elements could help, but I
  #       can't be arsed.
  local index_of_repeat=-1
  for (( i = 1; i < ${#array[@]}; i++ )); do
    if [[ "${array[$i]}" == "${array[0]}" ]]; then
      index_of_repeat=$i
      break
    fi
  done

  # reduce array to the actual killring
  if [[ $index_of_repeat != -1 ]]; then
    array=("${array[@]:0:$index_of_repeat}")
  fi

  local killring_size="${#array[@]}"
  
  # print killring
  local green='\x1b[32m'
  local reset='\x1b[0m'
  clear
  echo "${green}"Killring:"${reset}"
  for (( i = 0; i < ${#array[@]}; i++ )); do
    local display_index=$((i + 1)) 
    echo "${green}${display_index}${reset} ${array[$i]}"
  done

  local needed_pops=0
  local killring_position=$((current_position % killring_size))
  if [[ $killring_position != 0 ]]; then
    needed_pops=$((killring_size - killring_position))
  fi

  # doing the pops
  local command='\C-y'
  for (( i = 0; i < needed_pops; i++ )); do
    command="$command\ey"
  done

  # append 500 backspaces to clear the input (\C-?)
  # Forgive me, Lord.
  for (( i = 0; i < 500; i++ )); do
    command="$command\C-?"
  done
  write_to_input "$command"
  set -o history
}

# show the current killring
function killring () {
  set +o history

  # a killring has a maximum size of 10 in bash, so this should be enough to
  # figure out the contents
  local size=10
  
  # compose command to show killring.
  # - the command consists of pressing \C-y to yank 10 times to cover the
  #   entire killring.
  # - for some reason, \C-y stops the command generation if there's nothing in
  #   the killring, so we leave the command in a functional state in that
  #   situation, so that the user can press enter to proceed.
  # - Note: Your shell must be in "set -o emacs" mode for this to work. If 
  #   needed you could switch to emacs here and back to vi after the command
  #   ends.
  local command="__Killring_is_empty__Press_enter_to_continue <<'EOF'\nEOF"
  command="$command\C-y\C-a\C-d\C-d\C-d\n"
  for (( i = 1; i < size; i++ )); do
    command="$command\C-y\ey\n"
  done
  command="${command}EOF\n"
  write_to_input "$command"
}