Bash function to prompt using a menu

promptMenu.sh

#! /usr/bin/env bash

# Present a menu and prompt user to select one of the given options.
#
# usage:
# prompt_menu "<choices>" "<cols>:<width>" prompt="Choose one: " delim=":"
#  $1 - choices
#    contains the values to be seleted separated by newlines
#    Optionally, each value can be followed by a User friendly label that will
#    be displayed for that value.  The label if present must be appened to the value
#    following a delimiter.  The default delimiter is colon ':'
#  $2 - columns and width
#    By default the menu options are show in a single column.
#    For large menus is it sometimes better to display the choices in
#    more than one column.
#    This argument may consist of one or two integers separated by a colon ':'
#    The first (and possible only) integer is the number of columns desired.
#    The second integer is the amount of screen width that the entire menu
#    will use.  The colums widths will be evenly divided among this screen
#    width.  If the <width> column is not given, then the scren width
#    as reported by `tput cols` is used and if that fails then a value
#    of 80 is used as a last resort.
#    Normally, you will want to supply the width so that the menu does
#    not look spread out on wide monitors.
#  $3 - prompt
#    The prompt string show to the user.  If not given a default prompt
#    of "Choose one: " is  used.
#  $4 - delim
#    delimiter used to separate values from their associated labels.
#    This must be a single character.
#    If not given, a default delimiter of ':' is used.
#
#  return
#    The selected value is written to stdout
#    Use command substitution to save the return value
#
#  example:
#  choices='
#     international: YYYY-MM-DD (ISO)
#     us           : MM-DD-YYYY (United States)
#     europe       : DD-MM-YYYY (Europe)
#  '
#  date_format=`promptMenu "$choices"
#
#   # With two column layout:
#   date_format=`promptMenu "$choices" "2:80"
#
#   # With a custom prompt:
#  date_format=`promptMenu "$choices" "1" "Select date format:"`

promptMenu() {
  local choices="$1"
  local prompt="${3:-"Choose one:"}"
  local delim="${4:-":"}"
  local values=() labels=()
  local choice=-1 max_label=0 separator=""
  local response rest idx num_width num_choices
  local default_width num_cols menu_width

  if [[  -z "$choices" ]]; then
    printf "promptMenu: first argument (choices) is required\n" >&2
    return 1
  fi

  trim() {
    local var="$1"
    # remove leading whitespace characters
    var="${var#"${var%%[![:space:]]*}"}"
    # remove trailing whitespace characters
    var="${var%"${var##*[![:space:]]}"}"
    printf '%s' "$var"
  }



  default_width="$(tput cols)" || default_width=80

  # Set up columns
  if [[ -z "$2" ]]; then
    num_cols="1"
    menu_width="$default_width"
  else
    # Putting IFS=':' in the same line before set was not working!
    local save_IFS="$IFS"
    IFS=':'
    # Do not quote $2 here!
    set $2
    IFS="$save_IFS"
    num_cols="${1}"
    menu_width="${2:-$default_width}"
  fi

  while IFS="$delim" read -r value label; do
    value="$(trim "$value")"
    label="$(trim "$label")"
    [[ -z "$value" ]] && continue
    label=${label:-"$value"}
    values+=("$value")
    labels+=("$label")
  done <<< "$choices"

  for idx in "${labels[@]}"; do
    (( max_label="${#idx} > max_label ? ${#idx} : max_label" ))
  done

  num_choices="${#labels[@]}"
  num_width="${#num_choices}"

  # Acount for max label plus number plus ") "
  for (( idx=0; idx < max_label + num_width + 2; ++idx )); do
    separator="$separator-"
  done

  while [[ $choice == -1 ]]; do
    # Print the menu entires using pr to handle
    # the column layout.
    # Use pr to handle the display of columns
    for idx in "${!labels[@]}"; do
      printf "%${num_width}d) %s\n" $((idx + 1)) "${labels[$idx]}"
    done  | pr -t "-$num_cols" "-w$menu_width"
    printf -- "%s\n%s " "$separator" "$prompt"
    read -r response rest
    (( choice="response - 1" ))
    if [[ $choice -lt 0 || $choice -ge ${num_choices} ]]; then
      printf "'%s' is not a valid choice\n" "$response"
      choice=-1
    fi
  done >&2
  unset trim
  echo "${values[$choice]}"
}