Bourne shell function to prompt using a menu

promptMenuSH.sh

#! /usr/bin/env sh


# 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)
#  '
promptMenu() {
  choices="$1"
  prompt="${3:-"Choose one:"}"
  delim="${4:-":"}"

  default_width="`tput cols`" || default_width=80
  # Set up columns
  if [ -z "$2" ]; then
    num_cols="1"
    menu_width="$default_width"
  else
    # Putting the IFS= before set was not working!
    save_IFS="$IFS"
    IFS=':'
    # Do not quote $2 here!
    set $2
    IFS="$save_IFS"
    num_cols="${1}"
    menu_width="${2:-$default_width}"
  fi

  separator=""
  choices_file="/tmp/menu_choices.$$"
  choice=-1

  # Trim leading and trailing whitespace
  # from stdin and write to stdout.
  trim() {
    sed -e 's/^[ \t\n]*//' -e 's/[ \t\n]*$//'
  }

  #  Return 0 if the first argument is all digits
  is_numeric()
  {
      echo "$1" | grep -E -e '^[0-9]+$' >/dev/null 2>&1
  }

  # Pass in name of function to call for each value/label pair
  # $1 - the number of the chosen value
  # Writes the value to stdout
  value_for_index() {
    while IFS="$delim" read index value label; do
      if [ "$index" -eq "$1" ]; then
        printf "%s" "$value"
        return 0
      fi
    done <"$choices_file"
    return 1
  }
  
  iterate_choices() {
    lambda="$1"
    shift
    while IFS="$delim" read index value label; do
      [ -z "$label" ] && label="$value"
      "$lambda" "$index" "$value" "$label" "$@"
    done <"$choices_file"
  }

  get_max_label_len() {
    max_len=0

    get_max() {
      this_max="`printf "$3" | wc -c | trim`"
      [ "$this_max" -gt "$max_len" ] && max_len="$this_max"
    }

    iterate_choices "get_max"
    unset get_max
    printf "%s" $max_len
  }
  
  # Write the choices to stdout
  show_choices() {
    print_one() {
      printf "%${num_width}d) %s\n" "$1" "$3"
    }

    # Use pr to handle the display of columns
    iterate_choices "print_one" | pr -t "-$num_cols" "-w$menu_width"
    unset print_one
  }

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


  # Put the choices in a file.
  # We first normalize the entries:
  # - Skip blank lines
  # - Remove leading whitespace
  # - Remove whitespace before and after the delimiter (so the value is clean)
  # - Prepend a choice number field to each entry
  echo "$choices"             |
    awk 'NF > 0 { print $0 }' | 
    sed -e "s/^[\t ]*//" -e "s/[\t ]*${delim}[ \t]*/${delim}/" |
    awk -vdelim="$delim" '{ printf "%s%s%s\n", NR, delim, $0 }' > "$choices_file"  
  
  num_choices="`cat "$choices_file" | wc -l | trim`"
  max_label_len="`get_max_label_len`"
  num_width=`printf "%d" "$num_choices" | wc -c | trim`

  # plus two to account for  ") "
  idx=0
  idx_limit="`expr "$max_label_len" + "$num_width" + 2`"
  while [ "$idx" -lt "$idx_limit" ]; do
    separator="$separator-"
    idx="`expr "$idx" + 1`"
  done

  # Redirect all stdout to stderr for the menu display
  # We use stdout to return the chosen value.
  printf "\n" >&2
  show_choices >&2
  while [ "$choice" -eq -1 ]; do
    printf -- "%s\n%s " "$separator" "$prompt"
    IFS=' ' read response rest

    if is_numeric "$response" && [ "$response" -ge 1  ] && [ "$response" -le "$num_choices" ]; then
      choice="$response"
    else
      printf "'%s' is not a valid choice\n" "$response"
    fi
  done >&2

  printf "%s" "`value_for_index "$choice"`"
  rm -f "$choices_file" >/dev/null 2>/dev/null
  unset trim is_numeric value_for_index iterate_choices get_max_label_len show_choices
  return 0
}