Bourne shell function to prompt using a menu

promptMenuSH.sh

#! /usr/bin/env sh

# Trim leading and trailing spaces
# from stdin and write to stdout.
# Useful when getting numbers from wc -c, etc.
trim() {
  sed -e 's/^[ ]*//' -e 's/[ ]*$//'
}

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

# 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.
#  $4 - delim
#    delimiter used to separate values from their associated labels.
#    This must be a single character.
#    If not given, a default delimiter of ':' is used.
#
#  return
#    The selected value is written to stdout
#    Use command substitution to save the return value
#
#  examples:
#  choices='
#  international:YYYY-MM-DD (ISO)
#  us:MM-DD-YYYY (United States)
#  europe:DD-MM-YYYY (Europe)
#  '
#  date_format=`prompt_menu "$choices"
#
#  # With two column layout:
#  date_format=`prompt_menu "$choices" "2:80"
#
#  # With a custom prompt:
#  date_format=`prompt_menu "$choices" "1" "Select date format:"`

prompt_menu() {
  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="$TMPDIR/menu_choices.$$"
  choice=-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 "prompt_menu: first argument (choices) is required\n" >&2
    return 1
  fi

  AWK="awk"
  # On SunOS we must expliclty use Posix version of awk
  [ `uname -s` = SunOS ] && AWK=/usr/xpg4/bin/awk
  
  # Put the choices in a file with each
  # entry normalized:
  #  <number>:value:display
  echo "$choices"             |
    $AWK 'NF > 0 { print $0 }' | # Remove blank lines
    $AWK -F"$delim" '
        {
          OFS=delim
          gsub(/^ *| *$/, "", $1)  # trim leading and trailer spaces from field 1
          sub(/^ */, "", $2)       # trim leading spaces from field 2
          print NR, $1, $2         # Ouput <number>:value:display
        }' delim="$delim" > "$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" >&2
    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" >&2
    fi
  done

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