operators

#!/bin/bash

# Copyright (C) 2015 Benjamin Abendroth
# 
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

################################################################################
# Operators ####################################################################
################################################################################

is_even () {
  (( ${1?"$FUNCNAME: Missing operand"} % 2 == 0 ))
}

is_odd () {
  (( ${1?"$FUNCNAME: Missing operand"} % 2 == 1 ))
}

is_true () {
  grep -Eiq '\<(true|yes|y|j|enabled|on|1)\>' <<< "$@"
}

is_false () {
  grep -Eiq '\<(false|no|n|disabled|off|0|fail|failed)\>' <<< "$@"
}

is_root () {
  (( UID == 0 ))
}

is_digit () {
  case $1 in
    *[!0-9]*|"") return 1 ;;
    *) return 0
  esac
}

is_xdigit () {
  case $1 in
    *[!0-9a-fA-F]*|"") return 1 ;;
    *) return 0
  esac
}

is_alpha () {
  case $1 in
    *[!a-zA-Z]*|"") return 1 ;;
    *) return 0
  esac
}

is_alnum () {
  case $1 in
    *[!a-zA-Z0-9]*|"") return 1 ;;
    *) return 0
  esac
}

defined () {
  [[ ${!1-X} == ${!1-Y} ]]
}

has_value () {
  defined $1 && [[ -n ${!1} ]]
}

default () {
  has_value "$1" || declare -g $1="${2:-}"
}