calコマンド: groovy cal.groovy <year> <month>

cal.groovy

import static java.util.Calendar.*

def cal = Calendar.instance
def year = cal[YEAR]
def month = cal[MONTH]

if(args && args[0] && args[0].isInteger() && args[1] && args[1].isInteger()) {
  year = args[0].toInteger()
  month = args[1].toInteger()
  cal[YEAR] = year
  cal[MONTH] = (month-1) % 12
}

def String[][] calMatrix = new String[6][7]
def days, firstDow

println "${cal[YEAR]}/${cal[MONTH]+1}"
cal[DATE] = 1
days = cal.getActualMaximum(DATE)
firstDow = cal[DAY_OF_WEEK]

(0..5).each{ week ->
  (0..6).each{ day ->
    calMatrix[week][day] = " "*3
  }
}

(1..days).each{ d ->
  def day = (d + firstDow - 2) % 7
  def week = (d + firstDow -2).intdiv(7)
  calMatrix[week][day] = d.toString().padLeft(3," ")
}

println "Sun Mon Tue Wed Thu Fri Sat"
calMatrix.each{ week ->
  println week.join(" ")
}

CalendarクラスのGDKのサンプルとして