zsh/Functions/Calendar/calendar_showdate

emulate -L zsh
setopt extendedglob
zmodload -i zsh/datetime

local optm datefmt opt
integer optr replyset

zstyle -s ':datetime:calendar_showdate:' date-format datefmt ||
  datefmt="%a %b %d %H:%M:%S %Z %Y"

while [[ $argv[$OPTIND] != +* ]] && getopts "r" opt; do
  case $opt in
    (r)
    REPLY=0
    optr=1
    ;;
  esac
done
shift $(( OPTIND - 1 ))

(( optr )) || local REPLY

if (( ! $# )); then
  print "Usage: $0 datespec [ ... ]" >&2
  return 1
fi

while (( $# )); do
  optm=
  if [[ $1 = [-+]* ]]; then
    # relative
    [[ $1 = -* ]] && optm=-m
    1=${1[2,-1]}
    # if this is the first argument, use current time
    # don't make assumptions about type of reply in case global
    if (( ! replyset )); then
      REPLY=$EPOCHSECONDS
      replyset=1
    fi
  fi

  if (( replyset )); then
    calendar_scandate $optm -R $REPLY -aA $1 || return 1
    replyset=1
  else
    calendar_scandate -aA $1 || return 1
  fi

  shift
done

(( optr )) && return
strftime $datefmt $REPLY