Date Parser in Bash

date-parse.sh

# date_parse_str DATESTRING
#
# parse the DATESTRING.  It can be in one of several formats: YYYY-MM-DD,
# YYYY.MM.DD, YYYY/MM/DD, YYYY MM DD, DD MMM YYYY, MMM DD, YYYY, and DD/MM/YYYY
# (if EUROPEAN_DATES is set).
#
# Sets the variables: year, month, day  --- unless there was a parser failure

date_parse_str() {
  local date="${1:-`date +%F`}"
  local euro_format=
  weekday_name= tzone= timestr= year= month= day=
  case "$date" in
    *-*-*) date="${date//-/ }"                  ;;  # replace '-' with blanks
    *.*.*) date="${date//./ }"  ; euro_format=1 ;;  # replace '.' with blanks
    */*/*) date="${date//\// }"                 ;;  # repace '/' with blanks
  esac

  # YYYY MM DD
  if [[ "$date" =~ ([0-9]{4})\ ([ 0-9]{1,2})\ ([ 0-9]{1,2}) ]]; then # yyyy mm dd
    date_parse_ymd ${BASH_REMATCH[1]} ${BASH_REMATCH[2]} ${BASH_REMATCH[3]}

  # MMM DD, YYYY   or MMMM DD, YYYY
  elif [[ "$date" =~ ([[:alpha:]]+)\ +([0-9]{1,2}),?\ +([0-9]{4}) ]]; then
    date_parse_mmmdy ${BASH_REMATCH[1]} ${BASH_REMATCH[2]} ${BASH_REMATCH[3]}

  #  DD MMM YYYY
  elif [[ "$date" =~ ([0-9]{1,2})\ +([[:alpha:]]+)\ +([0-9]]{4}) ]]; then
    date_parse_mmmdy ${BASH_REMATCH[2]} ${BASH_REMATCH[1]} ${BASH_REMATCH[3]}

  # MM DD YYYY  or  DD MM YYYY
  elif [[ "$date" =~ ([0-9]{1,2})\ ([ 0-9]{1,2})\ ([0-9]{4}) ]] ; then # mm dd yyyy   or  dd mm yyyy
    if (( EUROPEAN_DATES || euro_format )) ; then
      date_parse_dmy ${BASH_REMATCH[1]} ${BASH_REMATCH[2]} ${BASH_REMATCH[3]}
    else
      date_parse_mdy ${BASH_REMATCH[1]} ${BASH_REMATCH[2]} ${BASH_REMATCH[3]}
    fi

  # WDAY MMM DD HH:MM:SS TZONE YYYY
  elif [[ "$date" =~ ([[:alpha:]]{2,9})\ ([[:alpha:]]{3,8})\ ([ 0-9]{2})\ ([0-9]{2}:[0-9]{2}:[0-9]{2})\ ([[:alnum:]]{3,9})\ ([0-9]{4}) ]] ; then
    date_parse_mmmdy ${BASH_REMATCH[2]} ${BASH_REMATCH[3]} ${BASH_REMATCH[6]}
    weekday_name=${BASH_REMATCH[1]} timestr="${BASH_REMATCH[4]}" tzone="${BASH_REMATCH[5]}"

  else  # failure -- leave no variables set
    :
  fi
}