#!/bin/bash
##-- date conversions	by Eugene Reimer 2003-September
## PREREQ: tolower  from http://ereimer.net/programs/general-purpose-scripts.htm
## USAGE:
##	datecvt YearMonthDay FORMAT	-- where FORMAT is same as used by the <date> cmd -- see man date
## EXAMPLES:
##	datecvt -r/books/BALLOT +%y%b%d	-- get modification-date of a file, in YYmmmDD format (silly example since date-command would do the same)
##	datecvt now     %y%b%d		-- get current-date in YYmmmDD format (another silly example)
##	datecvt 010815  %y%b%d		-- convert specified YYMMDD date to YYmmmDD format
##	datecvt 01aug15 %y%m%d		-- convert specified YYmmmDD date to YYMMDD format -- nonstd for <date>
##	datecvt 01aug   %y%m		-- convert specified YYmmm date to YYMM format	   -- nonstd for <date>
##	datecvt 01aug15 %Y-%m-%d	-- convert to YYYY-MM-DD as used in <convertdate-in-filenames>

[ $# -ne 2 ] && { echo "usage: datecvt DATE FORMAT"; exit; }
A=$1; B=$2; shift; shift
if [[ $A == [0-9]* ]]; then
  A=$(echo "$A" | tolower)
  Y=; while [ "$A" != "${A#[0-9]}" ];  do Y=$Y${A:0:1};  A=${A#[0-9]}; done
  M=; while [ "$A" != "${A#[a-z]}" ];  do M=$M${A:0:1};  A=${A#[a-z]}; done
  D=; while [ "$A" != "${A#[0-9]}" ];  do D=$D${A:0:1};  A=${A#[0-9]}; done
  if [ ${#Y} -lt 6 ] && [ ${#M} -eq 0 ]; then M=01; fi		##KLUDGE; use January if month omitted
  if [ ${#Y} -lt 6 ] && [ ${#D} -eq 0 ]; then D=01; fi		##KLUDGE; use 01 if day omitted;  fixed first test 2008-04-23
  if [ ${#M} -ge 3 ]; then M=$(date -d${M:0:3}01 +%m); fi	##convert alpha-month to numeric-month
  A=-d$Y$M$D
elif [[ $A == now ]]; then
  A=-dnow
fi

if [[ $B != +* ]];then B=+$B; fi				##new param, with or without leading plus-sign
date $A $B


exit
2008-04-23: modified 2nd param, eg: former Ymd is now [+]%Y%m%d, so can now get %Y-%m-%d style when wanted;
	now using in scalepix script, for alpha-month support;
2009-11: mk-calendar-8up-wallet-sized uses scalepix which uses this;  now published on my website;