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Full Discussion: Date Compare tool
Top Forums Shell Programming and Scripting Date Compare tool Post 303013016 by jim mcnamara on Tuesday 13th of February 2018 06:44:14 PM
Old 02-13-2018
Start simple.

First off, straight comparisons of known correctly entered dates in the YYYYMMDD format can be treated as plain numbers for comparisons in shell using: -eq, -ne, -gt, -lt
Code:
#!/bin/bash

d1=20180113
d2=20170113
printf "Dates are d1=%d d2=%d\n" $d1 $d2
# different versions of if-then-else 
[ $d1 -gt $d2 ] && echo 'greater' || echo 'not greater'

if [ $d1 -eq $d2 ] ; then
  echo 'equal'
else
  echo 'not equal'
fi
$ ./dcomp.shl
Dates are d1=20180113 d2=20170113
greater
not equal

Next the units for dates are days. To do further math like subtraction, you have to work on the number of days the date represents. Time and date in UNIX is epoch seconds.
So doing Julian dates in shell is somewhat tedious but is about the only way to proceed, i.e., convert a date to some kind epoch days. Epoch means the number of days since an arbitrary start date. For UNIX this is number of seconds since the first second in January 1, 1970. There are 86400 seconds per day. You can ignore leap seconds usually.

Chris (CFA) Johnson has a script in bash to do this. It is not beginner fodder.
Go here: Chris F.A. Johnson in Toronto, Ontario, Canada See if you can get a copy of the bash recipes book listed on this now-inactive site. Chris still posts here on UNIX Forums every once in a while.

Code:
secs=$(date -d 20110101 +%s)  # epoch seconds for Jan 1 2011
days=$(( secs % 86400 ))
echo "epoch days=$days"

[/code]

Last edited by jim mcnamara; 02-13-2018 at 07:53 PM..
 

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Date::Manip::Migration5to6(3pm) 			User Contributed Perl Documentation			   Date::Manip::Migration5to6(3pm)

NAME
Date::Manip::Migration5to6 - how to upgrade from 5.xx to 6.00 SYNOPSIS
When upgrading from Date::Manip 5.xx to 6.00, a few changes may be necessary to your scripts. The Date::Manip::Changes5to6 document lists in more detail the ways in which Date::Manip changed, but very few of these actually entail changes to your script. It should be noted that once the changes are made to your script, it will no longer run correctly in 5.xx. NECESSARY AND SUGGESTED CHANGES
The following changes are necessary, or strongly suggested: Reading config files with Date_Init If you use Date_Init to read any config files (if you do business mode calculations, you probably do), you should remove all of the following config variables from your call to Date_Init: GlobalCnf=FILE PersonalCnf=FILE PathSep=* IgnoreGlobalCnf=* PersonalCnfPath=* and replace them with: ConfigFile=FILE where FILE is now the full path to a config file. Also, the ConfigFile argument should be the first argument in Date_Init. Date_ConvTZ The Date_ConvTZ function has changed. It should now take 3 arguments: $date = Date_ConvTZ($date,$from,$to); If $from is not given, it defaults to the local time zone. If $to is not given, it defaults to the local time zone. The date is converted from the $from time zone into the $to time zone. Both should be any time zone (or alias) supported by Date::Manip. The old $errlevel argument is no longer handled. ConvTZ and TZ config variables If you use either the ConvTZ or TZ config variables, you should replace them with either SetDate or ForceDate. See the Date::Manip::Config document for information. The TZ variable will continue to work until Dec 2013 at which point it will be removed. Other deprecated config variables The following config variables have been deprecated, but will continue to function (though they will be removed at a future date): IntCharSet (removed Oct 2012) TZ (removed Dec 2013) The following variables have been removed. If you use any of them, you may need to modify your scripts: GlobalCnf PersonalCnf PathSep IgnoreGlobalCnf PersonalCnfPath ConvTZ Internal TodayIsMidnight DeltaSigns UpdateCurrTZ ResetWorkdDay today, yesterday, tomorrow If you parse the strings "today", "yesterday", or "tomorrow" in order to get the time now, or 24 hours in the past/future, this will no longer work. These strings now refer strictly to the date (so "today" is the current day at midnight, "yesterday" is the previous day at midnight, etc.). To get the time now, 24 hours ago, or 24 hours in the future, you would need to parse the strings "now", "-24:00:00", or "+24:00:00" respectively. Do not use Memoize In 5.xx, it was documented that you could use the module Memoize to speed up Date::Manip, especially when sorting dates. This information is no longer accurate. Using Memoize in conjunction with Date::Manip should have little impact on performance, and may lead to incorrect results, especially if you change config variables. Please see the Date::Manip::Changes5to6 (GENERAL CHANGES) document for more information. If you find other instances where it is necessary to modify your script, please email me so that I can add that information to this document. BUGS AND QUESTIONS
Please refer to the Date::Manip::Problems documentation for information on submitting bug reports or questions to the author. SEE ALSO
Date::Manip - main module documentation LICENSE
This script is free software; you can redistribute it and/or modify it under the same terms as Perl itself. AUTHOR
Sullivan Beck (sbeck@cpan.org) perl v5.14.2 2012-06-02 Date::Manip::Migration5to6(3pm)
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