BASH Script to Generate Exception Rules for DST of Brazil

Description

This BASH script produces as output code to be appended to zoneinfo configuration files of Brazil/East and America/Sao_Paulo. Read this before using it.

The source for Easter Day determination was taken from The Computus Wikipedia article.

Usage

It expects at least one year (with century) to produce exception rules (if any).

Use '-q' or '--quite' as the first argument to produce only exception rules on STDOUT, otherwise, extra output will be sent to STDERR.

See 'Notes' Section below.

The Basic Code

Determining Easter Day

Y=$1    # Year as a parameter (with century)
shift
let 'a = Y % 19'
let 'b = Y / 100'
let 'c = Y % 100'
let 'd = b / 4'
let 'e = b % 4'
let 'f = (b+8) / 25'
let 'g = (b - f + 1) / 3'
let 'h = (19 * a + b - d - g + 15) % 30'
let 'i = c / 4'
let 'k = c % 4'
let 'L = (32 + 2 * e + 2 * i - h - k) % 7'
let 'm = (a + 11 * h + 22 * L) / 451'
let 'month = (h + L - 7 * m + 114) / 31'
let 'day = ((h + L - 7 * m + 114) % 31) + 1'

Determining the Sunday of Carnival:

dayc=`date --date="$Y-$month-$day 12:00:00 utc -42 days" +"%d"`
monthc=`date --date="$Y-$month-$day 12:00:00 utc -42 days" +"%m"`

Read the date(1) manpage.

Determining if Carnival Sunday matches the last day of DST and generating appropriate exception rule if it happens so.

if [ $monthc == "02" ]; then # Only February matters
  if [ $dayc -gt 14 -a $dayc -lt 22 ]; then # earliest and last dates for 3rd Sunday
   
    # Carnival Sunday = DST ending day, postpone to next sunday
    let 'dayd = dayc +7'
    # Generate rule to STDOUT 
    echo "Rule  Brazil  $Y  only -    Feb  $dayd  0:00  0  -"
  fi
fi

Download:

Get a full sample implementation of the script.

Or if you are some kind of lazy / uninterested fellow, just paste the following lines and you're safe until 2038 Bug:

Rule  Brazil  2012  only  -    Feb  26  0:00  0  -
Rule  Brazil  2015  only  -    Feb  22  0:00  0  -
Rule  Brazil  2023  only  -    Feb  26  0:00  0  -
Rule  Brazil  2026  only  -    Feb  22  0:00  0  -
Rule  Brazil  2034  only  -    Feb  26  0:00  0  -
Rule  Brazil  2037  only  -    Feb  22  0:00  0  -

Read the zic(8) manpage.

Notes

• This script was designed to comply with decree #6.558 issued on 8th of September of 2008, and it regulates Brazilian Dayligh Saving Time.
• This script may produte unexpected results in 32 bits operating systems, when dealing with years beyond 2037. This is a design limitation on date libraries. Check for "year 2038 bug" on the Internet.

License

THIS PROGRAM IS FREE SOFTWARE: YOU CAN REDISTRIBUTE IT AND/OR MODIFY IT UNDER THE TERMS OF THE GNU GENERAL PUBLIC LICENSE AS PUBLISHED BY THE FREE SOFTWARE FOUNDATION, EITHER VERSION 3 OF THE LICENSE, OR (AT YOUR OPTION) ANY LATER VERSION.

THIS PROGRAM IS DISTRIBUTED IN THE HOPE THAT IT WILL BE USEFUL, BUT WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. SEE THE GNU GENERAL PUBLIC LICENSE FOR MORE DETAILS. SEE <http://www.gnu.org/licenses/>.