Last Friday of each month: Difference between revisions

=={{header|Shell Bourne}}==

<lang sh>

#!/bin/sh

# Free code, no limit work

# $Id: lastfridays,v 1.1 2011/11/10 00:48:16 gilles Exp gilles $

# usage :

# lastfridays 2012 # prints last fridays of months of year 2012

debug=${debug:-false}

#debug=true

epoch_year_day() {

#set -x

x_epoch=`expr ${2:-0} '*' 86400 + 43200`

date --date="${1:-1970}-01-01 UTC $x_epoch seconds" +%s

}

year_of_epoch() {

date --date="1970-01-01 UTC ${1:-0} seconds" +%Y

}

day_of_epoch() {

LC_ALL=C date --date="1970-01-01 UTC ${1:-0} seconds" +%A

}

date_of_epoch() {

date --date="1970-01-01 UTC ${1:-0} seconds" "+%Y-%m-%d"

}

month_of_epoch() {

date --date="1970-01-01 UTC ${1:-0} seconds" "+%m"

}

last_fridays() {

year=${1:-2012}

next_year=`expr $year + 1`

$debug && echo "next_year $next_year"

current_year=$year

day=0

previous_month=01

while test $current_year != $next_year; do

$debug && echo "day $day"

current_epoch=`epoch_year_day $year $day`

$debug && echo "current_epoch $current_epoch"

current_year=`year_of_epoch $current_epoch`

current_day=`day_of_epoch $current_epoch`

$debug && echo "current_day $current_day"

test $current_day = 'Friday' && current_friday=`date_of_epoch $current_epoch`

$debug && echo "current_friday $current_friday"

current_month=`month_of_epoch $current_epoch`

$debug && echo "current_month $current_month"

# Change of month => previous friday is the last of month

test "$previous_month" != "$current_month" \

&& echo $previous_friday

previous_month=$current_month

previous_friday=$current_friday

day=`expr $day + 1`

done

}

# main

last_fridays ${1:-2012}

</lang>

Sample execution:

<pre>

lastfridays 2012

2012-01-27

2012-02-24

2012-03-30

2012-04-27

2012-05-25

2012-06-29

2012-07-27

2012-08-31

2012-09-28

2012-10-26

2012-11-30

2012-12-28

</pre>