These programs were featured online at, Shell Corner, September 2003.
Perl and AWK Holiday Determination Routines 
by Bob Orlando

Shortcuts to the code (skip the descriptions for now Smiley face ):
    Dateplus Easy date manipulation program
    today_is.html Test program showing how to use
    holidays file Hopefully self-explanatory
    Holiday_dates.html Perl Macro that processes the holidays file
    holidays.awk AWK version that processes the same file Executes holidays.awk, providing examples of holiday and
business day testing

The following describes both Perl and AWK scripts developed for determining whether a given date is a holiday, or the nth business day of the month.  These routines are based on holiday algorithms from Marcos J. Montes ("American Secular Holidays") and Claus Tondering ("Frequently Asked Questions about Calendars").

Holiday Scheduling 
Job scheduling around holidays has always been a pain.  To prevent messing around with crons several times a year, I used to place a "holidays" file in, for example, /usr/local/bin.  The file contained the holiday date in yyyymmdd format, followed by the holiday name.  (See Dateplus  program for easy date manipulation.)  That worked, but every year I had to refresh the file with those dates that fall on, for example, the last Monday in May.  This meant remembering to edit the holidays file after the company calendar was set for the year.  Then, I came across the American Secular Holidays web site by Marcos J. Montes.

American Secular Holidays in Perl 
Montes cites Claus Tondering as his primary source, and Timothy Barmann, and Bobby Cossum for their contributions in simplifying the equations used in the alorithms.  This is significant for these algorithms provide a robust yet elegant method for identifying whether a given date is a holiday without constantly updating a configuration file.

Initially, I coded the algorithms in a Perl program function or subroutine, &holiday_date (in  Later I added another function, &load_holiday_array, to pull the necessary information from a holidays file.  Lastly, I put together a third function, &business_day, to return the nth business day's date (in the form yyyymmdd) for a given year and month (yyyymm).  All three functions (called in were subsequently rolled up into a single Perl macro, Holiday_dates.html (Business_day, which calls holiday_dates, has proven to be as useful as the holiday routine itself for those processes that must run, for example, on the second business day of the month.)

American Secular Holidays in AWK 
To make these algorithms and routines as portable as possible (as long as the porting OS has nawk or gawk), I rewrote the whole thing in [gn]awk.  Now practically any program with access to AWK can avail itself of these holiday date capabilities.  The AWK version of the program can return the nth business day, a multi-line yyyymmdd date list, or a single line of yyyymmdd holiday dates.  With those, you can easily determine whether the date you have is a holiday or specific business day.

Calculating Business Days 
I incorporated the business day calculation into my date routines because of a need to run a given process on the second business day of the month.  Once the holidays are known, business day calculation is relatively simple--just grab the month's days and remove holidays, Saturdays and Sundays.  For example, to provide the second business day, just pass a  "-b 2"  option to the program:

   bizday=`nawk -f holidays.awk -- -b 2 holidays`
   if [ `date "+%Y%m%d"` = $bizday ]; then
      echo "Today is the 2nd business day of the month."
      # Do whatever
Last business day and business day offset from the last business day (negative numbers) is also available in holidays.awk.  To retrieve the last business day of the month, specify the "last" option argument (optarg) for -b option (i.e., "-b last").  For the next-to-last business day of the month, provide "-b -1" as an option and optarg.

Holidays.awk is a well-behaved program in that it uses exit status to indicate success or failure.  As indicated in the documentation, all options except business day (-b), returning a zero status means the program completed successfully; non-zero indicates failure.  However, with the business day option, non-zero indicates success because it is the day of the month on which the business day falls.  Therefore, use the holidays.awk the exit status as the test comparand:

   nawk -f holidays.awk -- -b last holidays > /dev/null 2>&1

   if [ $? -eq `date +%d` ]; then
      echo "Today is the last business day of the month."
      # Do whatever
You can also combine -b with -m and -y to return the nth business day for a given month and year. If you request a business day (positive or negative) that is not found in the month, you receive an error message, and a 0 exit status indicating an error.

For those needing only an indication that today is a given business day, you can use the -t option in conjunction with -b. For example, using Unix cron (scheduler) we combine those options to set up a job to run only on the second business day of the month with as little as the following:

   00 02 2-5 * * /usr/local/bin/holidays.awk -- -b 2 -t \
     || some_program > some_program.out 2>&1
In this example, no holidays file is specified because we use the default, /usr/local/bin/holidays (you can change the program to point to wherever you wish to locate the file).  No nawk -f is used because the first line of holidays.awk uses the shebang syntax (#!/usr/bin/nawk -f) to execute itself.  (Obviously, the program must have the necessary execution permissions to run this way.)  With the -t option, holidays.awk returns true or false (which is not the same as success or failure), only running the called program if the day is, indeed, the second business day of the month.

Returning The Nth Weekday  (Awk Method) 
There appears to be as much interest in determining the nth weekday day as there is in business days, so I added an option to holidays.awk to return that.  To get the first Monday in the current month, simply pass a  "-d 1.Mon"  option to the program:

   fst_monday=`nawk -f holidays.awk -- -d 1.Mon`
An alternative syntax is also provided:  nawk -f holidays.awk -- -d 1.1

You can expand this to report the first Monday in any month and year like this.

   for mm in 1 2 3 4 5 6 7 8 9 10 11 12
      nawk -f holidays.awk -- -y $yyyy -m $mm -d 1.1
For the last Sunday in a month use 
   nawk -f holidays.awk -- -d last.Sun
For those preferring a simpler syntax: If your OS recognizes the  #!  (shebang) syntax, you can place a  #!/usr/bin/nawk -f  (or gawk) at the start of holidays.awk, thereby allowing you skip the  [gn]awk -f  during invocation and simply call it like this,
   holidays.awk -- -d last.Sun
   holidays.awk -- -d last.0
   holidays.awk -- -d 5.0
The Perl Method 
Nth day capability exists in, (see fst_monday in, but essentially, for the last Friday in May, call holiday_yyyymmdd subroutine like this:
   $last_friday = holiday_yyyymmdd(200405,"last",6);
   $last_sunday = holiday_yyyymmdd(200502,     5,0);
   $second_mon  = holiday_yyyymmdd(200502,     2,1);
Testing with executes holidays.awk, providing examples of holiday and business day testing.  Provided the holidays file is located properly, executing  on June 21, 2003 displays:
   Today's no holiday, get busy. :-((
   20030101 Wed. New Year's Day
   20030120 Mon. M.L.King Jr. Birthday
   20030526 Mon. Memorial Day
   20030704 Fri. Independence Day
   20030901 Mon. Labor Day
   20031127 Thu. Thanksgiving Day (US)
   20031128 Fri. Thanksgiving Day II (US)
   20031225 Thu. Christmas Day
   Today is NOT the 2nd business day (20030603) of the month.
   Today is NOT the last business day (20030630) of the month.
   Today is NOT the next-to-the-last business day (20030627) of the month.
As a real acid test, I include the next-to-last and last business days of every month from 2000 to 2010.  The  script concludes with a report for all holidays for the 21st century. 

The Holidays File 
Although second to the algorithms, the holidays file is central to both my Perl and AWK routines.  The file's directives allow for the handling of, for example, the Friday after U.S. Thanksgiving Day (Thursday).  For those organizations and companies that grant a Friday holiday when a day like Christmas or New Year's Day falls on a Saturday, or give a Monday holiday when those holidays fall on a Sunday, the holidays file provides the necessary vehicle.

After a brief description of holidays file layout, I'll discuss the the file itself, and see how three holidays are handled: Memorial Day, Thanksgiving Day (including the Friday after), and Christmas.

The file itself is a simple ASCII file available to to all programs.  It contains values that allow the calling program to calculate holidays either by given (fixed) month and day, or by day of a given week.  The general layout is as follows:

 # Mm N.Day Adj Holiday name # Comments

   Mm           = Month number (leading zeros NOT required)        = Nth day (1-5 and "last") "." weekday (0-6)
                  (Not every part is required.)
   Adj          = Can be either a +|- n days,
                  or weekday followed immediately by a +|- n days,
   Holiday name = How you want it spelled out--your call.
   Comments     = ignored.

Leading white space is ignored, as is everything following and including the octothorpe (#-sign). Here are the entries for the three holidays:

 # Mm N.Day.OnOrA Adj Holiday name                     # Comments        #
 # -- ----------- --- -------------------------------- ----------------- #
   05 last.1          Memorial Day                     # Last Mon in May
   11 4.4             Thanksgiving Day (US)            # 4th Thu in Nov
   11 4.4          +1 Thanksgiving Day II (US)
   12 25              Christmas Day                    # M-F
   12 25          6-1 Christmas Day (pre-holiday obs)  # Sat?  Use Fri
   12 25          0+1 Christmas Day (post-holiday obs) # Sun?  Use Mon
Memorial Day 
Memorial Day is the last Monday in May.  In the table the month is "05" (again, leading zero is unnecessary).  The last Monday is specified by the word "last" and not a 5 because the last Monday may not be the 5th Monday (there is no 5th Monday in May, 2003).  Monday is identified by the 1 following the dot (".1").  This is based on the 0-6 convention for representing Sunday through Saturday.

Thanksgiving Day 
Thanksgiving Day (U.S. observance) is the forth Thursday in November.  November is identified by the "11".  The fourth (nth) day is the first "4".  Thursday is the ".4".  Same method as was used for Memorial Day.  The day after Thanksgiving, Friday, is a little tricky.

Friday After Thanksgiving [Thurs]Day 
Contrary to what you might think, you cannot specify:

   11 4.5 Thanksgiving Day II (Friday)
since the fourth Friday might not follow the fourth Thursday of a given month.  Consider Thanksgiving Day, 2002--the fourth Thursday was November 28.  The fourth Friday fell on the 22nd.  So, to accurately capture the Friday after Thanksgiving Day, specify the same parameters for Thanksgiving, and an adjustment of +1:
   11 4.5 +1 Thanksgiving Day II (Friday)
Christmas is December 25.  Like New Year's Day (January 1) and Independence Day (July 4), Christmas is a fixed date.  Simply specifying  "12 25 Christmas Day"  in the holidays file returns "yyyy1225".  However, with many companies, if Christmas falls on a Saturday (day 6), the Friday before is observed by adjusting it by -1.  If it falls on a Sunday (day 0), the Monday following is observed by adjusting it by +1.  Hence, the three entries:
   12 25     Christmas Day                     # M-F
   12 25 6-1 Christmas Day (pre-holiday obs)   # Sat? Use Fri
   12 25 0+1 Christmas Day (post-holiday obs)  # Sun? Use Mon
New Year's Day 
New Year's Day is a fixed date, January 1, and like Christmas and Independence Day, it can be observed on the Friday before a Saturday occurrence or the Monday after a Sunday occurrence simply by setting it up like the Christmas example above.  However, some organizations use a post-holiday observance of New Year's Day when it falls on a Saturday simply so the holiday falls in the correct year.  You can do that by specifying New Year's Day as follows:
   01 01     New Year's Day                    # M-F
   01 01 6+2 New Year's Day (post-holiday obs) # Sat? Use Mon
   01 01 0+1 New Year's Day (post-holiday obs) # Sun? Also Mon
Remember, the  "6"  in our  "6+2"  means the actual date, January 1st, falls on a Saturday (day 6 in the 0-6 day-numbering schema), so adjust that date by +2 days (i.e. Saturday's date (01/01) plus two days (01/03).

Daylight Savings Time 
While the program is incapable of handling Daylight Savings dates in Iran where DST starts on the first day of Farvardin and ends the first day of Mehr, holidays.awk (v1.22) is capable of handling at least one set of unique Daylight Savings Time (DST) dates.  In the Falkland Islands, DST begins on the first Sunday on or after September 8th and ends on the first Sunday on or after April 6th.  Those exceptions (starting on or after a date in the month) are handled by specifying a holidays line like this:

   04 1.0.6 Falklands ST  # 1st Sun on/after Apr 6
   09 1.0.8 Falklands DST # 1st Sun on/after Sep 8

The  ".6"  in our  "1.0.6"  means Standard Time (ST) begins on the first Sunday (1.0) in April that falls on or after the 6th of April. Likewise, the  ".8"  in our  "1.0.8"  means DST begins on the first Sunday in September that comes on or after the 8th of September.

Since Daylight Savings dates are not usually holidays, you can also retrieve the Daylight Savings Time dates via the  -d option and bypass the need for the holidays file altogether.  Here are Daylight Savings Times for the United States (begins the second Sunday in March) and the Faulklands (begins on the first Sunday on/after September 8).

   holidays.awk -- -d 2.0   -m 3
   holidays.awk -- -d 1.0.8 -m 9
You can even set up a cron to test for Daylight Savings Time and perform some action if true.
   05 00 * 03 * [ `/usr/local/bin/holidays.awk -- -d 2.0 -m 3 -t` -eq 1 ] \
      && ... Some action ...

Clearly, none of my holiday work is possible without the algorithms presented by Montes, Tondering, Barmann, and Cossum.  The holidays file  and the logic to process that, are my contributions. Between the file and its processing methods, we are able to centralize holiday dates and manage their often troublesome adjustments.

Artificial  intelligence  is  no  match  for  natural  stupidity.
©Copyright Bob Orlando, 2003-2016
All rights reserved.
Last update:  Feb. 2, 2016
by Bob Orlando
Web Site of Bob Orlando: Instructor in Kuntao-Silat (Chinese kuntao and Dutch-Indonesian pukulan pentjak silat), author of two popular martial art books: "Indonesian Fighting Fundamentals" and "Martial Arts America: A Western Approach to Eastern Arts"; and producer of four martial art videos: Fighting Arts of Indonesia, Reflex Action, Fighting Footwork of Kuntao and Silat, Fighting Forms of Kuntao-Silat. Offering practical martial arts instruction to adults living in and throughout the Denver metropolitan area including, Lakewood, Littleton, Morrison, and Golden Colorado.