Code Examples -> Shell script to calculate the day of the week, given a date DD MM YYYY

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PHP Code Examples

Title :	Shell script to calculate the day of the week, given a date DD MM YYYY
Categories :	Shell Scripting, Date Time	Marc Loftus
Date :	Jul 01st 2005
Grade :	2 of 5 (graded 3 times)
Viewed :	17920
File :	No file for this code example.
Images :	No Images for this code example.

Search :	More code by Marc Loftus
Action :	Grade This Code Example
Tools :	My Examples List

Code

#!/bin/sh

# SAVE THIS CODE AS cala_day.sh
#
# Uses Zellers Congruence calculation to use a date and give
# the day of the week that date was.
#
# This function expects 3 Arguments,
# DAY MONTH YEAR
# then
# Returns a value between 0 and 6 to represent the day of the
# week where 0=Sun,1=Mon,...6=Sat
#
# e.g cala_day.sh 25 12 2005
#
# This formula is Year 2000 compliant.
# It is not compliant using dates previous to Oct 1752

#

# Adjust Month such that March becomes 1 month of
# year and Jan/Feb become 11/12 of previous year
# =============================================

if [ $MONTH -ge 3 ] ; then
MONTH=`expr $MONTH - 2`
else
MONTH=`expr $MONTH + 10`
fi

if [ $MONTH -eq 11 ] || [ $MONTH -eq 12 ] ; then
YEAR=`expr $YEAR - 1`
fi
# ==============================================

# Split YEAR into YEAR and CENTURY
# ================================
CENTURY=`expr $YEAR / 100`
YEAR=`expr $YEAR % 100`
# ================================

# Black Magic Time
# ================
# Z = (( 26*$MONTH - 2 ) / 10) + $DAY + $YEAR + ( $YEAR/4 ) + ( $CENTURY/4 ) - (
2 * $CENTURY) + 77) % 7
Z=`expr $ $MONTH \* 26 - 2 $ / 10`
Z=`expr $Z + $DAY + $YEAR`
Z=`expr $Z + $YEAR / 4`
Z=`expr $Z + $CENTURY / 4`
Z=`expr $Z - $CENTURY - $CENTURY + 77`
Z=`expr $Z % 7`
if [ $Z -lt 0 ] ; then
Z=`expr $Z + 7`
fi
# ================

echo $Z
# Sun 0
# Mon 1
# Tue 2
# Wed 3
# Thu 4
# Fri 5
# Sat 6
# ========================
}

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User Comments

	matthew waygood wrote : 1334 if [ $MONTH -ge 3 ] ; then MONTH=`expr $MONTH - 2` else MONTH=`expr $MONTH + 10` fi if [ $MONTH -eq 11 ] \|\| [ $MONTH -eq 12 ] ; then YEAR=`expr $YEAR - 1` fi Can be re-written as:- MONTH=`expr (($MONTH+9)%12)+1`;
	matthew waygood wrote :1335 `sorry not the year bit. Very interesting bit of code, got me looking into Zeller a bit.`