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Full Discussion: Subtraction
Top Forums Shell Programming and Scripting Subtraction Post 302621493 by methyl on Tuesday 10th of April 2012 01:06:52 PM
Old 04-10-2012
Beware that the script will go wrong in any January because you will be subtracting 2 from 1.

This may be more robust:

Code:
#!/bin/sh

month="`date +%m`"
year="`date +%Y`"
printf "%02d\n" ${month}

# Retaining Data for Current and Previous Month
case "${month}" in
        "01")   lmonth=11
                year=`expr ${year} - 1`
                ;;
        "02")   lmonth=12
                year=`expr ${year} - 1`
                ;;
        *)      lmonth=`expr ${month} - 2`
                ;;
esac
#
printf "%04d\n" ${year}
printf "%02d\n" ${lmonth}

 

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CAL(1)							    BSD General Commands Manual 						    CAL(1)

NAME
cal -- displays a calendar SYNOPSIS
cal [-smjy13] [[month] year] DESCRIPTION
Cal displays a simple calendar. If arguments are not specified, the current month is displayed. The options are as follows: -1 Display single month output. (This is the default.) -3 Display prev/current/next month output. -s Display Sunday as the first day of the week. (This is the default.) -m Display Monday as the first day of the week. -j Display Julian dates (days one-based, numbered from January 1). -y Display a calendar for the current year. A single parameter specifies the year (1 - 9999) to be displayed; note the year must be fully specified: ``cal 89'' will not display a calen- dar for 1989. Two parameters denote the month (1 - 12) and year. If no parameters are specified, the current month's calendar is displayed. A year starts on Jan 1. The Gregorian Reformation is assumed to have occurred in 1752 on the 3rd of September. By this time, most countries had recognized the ref- ormation (although a few did not recognize it until the early 1900's.) Ten days following that date were eliminated by the reformation, so the calendar for that month is a bit unusual. HISTORY
A cal command appeared in Version 6 AT&T UNIX. OTHER VERSIONS
Several much more elaborate versions of this program exist, with support for colors, holidays, birthdays, reminders and appointments, etc. For example, try the cal from http://home.sprynet.com/~cbagwell/projects.html or GNU gcal. BSD
June 6, 1993 BSD
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