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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)								   User Commands							    CAL(1)

NAME
cal - display a calendar SYNOPSIS
cal [options] [[[day] month] year] DESCRIPTION
cal displays a simple calendar. If no arguments are specified, the current month is displayed. OPTIONS
-1, --one Display single month output. (This is the default.) -3, --three Display prev/current/next month output. -s, --sunday Display Sunday as the first day of the week. -m, --monday Display Monday as the first day of the week. -j, --julian Display Julian dates (days one-based, numbered from January 1). -y, --year Display a calendar for the current year. -V, --version Display version information and exit. -h, --help Display help screen and exit. PARAMETERS
A single parameter specifies the year (1 - 9999) to be displayed; note the year must be fully specified: cal 89 will not display a calendar for 1989. Two parameters denote the month (1 - 12) and year. Three parameters denote the day (1-31), month and year, and the day will be highlighted if the calendar is displayed on a terminal. If no parameters are specified, the current month's calendar is displayed. A year starts on Jan 1. The first day of the week is determined by the locale. 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. AVAILABILITY
The cal command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/. util-linux June 2011 CAL(1)
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