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Full Discussion: Calculate given date - 1 day
Top Forums Shell Programming and Scripting Calculate given date - 1 day Post 302930321 by rbatte1 on Friday 2nd of January 2015 07:46:29 AM
Old 01-02-2015
If you don't have GNU date, then another alternative is perl if you have that. From your input date, we need to split it up the values and feed them in:-
Code:
#!/bin/ksh

input_date=$1

in_yyyy="${input_date%????}"     # Remove last four characters
in_dd="${input_date#??????}"     # Remove lead four characters
in_mm="${input_date#????}"       # Remove lead four characters
in_mm="${in_mm%??}"              # Remove last two characters from previously split value

((temp_mm=$in_mm-1))             # Reduce month by one as epoch counts from 1/1/1970 as zero

# Get time in seconds since epoch
perl -e "use Time::Local; print timelocal(0,0,0,$in_dd,$temp_mm,$in_yyyy), ;" | read in_seconds

# Go back one day in seconds
((out_seconds=$in_seconds-86400))

# Display answer in required format
perl -e 'use POSIX qw(strftime);print scalar(strftime "%Y%m%d", localtime $ARGV[0]), "\n";' $out_seconds

I hope that this meets the brief you have given us. There may be smarter ways to read & split the input date, so I'm open to suggestions.

Obviously some validity checking on the input would be wise else you will get various horrible messages from the perl

I've put it in a script called 254222 (thread number) and tested it as shown:-
Code:
$ 254222 20141220
20141219

$ 254222 20140301
20140228

$ 254222 20160301
20160229

$


I hope that this helps. I had fun with the challenge and I'm pretty sure I'm going to need it soon myself too, so thanks for the query Smilie


Robin
This User Gave Thanks to rbatte1 For This Post:
 

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Time(3pm)						  LogReport's Lire Documentation						 Time(3pm)

NAME
Lire::Time - parses and prints date in formats common to many log files. SYNOPSIS
use Lire::Time qw/ syslog2cal /; my @ltime = localtime; while ( <LOGFILE> ) { #... my $time = syslog2cal( $m, $d, $t, @ltime ); } DESCRIPTION
This module supplies many functions to parse dates in formats that you are likely to encounter in log files. It also offers many functions to format epoch time in useful format. NOTE ABOUT FUNCTION EXPORT Altough all documented functions are exported by default to the caller namespace, you should explicitely import the functions you require since exporting by default isn't recommanded by the perl modules guidelines. DATE PARSING FUNCTIONS
This module includes several functions that convert between a more human readable date format and UNIX epoch time. All parsing functions will return the number of seconds since Jan 1 1970 00:00:00 UTC and will die() when passed invalid arguments. date2cal() my $time = date2cal( $year, $month, $day, $time, [$timezone] ); my $time = date2cal( "2001 Mar 20 09:32:29 +0100" ); This function will convert a date in the date(1) default output format to UNIX epoch time. The function accepts either the date in a string or splitted on whitespace. If the timezone component is omitted, the local timezone is assumed (usually based on the value of the TZ environment variable). syslog2cal() my $time = syslog2cal( $month, $day, $time, $local_tm_ref ); my $time = syslog2cal( "Mar 11 13:21:00", $local_tm_ref ); This function will convert a date in the syslog default output format to UNIX epoch time. The function accepts either the date in a string or splitted on whitespace. Since the syslog format doesn't contain timezone information, the local timezone is assumed (usually determined by the TZ environment variable). The last argument is a reference to an array returned by localtime(). my $local_tm_ref = [localtime()]; It is used to determine the year. clf2cal() my $time = clf2cal( "[18/Mar/2001:15:59:30 +0100]" ); This function will convert a date as found in Common Log Format to UNIX epoch time. DATE FORMATING FUNCTIONS
This module includes some functions to convert date in UNIX epoch time to some more human readable output. All functions will die() when passed invalid arguments. cal2rfc() print cal2rfc( $time ); This function will convert a date in UNIX epoch time to the RFC822 format (used in email, for example). A RFC822 date looks like Wed, 30 May 2001 12:45:13 +0000 The timezone offset specification will correspond to the local timezone (usually determined by the TZ environment variable). cal2ymdhms() print cal2ymdhms( $time ); This function converts a date in UNIX epoch time to a string of the form: YYYYMMDDHHMMSS This representation will correspond the time in the local timezone (usually determined by the TZ environment variable.) getMonthName() print getMonthName( 0 ); # Gives 'Jan' This function takes as parameter a number (0-11) representing the month (as returned by localtime() for example) and will return the English abbreviated name of that month ( Jan, Feb, etc. ). AUTHOR
Joost van Baal <joostvb@logreport.org> VERSION
$Id: Time.pm,v 1.10 2006/07/23 13:16:30 vanbaal Exp $ COPYRIGHT
Copyright (C) 2000-2002 Stichting LogReport Foundation LogReport@LogReport.org This file is part of Lire. Lire is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program (see COPYING); if not, check with http://www.gnu.org/copyleft/gpl.html. Lire 2.1.1 2006-07-23 Time(3pm)
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