Difference between revisions of "Date Shift Script"
From assela Pathirana
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| Line 6: | Line 6: | ||
fmt="+%Y%m%d" | fmt="+%Y%m%d" | ||
if [ $# -lt 1 ]; then | if [ $# -lt 1 ]; then | ||
cat << EOF | |||
Usage: $0 ndates date [ADD/SUB] [fmt] | |||
default format is $fmt | |||
format should be YYYYMMDD or any other acceptable format for date command | |||
full precision down to seconds (if specified will be computed) but only | |||
up to date will be printed by default | |||
default is to add | |||
if third argument is SUB, then substracted | |||
if a forth argument is present, it is treated as the format specifier | |||
for output. e.g. '+%Y%m%d%H%M%S' to get full precision | |||
(Assela Pathirana, 2006) | |||
EOF | |||
exit 1 | exit 1 | ||
fi | fi | ||
| Line 23: | Line 27: | ||
thisdate=`date +'%s'` | thisdate=`date +'%s'` | ||
fi | fi | ||
if [ ! "$3" == 'SUB' ];then | if [ ! "$3" == 'SUB' ];then | ||
newdate=`echo $thisdate $dates|awk '{printf "%20i", $1-$2*24*3600}'` | |||
else | |||
newdate=`echo $thisdate $dates|awk '{printf "%20i", $1+$2*24*3600}'` | newdate=`echo $thisdate $dates|awk '{printf "%20i", $1+$2*24*3600}'` | ||
fi | fi | ||
if [ $# -ge 4 ]; then | if [ $# -ge 4 ]; then | ||
| Line 33: | Line 37: | ||
date --date=" 1970-01-01 00:00:00 UTC $newdate seconds" "$fmt" | date --date=" 1970-01-01 00:00:00 UTC $newdate seconds" "$fmt" | ||
</nowiki></pre> | |||
==Example Usage== | |||
# Add five days to 2006-03-01: <nowiki> | |||
</nowiki><pre><nowiki> | |||
$ dateshift 5 20060301 | |||
20060306 | |||
</nowiki></pre> | |||
# Add 12 hours to 20060304 06:00: <nowiki> | |||
</nowiki><pre><nowiki> | |||
$ dateshift .5 "20060304 06:00" "+%Y%m%d %H:%M" | |||
20060304 18:00 | |||
</nowiki></pre> | |||
# Subtract five days and six hours from 20060308: <nowiki> | |||
</nowiki><pre><nowiki> | |||
$ dateshift -5.25 20060308 "+%Y%m%d %H:%M" | |||
20060302 18:00 | |||
</nowiki></pre> | </nowiki></pre> | ||
Revision as of 01:51, 2 May 2006
Let's face it: Solar system is a mess as far as time units are concerned! There are some 365.2425 days and is reducing with time!! We have largely simplified the system by adopting various convensions in the standard calendar, still there are occational jumps of dates here are there. This causes numerous problems in writing programs that operate on dates. Perhaps the best bet is to use a standard date function provided by an operating system as the basis, for these systems have been widely researched and tested.
I have written the following UNIX script to add or substract number of days from a given date and print the result.
#!/bin/bash
fmt="+%Y%m%d"
if [ $# -lt 1 ]; then
cat << EOF
Usage: $0 ndates date [ADD/SUB] [fmt]
default format is $fmt
format should be YYYYMMDD or any other acceptable format for date command
full precision down to seconds (if specified will be computed) but only
up to date will be printed by default
default is to add
if third argument is SUB, then substracted
if a forth argument is present, it is treated as the format specifier
for output. e.g. '+%Y%m%d%H%M%S' to get full precision
(Assela Pathirana, 2006)
EOF
exit 1
fi
dates=$1
if [ $# -ge 2 ]; then
thisdate=`date --date "$2" +'%s'`
else
date=''
thisdate=`date +'%s'`
fi
if [ ! "$3" == 'SUB' ];then
newdate=`echo $thisdate $dates|awk '{printf "%20i", $1-$2*24*3600}'`
else
newdate=`echo $thisdate $dates|awk '{printf "%20i", $1+$2*24*3600}'`
fi
if [ $# -ge 4 ]; then
fmt=$4
fi
date --date=" 1970-01-01 00:00:00 UTC $newdate seconds" "$fmt"
Example Usage
- Add five days to 2006-03-01:
$ dateshift 5 20060301 20060306
- Add 12 hours to 20060304 06:00:
$ dateshift .5 "20060304 06:00" "+%Y%m%d %H:%M" 20060304 18:00
- Subtract five days and six hours from 20060308:
$ dateshift -5.25 20060308 "+%Y%m%d %H:%M" 20060302 18:00
