Linux Script- Date Manipulations

Question

I will set one date variable(Say \'08-JUN-2011\') and I want to do some calculations based on that date namely,
1. Have to get the first day of the given day\'s month.

Answer 1

Using dateutils' dround tool:

Current month:

$ dround today -1
2014-02-01

Previous month

$ dround today -31
2014-01-31

Last day of current month:

$ dround today +31
2014-02-28

Of course you can use a custom date instead of today, the idea is to round down or up to the desired day-of-the month, e.g. the next first-of-the-month given 2010-10-04:

$ dround 2010-10-04 +1d
2010-11-01

Answer 2

$ date +%m/01/%Y

I came here looking for a way to get the first day of the current month.

Answer 3

As you're using Linux, hhopefully you have the GNU date utility available. It can handle almost any description of a relative date that you think of.

Here are some examples

date --date="last month" +%Y-%m-%d
date --date="yesterday" +%Y-%m-%d
date --date="last month" +%b
x=$(date --date "10 days ago" +%Y/%m/%d)

To learn more about it see GNU Date examples

Once you use it some, you can shortcut your information gathering with date --help, which shows all the basic options (but is sometimes is hard to interpret.)

I hope this helps.

Answer 4

This is going to be convoluted in a shell script. You are better off using Date::Manip in perl, or something similar in another full-featured language. However, I can think of some ways to do this with the date command. First of all, you can use a --date parameter to set a starting point for date, like so:

$ date --date='08-JUN-2011'
Wed Jun  8 00:00:00 EDT 2011

You can get the previous date like this:

$ date --date='08-JUN-2011 -1 days'
Tue Jun  7 00:00:00 EDT 2011

For the last day of the month, I would just walking back from 31 until date does not fail. You can check $? for that

$ date --date='31-JUN-2011';echo $?
date: invalid date `31-JUN-2011'
1
$ date --date='30-JUN-2011';echo $?
Thu Jun 30 00:00:00 EDT 2011
0

For the first day of the month...that is usually 01 :)

Answer 5

Here's how to perform the manipulations using GNU date:

#!/bin/sh

USER_DATE=JUN-08-2011

# first day of the month
FIRST_DAY_OF_MONTH=$(date -d "$USER_DATE" +%b-01-%Y)

PREVIOUS_DAY=$(date -d "$USER_DATE -1 days" +%b-%d-%Y)

# last day of the month
FIRST_DAY_NEXT_MONTH=$(date -d "$USER_DATE +1 month" +%b-01-%Y)
LAST_DAY_OF_MONTH=$(date -d "$FIRST_DAY_NEXT_MONTH -1 day" +%b-%d-%Y)

echo "User date: $USER_DATE"
echo "1. First day of the month: $FIRST_DAY_OF_MONTH"
echo "2. Previous day: $PREVIOUS_DAY"
echo "3. Last day of the month: $LAST_DAY_OF_MONTH"

The output is:

User date: JUN-08-2011
1. First day of the month: Jun-01-2011
2. Previous day: Jun-07-2011
3. Last day of the month: Jun-30-2011