I want to increment the date under UNIX or Linux operating system while writing shell scripts. For example Apr/27/2011 should be incremented as Apr/28/2011 and so on. How do I increment a date in UNIX or Linux shell?

You can display time and date described by format (also known as relative date format) under GNU/date utility which is part of Linux and UNIX like operating systems. The default format is to display current date and time. To display tomorrows date, enter:
$ date
$ date --date="-1 days ago"
Sample outputs:

Wed Apr 27 02:29:59 IST 2011
Thu Apr 28 02:29:34 IST 2011

You can use bash for loop as follows:

#!/bin/bash
for i in {1..10}
do
   date --date="-$i days ago"
done

Sample outputs:

Thu Apr 28 02:33:02 IST 2011
Fri Apr 29 02:33:02 IST 2011
Sat Apr 30 02:33:02 IST 2011
Sun May  1 02:33:02 IST 2011
Mon May  2 02:33:02 IST 2011
Tue May  3 02:33:02 IST 2011
Wed May  4 02:33:02 IST 2011
Thu May  5 02:33:02 IST 2011
Fri May  6 02:33:02 IST 2011
Sat May  7 02:33:02 IST 2011

Change Date Format To DD/MM/YY

Use the following syntax:
$ date +"%d/%m/%y" --date="-5 days ago"
Here is update code:

#!/bin/bash
# Increment the date in dd/mm/yy format
for i in {1..10}
do
   date +"%d/%m/%y" --date="-$i days ago"
done

Sample outputs:

28/04/11
29/04/11
30/04/11
01/05/11
02/05/11
03/05/11
04/05/11
05/05/11
06/05/11
07/05/11

You can use the same technique in backup scripts to adjust date and time.

See also:

• Getting Yesterdays or Tomorrows day with Linux date command.
• How to use yest – a command line date/time manipulation and formatting program to add or subtract days, hours and/or minutes from a specified date.