Shell Programming and Scripting

Hi

I have shell script and I am facing the below issue to integrate the date calculation to the the script.

If I give the $1 as the date(20110701) then I need to get the 7 days ago date for the same format.(20110624).

At first I thought its a simple one to handle and I did a search in the forum but couldn't get this if we provide the date as the $1 argument.

For example:

if $1 = 20110601 ( The format I would provide)
then I need to calculate the date for 7 days ago i.e. 20110525.

Here I am not using the system current date but instead I have to calculate the 7 days ago date for the date that the user has given.

Could someone please help me out in this. Its really appreciated.

What is your system? What is your shell? This has a huge effect on the tools you have available for playing with dates. On some systems you can just date -d and print dates and timestamps for whatever time you want. Others might have awk or perl extensions for it. And a few obnoxious ones have no elegant way to handle it and must use an enormous ksh script to parse dates the hard way.

Hi

I am using Linux system -->

Linux xbdp5898pap 2.4.21-50.ELsmp #1 SMP Tue May 8 17:18:29 EDT 2007 i686 i686 i386 GNU/Linux

I am using Bash Shell.

Like if I use date -d then it would take the system date and then we can print wat we want.But Instead I would like to use the User's date(20110701) and then calculate the 7 days ago date (20110624) and print as an output.

Thanks for your thoughts. Really appreciate for your time.

You have GNU date, which supports -d, letting you input whatever date you want which makes this tons easier. Working on something

[edit] You stealth-edited my stealth edit, Jim
[edit] whoops, %Y%m%d not %Y%m%s!

Code:

# Get epoch seconds
USERDATE=$(date +%s -d 20110701)
# Subtract 1 week
((USERDATE -= (60*60*24*7) ))

# Convert from epoch seconds into YYYYMMDD.
# -d assumes strings beginning with @ are epoch seconds.
D=$(date -d "@$USERDATE" +"%Y%m%d")
echo "One week previous was $D"

This can help too:

Code:

~/unix.com$ date -d '7 days ago'

Hi Corona688,

Thanks for your reply.

But I am getting an error and couldn't figure this out.

Code:

#!/bin/sh

# Get epoch seconds
USERDATE=$(date +%s -d 20110701)
# Subtract 1 week
((USERDATE -= (60*60*24*7) ))

# Convert from epoch seconds into YYYYMMDD.
# -d assumes strings beginning with @ are epoch seconds.
D=$(date -d "@$USERDATE" +"%Y%m%d")
echo "One week previous was $D"

Code:

$ ./date.sh
date: invalid date `@1308888000'

One week previous was