Shell Programming and Scripting

Hi,

I am trying to write a code for changing header date of a file with a date of 6 month back.

Below is the header date on which I am working -
20080531
I want to change it as 20071130

Please suggest me in the way like ,I can change any date in a file with date of 6 months back.

Can someone please help me on this.

Many Thanks in advance..

Monalisa

do u know perl scripting ?

if yes, you can do it very simply ..

Thanks..

But I know shell scripting not perl..

Can you please help me to do this with shell scripting?

you can do it in awk or possibly with parameter substitution- part of standard shell.
Please show us sample input and desired output, and what shell you have: bash, ksh, etc.

Code:

D="20080531"
date -d "$D 6 month ago" +%Y%m%d

returns 20071201 which is correct.

Code:

perl -MDate::Manip -pi.bak -e 's/(\d{8})/UnixDate(DateCalc("-6 M", $1), "%Y%m%d")/eg' inputfile

That will subtract six months from all dates in "inputfile" which are in the eight-digit format you showed. remove the "g" at the end if you only want to do one. This code consider that an incoming date is an eight digit number, with no punctuation. If you expect to have no-punctuation, eight-digit numbers in the data, we can work on this some more.

Hope that Helps.

Don't work for me
Your solution is not universally valid , look like a Linux date , please state your environment next time , same for OP.

This works for me

Code:

# uname -v
FreeBSD 7.2-RELEASE-p7 #0: Sat Apr 10 23:18:49 JST 2010

# date -v -6m  "+%A %B %d %Y"
Friday October 23 2009