How can I find the current date minus seven days in Unix?

Question

I am trying to find the date that was seven days before today.

 CURRENT_DT=`date +"%F %T"`
 diff=$CURRENT_DT-7 
 echo $diff 

I am trying stuff like the above to find the 7 days less than from current date. Could anyone help me out please?

Answer 1

GNU date will to the math for you:

date --date "7 days ago"

Other version will require you to covert the current date into seconds since the UNIX epoch first, manually subtract 7 days' worth of seconds, and convert that back into the desired form. Consult the documentation for your version of date for details on how to convert to and from Unix timestamps. Here's an example using GNU date again:

x=$(date +%s)
x=$((x - 7 * 24 * 60 * 60))
date --date @$x

Answer 2

Here is a simple Perl script which (unlike the other examples) works with Unix:

perl -e 'use POSIX qw(ctime); printf "%s", ctime(time - (7 * 24 * 60 * 60));'

(Tested with Solaris 10, and a token Linux system, of course - with the caveat that Perl is not necessarily part of one's configuration, merely very likely).