A small variation on the solution offered above would be to use the inbuilt function time to generate the current date in seconds, then subtract 10 days (in seconds) from the result (as described above), and finally put the result into a calendar friendly format using localtime. You could use strftime (as I have done) to further format the result.

use POSIX qw(strftime);

my $thisday = time;
my $tenDaysPrevious = $thisday - 10*24*60*60;
$tenDaysPrevious = strftime "%m/%d/%Y", (localtime($tenDaysPrevious));