Shell Programming and Scripting

$ su -
# cpan
cpan> install DateTime
cpan> exit
# exit
$ cat script.pl
use strict;
use warnings;
use DateTime;

die "Usage: $0 [#months]\n" unless @ARGV && $ARGV[0] =~ /^\d+$/;

my $monthsBefore = $ARGV[0];

my $dt = DateTime->today();
$dt->set_day(1), print($dt->ymd('/'), "\n"), exit if $monthsBefore == 0;

my $cdt = $dt->clone();
$dt->set_day(1);

my $cmp = DateTime->compare($dt, $cdt);
--$monthsBefore if $cmp < 0;
$dt->subtract(months => $monthsBefore);
print $dt->ymd('/'), "\n";
$ perl script.pl 6
2010/08/01