Another way might be to use POSIX::strftime in a way similar to this:

#!/usr/bin/perl -w

use POSIX qw(strftime);
use strict;

my $thismonth = strftime "%m", localtime;

# strftime(fmt, sec, min, hour, mday, mon, year, wday = -1, yday = -1,
+ isdst = -1)
# don't forget that the months start counting from 0 as January
print strftime("%m", 0, 0, 0, 0, $thismonth-2, 0); #prints "05"
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