my $current_month = strftime "%m", localtime;
my $previous_month = $current_month - 1;
my $previous_month = sprintf("%02d", $previous_month);
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Last month with Time::Piece with month granularity

#!/usr/bin/perl --
use strict;
use warnings;
use Time::Piece qw/ localtime /;

Main( @ARGV );
exit( 0 );

sub Main {
    my $now = localtime;
    my $lastmonth = $now->prevmonth;
    print "$now\n$lastmonth\n";
}

sub Time::Piece::prevmonth {
    my $t= shift;
    if( ! ref $t ) { $t = localtime; }
    my $y = $t->year;
    my $m = $t->mon;
#~     if( $m == 12 ){ $m=1; $y++; } else { $m++;  }
    if( $m == 1 ){ $m=12; $y--; } else { $m--;  }
    my $nt = Time::Piece->strptime( "$y-$m", '%Y-%m'  );
}
__END__
Thu Oct 30 03:10:05 2014
Mon Sep  1 00:00:00 2014
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