That's fine until you get to the first day of the month:

$ perl -l
use strict;
use warnings;
my $db_name="2007_12_01_04_49_15";
my @date=split /_/,$db_name;
$date[2]=$date[2]-1;
$db_name=join '_',@date;
print $db_name;
__END__
2007_12_0_04_49_15
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Date and time calculations (e.g. month changes, leap years, timezones) are surprisingly difficult to get right. Don't reinvent the wheel. Use an existing module from .