If the data is still in mysql, I'd have mysql do the work, and use the DATE_FORMAT() function.

In more recent versions of mySQL, there's also the CONVERT_TZ() function (but you'll need to load the time zone tables)

The following should work in most versions of mysql:

date_format
  date_add('20050519112656',interval 4 hour),
  '%m-%d-%y %h:%i %p EST')
[download]

(I'd also personally suggest not using m/d/y ordering ... it might make sense to americans, but can cause lots of problems down the road... y/m/d tends to be more universal, as there's no ambiguity)

$_= '20050519112656';
s/^(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})/$2-$3-$1 $4:$5:$6/;
print
__OUTPUT__
05-19-2005 11:26:56
[download]

---------------

From http://www.mysqlfreaks.com/statements/68.php.

UNIX_TIMESTAMP:

Statement Info:
If called with no argument, returns a Unix timestamp (seconds since '1970-01-01 00:00:00' GMT) as an unsigned integer. If UNIX_TIMESTAMP() is called with a date argument, it returns the value of the argument as seconds since '1970-01-01 00:00:00' GMT. date may be a DATE string, a DATETIME string, a TIMESTAMP, or a number in the format YYMMDD or YYYYMMDD in local time.
Examples:
SELECT UNIX_TIMESTAMP();
-> 882226357

SELECT UNIX_TIMESTAMP('1997-10-04 22:23:00');
-> 875996580

So, you should be able to do something like UNIX_TIMESTAMP(fieldname) and have it convert for you. Why go through all the bother of doing it yourself?

You may like some of the date-related modules mentioned on The Perl Advent Calendar. See the articles on Date::Parse and DateTime.

However, my absolute favorite modules for this is Date::Manip. It does an amazing job of recognizing almost any date format. Here's some working code for your example:

$ perl -MDate::Manip -e'print UnixDate("20050519112656","%m-%d-%Y %I:%
+M %p %Z\n")'
05-19-2005 11:26 AM EDT
[download]

Notice that I didn't have to say what format the input was in!