"Broken-down time" means the typical array ($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst), and it correlates to the C standard library's struct tm.

Modules that are installed by default with Perl

• core functions
  • gmtime — converts a Unix/epoch time into broken-down time (or, in scalar context, to a string)
  • localtime — converts a Unix/epoch time into broken-down time (or, in scalar context, to a string)
  • time — gets the current Unix/epoch time
  • times — gets four current and cummulative times
• Time::Local — does the opposite of 'localtime' and 'gmtime' — converts an array of date-and-time-pieces (AKA a "broken-down time") back into a Unix/epoch time
• Time::Seconds — converts a seconds-based-interval into an equivalent interval of days, hours, months, etc. Probably often used in conjunction with Unix/epoch time-based times.
• Time::HiRes — high-resolution time routines
• Time::Piece — a core-module alternative to things like 'DateTime', 'Date::Manip', and 'Date::Simple'
  • Time::Piece->strptime() — parses a string into a Time::Piece object, using a format string [2]
• POSIX
  • POSIX::asctime() — converts broken-down time into a string (C function man page)
  • POSIX::ctime() — converts a Unix/epoch time into a string (C function man page)
  • POSIX::mktime() — converts broken-down time into a Unix/epoch time (i.e. what Time::Local does) (C function man page)
  • POSIX::strftime() — converts broken-down time into a string, using a format string
  • POSIX::tzname() (C function man page)
  • POSIX::tzset() (C function man page)

Important modules that don't get installed by default

• DateTime — river stage 4 ("what is a river stage?")
• Date::Manip — river stage 3
• Date::Format, Date::Parse — river stage 4
• Date::Simple — river stage 2

Parsing

• high-level
  • HTTP::Date
  • Date::Parse
  • Time::ParseDate
  • DateTime::Format::Natural
  • Date::Manip -- parse()
• medium-level
  • Time::Piece->strptime() [man page]
• low-level
  • Time::Local
  • POSIX::mktime()

If you're stuck using low-level parsing libraries, here is some useful information for writing custom date parsers.

Timezones

• $ENV{TZ} (list)
• DateTime::TimeZone
• Date::Manip::Zones
• POSIX::tzname()
• POSIX::tzset()

To change your script's local timezone at the top of the script:

use POSIX;

$ENV{TZ} = 'CST6CDT';
POSIX::tzset();

Formatting

• strftime() is the quintessential function here, and can be found in various places:
  • POSIX::strftime()
  • DateTime->strftime()
  • Date::Format
• rounding to English expressions (eg. "6 seconds ago", "4 days ago")
  • Time::Duration
  • DateTimeX::Format::Ago
  • DateTime::Format::Human::Duration