Help With Time Formats: UT, GMT, DST ,...

[DanBlather]

I am pulling my hair out trying to create an RSS feed with appropriate date and time filelds. I was up to 04:00 AM and now am too punchy to think remotely straight.

1. In a date/time in the format (I think this is RFC822):

Wed, 18 Oct 2006 12:48:58 -0700

Does that indicate a local time of 12:48:58 in a timezone 7 hours behind GMT (LA Time), or a GMT time of 12:48:58 that you have to subract 7 hours from if you want to display it in Los Angeles?

2. When LA changes to to PST do I then change -0700 to -0600, or will date SW do the appropriate stuff for me?

3. What’s the diff between UT and GMT?

[Duckster]

@DanBlather

Wed, 18 Oct 2006 12:48:58 -0700

Wouldn’t that be only for DST? The US Pacific coast is only -0700 during the summer but reverts back to -0800 once Daylight Saving ends.

“Greenwich Mean Time” (GMT) is a term originally referring to mean solar time at the Royal Observatory, Greenwich in England. It is now often used to refer to Coordinated Universal Time (UTC) when this is viewed as a time zone, although strictly UTC is an atomic time scale which only approximates GMT in the old sense. It is also used to refer to Universal Time (UT), which is the astronomical concept that directly replaced the original GMT.

Source: Greenwich Mean Time - Wikipedia

[Terminus_Est]

RFC 2822: Internet Message Format

The zone specifies the offset from Coordinated Universal Time (UTC, formerly referred to as “Greenwich Mean Time”) that the date and time-of-day represent. The “+” or “-” indicates whether the time-of-day is ahead of (i.e., east of) or behind (i.e., west of) Universal Time. The first two digits indicate the number of hours difference from Universal Time, and the last two digits indicate the number of minutes difference from Universal Time. (Hence, +hhmm means +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm) minutes). The form “+0000” SHOULD be used to indicate a time zone at Universal Time. Though “-0000” also indicates Universal Time, it is used to indicate that the time was generated on a system that may be in a local time zone other than Universal Time and therefore indicates that the date-time contains no information about the local time zone.

For your example 12:48:58 is the local time, which is 7 hours behind UTC. To get UTC, add 7 hours.

Whether the time offset will automatically switch for DST depends on the software you’re using to generate the datetime string. The standard Unix ‘date’ command should automatically adust for DST, assuming your system timezone environment has been properly set up.

[DanBlather]

@Terminus Est

RFC 2822 - Internet Message Format

For your example 12:48:58 is the local time, which is 7 hours behind UTC. To get UTC, add 7 hours.

Whether the time offset will automatically switch for DST depends on the software you’re using to generate the datetime string. The standard Unix ‘date’ command should automatically adust for DST, assuming your system timezone environment has been properly set up.

Thanks