I have a server running with the timezone set to UTC
. It seemed like that was generally a good practice (please correct me if I'm wrong).
Anyhow, one of the servers I connect to, in order to scp
files, is running on EDT
and stores files that I need to copy in the format /path/to/filename/data20120913
I looked at trying to rsync
files using something like find's -mtime -1
flag for files modified in the last day, but I didn't have any luck.
I don't mind just using scp
to copy the current day's file, but as of right now there is a 4-hour window where running date +%Y%m%d
will give a different day on each server and that bugs me a little.
Looking through man date
I see that I can have the time output as UTC
, but I don't see a way to have it output as another timezone like EDT
I suppose I could also use something like the GNU
date extension date -d 20100909 +%s
to get the date in seconds from the epoch, apply a manual 4 * 60 * 60
second calculation, and see about rendering that as a date – but then when daylight time kicks in it will still be an hour off.
Is there a simpler way to output the date in a YYYYMMDD
format for EDT
on a server that is set to UTC
?
Best Answer
You can set a timezone for the duration of the query, thusly:
Note the whitespace between the
TZ
setting and thedate
command. In Bourne-like andrc
-like shell, that sets theTZ
variable only for the command line. In other shells (csh
,tcsh
,fish
), you can always use theenv
command instead:tl;dr
On Linux systems. timezones are defined in files in the
/usr/share/zoneinfo
directory. This structure is often referred to as the "Olson database" to honor its founding contributor.The rules for each timezone are defined as text file lines which are then compiled into a binary file. The lines so compiled, define the zone name; a range of data and time during which the zone applies; an offset from UTC for the standard time; and the notation for defining how transition to-and-from daylight saving time occurs, if applicable.
For example, the directory "America" contains the requisite information for New York in the file
America/New_York
as used, above.Beware that the specification of a non-existent zone (file name) is silently ignored and UTC times are reported. For example, this reports an incorrect time:
The Single UNIX Specification, version-3, known as SUSv3 or POSIX-2001, notes that for portability, the character string that identifies the timezone description should begin with a colon character. Thus, we can also write:
As an alternative method to the specification of timezones using a pathname to a description file, SUSv3 describes the POSIX model. In this format, a string is defined as:
where
std
is the standard component name anddst
is the daylight saving one. Each name consists of three or more characters. Theoffset
is positive for timezones west of the prime meridian and negative for those east of the meridian. The offset is added to the local time to obtain UTC (formerly known as GMT). Thestart
andend
time fields indicate when the standard/daylight transitions occur.For example, in the Eastern United States, standard time is 5-hours earlier than UTC, and we can specify
EST5EDT
in lieu ofAmerica/New_York
. These alternatives are not always recognized, however, especially for zones outside of the United States and are best avoided.HP-UX (an SUSv3 compliant UNIX) uses textual rules in
/usr/lib/tztab
and the POSIX names like EST5EDT, CST6CDT, MST7MDT, PST8PDT. The file includes all of the historical rules for each time zone, akin to the Olson database.NOTE: You should be able to find all of the timezones by inspecting the following directory:
/usr/share/zoneinfo
.