Mail Archives: cygwin/2007/08/01/07:10:05
It appears that tcsh treats the "TZ" environmental variable in a special
way - upon entry into tcsh, some commands see TZ as set. Using unsetenv to
attempt to unset it is fruitless:
bash-3.2$ unset TZ
bash-3.2$ printenv TZ
bash-3.2$ echo $TZ
bash-3.2$ bash -c "printenv TZ"
bash-3.2$ tcsh
tcsh$ printenv TZ
tcsh$ echo $TZ
GMTST0GMTDT-1,M3.5.0/1,M10.5.0/2
tcsh$ bash -c "printenv TZ"
GMTST0GMTDT-1,M3.5.0/1,M10.5.0/2
tcsh$ unsetenv TZ
tcsh$ printenv TZ
tcsh$ echo $TZ
GMTST0GMTDT-1,M3.5.0/1,M10.5.0/2
tcsh$ bash -c "printenv TZ"
GMTST0GMTDT-1,M3.5.0/1,M10.5.0/2
Unfortunately our application requires TZ to be unset to function correctly
(see below for why).
Can anyone give me a pointer as to how to ensure TZ is unset in tcsh?
I have googled for "cygwin tcsh TZ" and searched the Cygwin mailing list
for "tcsh TZ", but have been unable to find any relevant threads.
I also looked briefly at the source for tcsh. From my investigations, it
appears that tcsh has various features related to time; the time of
execution of each command line is held in the history, and there is also
the facility to print the time in the prompt. As part of these facilities,
tcsh calls Cygwin functions such as ctime(), gettimeofday() and
localtime(), which call tzset(). tzset() sets the TZ environmental variable
if it is not currently set. This is then visible in the environment used
for some commands.
Why don't I simply get rid of the tcsh monstrosity and use a sensible shell
instead?
An excellent idea and my personal preference. Unfortunately this would
require considerable effort and thus the buy-in of my superiors, which is
not currently forthcoming. Additionally, the use of tcsh as an interactive
shell would need to be forbidden, which would be unpopular and difficult to
enforce both internally and with clients.
Why can't I just set TZ to the required value?
Our application uses both Cygwin binaries and binaries compiled using MSVC
from tcsh. There is no value for TZ that will produce correct time and date
information for both categories of binaries for all times of the year for
timezones outside the US that use DST. This is because the MSVC
implementation of tzset() assumes that daylight savings time is always one
hour, and starts and ends on the dates and times that happen to prevail in
the US at the time MSVC was written.
Thanks for your attention,
Roger Broadbent
All opinions expressed are my own and do not necessarily represent those of
DST International Limited.
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