The
clock
Command
The
clock
command has facilities for getting the current time, formatting time values, and scanning printed time strings to get an integer time value. The
clock
command was added in Tcl 7.5. Table 13-1 summarizes the
clock
command:
Table 13-1. The
clock
command.
|
clock clicks
|
A system-dependent high resolution counter.
|
|
clock format
value
?-format
str
?
|
Formats a clock value according to
str
.
|
|
clock scan
string
?-base
clock
? ?-gmt
boolean
?
|
Parses date
string
and return seconds value. The
clock
value determines the date.
|
|
clock seconds
|
Returns the current time in seconds.
|
The following command prints the current time:
clock format [clock seconds]
=> Sun Nov 24 14:57:04 1996
The
clock seconds
command returns the current time, in seconds since a starting
epoch
. The
clock format
command formats an integer value into a date string. It takes an optional argument that controls the format. The format strings contains % keywords that are
replaced
with the year, month, day, date, hours, minutes, and seconds, in various formats. The default string is:
%a %b %d %H:%M:%S %Z %Y
Tables 13-2 and 13-3 summarize the
clock
formatting strings:
Table 13-2. Clock formatting keywords.
|
%%
|
Inserts a
%
.
|
|
%a
|
Abbreviated weekday
name
(Mon, Tue, etc.).
|
|
%A
|
Full weekday name (Monday, Tuesday, etc.).
|
|
%b
|
Abbreviated month name (Jan, Feb, etc.).
|
|
%B
|
Full month name.
|
|
%c
|
Locale specific date and time (e.g.,
Nov 24 16:00:59 1996
).
|
|
%d
|
Day of month (01 ?31).
|
|
%H
|
Hour in 24-
hour
format (00 ?23).
|
|
%I
|
Hour in 12-hour format (01 ?12).
|
|
%j
|
Day of year (001 ?366).
|
|
%m
|
Month number (01 ?12).
|
|
%M
|
Minute (00 ?59).
|
|
%p
|
AM/PM indicator.
|
|
%S
|
Seconds (00 ?59).
|
|
%U
|
Week of year (00 ?52) when Sunday starts the week.
|
|
%w
|
Weekday number (Sunday = 0).
|
|
%W
|
Week of year (01 ?52) when Monday starts the week.
|
|
%x
|
Locale specific date format (e.g., Feb 19 1997).
|
|
%X
|
Locale specific time format (e.g., 20:10:13).
|
|
%y
|
Year without century (00 ?99).
|
|
%Y
|
Year with century (e.g. 1997).
|
|
%Z
|
Time zone name.
|
Table 13-3. UNIX-specific clock formatting keywords.
|
%D
|
Date as
%m/%d/%y
(e.g., 02/19/97).
|
|
%e
|
Day of month (1 ?31), no leading zeros.
|
|
%h
|
Abbreviated month name.
|
|
%n
|
Inserts a newline.
|
|
%r
|
Time as
%I:%M:%S %p
(e.g., 02:39:29 PM).
|
|
%R
|
Time as
%H:%M
(e.g., 14:39).
|
|
%t
|
Inserts a tab.
|
|
%T
|
Time as
%H:%M:%S
(e.g., 14:34:29).
|
{% if main.adsdop %}{% include 'adsenceinline.tpl' %}{% endif %}
The
clock clicks
command returns the value of the system's highest resolution clock. The units of the clicks are not defined. The main use of this command is to measure the relative time of different performance tuning trials. The following command counts the clicks per second over 10 seconds, which will vary from system to system:
Example 13-1 Calculating clicks per second.
set t1 [clock clicks]
after 10000 ;# See page 218
set t2 [clock clicks]
puts "[expr ($t2 - $t1)/10] Clicks/second"
=> 1001313 Clicks/second
The
clock scan
command parses a date string and returns a seconds value. The command handles a variety of date formats. If you leave off the year, the current year is assumed.
|
Year 2000 Compliance
|
Tcl implements the standard interpretation of two-digit year values, which is that 70?9 are 1970?999, 00?9 are 2000?069. Versions of Tcl before 8.0 did not properly deal with two-digit
years
in all cases. Note, however, that Tcl is limited by your system's time epoch and the number of bits in an integer. On Windows, Macintosh, and most UNIX systems, the clock epoch is January 1, 1970. A 32-bit integer can count enough seconds to reach forward into the year 2037, and backward to the year 1903. If you try to
clock scan
a date outside that range, Tcl will raise an error because the seconds counter will overflow or underflow. In this case, Tcl is just reflecting limitations of the underlying system.
If you leave out a date,
clock scan
assumes the current date. You can also use the
-base
option to specify a date. The following example uses the current time as the base, which is redundant:
clock scan "10:30:44 PM" -base [clock seconds]
=> 2931690644
The date parser allows these modifiers:
year
,
month
,
fortnight
(two weeks),
week
,
day
,
hour
,
minute
,
second
. You can put a positive or negative number in front of a modifier as a
multiplier
. For example:
clock format [clock scan "10:30:44 PM 1 week"]
=> Sun Dec 01 22:30:44 1996
clock format [clock scan "10:30:44 PM -1 week"]
Sun Nov 17 22:30:44 1996
You can also use
tomorrow
,
yesterday
,
today
,
now
,
last
,
this
,
next
, and
ago
, as modifiers.
clock format [clock scan "3 years ago"]
=> Wed Nov 24 17:06:46 1993
Both
clock format
and
clock scan
take a
-gmt
option that uses Greenwich Mean Time. Otherwise, the local time zone is used.
clock format [clock seconds] -gmt true
=> Sun Nov 24 09:25:29 1996
clock format [clock seconds] -gmt false
=> Sun Nov 24 17:25:34 1996
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