:TITLE: Time and Date - clock ;# ;# RCSID: $Header: /cvsroot/tcl/tcltutorial/original/Tcl41.lsn,v 1.1 2004/11/04 16:01:14 davidw Exp $ ;# Copyright (c) 1995 Clif Flynt ;# 9300 Fleming Rd. ;# Dexter, MI 48130 ;# clif@cflynt.com ;# See file "NOTICE" for licensing terms. ;# :LESSON_TEXT_START_LEVEL 0: The clock command provides access to the time and date functions in Tcl. Depending on the subcommands invoked, it can acquire the current time, or convert between different representations of time and date.
clock seconds
The clock seconds command returns the time in seconds since the epoch. The date of the epoch varies for different operating systems, thus this value is useful for comparison purposes, or as an input to the clock format command.

clock format clockValue ?-gmt boolean? ?-format string?
The format subcommand formats a clockvalue (as returned by clock clicks into a human readable string.

The -gmt switch takes a boolean as the second argument. If the boolean is 1 or True, then the time will be formatted as Greenwich Mean Time, otherwise, it will be formatted as local time.

The -format option controls what format the return will be in. The contents of the string argument to format has similar contents as the format statement (as discussed in lesson 19, 33 and 34). In addition, there are several more %* descriptors that can be used to describe the output.

These include:

clock scan dateString
The scan subcommand converts a human readable string to a system clock value, as would be returned by clock seconds

The dateString argument contains strings in these forms:

time
A time of day in one of the formats shown below. Meridian may be AM, or PM, or a capitalization variant. If it is not sepcified, then the hour (hh) is interpreted as a 24 hour clock. Zone may be a three letter description of a time zone, EST, PDT, etc.
  • hh:mm:ss ?meridian? ?zone?
  • hhmm ?meridian? ?zone?
date
A date in one of the formats shown below.
  • mm/dd/yy
  • mm/dd
  • monthname dd, yy
  • monthname dd
  • dd monthname yy
  • dd monthname
  • day, dd monthname yy
:TEXT_END: :LESSON_TEXT_START_LEVEL 1: The clock command provides access to the time and date functions in Tcl. Depending on the subcommands invoked, it can acquire the current time, or convert between different representations of time and date.

The clock command is a platform independent method of getting the display functionality of the unix date command, and provides access to the values returned by a unix gettime() call.

clock seconds
The clock seconds command returns the time in seconds since the epoch. The date of the epoch varies for different operating systems, thus this value is useful for comparison purposes, or as an input to the clock format command.

clock format clockValue ?-gmt boolean? ?-format string?
The format subcommand formats a clockvalue (as returned by clock clicks into a human readable string.

The -gmt switch takes a boolean as the second argument. If the boolean is 1 or True, then the time will be formatted as Greenwich Mean Time, otherwise, it will be formatted as local time.

The -format option controls what format the return will be in. The contents of the string argument to format has similar contents as the format statement (as discussed in lesson 19, 33 and 34). In addition, there are several more %* descriptors that can be used to describe the output.

These include:

clock scan dateString
The scan subcommand converts a human readable string to a system clock value, as would be returned by clock seconds

The dateString argument contains strings in these forms:

time
A time of day in one of the formats shown below. Meridian may be AM, or PM, or a capitalization variant. If it is not sepcified, then the hour (hh) is interpreted as a 24 hour clock. Zone may be a three letter description of a time zone, EST, PDT, etc.
  • hh:mm:ss ?meridian? ?zone?
  • hhmm ?meridian? ?zone?
date
A date in one of the formats shown below.
  • mm/dd/yy
  • mm/dd
  • monthname dd, yy
  • monthname dd
  • dd monthname yy
  • dd monthname
  • day, dd monthname yy
:TEXT_END: :LESSON_TEXT_START_LEVEL 2: Most computer systems track the current time and day by storing the number of seconds that have elapsed since an arbitrary date in memory. The start date (0 seconds) is usually referred to as the epoch, since that's when time starts (for that system). When you need to know the current date and time, the computer converts that value from seconds since the epoch into a user readable string.

In Tcl, the clock command provides access to the time and date functions. Depending on the subcommands invoked, it can acquire the current time, or convert between different representations of time and date.

clock seconds
The clock seconds command returns the time in seconds since the epoch. The date of the epoch varies for different operating systems, thus this value is useful for comparison purposes, or as an input to the clock format command.

clock format clockValue ?-gmt boolean? ?-format string?
The format subcommand formats a clockvalue (as returned by clock clicks into a human readable string.

The -gmt switch takes a boolean as the second argument. If the boolean is 1 or True, then the time will be formatted as Greenwich Mean Time, otherwise, it will be formatted as local time.

The -format option controls what format the return will be in. The contents of the string argument to format has similar contents as the format statement (as discussed in lesson 19, 33 and 34). In addition, there are several more %* descriptors that can be used to describe the output.

These include:

clock scan dateString
The scan subcommand converts a human readable string to a system clock value, as would be returned by clock seconds

The dateString argument contains strings in these forms:

time
A time of day in one of the formats shown below. Meridian may be AM, or PM, or a capitalization variant. If it is not sepcified, then the hour (hh) is interpreted as a 24 hour clock. Zone may be a three letter description of a time zone, EST, PDT, etc.
  • hh:mm:ss ?meridian? ?zone?
  • hhmm ?meridian? ?zone?
date
A date in one of the formats shown below.
  • mm/dd/yy
  • mm/dd
  • monthname dd, yy
  • monthname dd
  • dd monthname yy
  • dd monthname
  • day, dd monthname yy
:TEXT_END: :CODE_START: ;# Get the time in system seconds set systemTime [clock seconds] ;# Display that time using the hour, minute and second descriptors. puts "The time is: [clock format $systemTime -format %H:%M:%S]" ;# Display the date using a shorthand format puts "The date is: [clock format $systemTime -format %D]" ;# You can use complex format statements. puts [clock format $systemTime -format {Today is: %A, the %d of %B, %Y}] ;# And, this is the default output for the time, with no -format puts "\n the default format for the time is: [clock format $systemTime]\n" ;# The book and movie versions of 2001 had different dates for when the ;# HAL 9000 became alive. ;# We can use the scan command to figure out how many seconds they differed by set halBirthBook "Jan 12, 1997" set halBirthMovie "Jan 12, 1992" set bookSeconds [clock scan $halBirthBook] set movieSeconds [clock scan $halBirthMovie] puts "The book and movie versions of '2001, A Space Oddysey' had a" puts "discrepency of [expr $bookSeconds - $movieSeconds] seconds in how" puts "soon we would have sentient computers like the HAL 9000" :TEXT_END: