clock (n)
Obtain and manipulate time
SYNOPSIS
clock option ?arg arg ...?
DESCRIPTION
This command performs one of several operations that may obtain
or manipulate strings or values that represent some notion of
time. The option argument determines what action is carried
out by the command. The legal options (which may be
abbreviated) are:
clock clicks
Return a high-resolution time value as a system-dependent integer
value. The unit of the value is system-dependent but should be the
highest resolution clock available on the system such as a CPU cycle
counter. This value should only be used for the relative measurement
of elapsed time.
clock format clockValue ?-format string? ?-gmt boolean?
Converts an integer time value, typically returned by
clock seconds, clock scan, or the atime, mtime,
or ctime options of the file command, to human-readable
form. If the -format argument is present the next argument is a
string that describes how the date and time are to be formatted.
Field descriptors consist of a % followed by a field
descriptor character. All other characters are copied into the result.
Valid field descriptors are:
Abbreviated weekday name (Mon, Tue, etc.).
Full weekday name (Monday, Tuesday, etc.).
Abbreviated month name (Jan, Feb, etc.).
Locale specific date and time.
Hour in 24-hour format (00 - 23).
Hour in 12-hour format (00 - 12).
Week of year (01 - 52), Sunday is the first day of the week.
Weekday number (Sunday = 0).
Week of year (01 - 52), Monday is the first day of the week.
Locale specific date format.
Locale specific time format.
Year without century (00 - 99).
Year with century (e.g. 1990)
In addition, the following field descriptors may be supported on some
systems (e.g. Unix but not Windows):
Day of month (1 - 31), no leading zeros.
If the -format argument is not specified, the format string
"%a %b %d %H:%M:%S %Z %Y" is used. If the -gmt argument
is present the next argument must be a boolean which if true specifies
that the time will be formatted as Greenwich Mean Time. If false
then the local timezone will be used as defined by the operating
environment.
clock scan dateString ?-base clockVal? ?-gmt boolean?
Convert dateString to an integer clock value (see clock seconds).
This command can parse and convert virtually any standard date and/or time
string, which can include standard time zone mnemonics. If only a time is
specified, the current date is assumed. If the string does not contain a
time zone mnemonic, the local time zone is assumed, unless the -gmt
argument is true, in which case the clock value is calculated assuming
that the specified time is relative to Greenwich Mean Time.
If the -base flag is specified, the next argument should contain
an integer clock value. Only the date in this value is used, not the
time. This is useful for determining the time on a specific day or
doing other date-relative conversions.
The dateString consists of zero or more specifications of the
following form:
time
A time of day, which is of the form: hh?:mm?:ss??
?meridian? ?zone? or hhmm ?meridian?
?zone?. If no meridian is specified, hh is interpreted on
a 24-hour clock.
date
A specific month and day with optional year. The
acceptable formats are mm/dd?/yy?, monthname dd
?, yy?, dd monthname ?yy? and day, dd monthname
yy. The default year is the current year. If the year is less
than 100, we treat the years 00-68 as 2000-2068 and the years 69-99
as 1969-1999. Not all platforms can represent the years 38-70, so
an error may result if these years are used.
relative time
A specification relative to the current time. The format is number
unit acceptable units are year, fortnight, month, week, day,
hour, minute (or min), and second (or sec). The
unit can be specified as a singular or plural, as in 3 weeks.
These modifiers may also be specified:
tomorrow, yesterday, today, now,
last, this, next, ago.
The actual date is calculated according to the following steps.
First, any absolute date and/or time is processed and converted.
Using that time as the base, day-of-week specifications are added.
Next, relative specifications are used. If a date or day is
specified, and no absolute or relative time is given, midnight is
used. Finally, a correction is applied so that the correct hour of
the day is produced after allowing for daylight savings time
differences and the correct date is given when going from the end
of a long month to a short month.
clock seconds
Return the current date and time as a system-dependent integer value. The
unit of the value is seconds, allowing it to be used for relative time
calculations. The value is usually defined as total elapsed time from
an ``epoch''. You shouldn't assume the value of the epoch.
KEYWORDS
clock, date, time
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