Managing the Time of Day

The systime and strftime functions described in section Functions for Dealing with Time Stamps, provide the minimum functionality necessary for dealing with the time of day in human readable form. While strftime is extensive, the control formats are not necessarily easy to remember or intuitively obvious when reading a program.

The following function, gettimeofday, populates a user-supplied array with pre-formatted time information. It returns a string with the current time formatted in the same way as the date utility.

# gettimeofday --- get the time of day in a usable format
# Arnold Robbins, arnold@gnu.ai.mit.edu, Public Domain, May 1993
#
# Returns a string in the format of output of date(1)
# Populates the array argument time with individual values:
#    time["second"]       -- seconds (0 - 59)
#    time["minute"]       -- minutes (0 - 59)
#    time["hour"]         -- hours (0 - 23)
#    time["althour"]      -- hours (0 - 12)
#    time["monthday"]     -- day of month (1 - 31)
#    time["month"]        -- month of year (1 - 12)
#    time["monthname"]    -- name of the month
#    time["shortmonth"]   -- short name of the month
#    time["year"]         -- year within century (0 - 99)
#    time["fullyear"]     -- year with century (19xx or 20xx)
#    time["weekday"]      -- day of week (Sunday = 0)
#    time["altweekday"]   -- day of week (Monday = 0)
#    time["weeknum"]      -- week number, Sunday first day
#    time["altweeknum"]   -- week number, Monday first day
#    time["dayname"]      -- name of weekday
#    time["shortdayname"] -- short name of weekday
#    time["yearday"]      -- day of year (0 - 365)
#    time["timezone"]     -- abbreviation of timezone name
#    time["ampm"]         -- AM or PM designation

function gettimeofday(time,    ret, now, i)
{
    # get time once, avoids unnecessary system calls
    now = systime()

    # return date(1)-style output
    ret = strftime("%a %b %d %H:%M:%S %Z %Y", now)

    # clear out target array
    for (i in time)
        delete time[i]

    # fill in values, force numeric values to be
    # numeric by adding 0
    time["second"]       = strftime("%S", now) + 0
    time["minute"]       = strftime("%M", now) + 0
    time["hour"]         = strftime("%H", now) + 0
    time["althour"]      = strftime("%I", now) + 0
    time["monthday"]     = strftime("%d", now) + 0
    time["month"]        = strftime("%m", now) + 0
    time["monthname"]    = strftime("%B", now)
    time["shortmonth"]   = strftime("%b", now)
    time["year"]         = strftime("%y", now) + 0
    time["fullyear"]     = strftime("%Y", now) + 0
    time["weekday"]      = strftime("%w", now) + 0
    time["altweekday"]   = strftime("%u", now) + 0
    time["dayname"]      = strftime("%A", now)
    time["shortdayname"] = strftime("%a", now)
    time["yearday"]      = strftime("%j", now) + 0
    time["timezone"]     = strftime("%Z", now)
    time["ampm"]         = strftime("%p", now)
    time["weeknum"]      = strftime("%U", now) + 0
    time["altweeknum"]   = strftime("%W", now) + 0

    return ret
}

The string indices are easier to use and read than the various formats required by strftime. The alarm program presented in section An Alarm Clock Program, uses this function.

The gettimeofday function is presented above as it was written. A more general design for this function would have allowed the user to supply an optional timestamp value that would have been used instead of the current time.

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