GAWK: Effective AWK Programming

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196 GAWK: Effective AWK Programming# 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 modulo 100 (0 - 99)# time["fullyear"] -- full year# time["weekday"] -- day of week (Sunday = 0)# time["altweekday"] -- day of week (Monday = 0)# 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# time["weeknum"] -- week number, Sunday first day# time["altweeknum"] -- week number, Monday first dayfunction gettimeofday(time, ret, now, i){# get time once, avoids unnecessary system callsnow = systime()# return date(1)-style outputret = strftime("%a %b %d %H:%M:%S %Z %Y", now)# clear out target arraydelete time# fill in values, force numeric values to be# numeric by adding 0time["second"] = strftime("%S", now) + 0time["minute"] = strftime("%M", now) + 0time["hour"] = strftime("%H", now) + 0time["althour"] = strftime("%I", now) + 0time["monthday"] = strftime("%d", now) + 0time["month"] = strftime("%m", now) + 0time["monthname"] = strftime("%B", now)time["shortmonth"] = strftime("%b", now)time["year"] = strftime("%y", now) + 0time["fullyear"] = strftime("%Y", now) + 0time["weekday"] = strftime("%w", now) + 0time["altweekday"] = strftime("%u", now) + 0time["dayname"] = strftime("%A", now)time["shortdayname"] = strftime("%a", now)
Chapter 12: A Library of awk Functions 197}time["yearday"] = strftime("%j", now) + 0time["timezone"] = strftime("%Z", now)time["ampm"] = strftime("%p", now)time["weeknum"] = strftime("%U", now) + 0time["altweeknum"] = strftime("%W", now) + 0return retThe string indices are easier to use and read than the various formats required bystrftime. The alarm program presented in Section 13.3.2 [An Alarm Clock Program],page 236, uses this function. A more general design for the gettimeofday function wouldhave allowed the user to supply an optional timestamp value to use instead of the currenttime.12.3 Data File ManagementThis section presents functions that are useful for managing command-line data files.12.3.1 Noting Data File BoundariesThe BEGIN and END rules are each executed exactly once at the beginning and end ofyour awk program, respectively (see Section 6.1.4 [The BEGIN and END Special Patterns],page 99). We (the gawk authors) once had a user who mistakenly thought that the BEGINrule is executed at the beginning of each data file and the END rule is executed at the endof each data file. When informed that this was not the case, the user requested that weadd new special patterns to gawk, named BEGIN_FILE and END_FILE, that would have thedesired behavior. He even supplied us the code to do so.Adding these special patterns to gawk wasn’t necessary; the job can be done cleanlyin awk itself, as illustrated by the following library program. It arranges to call two usersuppliedfunctions, beginfile and endfile, at the beginning and end of each data file.Besides solving the problem in only nine(!) lines of code, it does so portably; this workswith any implementation of awk:# transfile.awk## Give the user a hook for filename transitions## The user must supply functions beginfile() and endfile()# that each take the name of the file being started or# finished, respectively.FILENAME != _oldfilename \{if (_oldfilename != "")endfile(_oldfilename)_oldfilename = FILENAMEbeginfile(FILENAME)}
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GAWK: Effective AWK Programming

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