GAWK: Effective AWK Programming

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148 GAWK: Effective AWK Programming%d The day of the month as a decimal number (01–31).%D Equivalent to specifying ‘%m/%d/%y’.%e The day of the month, padded with a space if it is only one digit.%F Equivalent to specifying ‘%Y-%m-%d’. This is the ISO 8601 date format.%g The year modulo 100 of the ISO week number, as a decimal number (00–99).For example, January 1, 1993 is in week 53 of 1992. Thus, the year of its ISOweek number is 1992, even though its year is 1993. Similarly, December 31,1973 is in week 1 of 1974. Thus, the year of its ISO week number is 1974, eventhough its year is 1973.%G The full year of the ISO week number, as a decimal number.%h Equivalent to ‘%b’.%H The hour (24-hour clock) as a decimal number (00–23).%I The hour (12-hour clock) as a decimal number (01–12).%j The day of the year as a decimal number (001–366).%m The month as a decimal number (01–12).%M The minute as a decimal number (00–59).%n A newline character (ASCII LF).%p The locale’s equivalent of the AM/PM designations associated with a 12-hourclock.%r The locale’s 12-hour clock time. (This is ‘%I:%M:%S %p’ in the "C" locale.)%R Equivalent to specifying ‘%H:%M’.%S The second as a decimal number (00–60).%t A TAB character.%T Equivalent to specifying ‘%H:%M:%S’.%u The weekday as a decimal number (1–7). Monday is day one.%U The week number of the year (the first Sunday as the first day of week one) asa decimal number (00–53).%V The week number of the year (the first Monday as the first day of week one) asa decimal number (01–53). The method for determining the week number is asspecified by ISO 8601. (To wit: if the week containing January 1 has four ormore days in the new year, then it is week one; otherwise it is week 53 of theprevious year and the next week is week one.)%w The weekday as a decimal number (0–6). Sunday is day zero.%W The week number of the year (the first Monday as the first day of week one) asa decimal number (00–53).%x The locale’s “appropriate” date representation. (This is ‘%A %B %d %Y’ in the"C" locale.)
Chapter 8: Functions 149%X The locale’s “appropriate” time representation. (This is ‘%T’ in the "C" locale.)%y The year modulo 100 as a decimal number (00–99).%Y The full year as a decimal number (e.g., 1995).%z The timezone offset in a +HHMM format (e.g., the format necessary to produceRFC 822/RFC 1036 date headers).%Z The time zone name or abbreviation; no characters if no time zone is determinable.%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy“Alternate representations” for the specifications that use only the second letter(‘%c’, ‘%C’, and so on). 12 (These facilitate compliance with the POSIX dateutility.)%% A literal ‘%’.If a conversion specifier is not one of the above, the behavior is undefined. 13Informally, a locale is the geographic place in which a program is meant to run. Forexample, a common way to abbreviate the date September 4, 1991 in the United Statesis “9/4/91.” In many countries in Europe, however, it is abbreviated “4.9.91.” Thus, the‘%x’ specification in a "US" locale might produce ‘9/4/91’, while in a "EUROPE" locale, itmight produce ‘4.9.91’. The ISO C standard defines a default "C" locale, which is anenvironment that is typical of what most C programmers are used to.For systems that are not yet fully standards-compliant, gawk supplies a copy of strftimefrom the GNU C Library. It supports all of the just listed format specifications. If thatversion is used to compile gawk (see Appendix B [Installing gawk], page 265), then thefollowing additional format specifications are available:%k The hour (24-hour clock) as a decimal number (0–23). Single-digit numbers arepadded with a space.%l The hour (12-hour clock) as a decimal number (1–12). Single-digit numbers arepadded with a space.%s The time as a decimal timestamp in seconds since the epoch.Additionally, the alternate representations are recognized but their normal representationsare used.This example is an awk implementation of the POSIX date utility. Normally, the dateutility prints the current date and time of day in a well-known format. However, if youprovide an argument to it that begins with a ‘+’, date copies nonformat specifier charactersto the standard output and interprets the current time according to the format specifiersin the string. For example:12 If you don’t understand any of this, don’t worry about it; these facilities are meant to make it easierto “internationalize” programs. Other internationalization features are described in Chapter 9 [Internationalizationwith gawk], page 160.13 This is because ISO C leaves the behavior of the C version of strftime undefined and gawk uses thesystem’s version of strftime if it’s there. Typically, the conversion specifier either does not appear inthe returned string or appears literally.
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