GAWK: Effective AWK Programming

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152 GAWK: Effective AWK ProgrammingBEGIN {printf "123 = %s\n", bits2str(123)printf "0123 = %s\n", bits2str(0123)printf "0x99 = %s\n", bits2str(0x99)comp = compl(0x99)printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp)shift = lshift(0x99, 2)printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift)shift = rshift(0x99, 2)printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift)}This program produces the following output when run:$ gawk -f testbits.awk⊣ 123 = 01111011⊣ 0123 = 01010011⊣ 0x99 = 10011001⊣ compl(0x99) = 0xffffff66 = 11111111111111111111111101100110⊣ lshift(0x99, 2) = 0x264 = 0000001001100100⊣ rshift(0x99, 2) = 0x26 = 00100110The bits2str function turns a binary number into a string. The number 1 represents abinary value where the rightmost bit is set to 1. Using this mask, the function repeatedlychecks the rightmost bit. ANDing the mask with the value indicates whether the rightmostbit is 1 or not. If so, a "1" is concatenated onto the front of the string. Otherwise, a "0"is added. The value is then shifted right by one bit and the loop continues until there areno more 1 bits.If the initial value is zero it returns a simple "0". Otherwise, at the end, it pads the valuewith zeros to represent multiples of 8-bit quantities. This is typical in modern computers.The main code in the BEGIN rule shows the difference between the decimal and octalvalues for the same numbers (see Section 5.1.2 [Octal and Hexadecimal Numbers], page 75),and then demonstrates the results of the compl, lshift, and rshift functions.8.1.7 Using gawk’s String-Translation Functionsgawk provides facilities for internationalizing awk programs. These include the functionsdescribed in the following list. The descriptions here are purposely brief. See Chapter 9[Internationalization with gawk], page 160, for the full story. Optional parameters areenclosed in square brackets ([ ]):dcgettext(string [, domain [, category]])This function returns the translation of string in text domain domain for localecategory category. The default value for domain is the current value ofTEXTDOMAIN. The default value for category is "LC_MESSAGES".dcngettext(string1, string2, number [, domain [, category]])This function returns the plural form used for number of the translation ofstring1 and string2 in text domain domain for locale category category. string1is the English singular variant of a message, and string2 the English pluralvariant of the same message. The default value for domain is the current valueof TEXTDOMAIN. The default value for category is "LC_MESSAGES".
Chapter 8: Functions 153bindtextdomain(directory [, domain])This function allows you to specify the directory in which gawk will look formessage translation files, in case they will not or cannot be placed in the “standard”locations (e.g., during testing). It returns the directory in which domainis “bound.”The default domain is the value of TEXTDOMAIN. If directory is the null string(""), then bindtextdomain returns the current binding for the given domain.8.2 User-Defined FunctionsComplicated awk programs can often be simplified by defining your own functions. Userdefinedfunctions can be called just like built-in ones (see Section 5.13 [Function Calls],page 93), but it is up to you to define them, i.e., to tell awk what they should do.8.2.1 Function Definition SyntaxDefinitions of functions can appear anywhere between the rules of an awk program. Thus,the general form of an awk program is extended to include sequences of rules and userdefinedfunction definitions. There is no need to put the definition of a function before alluses of the function. This is because awk reads the entire program before starting to executeany of it.The definition of a function named name looks like this:function name(parameter-list){body-of-function}name is the name of the function to define. A valid function name is like a valid variablename: a sequence of letters, digits, and underscores that doesn’t start with a digit. Withina single awk program, any particular name can only be used as a variable, array, or function.parameter-list is an optional list of the function’s arguments and local variable names,separated by commas. When the function is called, the argument names are used to holdthe argument values given in the call. The local variables are initialized to the empty string.A function cannot have two parameters with the same name, nor may it have a parameterwith the same name as the function itself.According to the POSIX standard, function parameters cannot have the same name asone of the special built-in variables (see Section 6.5 [Built-in Variables], page 110. Not allversions of awk enforce this restriction.The body-of-function consists of awk statements. It is the most important part of thedefinition, because it says what the function should actually do. The argument names existto give the body a way to talk about the arguments; local variables exist to give the bodyplaces to keep temporary values.Argument names are not distinguished syntactically from local variable names. Instead,the number of arguments supplied when the function is called determines how many argumentvariables there are. Thus, if three argument values are given, the first three names inparameter-list are arguments and the rest are local variables.
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