GAWK: Effective AWK Programming

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192 GAWK: Effective AWK Programming}If the assertion fails, you see a message similar to the following:mydata:1357: assertion failed: a = 17.1There is a small problem with this version of assert. An END rule is automaticallyadded to the program calling assert. Normally, if a program consists of just a BEGIN rule,the input files and/or standard input are not read. However, now that the program has anEND rule, awk attempts to read the input data files or standard input (see Section 6.1.4.1[Startup and Cleanup Actions], page 99), most likely causing the program to hang as itwaits for input.There is a simple workaround to this: make sure the BEGIN rule always ends with anexit statement.12.2.4 Rounding NumbersThe way printf and sprintf (see Section 4.5 [Using printf Statements for Fancier Printing],page 61) perform rounding often depends upon the system’s C sprintf subroutine.On many machines, sprintf rounding is “unbiased,” which means it doesn’t always rounda trailing ‘.5’ up, contrary to naive expectations. In unbiased rounding, ‘.5’ rounds toeven, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. This means that if youare using a format that does rounding (e.g., "%.0f"), you should check what your systemdoes. The following function does traditional rounding; it might be useful if your awk’sprintf does unbiased rounding:# round.awk --- do normal roundingfunction round(x, ival, aval, fraction){ival = int(x) # integer part, int() truncates# see if fractional partif (ival == x) # no fractionreturn ival # ensure no decimals}if (x < 0) {aval = -x # absolute valueival = int(aval)fraction = aval - ivalif (fraction >= .5)return int(x) - 1 # -2.5 --> -3elsereturn int(x) # -2.3 --> -2} else {fraction = x - ivalif (fraction >= .5)return ival + 1elsereturn ival}
Chapter 12: A Library of awk Functions 193# test harness{ print $0, round($0) }12.2.5 The Cliff Random Number GeneratorThe Cliff random number generator is a very simple random number generator that “passesthe noise sphere test for randomness by showing no structure.” It is easily programmed, inless than 10 lines of awk code:# cliff_rand.awk --- generate Cliff random numbersBEGIN { _cliff_seed = 0.1 }function cliff_rand(){_cliff_seed = (100 * log(_cliff_seed)) % 1if (_cliff_seed < 0)_cliff_seed = - _cliff_seedreturn _cliff_seed}This algorithm requires an initial “seed” of 0.1. Each new value uses the current seedas input for the calculation. If the built-in rand function (see Section 8.1.2 [Numeric Functions],page 130) isn’t random enough, you might try using this function instead.12.2.6 Translating Between Characters and NumbersOne commercial implementation of awk supplies a built-in function, ord, which takes acharacter and returns the numeric value for that character in the machine’s character set.If the string passed to ord has more than one character, only the first one is used.The inverse of this function is chr (from the function of the same name in Pascal), whichtakes a number and returns the corresponding character. Both functions are written verynicely in awk; there is no real reason to build them into the awk interpreter:# ord.awk --- do ord and chr# Global identifiers:# _ord_: numerical values indexed by characters# _ord_init: function to initialize _ord_BEGIN { _ord_init() }function _ord_init( low, high, i, t){low = sprintf("%c", 7) # BEL is ascii 7if (low == "\a") { # regular asciilow = 0high = 127} else if (sprintf("%c", 128 + 7) == "\a") {# ascii, mark paritylow = 128high = 255
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