GAWK: Effective AWK Programming

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256 GAWK: Effective AWK Programmingchange with new gawk releases, without requiring the system administrator toupdate it each time by adding the local functions.One user suggested that gawk be modified to automatically read these files upon startup.Instead, it would be very simple to modify igawk to do this. Since igawk can process nested‘@include’ directives, ‘default.awk’ could simply contain ‘@include’ statements for thedesired library functions.13.3.10 And Now For Something Completely DifferentThe following program was written by Davide Brini and is published on his website. It servesas his signature in the Usenet group comp.lang.awk. He supplies the following copyrightterms:Copyright c○ 2008 Davide BriniCopying and distribution of the code published in this page, with or withoutmodification, are permitted in any medium without royalty provided the copyrightnotice and this notice are preserved.Here is the program:awk ’BEGIN{O="~"~"~";o="=="=="==";o+=+o;x=O""O;while(X++
Appendix A: The Evolution of the awk Language 257Appendix A The Evolution of the awk LanguageThis book describes the GNU implementation of awk, which follows the POSIX specification.Many long-time awk users learned awk programming with the original awk implementationin Version 7 Unix. (This implementation was the basis for awk in Berkeley Unix, through4.3-Reno. Subsequent versions of Berkeley Unix, and systems derived from 4.4BSD-Lite,use various versions of gawk for their awk.) This chapter briefly describes the evolution ofthe awk language, with cross-references to other parts of the book where you can find moreinformation.A.1 Major Changes Between V7 and SVR3.1The awk language evolved considerably between the release of Version 7 Unix (1978) andthe new version that was first made generally available in System V Release 3.1 (1987).This section summarizes the changes, with cross-references to further details:• The requirement for ‘;’ to separate rules on a line (see Section 1.6 [awk StatementsVersus Lines], page 21).• User-defined functions and the return statement (see Section 8.2 [User-Defined Functions],page 153).• The delete statement (see Section 7.6 [The delete Statement], page 123).• The do-while statement (see Section 6.4.3 [The do-while Statement], page 104).• The built-in functions atan2, cos, sin, rand, and srand (see Section 8.1.2 [NumericFunctions], page 130).• The built-in functions gsub, sub, and match (see Section 8.1.3 [String-ManipulationFunctions], page 132).• The built-in functions close and system (see Section 8.1.4 [Input/Output Functions],page 143).• The ARGC, ARGV, FNR, RLENGTH, RSTART, and SUBSEP built-in variables (see Section 6.5[Built-in Variables], page 110).• Assignable $0.• The conditional expression using the ternary operator ‘?:’ (see Section 5.12 [ConditionalExpressions], page 92).• The expression ‘index-variable in array’ outside of ‘for’ statements (see Section 7.2[Referring to an Array Element], page 120).• The exponentiation operator ‘^’ (see Section 5.5 [Arithmetic Operators], page 81) andits assignment operator form ‘^=’ (see Section 5.7 [Assignment Expressions], page 83).• C-compatible operator precedence, which breaks some old awk programs (seeSection 5.14 [Operator Precedence (How Operators Nest)], page 94).• Regexps as the value of FS (see Section 3.5 [Specifying How Fields Are Separated],page 43) and as the third argument to the split function (see Section 8.1.3 [String-Manipulation Functions], page 132), rather than using only the first character of FS.• Dynamic regexps as operands of the ‘~’ and ‘!~’ operators (see Section 2.1 [How to UseRegular Expressions], page 24).
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