GAWK: Effective AWK Programming

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ivGAWK: Effective AWK Programming5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.1 Constant Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.1.1 Numeric and String Constants. . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.1.2 Octal and Hexadecimal Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 755.1.3 Regular Expression Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765.2 Using Regular Expression Constants. . . . . . . . . . . . . . . . . . . . . . . . . . . 765.3 Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785.3.1 Using Variables in a Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785.3.2 Assigning Variables on the Command Line. . . . . . . . . . . . . . . . 785.4 Conversion of Strings and Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 795.5 Arithmetic Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.6 String Concatenation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825.7 Assignment Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.8 Increment and Decrement Operators . . . . . . . . . . . . . . . . . . . . . . . . . . 865.9 True and False in awk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875.10 Variable Typing and Comparison Expressions . . . . . . . . . . . . . . . . 875.10.1 String Type Versus Numeric Type . . . . . . . . . . . . . . . . . . . . . . . 885.10.2 Comparison Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895.11 Boolean Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.12 Conditional Expressions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.13 Function Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 935.14 Operator Precedence (How Operators Nest) . . . . . . . . . . . . . . . . . . 946 Patterns, Actions, and Variables . . . . . . . . . . . . . 966.1 Pattern Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966.1.1 Regular Expressions as Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . 966.1.2 Expressions as Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966.1.3 Specifying Record Ranges with Patterns . . . . . . . . . . . . . . . . . . 986.1.4 The BEGIN and END Special Patterns . . . . . . . . . . . . . . . . . . . . . . 996.1.4.1 Startup and Cleanup Actions . . . . . . . . . . . . . . . . . . . . . . . . 996.1.4.2 Input/Output from BEGIN and END Rules . . . . . . . . . . . 1006.1.5 The Empty Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.2 Using Shell Variables in Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.3 Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016.4 Control Statements in Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026.4.1 The if-else Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026.4.2 The while Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1036.4.3 The do-while Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.4.4 The for Statement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.4.5 The switch Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056.4.6 The break Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066.4.7 The continue Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076.4.8 The next Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086.4.9 Using gawk’s nextfile Statement . . . . . . . . . . . . . . . . . . . . . . . 1096.4.10 The exit Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096.5 Built-in Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.5.1 Built-in Variables That Control awk . . . . . . . . . . . . . . . . . . . . . 1106.5.2 Built-in Variables That Convey Information . . . . . . . . . . . . . 113
v6.5.3 Using ARGC and ARGV. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1167 Arrays in awk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.1 Introduction to Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.2 Referring to an Array Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207.3 Assigning Array Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217.4 Basic Array Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217.5 Scanning All Elements of an Array . . . . . . . . . . . . . . . . . . . . . . . . . . . 1227.6 The delete Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237.7 Using Numbers to Subscript Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . 1247.8 Using Uninitialized Variables as Subscripts . . . . . . . . . . . . . . . . . . . 1257.9 Multidimensional Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1257.10 Scanning Multidimensional Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . 1277.11 Sorting Array Values and Indices with gawk . . . . . . . . . . . . . . . . . 1278 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308.1 Built-in Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308.1.1 Calling Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308.1.2 Numeric Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308.1.3 String-Manipulation Functions . . . . . . . . . . . . . . . . . . . . . . . . . . 1328.1.3.1 More About ‘\’ and ‘&’ with sub, gsub, and gensub. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1408.1.4 Input/Output Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1438.1.5 Using gawk’s Timestamp Functions . . . . . . . . . . . . . . . . . . . . . . 1468.1.6 Bit-Manipulation Functions of gawk . . . . . . . . . . . . . . . . . . . . . 1508.1.7 Using gawk’s String-Translation Functions . . . . . . . . . . . . . . . 1528.2 User-Defined Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1538.2.1 Function Definition Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1538.2.2 Function Definition Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 1548.2.3 Calling User-Defined Functions . . . . . . . . . . . . . . . . . . . . . . . . . . 1568.2.4 The return Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1578.2.5 Functions and Their Effects on Variable Typing . . . . . . . . . 1589 Internationalization with gawk. . . . . . . . . . . . . . . 1609.1 Internationalization and Localization . . . . . . . . . . . . . . . . . . . . . . . . . 1609.2 GNU gettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1609.3 Internationalizing awk Programs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1629.4 Translating awk Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1639.4.1 Extracting Marked Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1649.4.2 Rearranging printf Arguments . . . . . . . . . . . . . . . . . . . . . . . . . 1649.4.3 awk Portability Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1659.5 A Simple Internationalization Example . . . . . . . . . . . . . . . . . . . . . . . 1669.6 gawk Can Speak Your Language. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
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