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diff --git a/doc/gawk.info b/doc/gawk.info index f5f3413c..e34309cb 100644 --- a/doc/gawk.info +++ b/doc/gawk.info @@ -109,394 +109,437 @@ texts being (a) (see below), and with the Back-Cover Texts being (b) * GNU Free Documentation License:: The license for this Info file. * Index:: Concept and Variable Index. -* History:: The history of `gawk' and - `awk'. -* Names:: What name to use to find `awk'. -* This Manual:: Using this Info file. Includes - sample input files that you can use. -* Conventions:: Typographical Conventions. -* Manual History:: Brief history of the GNU project and this - Info file. -* How To Contribute:: Helping to save the world. -* Acknowledgments:: Acknowledgments. -* Running gawk:: How to run `gawk' programs; - includes command-line syntax. -* One-shot:: Running a short throwaway `awk' - program. -* Read Terminal:: Using no input files (input from terminal - instead). -* Long:: Putting permanent `awk' programs in - files. -* Executable Scripts:: Making self-contained `awk' - programs. -* Comments:: Adding documentation to `gawk' - programs. -* Quoting:: More discussion of shell quoting issues. -* DOS Quoting:: Quoting in Windows Batch Files. -* Sample Data Files:: Sample data files for use in the - `awk' programs illustrated in this - Info file. -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example using two - rules. -* More Complex:: A more complex example. -* Statements/Lines:: Subdividing or combining statements into - lines. -* Other Features:: Other Features of `awk'. -* When:: When to use `gawk' and when to use - other things. -* Command Line:: How to run `awk'. -* Options:: Command-line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* Naming Standard Input:: How to specify standard input with other - files. -* Environment Variables:: The environment variables `gawk' - uses. -* AWKPATH Variable:: Searching directories for `awk' - programs. -* Other Environment Variables:: The environment variables. -* Exit Status:: `gawk''s exit status. -* Include Files:: Including other files into your program. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Regexp Usage:: How to Use Regular Expressions. -* Escape Sequences:: How to write nonprinting characters. -* Regexp Operators:: Regular Expression Operators. -* Bracket Expressions:: What can go between `[...]'. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. -* Leftmost Longest:: How much text matches. -* Computed Regexps:: Using Dynamic Regexps. -* Locales:: How the locale affects things. -* Records:: Controlling how data is split into records. -* Fields:: An introduction to fields. -* Nonconstant Fields:: Nonconstant Field Numbers. -* Changing Fields:: Changing the Contents of a Field. -* Field Separators:: The field separator and how to change it. -* Default Field Splitting:: How fields are normally separated. -* Regexp Field Splitting:: Using regexps as the field separator. -* Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting `FS' from the command-line. -* Field Splitting Summary:: Some final points and a summary table. -* Constant Size:: Reading constant width data. -* Splitting By Content:: Defining Fields By Content -* Multiple Line:: Reading multi-line records. -* Getline:: Reading files under explicit program - control using the `getline' function. -* Plain Getline:: Using `getline' with no arguments. -* Getline/Variable:: Using `getline' into a variable. -* Getline/File:: Using `getline' from a file. -* Getline/Variable/File:: Using `getline' into a variable from a - file. -* Getline/Pipe:: Using `getline' from a pipe. -* Getline/Variable/Pipe:: Using `getline' into a variable from a - pipe. -* Getline/Coprocess:: Using `getline' from a coprocess. -* Getline/Variable/Coprocess:: Using `getline' into a variable from a - coprocess. -* Getline Notes:: Important things to know about - `getline'. -* Getline Summary:: Summary of `getline' Variants. -* Command line directories:: What happens if you put a directory on the - command line. -* Print:: The `print' statement. -* Print Examples:: Simple examples of `print' statements. -* Output Separators:: The output separators and how to change - them. -* OFMT:: Controlling Numeric Output With - `print'. -* Printf:: The `printf' statement. -* Basic Printf:: Syntax of the `printf' statement. -* Control Letters:: Format-control letters. -* Format Modifiers:: Format-specification modifiers. -* Printf Examples:: Several examples. -* Redirection:: How to redirect output to multiple files - and pipes. -* Special Files:: File name interpretation in `gawk'. - `gawk' allows access to inherited - file descriptors. -* Special FD:: Special files for I/O. -* Special Network:: Special files for network communications. -* Special Caveats:: Things to watch out for. -* Close Files And Pipes:: Closing Input and Output Files and Pipes. -* Values:: Constants, Variables, and Regular - Expressions. -* Constants:: String, numeric and regexp constants. -* Scalar Constants:: Numeric and string constants. -* Nondecimal-numbers:: What are octal and hex numbers. -* Regexp Constants:: Regular Expression constants. -* Using Constant Regexps:: When and how to use a regexp constant. -* Variables:: Variables give names to values for later - use. -* Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command-line and a - summary of command-line syntax. This is an - advanced method of input. -* Conversion:: The conversion of strings to numbers and - vice versa. -* All Operators:: `gawk''s operators. -* Arithmetic Ops:: Arithmetic operations (`+', `-', - etc.) -* Concatenation:: Concatenating strings. -* Assignment Ops:: Changing the value of a variable or a - field. -* Increment Ops:: Incrementing the numeric value of a - variable. -* Truth Values and Conditions:: Testing for true and false. -* Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types and how this - affects comparison of numbers and strings - with `<', etc. -* Variable Typing:: String type versus numeric type. -* Comparison Operators:: The comparison operators. -* POSIX String Comparison:: String comparison with POSIX rules. -* Boolean Ops:: Combining comparison expressions using - boolean operators `||' (``or''), - `&&' (``and'') and `!' (``not''). -* Conditional Exp:: Conditional expressions select between two - subexpressions under control of a third - subexpression. -* Function Calls:: A function call is an expression. -* Precedence:: How various operators nest. -* Pattern Overview:: What goes into a pattern. -* Regexp Patterns:: Using regexps as patterns. -* Expression Patterns:: Any expression can be used as a pattern. -* Ranges:: Pairs of patterns specify record ranges. -* BEGIN/END:: Specifying initialization and cleanup - rules. -* Using BEGIN/END:: How and why to use BEGIN/END rules. -* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. -* Empty:: The empty pattern, which matches every - record. -* BEGINFILE/ENDFILE:: Two special patterns for advanced control. -* Using Shell Variables:: How to use shell variables with - `awk'. -* Action Overview:: What goes into an action. -* Statements:: Describes the various control statements in - detail. -* If Statement:: Conditionally execute some `awk' - statements. -* While Statement:: Loop until some condition is satisfied. -* Do Statement:: Do specified action while looping until - some condition is satisfied. -* For Statement:: Another looping statement, that provides - initialization and increment clauses. -* Switch Statement:: Switch/case evaluation for conditional - execution of statements based on a value. -* Break Statement:: Immediately exit the innermost enclosing - loop. -* Continue Statement:: Skip to the end of the innermost enclosing - loop. -* Next Statement:: Stop processing the current input record. -* Nextfile Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of `awk'. -* Built-in Variables:: Summarizes the built-in variables. -* User-modified:: Built-in variables that you change to - control `awk'. -* Auto-set:: Built-in variables where `awk' - gives you information. -* ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. -* Array Basics:: The basics of arrays. -* Array Intro:: Introduction to Arrays -* Reference to Elements:: How to examine one element of an array. -* Assigning Elements:: How to change an element of an array. -* Array Example:: Basic Example of an Array -* Scanning an Array:: A variation of the `for' statement. It - loops through the indices of an array's - existing elements. -* Controlling Scanning:: Controlling the order in which arrays - are scanned. -* Delete:: The `delete' statement removes an - element from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in - `awk'. -* Uninitialized Subscripts:: Using Uninitialized variables as - subscripts. -* Multi-dimensional:: Emulating multidimensional arrays in - `awk'. -* Multi-scanning:: Scanning multidimensional arrays. -* Array Sorting:: Sorting array values and indices. -* Arrays of Arrays:: True multidimensional arrays. -* Built-in:: Summarizes the built-in functions. -* Calling Built-in:: How to call built-in functions. -* Numeric Functions:: Functions that work with numbers, including - `int()', `sin()' and - `rand()'. -* String Functions:: Functions for string manipulation, such as - `split()', `match()' and - `sprintf()'. -* Gory Details:: More than you want to know about `\' - and `&' with `sub()', - `gsub()', and `gensub()'. -* I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with timestamps. -* Bitwise Functions:: Functions for bitwise operations. -* Type Functions:: Functions for type information. -* I18N Functions:: Functions for string translation. -* User-defined:: Describes User-defined functions in detail. -* Definition Syntax:: How to write definitions and what they - mean. -* Function Example:: An example function definition and what it - does. -* Function Caveats:: Things to watch out for. -* Calling A Function:: Don't use spaces. -* Variable Scope:: Controlling variable scope. -* Pass By Value/Reference:: Passing parameters. -* Return Statement:: Specifying the value a function returns. -* Dynamic Typing:: How variable types can change at runtime. -* Indirect Calls:: Choosing the function to call at runtime. -* I18N and L10N:: Internationalization and Localization. -* Explaining gettext:: How GNU `gettext' works. -* Programmer i18n:: Features for the programmer. -* Translator i18n:: Features for the translator. -* String Extraction:: Extracting marked strings. -* Printf Ordering:: Rearranging `printf' arguments. -* I18N Portability:: `awk'-level portability issues. -* I18N Example:: A simple i18n example. -* Gawk I18N:: `gawk' is also internationalized. -* Nondecimal Data:: Allowing nondecimal input data. -* Two-way I/O:: Two-way communications with another - process. -* TCP/IP Networking:: Using `gawk' for network - programming. -* Profiling:: Profiling your `awk' programs. -* Library Names:: How to best name private global variables - in library functions. -* General Functions:: Functions that are of general use. -* Strtonum Function:: A replacement for the built-in - `strtonum()' function. -* Assert Function:: A function for assertions in `awk' - programs. -* Round Function:: A function for rounding if `sprintf()' - does not do it correctly. -* Cliff Random Function:: The Cliff Random Number Generator. -* Ordinal Functions:: Functions for using characters as numbers - and vice versa. -* Join Function:: A function to join an array into a string. -* Gettimeofday Function:: A function to get formatted times. -* Data File Management:: Functions for managing command-line data - files. -* Filetrans Function:: A function for handling data file - transitions. -* Rewind Function:: A function for rereading the current file. -* File Checking:: Checking that data files are readable. -* Empty Files:: Checking for zero-length files. -* Ignoring Assigns:: Treating assignments as file names. -* Getopt Function:: A function for processing command-line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group information. -* Running Examples:: How to run these examples. -* Clones:: Clones of common utilities. -* Cut Program:: The `cut' utility. -* Egrep Program:: The `egrep' utility. -* Id Program:: The `id' utility. -* Split Program:: The `split' utility. -* Tee Program:: The `tee' utility. -* Uniq Program:: The `uniq' utility. -* Wc Program:: The `wc' utility. -* Miscellaneous Programs:: Some interesting `awk' programs. -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the `tr' - utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a - history file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for `awk' that includes - files. -* Anagram Program:: Finding anagrams from a dictionary. -* Signature Program:: People do amazing things with too much time - on their hands. -* Debugging:: Introduction to `dgawk'. -* Debugging Concepts:: Debugging In General. -* Debugging Terms:: Additional Debugging Concepts. -* Awk Debugging:: Awk Debugging. -* Sample dgawk session:: Sample `dgawk' session. -* dgawk invocation:: `dgawk' Invocation. -* Finding The Bug:: Finding The Bug. -* List of Debugger Commands:: Main `dgawk' Commands. -* Breakpoint Control:: Control of breakpoints. -* Dgawk Execution Control:: Control of execution. -* Viewing And Changing Data:: Viewing and changing data. -* Dgawk Stack:: Dealing with the stack. -* Dgawk Info:: Obtaining information about the program and - the debugger state. -* Miscellaneous Dgawk Commands:: Miscellaneous Commands. -* Readline Support:: Readline Support. -* Dgawk Limitations:: Limitations and future plans. -* V7/SVR3.1:: The major changes between V7 and System V - Release 3.1. -* SVR4:: Minor changes between System V Releases 3.1 - and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from Brian Kernighan's - version of `awk'. -* POSIX/GNU:: The extensions in `gawk' not in - POSIX `awk'. -* Contributors:: The major contributors to `gawk'. -* Common Extensions:: Common Extensions Summary. -* Gawk Distribution:: What is in the `gawk' distribution. -* Getting:: How to get the distribution. -* Extracting:: How to extract the distribution. -* Distribution contents:: What is in the distribution. -* Unix Installation:: Installing `gawk' under various - versions of Unix. -* Quick Installation:: Compiling `gawk' under Unix. -* Additional Configuration Options:: Other compile-time options. -* Configuration Philosophy:: How it's all supposed to work. -* Non-Unix Installation:: Installation on Other Operating Systems. -* PC Installation:: Installing and Compiling `gawk' on - MS-DOS and OS/2. -* PC Binary Installation:: Installing a prepared distribution. -* PC Compiling:: Compiling `gawk' for MS-DOS, - Windows32, and OS/2. -* PC Testing:: Testing `gawk' on PC - Operating Systems. -* PC Using:: Running `gawk' on MS-DOS, Windows32 - and OS/2. -* Cygwin:: Building and running `gawk' for - Cygwin. -* MSYS:: Using `gawk' In The MSYS - Environment. -* VMS Installation:: Installing `gawk' on VMS. -* VMS Compilation:: How to compile `gawk' under VMS. -* VMS Installation Details:: How to install `gawk' under VMS. -* VMS Running:: How to run `gawk' under VMS. -* VMS Old Gawk:: An old version comes with some VMS systems. -* Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available `awk' - implementations. -* Compatibility Mode:: How to disable certain `gawk' - extensions. -* Additions:: Making Additions To `gawk'. -* Accessing The Source:: Accessing the Git repository. -* Adding Code:: Adding code to the main body of - `gawk'. -* New Ports:: Porting `gawk' to a new operating - system. -* Dynamic Extensions:: Adding new built-in functions to - `gawk'. -* Internals:: A brief look at some `gawk' - internals. -* Plugin License:: A note about licensing. -* Sample Library:: A example of new functions. -* Internal File Description:: What the new functions will do. -* Internal File Ops:: The code for internal file operations. -* Using Internal File Ops:: How to use an external extension. -* Future Extensions:: New features that may be implemented one - day. -* Basic High Level:: The high level view. -* Basic Data Typing:: A very quick intro to data types. -* Floating Point Issues:: Stuff to know about floating-point numbers. -* String Conversion Precision:: The String Value Can Lie. -* Unexpected Results:: Floating Point Numbers Are Not Abstract - Numbers. -* POSIX Floating Point Problems:: Standards Versus Existing Practice. +* History:: The history of `gawk' and + `awk'. +* Names:: What name to use to find `awk'. +* This Manual:: Using this Info file. Includes + sample input files that you can use. +* Conventions:: Typographical Conventions. +* Manual History:: Brief history of the GNU project and + this Info file. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. +* Running gawk:: How to run `gawk' programs; + includes command-line syntax. +* One-shot:: Running a short throwaway `awk' + program. +* Read Terminal:: Using no input files (input from + terminal instead). +* Long:: Putting permanent `awk' + programs in files. +* Executable Scripts:: Making self-contained `awk' + programs. +* Comments:: Adding documentation to `gawk' + programs. +* Quoting:: More discussion of shell quoting + issues. +* DOS Quoting:: Quoting in Windows Batch Files. +* Sample Data Files:: Sample data files for use in the + `awk' programs illustrated in + this Info file. +* Very Simple:: A very simple example. +* Two Rules:: A less simple one-line example using + two rules. +* More Complex:: A more complex example. +* Statements/Lines:: Subdividing or combining statements + into lines. +* Other Features:: Other Features of `awk'. +* When:: When to use `gawk' and when to + use other things. +* Command Line:: How to run `awk'. +* Options:: Command-line options and their + meanings. +* Other Arguments:: Input file names and variable + assignments. +* Naming Standard Input:: How to specify standard input with + other files. +* Environment Variables:: The environment variables + `gawk' uses. +* AWKPATH Variable:: Searching directories for `awk' + programs. +* Other Environment Variables:: The environment variables. +* Exit Status:: `gawk''s exit status. +* Include Files:: Including other files into your + program. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Regexp Usage:: How to Use Regular Expressions. +* Escape Sequences:: How to write nonprinting characters. +* Regexp Operators:: Regular Expression Operators. +* Bracket Expressions:: What can go between `[...]'. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. +* Leftmost Longest:: How much text matches. +* Computed Regexps:: Using Dynamic Regexps. +* Locales:: How the locale affects things. +* Records:: Controlling how data is split into + records. +* Fields:: An introduction to fields. +* Nonconstant Fields:: Nonconstant Field Numbers. +* Changing Fields:: Changing the Contents of a Field. +* Field Separators:: The field separator and how to change + it. +* Default Field Splitting:: How fields are normally separated. +* Regexp Field Splitting:: Using regexps as the field separator. +* Single Character Fields:: Making each character a separate field. +* Command Line Field Separator:: Setting `FS' from the + command-line. +* Field Splitting Summary:: Some final points and a summary table. +* Constant Size:: Reading constant width data. +* Splitting By Content:: Defining Fields By Content +* Multiple Line:: Reading multi-line records. +* Getline:: Reading files under explicit program + control using the `getline' + function. +* Plain Getline:: Using `getline' with no arguments. +* Getline/Variable:: Using `getline' into a variable. +* Getline/File:: Using `getline' from a file. +* Getline/Variable/File:: Using `getline' into a variable + from a file. +* Getline/Pipe:: Using `getline' from a pipe. +* Getline/Variable/Pipe:: Using `getline' into a variable + from a pipe. +* Getline/Coprocess:: Using `getline' from a coprocess. +* Getline/Variable/Coprocess:: Using `getline' into a variable + from a coprocess. +* Getline Notes:: Important things to know about + `getline'. +* Getline Summary:: Summary of `getline' Variants. +* Command line directories:: What happens if you put a directory on + the command line. +* Print:: The `print' statement. +* Print Examples:: Simple examples of `print' + statements. +* Output Separators:: The output separators and how to change + them. +* OFMT:: Controlling Numeric Output With + `print'. +* Printf:: The `printf' statement. +* Basic Printf:: Syntax of the `printf' statement. +* Control Letters:: Format-control letters. +* Format Modifiers:: Format-specification modifiers. +* Printf Examples:: Several examples. +* Redirection:: How to redirect output to multiple + files and pipes. +* Special Files:: File name interpretation in + `gawk'. `gawk' allows + access to inherited file descriptors. +* Special FD:: Special files for I/O. +* Special Network:: Special files for network + communications. +* Special Caveats:: Things to watch out for. +* Close Files And Pipes:: Closing Input and Output Files and + Pipes. +* Values:: Constants, Variables, and Regular + Expressions. +* Constants:: String, numeric and regexp constants. +* Scalar Constants:: Numeric and string constants. +* Nondecimal-numbers:: What are octal and hex numbers. +* Regexp Constants:: Regular Expression constants. +* Using Constant Regexps:: When and how to use a regexp constant. +* Variables:: Variables give names to values for + later use. +* Using Variables:: Using variables in your programs. +* Assignment Options:: Setting variables on the command-line + and a summary of command-line syntax. + This is an advanced method of input. +* Conversion:: The conversion of strings to numbers + and vice versa. +* All Operators:: `gawk''s operators. +* Arithmetic Ops:: Arithmetic operations (`+', + `-', etc.) +* Concatenation:: Concatenating strings. +* Assignment Ops:: Changing the value of a variable or a + field. +* Increment Ops:: Incrementing the numeric value of a + variable. +* Truth Values and Conditions:: Testing for true and false. +* Truth Values:: What is ``true'' and what is ``false''. +* Typing and Comparison:: How variables acquire types and how + this affects comparison of numbers and + strings with `<', etc. +* Variable Typing:: String type versus numeric type. +* Comparison Operators:: The comparison operators. +* POSIX String Comparison:: String comparison with POSIX rules. +* Boolean Ops:: Combining comparison expressions using + boolean operators `||' (``or''), + `&&' (``and'') and `!' + (``not''). +* Conditional Exp:: Conditional expressions select between + two subexpressions under control of a + third subexpression. +* Function Calls:: A function call is an expression. +* Precedence:: How various operators nest. +* Pattern Overview:: What goes into a pattern. +* Regexp Patterns:: Using regexps as patterns. +* Expression Patterns:: Any expression can be used as a + pattern. +* Ranges:: Pairs of patterns specify record + ranges. +* BEGIN/END:: Specifying initialization and cleanup + rules. +* Using BEGIN/END:: How and why to use BEGIN/END rules. +* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. +* BEGINFILE/ENDFILE:: Two special patterns for advanced + control. +* Empty:: The empty pattern, which matches every + record. +* Using Shell Variables:: How to use shell variables with + `awk'. +* Action Overview:: What goes into an action. +* Statements:: Describes the various control + statements in detail. +* If Statement:: Conditionally execute some + `awk' statements. +* While Statement:: Loop until some condition is satisfied. +* Do Statement:: Do specified action while looping until + some condition is satisfied. +* For Statement:: Another looping statement, that + provides initialization and increment + clauses. +* Switch Statement:: Switch/case evaluation for conditional + execution of statements based on a + value. +* Break Statement:: Immediately exit the innermost + enclosing loop. +* Continue Statement:: Skip to the end of the innermost + enclosing loop. +* Next Statement:: Stop processing the current input + record. +* Nextfile Statement:: Stop processing the current file. +* Exit Statement:: Stop execution of `awk'. +* Built-in Variables:: Summarizes the built-in variables. +* User-modified:: Built-in variables that you change to + control `awk'. +* Auto-set:: Built-in variables where `awk' + gives you information. +* ARGC and ARGV:: Ways to use `ARGC' and + `ARGV'. +* Array Basics:: The basics of arrays. +* Array Intro:: Introduction to Arrays +* Reference to Elements:: How to examine one element of an array. +* Assigning Elements:: How to change an element of an array. +* Array Example:: Basic Example of an Array +* Scanning an Array:: A variation of the `for' + statement. It loops through the indices + of an array's existing elements. +* Delete:: The `delete' statement removes an + element from an array. +* Numeric Array Subscripts:: How to use numbers as subscripts in + `awk'. +* Uninitialized Subscripts:: Using Uninitialized variables as + subscripts. +* Multi-dimensional:: Emulating multidimensional arrays in + `awk'. +* Multi-scanning:: Scanning multidimensional arrays. +* Arrays of Arrays:: True multidimensional arrays. +* Built-in:: Summarizes the built-in functions. +* Calling Built-in:: How to call built-in functions. +* Numeric Functions:: Functions that work with numbers, + including `int()', `sin()' + and `rand()'. +* String Functions:: Functions for string manipulation, such + as `split()', `match()' and + `sprintf()'. +* Gory Details:: More than you want to know about + `\' and `&' with + `sub()', `gsub()', and + `gensub()'. +* I/O Functions:: Functions for files and shell commands. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* Type Functions:: Functions for type information. +* I18N Functions:: Functions for string translation. +* User-defined:: Describes User-defined functions in + detail. +* Definition Syntax:: How to write definitions and what they + mean. +* Function Example:: An example function definition and what + it does. +* Function Caveats:: Things to watch out for. +* Calling A Function:: Don't use spaces. +* Variable Scope:: Controlling variable scope. +* Pass By Value/Reference:: Passing parameters. +* Return Statement:: Specifying the value a function + returns. +* Dynamic Typing:: How variable types can change at + runtime. +* Indirect Calls:: Choosing the function to call at + runtime. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability issues. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also + internationalized. +* Nondecimal Data:: Allowing nondecimal input data. +* Array Sorting:: Facilities for controlling array + traversal and sorting arrays. +* Controlling Array Traversal:: How to use PROCINFO["sorted_in"]. +* Controlling Scanning With A Function:: Using a function to control scanning. +* Controlling Scanning:: Controlling the order in which arrays + are scanned. +* Array Sorting Functions:: How to use `asort()' and + `asorti()'. +* Two-way I/O:: Two-way communications with another + process. +* TCP/IP Networking:: Using `gawk' for network + programming. +* Profiling:: Profiling your `awk' programs. +* Library Names:: How to best name private global + variables in library functions. +* General Functions:: Functions that are of general use. +* Strtonum Function:: A replacement for the built-in + `strtonum()' function. +* Assert Function:: A function for assertions in + `awk' programs. +* Round Function:: A function for rounding if + `sprintf()' does not do it + correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as + numbers and vice versa. +* Join Function:: A function to join an array into a + string. +* Gettimeofday Function:: A function to get formatted times. +* Data File Management:: Functions for managing command-line + data files. +* Filetrans Function:: A function for handling data file + transitions. +* Rewind Function:: A function for rereading the current + file. +* File Checking:: Checking that data files are readable. +* Empty Files:: Checking for zero-length files. +* Ignoring Assigns:: Treating assignments as file names. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user information. +* Group Functions:: Functions for getting group + information. +* Walking Arrays:: A function to walk arrays of arrays. +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Cut Program:: The `cut' utility. +* Egrep Program:: The `egrep' utility. +* Id Program:: The `id' utility. +* Split Program:: The `split' utility. +* Tee Program:: The `tee' utility. +* Uniq Program:: The `uniq' utility. +* Wc Program:: The `wc' utility. +* Miscellaneous Programs:: Some interesting `awk' + programs. +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the `tr' + utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage + count. +* History Sorting:: Eliminating duplicate entries from a + history file. +* Extract Program:: Pulling out programs from Texinfo + source files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for `awk' that + includes files. +* Anagram Program:: Finding anagrams from a dictionary. +* Signature Program:: People do amazing things with too much + time on their hands. +* Debugging:: Introduction to `dgawk'. +* Debugging Concepts:: Debugging In General. +* Debugging Terms:: Additional Debugging Concepts. +* Awk Debugging:: Awk Debugging. +* Sample dgawk session:: Sample `dgawk' session. +* dgawk invocation:: `dgawk' Invocation. +* Finding The Bug:: Finding The Bug. +* List of Debugger Commands:: Main `dgawk' Commands. +* Breakpoint Control:: Control of breakpoints. +* Dgawk Execution Control:: Control of execution. +* Viewing And Changing Data:: Viewing and changing data. +* Dgawk Stack:: Dealing with the stack. +* Dgawk Info:: Obtaining information about the program + and the debugger state. +* Miscellaneous Dgawk Commands:: Miscellaneous Commands. +* Readline Support:: Readline Support. +* Dgawk Limitations:: Limitations and future plans. +* V7/SVR3.1:: The major changes between V7 and System + V Release 3.1. +* SVR4:: Minor changes between System V Releases + 3.1 and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from Brian Kernighan's + version of `awk'. +* POSIX/GNU:: The extensions in `gawk' not in + POSIX `awk'. +* Common Extensions:: Common Extensions Summary. +* Contributors:: The major contributors to + `gawk'. +* Gawk Distribution:: What is in the `gawk' + distribution. +* Getting:: How to get the distribution. +* Extracting:: How to extract the distribution. +* Distribution contents:: What is in the distribution. +* Unix Installation:: Installing `gawk' under various + versions of Unix. +* Quick Installation:: Compiling `gawk' under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. +* Non-Unix Installation:: Installation on Other Operating + Systems. +* PC Installation:: Installing and Compiling `gawk' + on MS-DOS and OS/2. +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling `gawk' for MS-DOS, + Windows32, and OS/2. +* PC Testing:: Testing `gawk' on PC systems. +* PC Using:: Running `gawk' on MS-DOS, + Windows32 and OS/2. +* Cygwin:: Building and running `gawk' for + Cygwin. +* MSYS:: Using `gawk' In The MSYS + Environment. +* VMS Installation:: Installing `gawk' on VMS. +* VMS Compilation:: How to compile `gawk' under + VMS. +* VMS Installation Details:: How to install `gawk' under + VMS. +* VMS Running:: How to run `gawk' under VMS. +* VMS Old Gawk:: An old version comes with some VMS + systems. +* Bugs:: Reporting Problems and Bugs. +* Other Versions:: Other freely available `awk' + implementations. +* Compatibility Mode:: How to disable certain `gawk' + extensions. +* Additions:: Making Additions To `gawk'. +* Accessing The Source:: Accessing the Git repository. +* Adding Code:: Adding code to the main body of + `gawk'. +* New Ports:: Porting `gawk' to a new + operating system. +* Dynamic Extensions:: Adding new built-in functions to + `gawk'. +* Internals:: A brief look at some `gawk' + internals. +* Plugin License:: A note about licensing. +* Sample Library:: A example of new functions. +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +* Future Extensions:: New features that may be implemented + one day. +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point + numbers. +* String Conversion Precision:: The String Value Can Lie. +* Unexpected Results:: Floating Point Numbers Are Not Abstract + Numbers. +* POSIX Floating Point Problems:: Standards Versus Existing Practice. To Miriam, for making me complete. @@ -9638,7 +9681,6 @@ cannot have a variable and an array with the same name in the same * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. * Multi-dimensional:: Emulating multidimensional arrays in `awk'. -* Array Sorting:: Sorting array values and indices. * Arrays of Arrays:: True multidimensional arrays. @@ -9896,12 +9938,7 @@ File: gawk.info, Node: Scanning an Array, Prev: Array Example, Up: Array Basi 8.1.5 Scanning All Elements of an Array --------------------------------------- -* Menu: - -* Controlling Scanning:: Controlling the order in which arrays are scanned. -* Controlling Scanning With A Function:: Using a function to control scanning. - - In programs that use arrays, it is often necessary to use a loop that +In programs that use arrays, it is often necessary to use a loop that executes once for each element of an array. In other languages, where arrays are contiguous and indices are limited to positive integers, this is easy: all the valid indices can be found by counting from the @@ -9951,256 +9988,14 @@ statements in the loop body; it is not predictable whether the `for' loop will reach them. Similarly, changing VAR inside the loop may produce strange results. It is best to avoid such things. - -File: gawk.info, Node: Controlling Scanning, Next: Controlling Scanning With A Function, Up: Scanning an Array - -8.1.5.1 Controlling Array Scanning Order -........................................ - -As an extension, `gawk' makes it possible for you to loop over the + As an extension, `gawk' makes it possible for you to loop over the elements of an array in order, based on the value of -`PROCINFO["sorted_in"]' (*note Auto-set::). Several sorting options -are available: - -`ascending index string' - Order by indices compared as strings; this is the most basic sort. - (Internally, array indices are always strings, so with `a[2*5] = 1' - the index is actually `"10"' rather than numeric 10.) - -`ascending index number' - Order by indices but force them to be treated as numbers in the - process. Any index with non-numeric value will end up positioned - as if it were zero. - -`ascending value string' - Order by element values rather than by indices. Scalar values are - compared as strings. Subarrays, if present, come out last. - -`ascending value number' - Order by values but force scalar values to be treated as numbers - for the purpose of comparison. If there are subarrays, those - appear at the end of the sorted list. - -`descending index string' - Reverse order from the most basic sort. - -`descending index number' - Numeric indices ordered from high to low. - -`descending value string' - Element values, treated as strings, ordered from high to low. - Subarrays, if present, come out first. - -`descending value number' - Element values, treated as numbers, ordered from high to low. - Subarrays, if present, come out first. - -`unsorted' - Array elements are processed in arbitrary order, the normal `awk' - behavior. You can also get the normal behavior by just deleting - the `"sorted_in"' item from the `PROCINFO' array, if it previously - had a value assigned to it. - - The array traversal order is determined before the `for' loop starts -to run. Changing `PROCINFO["sorted_in"]' in the loop body will not -affect the loop. - - Portions of the sort specification string may be truncated or -omitted. The default is `ascending' for direction, `index' for sort -key type, and `string' for comparison mode. This implies that one can -simply assign the empty string, "", instead of "ascending index string" -to `PROCINFO["sorted_in"]' for the same effect. - - For example: - - $ gawk 'BEGIN { - > a[4] = 4 - > a[3] = 3 - > for (i in a) - > print i, a[i] - > }' - -| 4 4 - -| 3 3 - $ gawk 'BEGIN { - > PROCINFO["sorted_in"] = "asc index" - > a[4] = 4 - > a[3] = 3 - > for (i in a) - > print i, a[i] - > }' - -| 3 3 - -| 4 4 - - When sorting an array by element values, if a value happens to be a -subarray then it is considered to be greater than any string or numeric -value, regardless of what the subarray itself contains, and all -subarrays are treated as being equal to each other. Their order -relative to each other is determined by their index strings. - - -File: gawk.info, Node: Controlling Scanning With A Function, Prev: Controlling Scanning, Up: Scanning an Array - -8.1.5.2 Controlling Array Scanning Order With a User-defined Function -..................................................................... - -The value of `PROCINFO["sorted_in"]' can also be a function name. This -lets you traverse an array based on any custom criterion. The array -elements are ordered according to the return value of this function. -This comparison function should be defined with at least four arguments: - - function comp_func(i1, v1, i2, v2) - { - COMPARE ELEMENTS 1 AND 2 IN SOME FASHION - RETURN < 0; 0; OR > 0 - } - - Here, I1 and I2 are the indices, and V1 and V2 are the corresponding -values of the two elements being compared. Either V1 or V2, or both, -can be arrays if the array being traversed contains subarrays as -values. The three possible return values are interpreted this way: - - * If the return value of `comp_func(i1, v1, i2, v2)' is less than - zero, index I1 comes before index I2 during loop traversal. - - * If `comp_func(i1, v1, i2, v2)' returns zero, I1 and I2 come - together but the relative order with respect to each other is - undefined. - - * If the return value of `comp_func(i1, v1, i2, v2)' is greater than - zero, I1 comes after I2. - - The following comparison function can be used to scan an array in -numerical order of the indices: - - function cmp_num_idx(i1, v1, i2, v2) - { - # numerical index comparison, ascending order - return (i1 - i2) - } - - This function traverses an array based on an order by element values -rather than by indices: - - function cmp_str_val(i1, v1, i2, v2) - { - # string value comparison, ascending order - v1 = v1 "" - v2 = v2 "" - if (v1 < v2) - return -1 - return (v1 != v2) - } - - Here is a comparison function to make all numbers, and numeric -strings without any leading or trailing spaces, come out first during -loop traversal: - - function cmp_num_str_val(i1, v1, i2, v2, n1, n2) - { - # numbers before string value comparison, ascending order - n1 = v1 + 0 - n2 = v2 + 0 - if (n1 == v1) - return (n2 == v2) ? (n1 - n2) : -1 - else if (n2 == v2) - return 1 - return (v1 < v2) ? -1 : (v1 != v2) - } - - Consider sorting the entries of a GNU/Linux system password file -according to login names. The following program which sorts records by -a specific field position can be used for this purpose: - - # sort.awk --- simple program to sort by field position - # field position is specified by the global variable POS - - function cmp_field(i1, v1, i2, v2) - { - # comparison by value, as string, and ascending order - return v1[POS] < v2[POS] ? -1 : (v1[POS] != v2[POS]) - } - - { - for (i = 1; i <= NF; i++) - a[NR][i] = $i - } - - END { - PROCINFO["sorted_in"] = "cmp_field" - if (POS < 1 || POS > NF) - POS = 1 - for (i in a) { - for (j = 1; j <= NF; j++) - printf("%s%c", a[i][j], j < NF ? ":" : "") - print "" - } - } - - The first field in each entry of the password file is the user's -login name, and the fields are seperated by colons. Running the -program produces the following output: - - $ gawk -vPOS=1 -F: -f sort.awk /etc/passwd - -| adm:x:3:4:adm:/var/adm:/sbin/nologin - -| apache:x:48:48:Apache:/var/www:/sbin/nologin - -| avahi:x:70:70:Avahi daemon:/:/sbin/nologin - ... - - The comparison normally should always return the same value when -given a specific pair of array elements as its arguments. If -inconsistent results are returned then the order is undefined. This -behavior is sometimes exploited to introduce random order in otherwise -seemingly ordered data: - - function cmp_randomize(i1, v1, i2, v2) - { - # random order - return (2 - 4 * rand()) - } - - As mentioned above, the order of the indices is arbitrary if two -elements compare equal. This is usually not a problem, but letting the -tied elements come out in arbitrary order can be an issue, especially -when comparing item values. The partial ordering of the equal elements -may change during the next loop traversal, if other elements are added -or removed from the array. One way to resolve ties when comparing -elements with otherwise equal values is to include the indices in the -comparison rules. Note that doing this may make the loop traversal -less efficient, so consider it only if necessary. The following -comparison functions force a deterministic order, and are based on the -fact that the indices of two elements are never equal: +`PROCINFO["sorted_in"]' (*note Auto-set::). This is an advanced +feature, so discussion of it is delayed until *note Controlling Array +Traversal::. - function cmp_numeric(i1, v1, i2, v2) - { - # numerical value (and index) comparison, descending order - return (v1 != v2) ? (v2 - v1) : (i2 - i1) - } - - function cmp_string(i1, v1, i2, v2) - { - # string value (and index) comparison, descending order - v1 = v1 i1 - v2 = v2 i2 - return (v1 > v2) ? -1 : (v1 != v2) - } - - A custom comparison function can often simplify ordered loop -traversal, and the the sky is really the limit when it comes to -designing such a function. - - When string comparisons are made during a sort, either for element -values where one or both aren't numbers, or for element indices handled -as strings, the value of `IGNORECASE' (*note Built-in Variables::) -controls whether the comparisons treat corresponding uppercase and -lowercase letters as equivalent or distinct. - - All sorting based on `PROCINFO["sorted_in"]' is disabled in POSIX -mode, since the `PROCINFO' array is not special in that case. - - As a side note, sorting the array indices before traversing the -array has been reported to add 15% to 20% overhead to the execution -time of `awk' programs. For this reason, sorted array traversal is not -the default. + In addition, `gawk' provides built-in functions for sorting arrays; +see *note Array Sorting Functions::. File: gawk.info, Node: Delete, Next: Numeric Array Subscripts, Prev: Array Basics, Up: Arrays @@ -10376,7 +10171,7 @@ string as a subscript if `--lint' is provided on the command line (*note Options::). -File: gawk.info, Node: Multi-dimensional, Next: Array Sorting, Prev: Uninitialized Subscripts, Up: Arrays +File: gawk.info, Node: Multi-dimensional, Next: Arrays of Arrays, Prev: Uninitialized Subscripts, Up: Arrays 8.5 Multidimensional Arrays =========================== @@ -10502,105 +10297,9 @@ The result is to set `separate[1]' to `"1"' and `separate[2]' to recovered. -File: gawk.info, Node: Array Sorting, Next: Arrays of Arrays, Prev: Multi-dimensional, Up: Arrays - -8.6 Sorting Array Values and Indices with `gawk' -================================================ - -The order in which an array is scanned with a `for (i in array)' loop -is essentially arbitrary. In most `awk' implementations, sorting an -array requires writing a `sort' function. While this can be -educational for exploring different sorting algorithms, usually that's -not the point of the program. `gawk' provides the built-in `asort()' -and `asorti()' functions (*note String Functions::) for sorting arrays. -For example: - - POPULATE THE ARRAY data - n = asort(data) - for (i = 1; i <= n; i++) - DO SOMETHING WITH data[i] - - After the call to `asort()', the array `data' is indexed from 1 to -some number N, the total number of elements in `data'. (This count is -`asort()''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so -on. The array elements are compared as strings. - - An important side effect of calling `asort()' is that _the array's -original indices are irrevocably lost_. As this isn't always -desirable, `asort()' accepts a second argument: - - POPULATE THE ARRAY source - n = asort(source, dest) - for (i = 1; i <= n; i++) - DO SOMETHING WITH dest[i] - - In this case, `gawk' copies the `source' array into the `dest' array -and then sorts `dest', destroying its indices. However, the `source' -array is not affected. - - `asort()' and `asorti()' accept a third string argument to control -the comparison rule for the array elements, and the direction of the -sorted results. The valid comparison modes are `string' and `number', -and the direction can be either `ascending' or `descending'. Either -mode or direction, or both, can be omitted in which case the defaults, -`string' or `ascending' is assumed for the comparison mode and the -direction, respectively. Seperate comparison mode from direction with -a single space, and they can appear in any order. To compare the -elements as numbers, and to reverse the elements of the `dest' array, -the call to asort in the above example can be replaced with: - - asort(source, dest, "descending number") - - The third argument to `asort()' can also be a user-defined function -name which is used to order the array elements before constructing the -result array. *Note Scanning an Array::, for more information. - - Often, what's needed is to sort on the values of the _indices_ -instead of the values of the elements. To do that, use the `asorti()' -function. The interface is identical to that of `asort()', except that -the index values are used for sorting, and become the values of the -result array: - - { source[$0] = some_func($0) } - - END { - n = asorti(source, dest) - for (i = 1; i <= n; i++) { - Work with sorted indices directly: - DO SOMETHING WITH dest[i] - ... - Access original array via sorted indices: - DO SOMETHING WITH source[dest[i]] - } - } - - Sorting the array by replacing the indices provides maximal -flexibility. To traverse the elements in decreasing order, use a loop -that goes from N down to 1, either over the elements or over the -indices. This is an alternative to specifying `descending' for the -sorting order using the optional third argument. - - Copying array indices and elements isn't expensive in terms of -memory. Internally, `gawk' maintains "reference counts" to data. For -example, when `asort()' copies the first array to the second one, there -is only one copy of the original array elements' data, even though both -arrays use the values. - - Because `IGNORECASE' affects string comparisons, the value of -`IGNORECASE' also affects sorting for both `asort()' and `asorti()'. -Note also that the locale's sorting order does _not_ come into play; -comparisons are based on character values only.(1) Caveat Emptor. - - ---------- Footnotes ---------- - - (1) This is true because locale-based comparison occurs only when in -POSIX compatibility mode, and since `asort()' and `asorti()' are `gawk' -extensions, they are not available in that case. - - -File: gawk.info, Node: Arrays of Arrays, Prev: Array Sorting, Up: Arrays +File: gawk.info, Node: Arrays of Arrays, Prev: Multi-dimensional, Up: Arrays -8.7 Arrays of Arrays +8.6 Arrays of Arrays ==================== `gawk' supports arrays of arrays. Elements of a subarray are referred @@ -10972,8 +10671,8 @@ pound sign (`#'): `IGNORECASE' affects the sorting. The third argument can also be a user-defined function name in which case the value returned by the function is used to order the array elements before - constructing the result array. *Note Scanning an Array::, for - more information. + constructing the result array. *Note Array Sorting Functions::, + for more information. For example, if the contents of `a' are as follows: @@ -10998,8 +10697,8 @@ pound sign (`#'): asort(a, a, "descending") The `asort()' function is described in more detail in *note Array - Sorting::. `asort()' is a `gawk' extension; it is not available - in compatibility mode (*note Options::). + Sorting Functions::. `asort()' is a `gawk' extension; it is not + available in compatibility mode (*note Options::). `asorti(SOURCE [, DEST [, HOW ] ]) #' Return the number of elements in the array SOURCE. It works @@ -11007,8 +10706,8 @@ pound sign (`#'): of the values. (Here too, `IGNORECASE' affects the sorting.) The `asorti()' function is described in more detail in *note Array - Sorting::. `asorti()' is a `gawk' extension; it is not available - in compatibility mode (*note Options::). + Sorting Functions::. `asorti()' is a `gawk' extension; it is not + available in compatibility mode (*note Options::). `gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #' Search the target string TARGET for matches of the regular @@ -13678,7 +13377,8 @@ File: gawk.info, Node: Advanced Features, Next: Library Functions, Prev: Inte This major node discusses advanced features in `gawk'. It's a bit of a "grab bag" of items that are otherwise unrelated to each other. First, a command-line option allows `gawk' to recognize nondecimal -numbers in input data, not just in `awk' programs. Next, two-way I/O, +numbers in input data, not just in `awk' programs. Then, `gawk''s +special features for sorting arrays are presented. Next, two-way I/O, discussed briefly in earlier parts of this Info file, is described in full detail, along with the basics of TCP/IP networking. Finally, `gawk' can "profile" an `awk' program, making it possible to tune it @@ -13691,12 +13391,14 @@ and likely to change, its description is relegated to an appendix. * Menu: * Nondecimal Data:: Allowing nondecimal input data. +* Array Sorting:: Facilities for controlling array traversal and + sorting arrays. * Two-way I/O:: Two-way communications with another process. * TCP/IP Networking:: Using `gawk' for network programming. * Profiling:: Profiling your `awk' programs. -File: gawk.info, Node: Nondecimal Data, Next: Two-way I/O, Up: Advanced Features +File: gawk.info, Node: Nondecimal Data, Next: Array Sorting, Up: Advanced Features 11.1 Allowing Nondecimal Input Data =================================== @@ -13738,9 +13440,418 @@ request it. surprising results. -File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Nondecimal Data, Up: Advanced Features +File: gawk.info, Node: Array Sorting, Next: Two-way I/O, Prev: Nondecimal Data, Up: Advanced Features + +11.2 Controlling Array Traversal and Array Sorting +================================================== + +`gawk' lets you control the order in which `for (i in array)' loops +will traverse an array. + + In addition, two built-in functions, `asort()' and `asorti()', let +you sort arrays based on the array values and indices, respectively. +These two functions also provide control over the sorting criteria used +to order the elements during sorting. + +* Menu: + +* Controlling Array Traversal:: How to use PROCINFO["sorted_in"]. +* Array Sorting Functions:: How to use `asort()' and `asorti()'. + + +File: gawk.info, Node: Controlling Array Traversal, Next: Array Sorting Functions, Up: Array Sorting + +11.2.1 Controlling Array Traversal +---------------------------------- + +By default, the order in which a `for (i in array)' loop will scan an +array is not defined; it is generally based upon the internal +implementation of arrays inside `awk'. + + Often, though, it is desirable to be able to loop over the elements +in a particular order that you, the programmer, choose. `gawk' lets +you do this; this node describes how. + +* Menu: + +* Controlling Scanning With A Function:: Using a function to control scanning. +* Controlling Scanning:: Controlling the order in which arrays + are scanned. + + +File: gawk.info, Node: Controlling Scanning With A Function, Next: Controlling Scanning, Up: Controlling Array Traversal + +11.2.1.1 Controlling Array Scanning Order With a User-defined Function +...................................................................... + +The value of `PROCINFO["sorted_in"]' can be a function name. This lets +you traverse an array based on any custom criterion. The array +elements are ordered according to the return value of this function. +This comparison function should be defined with at least four arguments: + + function comp_func(i1, v1, i2, v2) + { + COMPARE ELEMENTS 1 AND 2 IN SOME FASHION + RETURN < 0; 0; OR > 0 + } + + Here, I1 and I2 are the indices, and V1 and V2 are the corresponding +values of the two elements being compared. Either V1 or V2, or both, +can be arrays if the array being traversed contains subarrays as +values. The three possible return values are interpreted this way: + + * If the return value of `comp_func(i1, v1, i2, v2)' is less than + zero, index I1 comes before index I2 during loop traversal. + + * If `comp_func(i1, v1, i2, v2)' returns zero, I1 and I2 come + together but the relative order with respect to each other is + undefined. + + * If the return value of `comp_func(i1, v1, i2, v2)' is greater than + zero, I1 comes after I2. + + The following comparison function can be used to scan an array in +numerical order of the indices: + + function cmp_num_idx(i1, v1, i2, v2) + { + # numerical index comparison, ascending order + return (i1 - i2) + } + + This function traverses an array based on the string order of the +element values rather than by indices: + + function cmp_str_val(i1, v1, i2, v2) + { + # string value comparison, ascending order + v1 = v1 "" + v2 = v2 "" + if (v1 < v2) + return -1 + return (v1 != v2) + } + + Here is a comparison function to make all numbers, and numeric +strings without any leading or trailing spaces, come out first during +loop traversal: + + function cmp_num_str_val(i1, v1, i2, v2, n1, n2) + { + # numbers before string value comparison, ascending order + n1 = v1 + 0 + n2 = v2 + 0 + if (n1 == v1) + return (n2 == v2) ? (n1 - n2) : -1 + else if (n2 == v2) + return 1 + return (v1 < v2) ? -1 : (v1 != v2) + } + + *FIXME*: Put in a fuller example here of some data and show the +different results when traversing. + + Consider sorting the entries of a GNU/Linux system password file +according to login names. The following program which sorts records by +a specific field position can be used for this purpose: + + # sort.awk --- simple program to sort by field position + # field position is specified by the global variable POS + + function cmp_field(i1, v1, i2, v2) + { + # comparison by value, as string, and ascending order + return v1[POS] < v2[POS] ? -1 : (v1[POS] != v2[POS]) + } + + { + for (i = 1; i <= NF; i++) + a[NR][i] = $i + } + + END { + PROCINFO["sorted_in"] = "cmp_field" + if (POS < 1 || POS > NF) + POS = 1 + for (i in a) { + for (j = 1; j <= NF; j++) + printf("%s%c", a[i][j], j < NF ? ":" : "") + print "" + } + } + + The first field in each entry of the password file is the user's +login name, and the fields are seperated by colons. Each record +defines a subarray, which each field as an element in the subarray. +Running the program produces the following output: + + $ gawk -vPOS=1 -F: -f sort.awk /etc/passwd + -| adm:x:3:4:adm:/var/adm:/sbin/nologin + -| apache:x:48:48:Apache:/var/www:/sbin/nologin + -| avahi:x:70:70:Avahi daemon:/:/sbin/nologin + ... + + The comparison normally should always return the same value when +given a specific pair of array elements as its arguments. If +inconsistent results are returned then the order is undefined. This +behavior is sometimes exploited to introduce random order in otherwise +seemingly ordered data: + + function cmp_randomize(i1, v1, i2, v2) + { + # random order + return (2 - 4 * rand()) + } + + As mentioned above, the order of the indices is arbitrary if two +elements compare equal. This is usually not a problem, but letting the +tied elements come out in arbitrary order can be an issue, especially +when comparing item values. The partial ordering of the equal elements +may change during the next loop traversal, if other elements are added +or removed from the array. One way to resolve ties when comparing +elements with otherwise equal values is to include the indices in the +comparison rules. Note that doing this may make the loop traversal +less efficient, so consider it only if necessary. The following +comparison functions force a deterministic order, and are based on the +fact that the indices of two elements are never equal: + + function cmp_numeric(i1, v1, i2, v2) + { + # numerical value (and index) comparison, descending order + return (v1 != v2) ? (v2 - v1) : (i2 - i1) + } + + function cmp_string(i1, v1, i2, v2) + { + # string value (and index) comparison, descending order + v1 = v1 i1 + v2 = v2 i2 + return (v1 > v2) ? -1 : (v1 != v2) + } + + A custom comparison function can often simplify ordered loop +traversal, and the the sky is really the limit when it comes to +designing such a function. + + When string comparisons are made during a sort, either for element +values where one or both aren't numbers, or for element indices handled +as strings, the value of `IGNORECASE' (*note Built-in Variables::) +controls whether the comparisons treat corresponding uppercase and +lowercase letters as equivalent or distinct. + + Another point to keep in mind is that in the case of subarrays the +element values can themselves be arrays; a production comparison +function should use the `isarray()' function (*note Type Functions::), +to check for this, and choose a defined sorting order for subarrays. + + All sorting based on `PROCINFO["sorted_in"]' is disabled in POSIX +mode, since the `PROCINFO' array is not special in that case. + + As a side note, sorting the array indices before traversing the +array has been reported to add 15% to 20% overhead to the execution +time of `awk' programs. For this reason, sorted array traversal is not +the default. + + +File: gawk.info, Node: Controlling Scanning, Prev: Controlling Scanning With A Function, Up: Controlling Array Traversal + +11.2.1.2 Controlling Array Scanning Order +......................................... + +As described in *note Controlling Scanning With A Function::, you can +provide the name of a function as the value of `PROCINFO["sorted_in"]' +to specify custom sorting criteria. + + Often, though, you may wish to do something simple, such as "sort +based on comparing the indices in ascending order," or "sort based on +comparing the values in descending order." Having to write a simple +comparison function for this purpose for use in all of your programs +becomes tedious. For the most likely simple cases `gawk' provides the +option of supplying special names that do the requested sorting for you. +You can think of them as "predefined" sorting functions, if you like, +although the names purposely include characters that are not valid in +real `awk' function names. + + The following special values are available: + +`"@ind_str_asc"' + Order by indices compared as strings; this is the most basic sort. + (Internally, array indices are always strings, so with `a[2*5] = 1' + the index is actually `"10"' rather than numeric 10.) + +`"@ind_num_asc"' + Order by indices but force them to be treated as numbers in the + process. Any index with non-numeric value will end up positioned + as if it were zero. + +`"@val_type_asc"' + Order by element values rather than indices. Ordering is by the + type assigned to the element (*note Typing and Comparison::). All + numeric values come before all string values, which in turn come + before all subarrays. + +`"@val_str_asc"' + Order by element values rather than by indices. Scalar values are + compared as strings. Subarrays, if present, come out last. + +`"@val_num_asc"' + Order by values but force scalar values to be treated as numbers + for the purpose of comparison. If there are subarrays, those + appear at the end of the sorted list. + +`"@ind_str_desc"' + Reverse order from the most basic sort. + +`"@ind_num_desc"' + Numeric indices ordered from high to low. + +`"@val_type_desc"' + Element values, based on type, in descending order. + +`"@val_str_desc"' + Element values, treated as strings, ordered from high to low. + Subarrays, if present, come out first. + +`"@val_num_desc"' + Element values, treated as numbers, ordered from high to low. + Subarrays, if present, come out first. + +`"@unsorted"' + Array elements are processed in arbitrary order, which is the + normal `awk' behavior. You can also get the normal behavior by just + deleting the `"sorted_in"' element from the `PROCINFO' array, if + it previously had a value assigned to it. + + The array traversal order is determined before the `for' loop starts +to run. Changing `PROCINFO["sorted_in"]' in the loop body will not +affect the loop. + + For example: + + $ gawk 'BEGIN { + > a[4] = 4 + > a[3] = 3 + > for (i in a) + > print i, a[i] + > }' + -| 4 4 + -| 3 3 + $ gawk 'BEGIN { + > PROCINFO["sorted_in"] = "@str_ind_asc" + > a[4] = 4 + > a[3] = 3 + > for (i in a) + > print i, a[i] + > }' + -| 3 3 + -| 4 4 + + When sorting an array by element values, if a value happens to be a +subarray then it is considered to be greater than any string or numeric +value, regardless of what the subarray itself contains, and all +subarrays are treated as being equal to each other. Their order +relative to each other is determined by their index strings. + + +File: gawk.info, Node: Array Sorting Functions, Prev: Controlling Array Traversal, Up: Array Sorting + +11.2.2 Sorting Array Values and Indices with `gawk' +--------------------------------------------------- + +The order in which an array is scanned with a `for (i in array)' loop +is essentially arbitrary. In most `awk' implementations, sorting an +array requires writing a `sort' function. While this can be +educational for exploring different sorting algorithms, usually that's +not the point of the program. `gawk' provides the built-in `asort()' +and `asorti()' functions (*note String Functions::) for sorting arrays. +For example: + + POPULATE THE ARRAY data + n = asort(data) + for (i = 1; i <= n; i++) + DO SOMETHING WITH data[i] + + After the call to `asort()', the array `data' is indexed from 1 to +some number N, the total number of elements in `data'. (This count is +`asort()''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so +on. The array elements are compared as strings. + + An important side effect of calling `asort()' is that _the array's +original indices are irrevocably lost_. As this isn't always +desirable, `asort()' accepts a second argument: + + POPULATE THE ARRAY source + n = asort(source, dest) + for (i = 1; i <= n; i++) + DO SOMETHING WITH dest[i] + + In this case, `gawk' copies the `source' array into the `dest' array +and then sorts `dest', destroying its indices. However, the `source' +array is not affected. + + `asort()' and `asorti()' accept a third string argument to control +the comparison rule for the array elements, and the direction of the +sorted results. The valid comparison modes are `string' and `number', +and the direction can be either `ascending' or `descending'. Either +mode or direction, or both, can be omitted in which case the defaults, +`string' or `ascending' is assumed for the comparison mode and the +direction, respectively. Seperate comparison mode from direction with +a single space, and they can appear in any order. To compare the +elements as numbers, and to reverse the elements of the `dest' array, +the call to asort in the above example can be replaced with: + + asort(source, dest, "descending number") + + The third argument to `asort()' can also be a user-defined function +name which is used to order the array elements before constructing the +result array. *Note Scanning an Array::, for more information. + + Often, what's needed is to sort on the values of the _indices_ +instead of the values of the elements. To do that, use the `asorti()' +function. The interface is identical to that of `asort()', except that +the index values are used for sorting, and become the values of the +result array: + + { source[$0] = some_func($0) } + + END { + n = asorti(source, dest) + for (i = 1; i <= n; i++) { + Work with sorted indices directly: + DO SOMETHING WITH dest[i] + ... + Access original array via sorted indices: + DO SOMETHING WITH source[dest[i]] + } + } + + Sorting the array by replacing the indices provides maximal +flexibility. To traverse the elements in decreasing order, use a loop +that goes from N down to 1, either over the elements or over the +indices. This is an alternative to specifying `descending' for the +sorting order using the optional third argument. + + Copying array indices and elements isn't expensive in terms of +memory. Internally, `gawk' maintains "reference counts" to data. For +example, when `asort()' copies the first array to the second one, there +is only one copy of the original array elements' data, even though both +arrays use the values. + + Because `IGNORECASE' affects string comparisons, the value of +`IGNORECASE' also affects sorting for both `asort()' and `asorti()'. +Note also that the locale's sorting order does _not_ come into play; +comparisons are based on character values only.(1) Caveat Emptor. + + ---------- Footnotes ---------- + + (1) This is true because locale-based comparison occurs only when in +POSIX compatibility mode, and since `asort()' and `asorti()' are `gawk' +extensions, they are not available in that case. + + +File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Array Sorting, Up: Advanced Features -11.2 Two-Way Communications with Another Process +11.3 Two-Way Communications with Another Process ================================================ From: brennan@whidbey.com (Mike Brennan) @@ -13875,7 +13986,7 @@ regular pipes. File: gawk.info, Node: TCP/IP Networking, Next: Profiling, Prev: Two-way I/O, Up: Advanced Features -11.3 Using `gawk' for Network Programming +11.4 Using `gawk' for Network Programming ========================================= `EMISTERED': @@ -13952,7 +14063,7 @@ examples. File: gawk.info, Node: Profiling, Prev: TCP/IP Networking, Up: Advanced Features -11.4 Profiling Your `awk' Programs +11.5 Profiling Your `awk' Programs ================================== You may produce execution traces of your `awk' programs. This is done @@ -19603,8 +19714,8 @@ you can find more information. * SVR4:: Minor changes between System V Releases 3.1 and 4. * POSIX:: New features from the POSIX standard. -* BTL:: New features from Brian Kernighan's - version of `awk'. +* BTL:: New features from Brian Kernighan's version of + `awk'. * POSIX/GNU:: The extensions in `gawk' not in POSIX `awk'. * Common Extensions:: Common Extensions Summary. @@ -19916,6 +20027,8 @@ the current version of `gawk'. - Tandem (non-POSIX) + - Prestandard VAX C compiler for VAX/VMS + @@ -19991,9 +20104,9 @@ Info file, in approximate chronological order: documentation. * Michal Jaegermann provided the port to Atari systems and its - documentation. He continues to provide portability checking with - DEC Alpha systems, and has done a lot of work to make sure `gawk' - works on non-32-bit systems. + documentation. (This port is no longer supported.) He continues + to provide portability checking with DEC Alpha systems, and has + done a lot of work to make sure `gawk' works on non-32-bit systems. * Fred Fish provided the port to Amiga systems and its documentation. (With Fred's sad passing, this is no longer supported.) @@ -24696,11 +24809,11 @@ Index * arrays, elements, assigning: Assigning Elements. (line 6) * arrays, elements, deleting: Delete. (line 6) * arrays, elements, installing: Internals. (line 79) -* arrays, elements, order of: Scanning an Array. (line 53) +* arrays, elements, order of: Scanning an Array. (line 48) * arrays, elements, referencing: Reference to Elements. (line 6) * arrays, elements, retrieving number of: String Functions. (line 29) -* arrays, for statement and: Scanning an Array. (line 25) +* arrays, for statement and: Scanning an Array. (line 20) * arrays, IGNORECASE variable and: Array Intro. (line 92) * arrays, indexing: Array Intro. (line 50) * arrays, merging into strings: Join Function. (line 6) @@ -24708,8 +24821,10 @@ Index * arrays, multidimensional, scanning: Multi-scanning. (line 11) * arrays, names of: Arrays. (line 18) * arrays, scanning: Scanning an Array. (line 6) -* arrays, sorting: Array Sorting. (line 6) -* arrays, sorting, IGNORECASE variable and: Array Sorting. (line 85) +* arrays, sorting: Array Sorting Functions. + (line 6) +* arrays, sorting, IGNORECASE variable and: Array Sorting Functions. + (line 85) * arrays, sparse: Array Intro. (line 71) * arrays, subscripts: Numeric Array Subscripts. (line 6) @@ -24719,9 +24834,11 @@ Index (line 55) * ASCII <1>: Glossary. (line 137) * ASCII: Ordinal Functions. (line 45) -* asort() function (gawk) <1>: String Functions. (line 29) -* asort() function (gawk): Array Sorting. (line 6) -* asort() function (gawk), arrays, sorting: Array Sorting. (line 6) +* asort() function (gawk) <1>: Array Sorting Functions. + (line 6) +* asort() function (gawk): String Functions. (line 29) +* asort() function (gawk), arrays, sorting: Array Sorting Functions. + (line 6) * asorti() function (gawk): String Functions. (line 77) * assert() function (C library): Assert Function. (line 6) * assert() user-defined function: Assert Function. (line 28) @@ -25386,7 +25503,7 @@ Index (line 6) * elements in arrays, assigning: Assigning Elements. (line 6) * elements in arrays, deleting: Delete. (line 6) -* elements in arrays, order of: Scanning an Array. (line 53) +* elements in arrays, order of: Scanning an Array. (line 48) * elements in arrays, scanning: Scanning an Array. (line 6) * email address for bug reports, bug-gawk@gnu.org: Bugs. (line 30) * EMISTERED: TCP/IP Networking. (line 6) @@ -25617,7 +25734,7 @@ Index * FNR variable: Records. (line 6) * FNR variable, changing: Auto-set. (line 229) * for statement: For Statement. (line 6) -* for statement, in arrays: Scanning an Array. (line 25) +* for statement, in arrays: Scanning an Array. (line 20) * force_number() internal function: Internals. (line 27) * force_string() internal function: Internals. (line 32) * force_wstring() internal function: Internals. (line 37) @@ -25751,8 +25868,9 @@ Index * gawk, function arguments and: Calling Built-in. (line 16) * gawk, functions, adding: Dynamic Extensions. (line 10) * gawk, hexadecimal numbers and: Nondecimal-numbers. (line 42) -* gawk, IGNORECASE variable in <1>: String Functions. (line 29) -* gawk, IGNORECASE variable in <2>: Array Sorting. (line 85) +* gawk, IGNORECASE variable in <1>: Array Sorting Functions. + (line 85) +* gawk, IGNORECASE variable in <2>: String Functions. (line 29) * gawk, IGNORECASE variable in <3>: Array Intro. (line 92) * gawk, IGNORECASE variable in <4>: User-modified. (line 82) * gawk, IGNORECASE variable in: Case-sensitivity. (line 26) @@ -25910,12 +26028,14 @@ Index * if statement, actions, changing: Ranges. (line 25) * igawk.sh program: Igawk Program. (line 124) * ignore debugger command: Breakpoint Control. (line 86) -* IGNORECASE variable <1>: String Functions. (line 29) -* IGNORECASE variable <2>: Array Sorting. (line 85) +* IGNORECASE variable <1>: Array Sorting Functions. + (line 85) +* IGNORECASE variable <2>: String Functions. (line 29) * IGNORECASE variable <3>: Array Intro. (line 92) * IGNORECASE variable <4>: User-modified. (line 82) * IGNORECASE variable: Case-sensitivity. (line 26) -* IGNORECASE variable, array sorting and: Array Sorting. (line 85) +* IGNORECASE variable, array sorting and: Array Sorting Functions. + (line 85) * IGNORECASE variable, array subscripts and: Array Intro. (line 92) * IGNORECASE variable, in example programs: Library Functions. (line 42) @@ -25928,7 +26048,7 @@ Index * in operator <3>: Precedence. (line 83) * in operator: Comparison Operators. (line 11) -* in operator, arrays and <1>: Scanning an Array. (line 22) +* in operator, arrays and <1>: Scanning an Array. (line 17) * in operator, arrays and: Reference to Elements. (line 37) * increment operators: Increment Ops. (line 6) @@ -26593,7 +26713,8 @@ Index * recursive functions: Definition Syntax. (line 73) * redirection of input: Getline/File. (line 6) * redirection of output: Redirection. (line 6) -* reference counting, sorting arrays: Array Sorting. (line 79) +* reference counting, sorting arrays: Array Sorting Functions. + (line 79) * regexp constants <1>: Comparison Operators. (line 103) * regexp constants <2>: Regexp Constants. (line 6) @@ -26751,7 +26872,8 @@ Index * side effects: Concatenation. (line 42) * side effects, array indexing: Reference to Elements. (line 42) -* side effects, asort() function: Array Sorting. (line 24) +* side effects, asort() function: Array Sorting Functions. + (line 24) * side effects, assignment expressions: Assignment Ops. (line 23) * side effects, Boolean operators: Boolean Ops. (line 30) * side effects, conditional expressions: Conditional Exp. (line 22) @@ -26781,7 +26903,8 @@ Index * Skywalker, Luke: Undocumented. (line 6) * sleep utility: Alarm Program. (line 109) * Solaris, POSIX-compliant awk: Other Versions. (line 86) -* sort function, arrays, sorting: Array Sorting. (line 6) +* sort function, arrays, sorting: Array Sorting Functions. + (line 6) * sort utility: Word Sorting. (line 50) * sort utility, coprocesses and: Two-way I/O. (line 83) * sorting characters in different languages: Explaining gettext. @@ -27132,407 +27255,409 @@ Index Tag Table: Node: Top1346 -Node: Foreword29926 -Node: Preface34271 -Ref: Preface-Footnote-137238 -Ref: Preface-Footnote-237344 -Node: History37576 -Node: Names39967 -Ref: Names-Footnote-141444 -Node: This Manual41516 -Ref: This Manual-Footnote-146464 -Node: Conventions46564 -Node: Manual History48698 -Ref: Manual History-Footnote-151968 -Ref: Manual History-Footnote-252009 -Node: How To Contribute52083 -Node: Acknowledgments53227 -Node: Getting Started57558 -Node: Running gawk59937 -Node: One-shot61123 -Node: Read Terminal62348 -Ref: Read Terminal-Footnote-163998 -Ref: Read Terminal-Footnote-264274 -Node: Long64445 -Node: Executable Scripts65821 -Ref: Executable Scripts-Footnote-167690 -Ref: Executable Scripts-Footnote-267792 -Node: Comments68243 -Node: Quoting70710 -Node: DOS Quoting75333 -Node: Sample Data Files76008 -Node: Very Simple79040 -Node: Two Rules83639 -Node: More 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