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diff --git a/doc/gawktexi.in b/doc/gawktexi.in index 8034a6b6..9f20f608 100644 --- a/doc/gawktexi.in +++ b/doc/gawktexi.in @@ -2564,9 +2564,7 @@ for programs that are provided on the @command{awk} command line. (Also, placing the program in a file allows us to use a literal single quote in the program text, instead of the magic @samp{\47}.) -@c STARTOFRANGE sq1x @cindex single quote (@code{'}) in @command{gawk} command lines -@c STARTOFRANGE qs2x @cindex @code{'} (single quote) in @command{gawk} command lines If you want to clearly identify an @command{awk} program file as such, you can add the extension @file{.awk} to the @value{FN}. This doesn't @@ -2884,8 +2882,6 @@ $ @kbd{awk "BEGIN @{ print \"Here is a single quote <'>\" @}"} @end example @noindent -@c ENDOFRANGE sq1x -@c ENDOFRANGE qs2x This option is also painful, because double quotes, backslashes, and dollar signs are very common in more advanced @command{awk} programs. @@ -3221,8 +3217,13 @@ no actions run. After processing all the rules that match the line (and perhaps there are none), @command{awk} reads the next line. (However, -@pxref{Next Statement}, +@DBPXREF{Next Statement} +@ifdocbook +and @DBREF{Nextfile Statement}.) +@end ifdocbook +@ifnotdocbook and also @pxref{Nextfile Statement}.) +@end ifnotdocbook This continues until the program reaches the end of the file. For example, the following @command{awk} program contains two rules: @@ -3487,7 +3488,7 @@ performing bit manipulation, for runtime string translation (internationalizatio determining the type of a variable, and array sorting. -As we develop our presentation of the @command{awk} language, we introduce +As we develop our presentation of the @command{awk} language, we will introduce most of the variables and many of the functions. They are described systematically in @DBREF{Built-in Variables} and in @ref{Built-in}. @@ -3541,7 +3542,7 @@ and Perl.} @c FIXME: Review this chapter for summary of builtin functions called. @itemize @value{BULLET} @item -Programs in @command{awk} consist of @var{pattern}-@var{action} pairs. +Programs in @command{awk} consist of @var{pattern}--@var{action} pairs. @item An @var{action} without a @var{pattern} always runs. The default @@ -3570,7 +3571,7 @@ part of a larger shell script (or MS-Windows batch file). You may use backslash continuation to continue a source line. Lines are automatically continued after a comma, open brace, question mark, colon, -@samp{||}, @samp{&&}, @code{do} and @code{else}. +@samp{||}, @samp{&&}, @code{do}, and @code{else}. @end itemize @node Invoking Gawk @@ -3645,20 +3646,16 @@ warning that the program is empty. @node Options @section Command-Line Options -@c STARTOFRANGE ocl @cindex options, command-line -@c STARTOFRANGE clo @cindex command line, options -@c STARTOFRANGE gnulo @cindex GNU long options -@c STARTOFRANGE longo @cindex options, long Options begin with a dash and consist of a single character. GNU-style long options consist of two dashes and a keyword. The keyword can be abbreviated, as long as the abbreviation allows the option -to be uniquely identified. If the option takes an argument, then the -keyword is either immediately followed by an equals sign (@samp{=}) and the +to be uniquely identified. If the option takes an argument, either the +keyword is immediately followed by an equals sign (@samp{=}) and the argument's value, or the keyword and the argument's value are separated by whitespace. If a particular option with a value is given more than once, it is the @@ -3685,7 +3682,7 @@ Set the @code{FS} variable to @var{fs} @cindex @option{-f} option @cindex @option{--file} option @cindex @command{awk} programs, location of -Read @command{awk} program source from @var{source-file} +Read the @command{awk} program source from @var{source-file} instead of in the first nonoption argument. This option may be given multiple times; the @command{awk} program consists of the concatenation of the contents of @@ -3740,8 +3737,6 @@ by the user that could start with @samp{-}. It is also useful for passing options on to the @command{awk} program; see @ref{Getopt Function}. @end table -@c ENDOFRANGE gnulo -@c ENDOFRANGE longo The following list describes @command{gawk}-specific options: @@ -3753,14 +3748,14 @@ The following list describes @command{gawk}-specific options: @cindex @option{--characters-as-bytes} option Cause @command{gawk} to treat all input data as single-byte characters. In addition, all output written with @code{print} or @code{printf} -are treated as single-byte characters. +is treated as single-byte characters. Normally, @command{gawk} follows the POSIX standard and attempts to process its input data according to the current locale (@pxref{Locales}). This can often involve converting multibyte characters into wide characters (internally), and can lead to problems or confusion if the input data does not contain valid -multibyte characters. This option is an easy way to tell @command{gawk}: -``hands off my data!''. +multibyte characters. This option is an easy way to tell @command{gawk}, +``Hands off my data!'' @item @option{-c} @itemx @option{--traditional} @@ -3817,7 +3812,7 @@ Enable debugging of @command{awk} programs By default, the debugger reads commands interactively from the keyboard (standard input). The optional @var{file} argument allows you to specify a file with a list -of commands for the debugger to execute non-interactively. +of commands for the debugger to execute noninteractively. No space is allowed between the @option{-D} and @var{file}, if @var{file} is supplied. @@ -3877,7 +3872,7 @@ with @samp{#!} scripts (@pxref{Executable Scripts}), like so: @cindex portable object files, generating @cindex files, portable object, generating Analyze the source program and -generate a GNU @command{gettext} Portable Object Template file on standard +generate a GNU @command{gettext} portable object template file on standard output for all string constants that have been marked for translation. @xref{Internationalization}, for information about this option. @@ -3889,7 +3884,7 @@ for information about this option. @cindex GNU long options, printing list of @cindex options, printing list of @cindex printing, list of options -Print a ``usage'' message summarizing the short and long style options +Print a ``usage'' message summarizing the short- and long-style options that @command{gawk} accepts and then exit. @item @option{-i} @var{source-file} @@ -3899,7 +3894,7 @@ that @command{gawk} accepts and then exit. @cindex @command{awk} programs, location of Read an @command{awk} source library from @var{source-file}. This option is completely equivalent to using the @code{@@include} directive inside -your program. This option is very similar to the @option{-f} option, +your program. It is very similar to the @option{-f} option, but there are two important differences. First, when @option{-i} is used, the program source is not loaded if it has been previously loaded, whereas with @option{-f}, @command{gawk} always loads the file. @@ -3984,7 +3979,7 @@ when parsing numeric input data (@pxref{Locales}). @cindex @option{-o} option @cindex @option{--pretty-print} option Enable pretty-printing of @command{awk} programs. -By default, output program is created in a file named @file{awkprof.out} +By default, the output program is created in a file named @file{awkprof.out} (@pxref{Profiling}). The optional @var{file} argument allows you to specify a different @value{FN} for the output. @@ -4028,7 +4023,7 @@ in the left margin, and function call counts for each function. Operate in strict POSIX mode. This disables all @command{gawk} extensions (just like @option{--traditional}) and disables all extensions not allowed by POSIX. -@xref{Common Extensions}, for a summary of the extensions +@DBXREF{Common Extensions} for a summary of the extensions in @command{gawk} that are disabled by this option. Also, the following additional @@ -4149,7 +4144,7 @@ source of data.) Because it is clumsy using the standard @command{awk} mechanisms to mix source file and command-line @command{awk} programs, @command{gawk} provides the @option{-e} option. This does not require you to -pre-empt the standard input for your source code; it allows you to easily +preempt the standard input for your source code; it allows you to easily mix command-line and library source code (@pxref{AWKPATH Variable}). As with @option{-f}, the @option{-e} and @option{-i} options may also be used multiple times on the command line. @@ -4195,8 +4190,6 @@ setenv POSIXLY_CORRECT true Having @env{POSIXLY_CORRECT} set is not recommended for daily use, but it is good for testing the portability of your programs to other environments. -@c ENDOFRANGE ocl -@c ENDOFRANGE clo @node Other Arguments @section Other Command-Line Arguments @@ -4339,7 +4332,7 @@ file, unless the file is in the current directory. But with @command{gawk}, if the @value{FN} supplied to the @option{-f} or @option{-i} options does not contain a directory separator @samp{/}, then @command{gawk} searches a list of -directories (called the @dfn{search path}), one by one, looking for a +directories (called the @dfn{search path}) one by one, looking for a file with the specified name. The search path is a string consisting of directory names @@ -4380,9 +4373,9 @@ as an entry in the path or write a null entry in the path. Different past versions of @command{gawk} would also look explicitly in the current directory, either before or after the path search. As of -@value{PVERSION} 4.1.2, this no longer happens, and if you wish to look +@value{PVERSION} 4.1.2, this no longer happens; if you wish to look in the current directory, you must include @file{.} either as a separate -entry, or as a null entry in the search path. +entry or as a null entry in the search path. @end quotation The default value for @env{AWKPATH} is @@ -4498,7 +4491,7 @@ If this variable exists, @command{gawk} includes the @value{FN} and line number within the @command{gawk} source code from which warning and/or fatal messages are generated. Its purpose is to help isolate the source of a -message, as there are multiple places which produce the +message, as there are multiple places that produce the same warning or error message. @item GAWK_NO_DFA @@ -4514,16 +4507,16 @@ This specifies the amount by which @command{gawk} should grow its internal evaluation stack, when needed. @item INT_CHAIN_MAX -The intended maximum number of items @command{gawk} will maintain on a +This specifies intended maximum number of items @command{gawk} will maintain on a hash chain for managing arrays indexed by integers. @item STR_CHAIN_MAX -The intended maximum number of items @command{gawk} will maintain on a +This specifies intended maximum number of items @command{gawk} will maintain on a hash chain for managing arrays indexed by strings. @item TIDYMEM If this variable exists, @command{gawk} uses the @code{mtrace()} library -calls from GNU LIBC to help track down possible memory leaks. +calls from the GNU C library to help track down possible memory leaks. @end table @node Exit Status @@ -4560,7 +4553,7 @@ The @code{@@include} keyword can be used to read external @command{awk} source files. This gives you the ability to split large @command{awk} source files into smaller, more manageable pieces, and also lets you reuse common @command{awk} code from various @command{awk} scripts. In other words, you can group -together @command{awk} functions, used to carry out specific tasks, +together @command{awk} functions used to carry out specific tasks into external files. These files can be used just like function libraries, using the @code{@@include} keyword in conjunction with the @env{AWKPATH} environment variable. Note that source files may also be included @@ -4650,11 +4643,12 @@ of the @env{AWKPATH} variable in command-line file searches This is very helpful in constructing @command{gawk} function libraries. If you have a large script with useful, general-purpose @command{awk} functions, you can break it down into library files and put those files -in a special directory. You can then include those ``libraries,'' using -either the full pathnames of the files, or by setting the @env{AWKPATH} +in a special directory. You can then include those ``libraries,'' +either by using the full pathnames of the files, or by setting the @env{AWKPATH} environment variable accordingly and then using @code{@@include} with -just the file part of the full pathname. Of course, you can have more -than one directory to keep library files; the more complex the working +just the file part of the full pathname. Of course, +you can keep library files in more than one directory; +the more complex the working environment is, the more directories you may need to organize the files to be included. @@ -4667,8 +4661,8 @@ In particular, @code{@@include} is very useful for writing CGI scripts to be run from web pages. As mentioned in @ref{AWKPATH Variable}, the current directory is always -searched first for source files, before searching in @env{AWKPATH}, -and this also applies to files named with @code{@@include}. +searched first for source files, before searching in @env{AWKPATH}; +this also applies to files named with @code{@@include}. @node Loading Shared Libraries @section Loading Dynamic Extensions into Your Program @@ -4722,8 +4716,8 @@ It also describes the @code{ordchr} extension. @cindex features, deprecated @cindex obsolete features This @value{SECTION} describes features and/or command-line options from -previous releases of @command{gawk} that are either not available in the -current version or that are still supported but deprecated (meaning that +previous releases of @command{gawk} that either are not available in the +current version or are still supported but deprecated (meaning that they will @emph{not} be in the next release). The process-related special files @file{/dev/pid}, @file{/dev/ppid}, @@ -4820,7 +4814,7 @@ to run @command{awk}. @item The three standard options for all versions of @command{awk} are -@option{-f}, @option{-F} and @option{-v}. @command{gawk} supplies these +@option{-f}, @option{-F}, and @option{-v}. @command{gawk} supplies these and many others, as well as corresponding GNU-style long options. @item @@ -4857,13 +4851,12 @@ and @option{-f} command-line options. @item @command{gawk} allows you to load additional functions written in C or C++ using the @code{@@load} statement and/or the @option{-l} option. -(This advanced feature is described later on in @ref{Dynamic Extensions}.) +(This advanced feature is described later, in @ref{Dynamic Extensions}.) @end itemize @node Regexp @chapter Regular Expressions @cindex regexp -@c STARTOFRANGE regexp @cindex regular expressions A @dfn{regular expression}, or @dfn{regexp}, is a way of describing a @@ -5070,7 +5063,7 @@ Horizontal TAB, @kbd{Ctrl-i}, ASCII code 9 (HT). @cindex @code{\} (backslash), @code{\v} escape sequence @cindex backslash (@code{\}), @code{\v} escape sequence @item \v -Vertical tab, @kbd{Ctrl-k}, ASCII code 11 (VT). +Vertical TAB, @kbd{Ctrl-k}, ASCII code 11 (VT). @cindex @code{\} (backslash), @code{\}@var{nnn} escape sequence @cindex backslash (@code{\}), @code{\}@var{nnn} escape sequence @@ -5145,7 +5138,7 @@ characters @samp{a+b}. @cindex @code{\} (backslash), in escape sequences @cindex portability For complete portability, do not use a backslash before any character not -shown in the previous list and that is not an operator. +shown in the previous list or that is not an operator. @c 11/2014: Moved so as to not stack sidebars @sidebar Backslash Before Regular Characters @@ -5224,7 +5217,6 @@ escape sequences literally when used in regexp constants. Thus, @node Regexp Operators @section Regular Expression Operators -@c STARTOFRANGE regexpo @cindex regular expressions, operators @cindex metacharacters in regular expressions @@ -5242,7 +5234,7 @@ are recognized and converted into corresponding real characters as the very first step in processing regexps. Here is a list of metacharacters. All characters that are not escape -sequences and that are not listed in the following stand for themselves: +sequences and that are not listed here stand for themselves: @c Use @asis so the docbook comes out ok. Sigh. @table @asis @@ -5365,7 +5357,7 @@ just @samp{p} if no @samp{h}s are present. There are two subtle points to understand about how @samp{*} works. First, the @samp{*} applies only to the single preceding regular expression component (e.g., in @samp{ph*}, it applies just to the @samp{h}). -To cause @samp{*} to apply to a larger sub-expression, use parentheses: +To cause @samp{*} to apply to a larger subexpression, use parentheses: @samp{(ph)*} matches @samp{ph}, @samp{phph}, @samp{phphph}, and so on. Second, @samp{*} finds as many repetitions as possible. If the text @@ -5404,10 +5396,10 @@ is repeated at least @var{n} times: Matches @samp{whhhy}, but not @samp{why} or @samp{whhhhy}. @item wh@{3,5@}y -Matches @samp{whhhy}, @samp{whhhhy}, or @samp{whhhhhy}, only. +Matches @samp{whhhy}, @samp{whhhhy}, or @samp{whhhhhy} only. @item wh@{2,@}y -Matches @samp{whhy} or @samp{whhhy}, and so on. +Matches @samp{whhy}, @samp{whhhy}, and so on. @end table @cindex POSIX @command{awk}, interval expressions in @@ -5456,11 +5448,9 @@ usage as a syntax error. If @command{gawk} is in compatibility mode (@pxref{Options}), interval expressions are not available in regular expressions. -@c ENDOFRANGE regexpo @node Bracket Expressions @section Using Bracket Expressions -@c STARTOFRANGE charlist @cindex bracket expressions @cindex bracket expressions, range expressions @cindex range expressions (regexps) @@ -5536,7 +5526,7 @@ POSIX standard. (a space is printable but not visible, whereas an @samp{a} is both) @item @code{[:lower:]} @tab Lowercase alphabetic characters @item @code{[:print:]} @tab Printable characters (characters that are not control characters) -@item @code{[:punct:]} @tab Punctuation characters (characters that are not letters, digits +@item @code{[:punct:]} @tab Punctuation characters (characters that are not letters, digits, control characters, or space characters) @item @code{[:space:]} @tab Space characters (such as space, TAB, and formfeed, to name a few) @item @code{[:upper:]} @tab Uppercase alphabetic characters @@ -5556,11 +5546,11 @@ and numeric characters in your character set. @c Date: Tue, 01 Jul 2014 07:39:51 +0200 @c From: Hermann Peifer <peifer@gmx.eu> Some utilities that match regular expressions provide a nonstandard -@code{[:ascii:]} character class; @command{awk} does not. However, you -can simulate such a construct using @code{[\x00-\x7F]}. This matches +@samp{[:ascii:]} character class; @command{awk} does not. However, you +can simulate such a construct using @samp{[\x00-\x7F]}. This matches all values numerically between zero and 127, which is the defined range of the ASCII character set. Use a complemented character list -(@code{[^\x00-\x7F]}) to match any single-byte characters that are not +(@samp{[^\x00-\x7F]}) to match any single-byte characters that are not in the ASCII range. @cindex bracket expressions, collating elements @@ -5589,8 +5579,8 @@ Locale-specific names for a list of characters that are equal. The name is enclosed between @samp{[=} and @samp{=]}. For example, the name @samp{e} might be used to represent all of -``e,'' ``@`e,'' and ``@'e.'' In this case, @samp{[[=e=]]} is a regexp -that matches any of @samp{e}, @samp{@'e}, or @samp{@`e}. +``e,'' ``@^e,'' ``@`e,'' and ``@'e.'' In this case, @samp{[[=e=]]} is a regexp +that matches any of @samp{e}, @samp{@^e}, @samp{@'e}, or @samp{@`e}. @end table These features are very valuable in non-English-speaking locales. @@ -5604,7 +5594,6 @@ expression matching currently recognize only POSIX character classes; they do not recognize collating symbols or equivalence classes. @end quotation @c maybe one day ... -@c ENDOFRANGE charlist @node Leftmost Longest @section How Much Text Matches? @@ -5620,7 +5609,7 @@ echo aaaabcd | awk '@{ sub(/a+/, "<A>"); print @}' This example uses the @code{sub()} function to make a change to the input record. (@code{sub()} replaces the first instance of any text matched by the first argument with the string provided as the second argument; -@pxref{String Functions}). Here, the regexp @code{/a+/} indicates ``one +@pxref{String Functions}.) Here, the regexp @code{/a+/} indicates ``one or more @samp{a} characters,'' and the replacement text is @samp{<A>}. The input contains four @samp{a} characters. @@ -5648,9 +5637,7 @@ and also @pxref{Field Separators}). @node Computed Regexps @section Using Dynamic Regexps -@c STARTOFRANGE dregexp @cindex regular expressions, computed -@c STARTOFRANGE regexpd @cindex regular expressions, dynamic @cindex @code{~} (tilde), @code{~} operator @cindex tilde (@code{~}), @code{~} operator @@ -5676,14 +5663,14 @@ and tests whether the input record matches this regexp. @quotation NOTE When using the @samp{~} and @samp{!~} -operators, there is a difference between a regexp constant +operators, be aware that there is a difference between a regexp constant enclosed in slashes and a string constant enclosed in double quotes. If you are going to use a string constant, you have to understand that the string is, in essence, scanned @emph{twice}: the first time when @command{awk} reads your program, and the second time when it goes to match the string on the lefthand side of the operator with the pattern on the right. This is true of any string-valued expression (such as -@code{digits_regexp}, shown previously), not just string constants. +@code{digits_regexp}, shown in the previous example), not just string constants. @end quotation @cindex regexp constants, slashes vs.@: quotes @@ -5757,17 +5744,13 @@ $ @kbd{awk '$0 ~ /[ \t\n]/'} @command{gawk} does not have this problem, and it isn't likely to occur often in practice, but it's worth noting for future reference. @end sidebar -@c ENDOFRANGE dregexp -@c ENDOFRANGE regexpd @node GNU Regexp Operators @section @command{gawk}-Specific Regexp Operators @c This section adapted (long ago) from the regex-0.12 manual -@c STARTOFRANGE regexpg @cindex regular expressions, operators, @command{gawk} -@c STARTOFRANGE gregexp @cindex @command{gawk}, regular expressions, operators @cindex operators, GNU-specific @cindex regular expressions, operators, for words @@ -5843,7 +5826,7 @@ matches either @samp{ball} or @samp{balls}, as a separate word. @item \B Matches the empty string that occurs between two word-constituent characters. For example, -@code{/\Brat\B/} matches @samp{crate} but it does not match @samp{dirty rat}. +@code{/\Brat\B/} matches @samp{crate}, but it does not match @samp{dirty rat}. @samp{\B} is essentially the opposite of @samp{\y}. @end table @@ -5862,14 +5845,14 @@ The operators are: @cindex backslash (@code{\}), @code{\`} operator (@command{gawk}) @cindex @code{\} (backslash), @code{\`} operator (@command{gawk}) Matches the empty string at the -beginning of a buffer (string). +beginning of a buffer (string) @c @cindex operators, @code{\'} (@command{gawk}) @cindex backslash (@code{\}), @code{\'} operator (@command{gawk}) @cindex @code{\} (backslash), @code{\'} operator (@command{gawk}) @item \' Matches the empty string at the -end of a buffer (string). +end of a buffer (string) @end table @cindex @code{^} (caret), regexp operator @@ -5932,15 +5915,11 @@ Allow interval expressions in regexps, if @option{--traditional} has been provided. Otherwise, interval expressions are available by default. @end table -@c ENDOFRANGE gregexp -@c ENDOFRANGE regexpg @node Case-sensitivity @section Case Sensitivity in Matching -@c STARTOFRANGE regexpcs @cindex regular expressions, case sensitivity -@c STARTOFRANGE csregexp @cindex case sensitivity, regexps and Case is normally significant in regular expressions, both when matching ordinary characters (i.e., not metacharacters) and inside bracket @@ -6032,8 +6011,6 @@ the right thing.} The value of @code{IGNORECASE} has no effect if @command{gawk} is in compatibility mode (@pxref{Options}). Case is always significant in compatibility mode. -@c ENDOFRANGE csregexp -@c ENDOFRANGE regexpcs @node Regexp Summary @section Summary @@ -6080,12 +6057,10 @@ versions, use @code{tolower()} or @code{toupper()}. @end itemize -@c ENDOFRANGE regexp @node Reading Files @chapter Reading Input Files -@c STARTOFRANGE infir @cindex reading input files @cindex input files, reading @cindex input files @@ -6110,7 +6085,7 @@ This makes it more convenient for programs to work on the parts of a record. @cindex @code{getline} command On rare occasions, you may need to use the @code{getline} command. -The @code{getline} command is valuable, both because it +The @code{getline} command is valuable both because it can do explicit input from any number of files, and because the files used with it do not have to be named on the @command{awk} command line (@pxref{Getline}). @@ -6136,9 +6111,7 @@ used with it do not have to be named on the @command{awk} command line @node Records @section How Input Is Split into Records -@c STARTOFRANGE inspl @cindex input, splitting into records -@c STARTOFRANGE recspl @cindex records, splitting input into @cindex @code{NR} variable @cindex @code{FNR} variable @@ -6163,8 +6136,8 @@ never automatically reset to zero. Records are separated by a character called the @dfn{record separator}. By default, the record separator is the newline character. This is why records are, by default, single lines. -A different character can be used for the record separator by -assigning the character to the predefined variable @code{RS}. +To use a different character for the record separator, +simply assign that character to the predefined variable @code{RS}. @cindex newlines, as record separators @cindex @code{RS} variable @@ -6187,8 +6160,8 @@ awk 'BEGIN @{ RS = "u" @} @noindent changes the value of @code{RS} to @samp{u}, before reading any input. -This is a string whose first character is the letter ``u''; as a result, records -are separated by the letter ``u.'' Then the input file is read, and the second +The new value is a string whose first character is the letter ``u''; as a result, records +are separated by the letter ``u''. Then the input file is read, and the second rule in the @command{awk} program (the action with no pattern) prints each record. Because each @code{print} statement adds a newline at the end of its output, this @command{awk} program copies the input @@ -6249,8 +6222,8 @@ Bill 555-1675 bill.drowning@@hotmail.com A @end example @noindent -It contains no @samp{u} so there is no reason to split the record, -unlike the others which have one or more occurrences of the @samp{u}. +It contains no @samp{u}, so there is no reason to split the record, +unlike the others, which each have one or more occurrences of the @samp{u}. In fact, this record is treated as part of the previous record; the newline separating them in the output is the original newline in the @value{DF}, not the one added by @@ -6345,7 +6318,7 @@ contains the same single character. However, when @code{RS} is a regular expression, @code{RT} contains the actual input text that matched the regular expression. -If the input file ended without any text that matches @code{RS}, +If the input file ends without any text matching @code{RS}, @command{gawk} sets @code{RT} to the null string. The following example illustrates both of these features. @@ -6438,8 +6411,6 @@ character as a record separator. However, this is a special case: whole files. If you are using @command{gawk}, see @DBREF{Extension Sample Readfile} for another option. @end sidebar -@c ENDOFRANGE inspl -@c ENDOFRANGE recspl @node Fields @section Examining Fields @@ -6447,7 +6418,6 @@ Readfile} for another option. @cindex examining fields @cindex fields @cindex accessing fields -@c STARTOFRANGE fiex @cindex fields, examining @cindex POSIX @command{awk}, field separators and @cindex field separators, POSIX and @@ -6472,11 +6442,11 @@ simple @command{awk} programs so powerful. @cindex @code{$} (dollar sign), @code{$} field operator @cindex dollar sign (@code{$}), @code{$} field operator @cindex field operators@comma{} dollar sign as -You use a dollar-sign (@samp{$}) +You use a dollar sign (@samp{$}) to refer to a field in an @command{awk} program, followed by the number of the field you want. Thus, @code{$1} refers to the first field, @code{$2} to the second, and so on. -(Unlike the Unix shells, the field numbers are not limited to single digits. +(Unlike in the Unix shells, the field numbers are not limited to single digits. @code{$127} is the 127th field in the record.) For example, suppose the following is a line of input: @@ -6502,7 +6472,7 @@ If you try to reference a field beyond the last one (such as @code{$8} when the record has only seven fields), you get the empty string. (If used in a numeric operation, you get zero.) -The use of @code{$0}, which looks like a reference to the ``zero-th'' field, is +The use of @code{$0}, which looks like a reference to the ``zeroth'' field, is a special case: it represents the whole input record. Use it when you are not interested in specific fields. Here are some more examples: @@ -6528,7 +6498,6 @@ $ @kbd{awk '/li/ @{ print $1, $NF @}' mail-list} @print{} Julie F @print{} Samuel A @end example -@c ENDOFRANGE fiex @node Nonconstant Fields @section Nonconstant Field Numbers @@ -6558,13 +6527,13 @@ awk '@{ print $(2*2) @}' mail-list @end example @command{awk} evaluates the expression @samp{(2*2)} and uses -its value as the number of the field to print. The @samp{*} sign +its value as the number of the field to print. The @samp{*} represents multiplication, so the expression @samp{2*2} evaluates to four. The parentheses are used so that the multiplication is done before the @samp{$} operation; they are necessary whenever there is a binary operator@footnote{A @dfn{binary operator}, such as @samp{*} for multiplication, is one that takes two operands. The distinction -is required, because @command{awk} also has unary (one-operand) +is required because @command{awk} also has unary (one-operand) and ternary (three-operand) operators.} in the field-number expression. This example, then, prints the type of relationship (the fourth field) for every line of the file @@ -6589,7 +6558,6 @@ evaluating @code{NF} and using its value as a field number. @node Changing Fields @section Changing the Contents of a Field -@c STARTOFRANGE ficon @cindex fields, changing contents of The contents of a field, as seen by @command{awk}, can be changed within an @command{awk} program; this changes what @command{awk} perceives as the @@ -6745,7 +6713,7 @@ rebuild @code{$0} when @code{NF} is decremented. Finally, there are times when it is convenient to force @command{awk} to rebuild the entire record, using the current -value of the fields and @code{OFS}. To do this, use the +values of the fields and @code{OFS}. To do this, use the seemingly innocuous assignment: @example @@ -6769,7 +6737,7 @@ such as @code{sub()} and @code{gsub()} It is important to remember that @code{$0} is the @emph{full} record, exactly as it was read from the input. This includes any leading or trailing whitespace, and the exact whitespace (or other -characters) that separate the fields. +characters) that separates the fields. It is a common error to try to change the field separators in a record simply by setting @code{FS} and @code{OFS}, and then @@ -6781,7 +6749,6 @@ itself. Instead, you must force the record to be rebuilt, typically with a statement such as @samp{$1 = $1}, as described earlier. @end sidebar -@c ENDOFRANGE ficon @node Field Separators @section Specifying How Fields Are Separated @@ -6797,9 +6764,7 @@ with a statement such as @samp{$1 = $1}, as described earlier. @cindex @code{FS} variable @cindex fields, separating -@c STARTOFRANGE fisepr @cindex field separators -@c STARTOFRANGE fisepg @cindex fields, separating The @dfn{field separator}, which is either a single character or a regular expression, controls the way @command{awk} splits an input record into fields. @@ -6865,7 +6830,7 @@ John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139 @end example @noindent -The same program would extract @samp{@bullet{}LXIX}, instead of +The same program would extract @samp{@bullet{}LXIX} instead of @samp{@bullet{}29@bullet{}Oak@bullet{}St.}. If you were expecting the program to print the address, you would be surprised. The moral is to choose your data layout and @@ -6899,9 +6864,7 @@ rules. @node Regexp Field Splitting @subsection Using Regular Expressions to Separate Fields -@c STARTOFRANGE regexpfs @cindex regular expressions, as field separators -@c STARTOFRANGE fsregexp @cindex field separators, regular expressions as The previous @value{SUBSECTION} discussed the use of single characters or simple strings as the @@ -7005,8 +6968,6 @@ $ @kbd{echo 'xxAA xxBxx C' |} @print{} -->xxBxx<-- @print{} -->C<-- @end example -@c ENDOFRANGE regexpfs -@c ENDOFRANGE fsregexp @node Single Character Fields @subsection Making Each Character a Separate Field @@ -7130,7 +7091,7 @@ choosing your field and record separators. @cindex Unix @command{awk}, password files@comma{} field separators and Perhaps the most common use of a single character as the field separator occurs when processing the Unix system password file. On many Unix -systems, each user has a separate entry in the system password file, one +systems, each user has a separate entry in the system password file, with one line per user. The information in these lines is separated by colons. The first field is the user's login name and the second is the user's encrypted or shadow password. (A shadow password is indicated by the @@ -7171,7 +7132,7 @@ When you do this, @code{$1} is the same as @code{$0}. According to the POSIX standard, @command{awk} is supposed to behave as if each record is split into fields at the time it is read. In particular, this means that if you change the value of @code{FS} -after a record is read, the value of the fields (i.e., how they were split) +after a record is read, the values of the fields (i.e., how they were split) should reflect the old value of @code{FS}, not the new one. @cindex dark corner, field separators @@ -7184,10 +7145,7 @@ using the @emph{current} value of @code{FS}! @value{DARKCORNER} This behavior can be difficult to diagnose. The following example illustrates the difference -between the two methods. -(The @command{sed}@footnote{The @command{sed} utility is a ``stream editor.'' -Its behavior is also defined by the POSIX standard.} -command prints just the first line of @file{/etc/passwd}.) +between the two methods: @example sed 1q /etc/passwd | awk '@{ FS = ":" ; print $1 @}' @@ -7207,6 +7165,10 @@ prints the full first line of the file, something like: @example root:x:0:0:Root:/: @end example + +(The @command{sed}@footnote{The @command{sed} utility is a ``stream editor.'' +Its behavior is also defined by the POSIX standard.} +command prints just the first line of @file{/etc/passwd}.) @end sidebar @node Field Splitting Summary @@ -7267,8 +7229,6 @@ do it for you (e.g., @samp{FS = "[c]"}). In this case, @code{IGNORECASE} will take effect. @end sidebar -@c ENDOFRANGE fisepr -@c ENDOFRANGE fisepg @node Constant Size @section Reading Fixed-Width Data @@ -7383,7 +7343,7 @@ In order to tell which kind of field splitting is in effect, use @code{PROCINFO["FS"]} (@pxref{Auto-set}). The value is @code{"FS"} if regular field splitting is being used, -or it is @code{"FIELDWIDTHS"} if fixed-width field splitting is being used: +or @code{"FIELDWIDTHS"} if fixed-width field splitting is being used: @example if (PROCINFO["FS"] == "FS") @@ -7419,14 +7379,14 @@ what they are, and not by what they are not. The most notorious such case is so-called @dfn{comma-separated values} (CSV) data. Many spreadsheet programs, for example, can export their data into text files, where each record is -terminated with a newline, and fields are separated by commas. If only -commas separated the data, there wouldn't be an issue. The problem comes when +terminated with a newline, and fields are separated by commas. If +commas only separated the data, there wouldn't be an issue. The problem comes when one of the fields contains an @emph{embedded} comma. In such cases, most programs embed the field in double quotes.@footnote{The CSV format lacked a formal standard definition for many years. @uref{http://www.ietf.org/rfc/rfc4180.txt, RFC 4180} standardizes the most common practices.} -So we might have data like this: +So, we might have data like this: @example @c file eg/misc/addresses.csv @@ -7512,8 +7472,8 @@ of cases, and the @command{gawk} developers are satisfied with that. @end quotation As written, the regexp used for @code{FPAT} requires that each field -have a least one character. A straightforward modification -(changing changed the first @samp{+} to @samp{*}) allows fields to be empty: +contain at least one character. A straightforward modification +(changing the first @samp{+} to @samp{*}) allows fields to be empty: @example FPAT = "([^,]*)|(\"[^\"]+\")" @@ -7523,20 +7483,17 @@ Finally, the @code{patsplit()} function makes the same functionality available for splitting regular strings (@pxref{String Functions}). To recap, @command{gawk} provides three independent methods -to split input records into fields. @command{gawk} uses whichever -mechanism was last chosen based on which of the three -variables---@code{FS}, @code{FIELDWIDTHS}, and @code{FPAT}---was +to split input records into fields. +The mechanism used is based on which of the three +variables---@code{FS}, @code{FIELDWIDTHS}, or @code{FPAT}---was last assigned to. @node Multiple Line @section Multiple-Line Records @cindex multiple-line records -@c STARTOFRANGE recm @cindex records, multiline -@c STARTOFRANGE imr @cindex input, multiline records -@c STARTOFRANGE frm @cindex files, reading, multiline records @cindex input, files, See input files In some databases, a single line cannot conveniently hold all the @@ -7571,7 +7528,7 @@ at the end of the record and one or more blank lines after the record. In addition, a regular expression always matches the longest possible sequence when there is a choice (@pxref{Leftmost Longest}). -So the next record doesn't start until +So, the next record doesn't start until the first nonblank line that follows---no matter how many blank lines appear in a row, they are considered one record separator. @@ -7586,10 +7543,10 @@ In the second case, this special processing is not done. @cindex field separator, in multiline records @cindex @code{FS}, in multiline records Now that the input is separated into records, the second step is to -separate the fields in the record. One way to do this is to divide each +separate the fields in the records. One way to do this is to divide each of the lines into fields in the normal manner. This happens by default as the result of a special feature. When @code{RS} is set to the empty -string, @emph{and} @code{FS} is set to a single character, +string @emph{and} @code{FS} is set to a single character, the newline character @emph{always} acts as a field separator. This is in addition to whatever field separations result from @code{FS}.@footnote{When @code{FS} is the null string (@code{""}) @@ -7604,7 +7561,7 @@ want the newline character to separate fields, because there is no way to prevent it. However, you can work around this by using the @code{split()} function to break up the record manually (@pxref{String Functions}). -If you have a single character field separator, you can work around +If you have a single-character field separator, you can work around the special feature in a different way, by making @code{FS} into a regexp for that single character. For example, if the field separator is a percent character, instead of @@ -7612,10 +7569,10 @@ separator is a percent character, instead of Another way to separate fields is to put each field on a separate line: to do this, just set the -variable @code{FS} to the string @code{"\n"}. (This single -character separator matches a single newline.) +variable @code{FS} to the string @code{"\n"}. +(This single-character separator matches a single newline.) A practical example of a @value{DF} organized this way might be a mailing -list, where each entry is separated by blank lines. Consider a mailing +list, where blank lines separate the entries. Consider a mailing list in a file named @file{addresses}, which looks like this: @example @@ -7703,20 +7660,15 @@ If not in compatibility mode (@pxref{Options}), @command{gawk} sets @code{RT} to the input text that matched the value specified by @code{RS}. But if the input file ended without any text that matches @code{RS}, then @command{gawk} sets @code{RT} to the null string. -@c ENDOFRANGE recm -@c ENDOFRANGE imr -@c ENDOFRANGE frm @node Getline @section Explicit Input with @code{getline} -@c STARTOFRANGE getl @cindex @code{getline} command, explicit input with -@c STARTOFRANGE inex @cindex input, explicit So far we have been getting our input data from @command{awk}'s main input stream---either the standard input (usually your keyboard, sometimes -the output from another program) or from the +the output from another program) or the files specified on the command line. The @command{awk} language has a special built-in command called @code{getline} that can be used to read input under your explicit control. @@ -7900,7 +7852,7 @@ free @end example The @code{getline} command used in this way sets only the variables -@code{NR}, @code{FNR}, and @code{RT} (and of course, @var{var}). +@code{NR}, @code{FNR}, and @code{RT} (and, of course, @var{var}). The record is not split into fields, so the values of the fields (including @code{$0}) and the value of @code{NF} do not change. @@ -7915,7 +7867,7 @@ the value of @code{NF} do not change. @cindex left angle bracket (@code{<}), @code{<} operator (I/O) @cindex operators, input/output Use @samp{getline < @var{file}} to read the next record from @var{file}. -Here @var{file} is a string-valued expression that +Here, @var{file} is a string-valued expression that specifies the @value{FN}. @samp{< @var{file}} is called a @dfn{redirection} because it directs input to come from a different place. For example, the following @@ -8093,7 +8045,7 @@ of a construct like @samp{@w{"echo "} "date" | getline}. Most versions, including the current version, treat it at as @samp{@w{("echo "} "date") | getline}. (This is also how BWK @command{awk} behaves.) -Some versions changed and treated it as +Some versions instead treat it as @samp{@w{"echo "} ("date" | getline)}. (This is how @command{mawk} behaves.) In short, @emph{always} use explicit parentheses, and then you won't @@ -8141,7 +8093,7 @@ program to be portable to other @command{awk} implementations. @cindex operators, input/output @cindex differences in @command{awk} and @command{gawk}, input/output operators -Input into @code{getline} from a pipe is a one-way operation. +Reading input into @code{getline} from a pipe is a one-way operation. The command that is started with @samp{@var{command} | getline} only sends data @emph{to} your @command{awk} program. @@ -8151,7 +8103,7 @@ for processing and then read the results back. communications are possible. This is done with the @samp{|&} operator. Typically, you write data to the coprocess first and then -read results back, as shown in the following: +read the results back, as shown in the following: @example print "@var{some query}" |& "db_server" @@ -8234,7 +8186,7 @@ also @pxref{Auto-set}.) @item Using @code{FILENAME} with @code{getline} (@samp{getline < FILENAME}) -is likely to be a source for +is likely to be a source of confusion. @command{awk} opens a separate input stream from the current input file. However, by not using a variable, @code{$0} and @code{NF} are still updated. If you're doing this, it's @@ -8242,9 +8194,15 @@ probably by accident, and you should reconsider what it is you're trying to accomplish. @item -@DBREF{Getline Summary} presents a table summarizing the +@ifdocbook +The next section +@end ifdocbook +@ifnotdocbook +@ref{Getline Summary}, +@end ifnotdocbook +presents a table summarizing the @code{getline} variants and which variables they can affect. -It is worth noting that those variants which do not use redirection +It is worth noting that those variants that do not use redirection can cause @code{FILENAME} to be updated if they cause @command{awk} to start reading a new input file. @@ -8253,7 +8211,7 @@ can cause @code{FILENAME} to be updated if they cause If the variable being assigned is an expression with side effects, different versions of @command{awk} behave differently upon encountering end-of-file. Some versions don't evaluate the expression; many versions -(including @command{gawk}) do. Here is an example, due to Duncan Moore: +(including @command{gawk}) do. Here is an example, courtesy of Duncan Moore: @ignore Date: Sun, 01 Apr 2012 11:49:33 +0100 @@ -8270,7 +8228,7 @@ BEGIN @{ @noindent Here, the side effect is the @samp{++c}. Is @code{c} incremented if -end of file is encountered, before the element in @code{a} is assigned? +end-of-file is encountered before the element in @code{a} is assigned? @command{gawk} treats @code{getline} like a function call, and evaluates the expression @samp{a[++c]} before attempting to read from @file{f}. @@ -8302,9 +8260,6 @@ Note: for each variant, @command{gawk} sets the @code{RT} predefined variable. @item @var{command} @code{|& getline} @var{var} @tab Sets @var{var} and @code{RT} @tab @command{gawk} @end multitable @end float -@c ENDOFRANGE getl -@c ENDOFRANGE inex -@c ENDOFRANGE infir @node Read Timeout @section Reading Input with a Timeout @@ -8315,8 +8270,8 @@ This @value{SECTION} describes a feature that is specific to @command{gawk}. You may specify a timeout in milliseconds for reading input from the keyboard, a pipe, or two-way communication, including TCP/IP sockets. This can be done -on a per input, command, or connection basis, by setting a special element -in the @code{PROCINFO} array (@pxref{Auto-set}): +on a per-input, per-command, or per-connection basis, by setting a special +element in the @code{PROCINFO} array (@pxref{Auto-set}): @example PROCINFO["input_name", "READ_TIMEOUT"] = @var{timeout in milliseconds} @@ -8347,7 +8302,7 @@ while ((getline < "/dev/stdin") > 0) @end example @command{gawk} terminates the read operation if input does not -arrive after waiting for the timeout period, returns failure +arrive after waiting for the timeout period, returns failure, and sets @code{ERRNO} to an appropriate string value. A negative or zero value for the timeout is the same as specifying no timeout at all. @@ -8397,7 +8352,7 @@ If the @code{PROCINFO} element is not present and the @command{gawk} uses its value to initialize the timeout value. The exclusive use of the environment variable to specify timeout has the disadvantage of not being able to control it -on a per command or connection basis. +on a per-command or per-connection basis. @command{gawk} considers a timeout event to be an error even though the attempt to read from the underlying device may @@ -8463,7 +8418,7 @@ The possibilities are as follows: @item After splitting the input into records, @command{awk} further splits -the record into individual fields, named @code{$1}, @code{$2}, and so +the records into individual fields, named @code{$1}, @code{$2}, and so on. @code{$0} is the whole record, and @code{NF} indicates how many fields there are. The default way to split fields is between whitespace characters. @@ -8479,12 +8434,12 @@ thing. Decrementing @code{NF} throws away fields and rebuilds the record. @item Field splitting is more complicated than record splitting: -@multitable @columnfractions .40 .45 .15 +@multitable @columnfractions .40 .40 .20 @headitem Field separator value @tab Fields are split @dots{} @tab @command{awk} / @command{gawk} @item @code{FS == " "} @tab On runs of whitespace @tab @command{awk} @item @code{FS == @var{any single character}} @tab On that character @tab @command{awk} @item @code{FS == @var{regexp}} @tab On text matching the regexp @tab @command{awk} -@item @code{FS == ""} @tab Each individual character is a separate field @tab @command{gawk} +@item @code{FS == ""} @tab Such that each individual character is a separate field @tab @command{gawk} @item @code{FIELDWIDTHS == @var{list of columns}} @tab Based on character position @tab @command{gawk} @item @code{FPAT == @var{regexp}} @tab On the text surrounding text matching the regexp @tab @command{gawk} @end multitable @@ -8501,11 +8456,11 @@ This can also be done using command-line variable assignment. Use @code{PROCINFO["FS"]} to see how fields are being split. @item -Use @code{getline} in its various forms to read additional records, +Use @code{getline} in its various forms to read additional records from the default input stream, from a file, or from a pipe or coprocess. @item -Use @code{PROCINFO[@var{file}, "READ_TIMEOUT"]} to cause reads to timeout +Use @code{PROCINFO[@var{file}, "READ_TIMEOUT"]} to cause reads to time out for @var{file}. @item @@ -8539,7 +8494,6 @@ That can be fixed by making one simple change. What is it? @node Printing @chapter Printing Output -@c STARTOFRANGE prnt @cindex printing @cindex output, printing, See printing One of the most common programming actions is to @dfn{print}, or output, @@ -8555,7 +8509,6 @@ columns, whether to use exponential notation or not, and so on. For printing with specifications, you need the @code{printf} statement (@pxref{Printf}). -@c STARTOFRANGE prnts @cindex @code{print} statement @cindex @code{printf} statement Besides basic and formatted printing, this @value{CHAPTER} @@ -8616,7 +8569,7 @@ space is printed between any two items. Note that the @code{print} statement is a statement and not an expression---you can't use it in the pattern part of a -@var{pattern}-@var{action} statement, for example. +pattern--action statement, for example. @node Print Examples @section @code{print} Statement Examples @@ -8735,7 +8688,6 @@ You can continue either a @code{print} or @code{printf} statement simply by putting a newline after any comma (@pxref{Statements/Lines}). @end quotation -@c ENDOFRANGE prnts @node Output Separators @section Output Separators @@ -8808,7 +8760,7 @@ runs together on a single line. @cindex numeric, output format @cindex formats@comma{} numeric output When printing numeric values with the @code{print} statement, -@command{awk} internally converts the number to a string of characters +@command{awk} internally converts each number to a string of characters and prints that string. @command{awk} uses the @code{sprintf()} function to do this conversion (@pxref{String Functions}). @@ -8848,7 +8800,6 @@ if @code{OFMT} contains anything but a floating-point conversion specification. @node Printf @section Using @code{printf} Statements for Fancier Printing -@c STARTOFRANGE printfs @cindex @code{printf} statement @cindex output, formatted @cindex formatting output @@ -8880,7 +8831,7 @@ printf @var{format}, @var{item1}, @var{item2}, @dots{} @noindent As for @code{print}, the entire list of arguments may optionally be enclosed in parentheses. Here too, the parentheses are necessary if any -of the item expressions use the @samp{>} relational operator; otherwise, +of the item expressions uses the @samp{>} relational operator; otherwise, it can be confused with an output redirection (@pxref{Redirection}). @cindex format specifiers @@ -8911,7 +8862,7 @@ $ @kbd{awk 'BEGIN @{} @end example @noindent -Here, neither the @samp{+} nor the @samp{OUCH!} appear in +Here, neither the @samp{+} nor the @samp{OUCH!} appears in the output message. @node Control Letters @@ -8958,8 +8909,8 @@ The two control letters are equivalent. (The @samp{%i} specification is for compatibility with ISO C.) @item @code{%e}, @code{%E} -Print a number in scientific (exponential) notation; -for example: +Print a number in scientific (exponential) notation. +For example: @example printf "%4.3e\n", 1950 @@ -8996,7 +8947,7 @@ The special ``not a number'' value formats as @samp{-nan} or @samp{nan} (@pxref{Math Definitions}). @item @code{%F} -Like @samp{%f} but the infinity and ``not a number'' values are spelled +Like @samp{%f}, but the infinity and ``not a number'' values are spelled using uppercase letters. The @samp{%F} format is a POSIX extension to ISO C; not all systems @@ -9046,7 +8997,6 @@ values or do something else entirely. @node Format Modifiers @subsection Modifiers for @code{printf} Formats -@c STARTOFRANGE pfm @cindex @code{printf} statement, modifiers @cindex modifiers@comma{} in format specifiers A format specification can also include @dfn{modifiers} that can control @@ -9085,7 +9035,7 @@ messages at runtime. which describes how and why to use positional specifiers. For now, we ignore them. -@item - (Minus) +@item - @r{(Minus)} The minus sign, used before the width modifier (see later on in this list), says to left-justify @@ -9241,7 +9191,7 @@ printf "%" w "." p "s\n", s @end example @noindent -This is not particularly easy to read but it does work. +This is not particularly easy to read, but it does work. @c @cindex lint checks @cindex troubleshooting, fatal errors, @code{printf} format strings @@ -9252,7 +9202,6 @@ format strings. These are not valid in @command{awk}. Most @command{awk} implementations silently ignore them. If @option{--lint} is provided on the command line (@pxref{Options}), @command{gawk} warns about their use. If @option{--posix} is supplied, their use is a fatal error. -@c ENDOFRANGE pfm @node Printf Examples @subsection Examples Using @code{printf} @@ -9288,7 +9237,7 @@ $ @kbd{awk '@{ printf "%-10s %s\n", $1, $2 @}' mail-list} @end example In this case, the phone numbers had to be printed as strings because -the numbers are separated by a dash. Printing the phone numbers as +the numbers are separated by dashes. Printing the phone numbers as numbers would have produced just the first three digits: @samp{555}. This would have been pretty confusing. @@ -9333,14 +9282,11 @@ awk 'BEGIN @{ format = "%-10s %s\n" @{ printf format, $1, $2 @}' mail-list @end example -@c ENDOFRANGE printfs @node Redirection @section Redirecting Output of @code{print} and @code{printf} -@c STARTOFRANGE outre @cindex output redirection -@c STARTOFRANGE reout @cindex redirection of output @cindex @option{--sandbox} option, output redirection with @code{print}, @code{printf} So far, the output from @code{print} and @code{printf} has gone @@ -9351,7 +9297,7 @@ This is called @dfn{redirection}. @quotation NOTE When @option{--sandbox} is specified (@pxref{Options}), -redirecting output to files, pipes and coprocesses is disabled. +redirecting output to files, pipes, and coprocesses is disabled. @end quotation A redirection appears after the @code{print} or @code{printf} statement. @@ -9404,7 +9350,7 @@ Each output file contains one name or number per line. @cindex @code{>} (right angle bracket), @code{>>} operator (I/O) @cindex right angle bracket (@code{>}), @code{>>} operator (I/O) @item print @var{items} >> @var{output-file} -This redirection prints the items into the pre-existing output file +This redirection prints the items into the preexisting output file named @var{output-file}. The difference between this and the single-@samp{>} redirection is that the old contents (if any) of @var{output-file} are not erased. Instead, the @command{awk} output is @@ -9443,7 +9389,7 @@ The unsorted list is written with an ordinary redirection, while the sorted list is written by piping through the @command{sort} utility. The next example uses redirection to mail a message to the mailing -list @samp{bug-system}. This might be useful when trouble is encountered +list @code{bug-system}. This might be useful when trouble is encountered in an @command{awk} script run periodically for system maintenance: @example @@ -9474,15 +9420,23 @@ This redirection prints the items to the input of @var{command}. The difference between this and the single-@samp{|} redirection is that the output from @var{command} can be read with @code{getline}. -Thus @var{command} is a @dfn{coprocess}, which works together with, -but subsidiary to, the @command{awk} program. +Thus, @var{command} is a @dfn{coprocess}, which works together with +but is subsidiary to the @command{awk} program. This feature is a @command{gawk} extension, and is not available in POSIX @command{awk}. -@DBXREF{Getline/Coprocess} +@ifnotdocbook +@xref{Getline/Coprocess}, for a brief discussion. -@DBXREF{Two-way I/O} +@xref{Two-way I/O}, +for a more complete discussion. +@end ifnotdocbook +@ifdocbook +@DBXREF{Getline/Coprocess} +for a brief discussion and +@DBREF{Two-way I/O} for a more complete discussion. +@end ifdocbook @end table Redirecting output using @samp{>}, @samp{>>}, @samp{|}, or @samp{|&} @@ -9507,7 +9461,7 @@ This is indeed how redirections must be used from the shell. But in @command{awk}, it isn't necessary. In this kind of case, a program should use @samp{>} for all the @code{print} statements, because the output file is only opened once. (It happens that if you mix @samp{>} and @samp{>>} -that output is produced in the expected order. However, mixing the operators +output is produced in the expected order. However, mixing the operators for the same file is definitely poor style, and is confusing to readers of your program.) @@ -9557,11 +9511,9 @@ It then sends the list to the shell for execution. @DBXREF{Shell Quoting} for a function that can help in generating command lines to be fed to the shell. @end sidebar -@c ENDOFRANGE outre -@c ENDOFRANGE reout @node Special FD -@section Special Files for Standard Pre-Opened Data Streams +@section Special Files for Standard Preopened Data Streams @cindex standard input @cindex input, standard @cindex standard output @@ -9574,7 +9526,7 @@ command lines to be fed to the shell. Running programs conventionally have three input and output streams already available to them for reading and writing. These are known as the @dfn{standard input}, @dfn{standard output}, and @dfn{standard -error output}. These open streams (and any other open file or pipe) +error output}. These open streams (and any other open files or pipes) are often referred to by the technical term @dfn{file descriptors}. These streams are, by default, connected to your keyboard and screen, but @@ -9612,7 +9564,7 @@ that is connected to your keyboard and screen. It represents the ``terminal,''@footnote{The ``tty'' in @file{/dev/tty} stands for ``Teletype,'' a serial terminal.} which on modern systems is a keyboard and screen, not a serial console.) -This generally has the same effect but not always: although the +This generally has the same effect, but not always: although the standard error stream is usually the screen, it can be redirected; when that happens, writing to the screen is not correct. In fact, if @command{awk} is run from a background job, it may not have a @@ -9657,7 +9609,7 @@ print "Serious error detected!" > "/dev/stderr" @cindex troubleshooting, quotes with file names Note the use of quotes around the @value{FN}. -Like any other redirection, the value must be a string. +Like with any other redirection, the value must be a string. It is a common error to omit the quotes, which leads to confusing results. @@ -9668,7 +9620,6 @@ invoked with the @option{--traditional} option (@pxref{Options}). @node Special Files @section Special @value{FFN}s in @command{gawk} -@c STARTOFRANGE gfn @cindex @command{gawk}, file names in Besides access to standard input, standard output, and standard error, @@ -9684,7 +9635,7 @@ TCP/IP networking. @end menu @node Other Inherited Files -@subsection Accessing Other Open Files With @command{gawk} +@subsection Accessing Other Open Files with @command{gawk} Besides the @code{/dev/stdin}, @code{/dev/stdout}, and @code{/dev/stderr} special @value{FN}s mentioned earlier, @command{gawk} provides syntax @@ -9741,7 +9692,7 @@ special @value{FN}s that @command{gawk} provides: @cindex compatibility mode (@command{gawk}), file names @cindex file names, in compatibility mode @item -Recognition of the @value{FN}s for the three standard pre-opened +Recognition of the @value{FN}s for the three standard preopened files is disabled only in POSIX mode. @item @@ -9754,23 +9705,18 @@ compatibility mode (either @option{--traditional} or @option{--posix}; interprets these special @value{FN}s. For example, using @samp{/dev/fd/4} for output actually writes on file descriptor 4, and not on a new -file descriptor that is @code{dup()}'ed from file descriptor 4. Most of +file descriptor that is @code{dup()}ed from file descriptor 4. Most of the time this does not matter; however, it is important to @emph{not} close any of the files related to file descriptors 0, 1, and 2. Doing so results in unpredictable behavior. @end itemize -@c ENDOFRANGE gfn @node Close Files And Pipes @section Closing Input and Output Redirections @cindex files, output, See output files -@c STARTOFRANGE ifc @cindex input files, closing -@c STARTOFRANGE ofc @cindex output, files@comma{} closing -@c STARTOFRANGE pc @cindex pipe, closing -@c STARTOFRANGE cc @cindex coprocesses, closing @cindex @code{getline} command, coprocesses@comma{} using from @@ -9976,18 +9922,14 @@ This value is zero if the close succeeds, or @minus{}1 if it fails. The POSIX standard is very vague; it says that @code{close()} -returns zero on success and nonzero otherwise. In general, +returns zero on success and a nonzero value otherwise. In general, different implementations vary in what they report when closing -pipes; thus the return value cannot be used portably. +pipes; thus, the return value cannot be used portably. @value{DARKCORNER} In POSIX mode (@pxref{Options}), @command{gawk} just returns zero when closing a pipe. @end sidebar -@c ENDOFRANGE ifc -@c ENDOFRANGE ofc -@c ENDOFRANGE pc -@c ENDOFRANGE cc @node Output Summary @section Summary @@ -10001,8 +9943,8 @@ for numeric values for the @code{print} statement. @item The @code{printf} statement provides finer-grained control over output, -with format control letters for different data types and various flags -that modify the behavior of the format control letters. +with format-control letters for different data types and various flags +that modify the behavior of the format-control letters. @item Output from both @code{print} and @code{printf} may be redirected to @@ -10051,11 +9993,9 @@ BEGIN @{ print "Serious error detected!" > /dev/stderr @} @end enumerate @c EXCLUDE END -@c ENDOFRANGE prnt @node Expressions @chapter Expressions -@c STARTOFRANGE exps @cindex expressions Expressions are the basic building blocks of @command{awk} patterns @@ -10066,7 +10006,7 @@ can assign a new value to a variable or a field by using an assignment operator. An expression can serve as a pattern or action statement on its own. Most other kinds of statements contain one or more expressions that specify the data on which to -operate. As in other languages, expressions in @command{awk} include +operate. As in other languages, expressions in @command{awk} can include variables, array references, constants, and function calls, as well as combinations of these with various operators. @@ -10085,7 +10025,7 @@ combinations of these with various operators. Expressions are built up from values and the operations performed upon them. This @value{SECTION} describes the elementary objects -which provide the values used in expressions. +that provide the values used in expressions. @menu * Constants:: String, numeric and regexp constants. @@ -10098,7 +10038,6 @@ which provide the values used in expressions. @node Constants @subsection Constant Expressions -@c STARTOFRANGE cnst @cindex constants, types of The simplest type of expression is the @dfn{constant}, which always has @@ -10136,7 +10075,7 @@ have the same value: @end example @cindex string constants -A string constant consists of a sequence of characters enclosed in +A @dfn{string constant} consists of a sequence of characters enclosed in double quotation marks. For example: @example @@ -10148,7 +10087,7 @@ double quotation marks. For example: @cindex strings, length limitations represents the string whose contents are @samp{parrot}. Strings in @command{gawk} can be of any length, and they can contain any of the possible -eight-bit ASCII characters including ASCII @sc{nul} (character code zero). +eight-bit ASCII characters, including ASCII @sc{nul} (character code zero). Other @command{awk} implementations may have difficulty with some character codes. @@ -10163,15 +10102,15 @@ In @command{awk}, all numbers are in decimal (i.e., base 10). Many other programming languages allow you to specify numbers in other bases, often octal (base 8) and hexadecimal (base 16). In octal, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, and so on. -Just as @samp{11}, in decimal, is 1 times 10 plus 1, so -@samp{11}, in octal, is 1 times 8, plus 1. This equals 9 in decimal. +Just as @samp{11} in decimal is 1 times 10 plus 1, so +@samp{11} in octal is 1 times 8 plus 1. This equals 9 in decimal. In hexadecimal, there are 16 digits. Because the everyday decimal number system only has ten digits (@samp{0}--@samp{9}), the letters @samp{a} through @samp{f} are used to represent the rest. (Case in the letters is usually irrelevant; hexadecimal @samp{a} and @samp{A} have the same value.) -Thus, @samp{11}, in -hexadecimal, is 1 times 16 plus 1, which equals 17 in decimal. +Thus, @samp{11} in +hexadecimal is 1 times 16 plus 1, which equals 17 in decimal. Just by looking at plain @samp{11}, you can't tell what base it's in. So, in C, C++, and other languages derived from C, @@ -10182,13 +10121,13 @@ and hexadecimal numbers start with a leading @samp{0x} or @samp{0X}: @table @code @item 11 -Decimal value 11. +Decimal value 11 @item 011 -Octal 11, decimal value 9. +Octal 11, decimal value 9 @item 0x11 -Hexadecimal 11, decimal value 17. +Hexadecimal 11, decimal value 17 @end table This example shows the difference: @@ -10216,11 +10155,11 @@ you can use the @code{strtonum()} function (@pxref{String Functions}) to convert the data into a number. Most of the time, you will want to use octal or hexadecimal constants -when working with the built-in bit manipulation functions; +when working with the built-in bit-manipulation functions; see @DBREF{Bitwise Functions} for more information. -Unlike some early C implementations, @samp{8} and @samp{9} are not +Unlike in some early C implementations, @samp{8} and @samp{9} are not valid in octal constants. For example, @command{gawk} treats @samp{018} as decimal 18: @@ -10255,19 +10194,17 @@ $ @kbd{gawk 'BEGIN @{ printf "0x11 is <%s>\n", 0x11 @}'} @node Regexp Constants @subsubsection Regular Expression Constants -@c STARTOFRANGE rec @cindex regexp constants @cindex @code{~} (tilde), @code{~} operator @cindex tilde (@code{~}), @code{~} operator @cindex @code{!} (exclamation point), @code{!~} operator @cindex exclamation point (@code{!}), @code{!~} operator -A regexp constant is a regular expression description enclosed in +A @dfn{regexp constant} is a regular expression description enclosed in slashes, such as @code{@w{/^beginning and end$/}}. Most regexps used in @command{awk} programs are constant, but the @samp{~} and @samp{!~} matching operators can also match computed or dynamic regexps (which are typically just ordinary strings or variables that contain a regexp, -but could be a more complex expression). -@c ENDOFRANGE cnst +but could be more complex expressions). @node Using Constant Regexps @subsection Using Regular Expression Constants @@ -10347,7 +10284,7 @@ the third argument of @code{split()} to be a regexp constant, but some older implementations do not. @value{DARKCORNER} Because some built-in functions accept regexp constants as arguments, -it can be confusing when attempting to use regexp constants as arguments +confusion can arise when attempting to use regexp constants as arguments to user-defined functions (@pxref{User-defined}). For example: @example @@ -10373,19 +10310,18 @@ function mysub(pat, repl, str, global) In this example, the programmer wants to pass a regexp constant to the user-defined function @code{mysub()}, which in turn passes it on to either @code{sub()} or @code{gsub()}. However, what really happens is that -the @code{pat} parameter is either one or zero, depending upon whether +the @code{pat} parameter is assigned a value of either one or zero, depending upon whether or not @code{$0} matches @code{/hi/}. @command{gawk} issues a warning when it sees a regexp constant used as a parameter to a user-defined function, because passing a truth value in this way is probably not what was intended. -@c ENDOFRANGE rec @node Variables @subsection Variables @cindex variables, user-defined @cindex user-defined, variables -Variables are ways of storing values at one point in your program for +@dfn{Variables} are ways of storing values at one point in your program for use later in another part of your program. They can be manipulated entirely within the program text, and they can also be assigned values on the @command{awk} command line. @@ -10413,17 +10349,17 @@ are distinct variables. A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with @dfn{assignment operators}, @dfn{increment operators}, and -@dfn{decrement operators}. -@xref{Assignment Ops}. +@dfn{decrement operators} +(@pxref{Assignment Ops}). In addition, the @code{sub()} and @code{gsub()} functions can change a variable's value, and the @code{match()}, @code{split()}, and @code{patsplit()} functions can change the contents of their -array parameters. @xref{String Functions}. +array parameters (@pxref{String Functions}). @cindex variables, built-in @cindex variables, initializing A few variables have special built-in meanings, such as @code{FS} (the -field separator), and @code{NF} (the number of fields in the current input +field separator) and @code{NF} (the number of fields in the current input record). @DBXREF{Built-in Variables} for a list of the predefined variables. These predefined variables can be used and assigned just like all other variables, but their values are also used or changed automatically by @@ -10651,7 +10587,7 @@ point, so the default behavior was restored to use a period as the decimal point character. You can use the @option{--use-lc-numeric} option (@pxref{Options}) to force @command{gawk} to use the locale's decimal point character. (@command{gawk} also uses the locale's decimal -point character when in POSIX mode, either via @option{--posix}, or the +point character when in POSIX mode, either via @option{--posix} or the @env{POSIXLY_CORRECT} environment variable, as shown previously.) @ref{table-locale-affects} describes the cases in which the locale's decimal @@ -10669,7 +10605,7 @@ features have not been described yet. @end multitable @end float -Finally, modern day formal standards and IEEE standard floating-point +Finally, modern-day formal standards and the IEEE standard floating-point representation can have an unusual but important effect on the way @command{gawk} converts some special string values to numbers. The details are presented in @ref{POSIX Floating Point Problems}. @@ -10677,7 +10613,7 @@ are presented in @ref{POSIX Floating Point Problems}. @node All Operators @section Operators: Doing Something with Values -This @value{SECTION} introduces the @dfn{operators} which make use +This @value{SECTION} introduces the @dfn{operators} that make use of the values provided by constants and variables. @menu @@ -10855,7 +10791,7 @@ print "something meaningful" > file name @noindent This produces a syntax error with some versions of Unix @command{awk}.@footnote{It happens that BWK -@command{awk}, @command{gawk} and @command{mawk} all ``get it right,'' +@command{awk}, @command{gawk}, and @command{mawk} all ``get it right,'' but you should not rely on this.} It is necessary to use the following: @@ -10944,11 +10880,8 @@ you're never quite sure what you'll get. @node Assignment Ops @subsection Assignment Expressions -@c STARTOFRANGE asop @cindex assignment operators -@c STARTOFRANGE opas @cindex operators, assignment -@c STARTOFRANGE exas @cindex expressions, assignment @cindex @code{=} (equals sign), @code{=} operator @cindex equals sign (@code{=}), @code{=} operator @@ -11108,7 +11041,7 @@ and @ifdocbook @DBREF{Numeric Functions} @end ifdocbook -for more information). +for more information.) This example illustrates an important fact about assignment operators: the lefthand expression is only evaluated @emph{once}. @@ -11144,17 +11077,17 @@ to a number. @caption{Arithmetic assignment operators} @multitable @columnfractions .30 .70 @headitem Operator @tab Effect -@item @var{lvalue} @code{+=} @var{increment} @tab Add @var{increment} to the value of @var{lvalue} -@item @var{lvalue} @code{-=} @var{decrement} @tab Subtract @var{decrement} from the value of @var{lvalue} -@item @var{lvalue} @code{*=} @var{coefficient} @tab Multiply the value of @var{lvalue} by @var{coefficient} -@item @var{lvalue} @code{/=} @var{divisor} @tab Divide the value of @var{lvalue} by @var{divisor} -@item @var{lvalue} @code{%=} @var{modulus} @tab Set @var{lvalue} to its remainder by @var{modulus} +@item @var{lvalue} @code{+=} @var{increment} @tab Add @var{increment} to the value of @var{lvalue}. +@item @var{lvalue} @code{-=} @var{decrement} @tab Subtract @var{decrement} from the value of @var{lvalue}. +@item @var{lvalue} @code{*=} @var{coefficient} @tab Multiply the value of @var{lvalue} by @var{coefficient}. +@item @var{lvalue} @code{/=} @var{divisor} @tab Divide the value of @var{lvalue} by @var{divisor}. +@item @var{lvalue} @code{%=} @var{modulus} @tab Set @var{lvalue} to its remainder by @var{modulus}. @cindex common extensions, @code{**=} operator @cindex extensions, common@comma{} @code{**=} operator @cindex @command{awk} language, POSIX version @cindex POSIX @command{awk} -@item @var{lvalue} @code{^=} @var{power} @tab -@item @var{lvalue} @code{**=} @var{power} @tab Raise @var{lvalue} to the power @var{power} @value{COMMONEXT} +@item @var{lvalue} @code{^=} @var{power} @tab Raise @var{lvalue} to the power @var{power}. +@item @var{lvalue} @code{**=} @var{power} @tab Raise @var{lvalue} to the power @var{power}. @value{COMMONEXT} @end multitable @end float @@ -11202,16 +11135,11 @@ awk '/[=]=/' /dev/null @command{gawk} does not have this problem; BWK @command{awk} and @command{mawk} also do not. @end sidebar -@c ENDOFRANGE exas -@c ENDOFRANGE opas -@c ENDOFRANGE asop @node Increment Ops @subsection Increment and Decrement Operators -@c STARTOFRANGE inop @cindex increment operators -@c STARTOFRANGE opde @cindex operators, decrement/increment @dfn{Increment} and @dfn{decrement operators} increase or decrease the value of a variable by one. An assignment operator can do the same thing, so @@ -11259,7 +11187,6 @@ just like variables. (Use @samp{$(i++)} when you want to do a field reference and a variable increment at the same time. The parentheses are necessary because of the precedence of the field reference operator @samp{$}.) -@c STARTOFRANGE deop @cindex decrement operators The decrement operator @samp{--} works just like @samp{++}, except that it subtracts one instead of adding it. As with @samp{++}, it can be used before @@ -11299,8 +11226,8 @@ like @samp{@var{lvalue}++}, but instead of adding, it subtracts.) @cindex evaluation order @cindex Marx, Groucho @quotation -@i{Doctor, doctor! It hurts when I do this!@* -So don't do that!} +@i{Doctor, it hurts when I do this!@* +Then don't do that!} @author Groucho Marx @end quotation @@ -11324,7 +11251,7 @@ print b @cindex side effects In other words, when do the various side effects prescribed by the postfix operators (@samp{b++}) take effect? -When side effects happen is @dfn{implementation defined}. +When side effects happen is @dfn{implementation-defined}. In other words, it is up to the particular version of @command{awk}. The result for the first example may be 12 or 13, and for the second, it may be 22 or 23. @@ -11335,15 +11262,12 @@ You should avoid such things in your own programs. @c You'll sleep better at night and be able to look at yourself @c in the mirror in the morning. @end sidebar -@c ENDOFRANGE inop -@c ENDOFRANGE opde -@c ENDOFRANGE deop @node Truth Values and Conditions @section Truth Values and Conditions -In certain contexts, expression values also serve as ``truth values''; (i.e., -they determine what should happen next as the program runs). This +In certain contexts, expression values also serve as ``truth values''; i.e., +they determine what should happen next as the program runs. This @value{SECTION} describes how @command{awk} defines ``true'' and ``false'' and how values are compared. @@ -11402,19 +11326,15 @@ the string constant @code{"0"} is actually true, because it is non-null. @author Douglas Adams, @cite{The Hitchhiker's Guide to the Galaxy} @end quotation -@c STARTOFRANGE comex @cindex comparison expressions -@c STARTOFRANGE excom @cindex expressions, comparison @cindex expressions, matching, See comparison expressions @cindex matching, expressions, See comparison expressions @cindex relational operators, See comparison operators @cindex operators, relational, See operators@comma{} comparison -@c STARTOFRANGE varting @cindex variable typing -@c STARTOFRANGE vartypc @cindex variables, types of, comparison expressions and -Unlike other programming languages, @command{awk} variables do not have a +Unlike in other programming languages, in @command{awk} variables do not have a fixed type. Instead, they can be either a number or a string, depending upon the value that is assigned to them. We look now at how variables are typed, and how @command{awk} @@ -11443,20 +11363,20 @@ Variable typing follows these rules: @itemize @value{BULLET} @item -A numeric constant or the result of a numeric operation has the @var{numeric} +A numeric constant or the result of a numeric operation has the @dfn{numeric} attribute. @item -A string constant or the result of a string operation has the @var{string} +A string constant or the result of a string operation has the @dfn{string} attribute. @item Fields, @code{getline} input, @code{FILENAME}, @code{ARGV} elements, @code{ENVIRON} elements, and the elements of an array created by @code{match()}, @code{split()}, and @code{patsplit()} that are numeric -strings have the @var{strnum} attribute. Otherwise, they have -the @var{string} attribute. Uninitialized variables also have the -@var{strnum} attribute. +strings have the @dfn{strnum} attribute. Otherwise, they have +the @dfn{string} attribute. Uninitialized variables also have the +@dfn{strnum} attribute. @item Attributes propagate across assignments but are not changed by @@ -11600,13 +11520,13 @@ constant, then a string comparison is performed. Otherwise, a numeric comparison is performed. This point bears additional emphasis: All user input is made of characters, -and so is first and foremost of @var{string} type; input strings -that look numeric are additionally given the @var{strnum} attribute. +and so is first and foremost of string type; input strings +that look numeric are additionally given the strnum attribute. Thus, the six-character input string @w{@samp{ +3.14}} receives the -@var{strnum} attribute. In contrast, the eight characters +strnum attribute. In contrast, the eight characters @w{@code{" +3.14"}} appearing in program text comprise a string constant. The following examples print @samp{1} when the comparison between -the two different constants is true, @samp{0} otherwise: +the two different constants is true, and @samp{0} otherwise: @c 22.9.2014: Tested with mawk and BWK awk, got same results. @example @@ -11736,7 +11656,7 @@ $ @kbd{echo 1e2 3 | awk '@{ print ($1 < $2) ? "true" : "false" @}'} @noindent the result is @samp{false} because both @code{$1} and @code{$2} are user input. They are numeric strings---therefore both have -the @var{strnum} attribute, dictating a numeric comparison. +the strnum attribute, dictating a numeric comparison. The purpose of the comparison rules and the use of numeric strings is to attempt to produce the behavior that is ``least surprising,'' while still ``doing the right thing.'' @@ -11795,7 +11715,7 @@ characters sort, as defined by the locale (for more discussion, @pxref{Locales}). This order is usually very different from the results obtained when doing straight character-by-character comparison.@footnote{Technically, string comparison is supposed -to behave the same way as if the strings are compared with the C +to behave the same way as if the strings were compared with the C @code{strcoll()} function.} Because this behavior differs considerably from existing practice, @@ -11812,19 +11732,13 @@ $ @kbd{gawk --posix 'BEGIN @{ printf("ABC < abc = %s\n",} @print{} ABC < abc = FALSE @end example -@c ENDOFRANGE comex -@c ENDOFRANGE excom -@c ENDOFRANGE vartypc -@c ENDOFRANGE varting @node Boolean Ops @subsection Boolean Expressions @cindex and Boolean-logic operator @cindex or Boolean-logic operator @cindex not Boolean-logic operator -@c STARTOFRANGE exbo @cindex expressions, Boolean -@c STARTOFRANGE boex @cindex Boolean expressions @cindex operators, Boolean, See Boolean expressions @cindex Boolean operators, See Boolean expressions @@ -11908,7 +11822,7 @@ BEGIN @{ if (! ("HOME" in ENVIRON)) @cindex vertical bar (@code{|}), @code{||} operator The @samp{&&} and @samp{||} operators are called @dfn{short-circuit} operators because of the way they work. Evaluation of the full expression -is ``short-circuited'' if the result can be determined part way through +is ``short-circuited'' if the result can be determined partway through its evaluation. @cindex line continuations @@ -11970,8 +11884,6 @@ next record, and start processing the rules over again at the top. The reason it's there is to avoid printing the bracketing @samp{START} and @samp{END} lines. @end quotation -@c ENDOFRANGE exbo -@c ENDOFRANGE boex @node Conditional Exp @subsection Conditional Expressions @@ -11982,8 +11894,8 @@ The reason it's there is to avoid printing the bracketing A @dfn{conditional expression} is a special kind of expression that has three operands. It allows you to use one expression's value to select one of two other expressions. -The conditional expression is the same as in the C language, -as shown here: +The conditional expression in @command{awk} is the same as in the C +language, as shown here: @example @var{selector} ? @var{if-true-exp} : @var{if-false-exp} @@ -11992,8 +11904,8 @@ as shown here: @noindent There are three subexpressions. The first, @var{selector}, is always computed first. If it is ``true'' (not zero or not null), then -@var{if-true-exp} is computed next and its value becomes the value of -the whole expression. Otherwise, @var{if-false-exp} is computed next +@var{if-true-exp} is computed next, and its value becomes the value of +the whole expression. Otherwise, @var{if-false-exp} is computed next, and its value becomes the value of the whole expression. For example, the following expression produces the absolute value of @code{x}: @@ -12041,7 +11953,7 @@ ask for it by name at any point in the program. For example, the function @code{sqrt()} computes the square root of a number. @cindex functions, built-in -A fixed set of functions are @dfn{built-in}, which means they are +A fixed set of functions are @dfn{built in}, which means they are available in every @command{awk} program. The @code{sqrt()} function is one of these. @DBXREF{Built-in} for a list of built-in functions and their descriptions. In addition, you can define @@ -12150,9 +12062,7 @@ $ @kbd{awk -f matchit.awk} @node Precedence @section Operator Precedence (How Operators Nest) -@c STARTOFRANGE prec @cindex precedence -@c STARTOFRANGE oppr @cindex operators, precedence @dfn{Operator precedence} determines how operators are grouped when @@ -12217,7 +12127,7 @@ Increment, decrement. @cindex @code{*} (asterisk), @code{**} operator @cindex asterisk (@code{*}), @code{**} operator @item @code{^ **} -Exponentiation. These operators group right-to-left. +Exponentiation. These operators group right to left. @cindex @code{+} (plus sign), @code{+} operator @cindex plus sign (@code{+}), @code{+} operator @@ -12283,7 +12193,7 @@ statements belong to the statement level, not to expressions. The redirection does not produce an expression that could be the operand of another operator. As a result, it does not make sense to use a redirection operator near another operator of lower precedence without -parentheses. Such combinations (e.g., @samp{print foo > a ? b : c}), +parentheses. Such combinations (e.g., @samp{print foo > a ? b : c}) result in syntax errors. The correct way to write this statement is @samp{print foo > (a ? b : c)}. @@ -12301,17 +12211,17 @@ Array membership. @cindex @code{&} (ampersand), @code{&&} operator @cindex ampersand (@code{&}), @code{&&} operator @item @code{&&} -Logical ``and''. +Logical ``and.'' @cindex @code{|} (vertical bar), @code{||} operator @cindex vertical bar (@code{|}), @code{||} operator @item @code{||} -Logical ``or''. +Logical ``or.'' @cindex @code{?} (question mark), @code{?:} operator @cindex question mark (@code{?}), @code{?:} operator @item @code{?:} -Conditional. This operator groups right-to-left. +Conditional. This operator groups right to left. @cindex @code{+} (plus sign), @code{+=} operator @cindex plus sign (@code{+}), @code{+=} operator @@ -12328,7 +12238,7 @@ Conditional. This operator groups right-to-left. @cindex @code{^} (caret), @code{^=} operator @cindex caret (@code{^}), @code{^=} operator @item @code{= += -= *= /= %= ^= **=} -Assignment. These operators group right-to-left. +Assignment. These operators group right to left. @end table @cindex POSIX @command{awk}, @code{**} operator and @@ -12337,8 +12247,6 @@ Assignment. These operators group right-to-left. The @samp{|&}, @samp{**}, and @samp{**=} operators are not specified by POSIX. For maximum portability, do not use them. @end quotation -@c ENDOFRANGE prec -@c ENDOFRANGE oppr @node Locales @section Where You Are Makes a Difference @@ -12404,8 +12312,8 @@ Locales can influence the conversions. @item @command{awk} provides the usual arithmetic operators (addition, subtraction, multiplication, division, modulus), and unary plus and minus. -It also provides comparison operators, boolean operators, array membership -testing, and regexp +It also provides comparison operators, Boolean operators, an array membership +testing operator, and regexp matching operators. String concatenation is accomplished by placing two expressions next to each other; there is no explicit operator. The three-operand @samp{?:} operator provides an ``if-else'' test within @@ -12416,7 +12324,7 @@ Assignment operators provide convenient shorthands for common arithmetic operations. @item -In @command{awk}, a value is considered to be true if it is non-zero +In @command{awk}, a value is considered to be true if it is nonzero @emph{or} non-null. Otherwise, the value is false. @item @@ -12425,7 +12333,7 @@ lifetime. The type determines how it behaves in comparisons (string or numeric). @item -Function calls return a value which may be used as part of a larger +Function calls return a value that may be used as part of a larger expression. Expressions used to pass parameter values are fully evaluated before the function is called. @command{awk} provides built-in and user-defined functions; this is described in @@ -12442,11 +12350,9 @@ program, and occasionally the format for data read as input. @end itemize -@c ENDOFRANGE exps @node Patterns and Actions @chapter Patterns, Actions, and Variables -@c STARTOFRANGE pat @cindex patterns As you have already seen, each @command{awk} statement consists of @@ -12454,7 +12360,7 @@ a pattern with an associated action. This @value{CHAPTER} describes how you build patterns and actions, what kinds of things you can do within actions, and @command{awk}'s predefined variables. -The pattern-action rules and the statements available for use +The pattern--action rules and the statements available for use within actions form the core of @command{awk} programming. In a sense, everything covered up to here has been the foundation @@ -12645,7 +12551,7 @@ patterns. Likewise, the special patterns @code{BEGIN}, @code{END}, which never match any input record, are not expressions and cannot appear inside Boolean patterns. -The precedence of the different operators which can appear in +The precedence of the different operators that can appear in patterns is described in @ref{Precedence}. @node Ranges @@ -12671,7 +12577,7 @@ prints every record in @file{myfile} between @samp{on}/@samp{off} pairs, inclusi A range pattern starts out by matching @var{begpat} against every input record. When a record matches @var{begpat}, the range pattern is -@dfn{turned on} and the range pattern matches this record as well. As long as +@dfn{turned on}, and the range pattern matches this record as well. As long as the range pattern stays turned on, it automatically matches every input record read. The range pattern also matches @var{endpat} against every input record; when this succeeds, the range pattern is @dfn{turned off} again @@ -12742,9 +12648,7 @@ a range pattern. @value{DARKCORNER} @node BEGIN/END @subsection The @code{BEGIN} and @code{END} Special Patterns -@c STARTOFRANGE beg @cindex @code{BEGIN} pattern -@c STARTOFRANGE end @cindex @code{END} pattern All the patterns described so far are for matching input records. The @code{BEGIN} and @code{END} special patterns are different. @@ -12817,7 +12721,7 @@ using library functions. for a number of useful library functions. If an @command{awk} program has only @code{BEGIN} rules and no -other rules, then the program exits after the @code{BEGIN} rule is +other rules, then the program exits after the @code{BEGIN} rules are run.@footnote{The original version of @command{awk} kept reading and ignoring input until the end of the file was seen.} However, if an @code{END} rule exists, then the input is read, even if there are @@ -12845,7 +12749,7 @@ Another way is simply to assign a value to @code{$0}. @cindex @code{print} statement, @code{BEGIN}/@code{END} patterns and @cindex @code{BEGIN} pattern, @code{print} statement and @cindex @code{END} pattern, @code{print} statement and -The second point is similar to the first but from the other direction. +The second point is similar to the first, but from the other direction. Traditionally, due largely to implementation issues, @code{$0} and @code{NF} were @emph{undefined} inside an @code{END} rule. The POSIX standard specifies that @code{NF} is available in an @code{END} @@ -12882,8 +12786,6 @@ are not valid in an @code{END} rule, because all the input has been read. @ifdocbook @DBREF{Nextfile Statement}.) @end ifdocbook -@c ENDOFRANGE beg -@c ENDOFRANGE end @node BEGINFILE/ENDFILE @subsection The @code{BEGINFILE} and @code{ENDFILE} Special Patterns @@ -12936,7 +12838,7 @@ fatal error. @item If you have written extensions that modify the record handling (by -inserting an ``input parser,'' @pxref{Input Parsers}), you can invoke +inserting an ``input parser''; @pxref{Input Parsers}), you can invoke them at this point, before @command{gawk} has started processing the file. (This is a @emph{very} advanced feature, currently used only by the @uref{http://gawkextlib.sourceforge.net, @code{gawkextlib} project}.) @@ -12947,8 +12849,8 @@ the last record in an input file. For the last input file, it will be called before any @code{END} rules. The @code{ENDFILE} rule is executed even for empty input files. -Normally, when an error occurs when reading input in the normal input -processing loop, the error is fatal. However, if an @code{ENDFILE} +Normally, when an error occurs when reading input in the normal +input-processing loop, the error is fatal. However, if an @code{ENDFILE} rule is present, the error becomes non-fatal, and instead @code{ERRNO} is set. This makes it possible to catch and process I/O errors at the level of the @command{awk} program. @@ -12957,7 +12859,7 @@ level of the @command{awk} program. The @code{next} statement (@pxref{Next Statement}) is not allowed inside either a @code{BEGINFILE} or an @code{ENDFILE} rule. The @code{nextfile} statement is allowed only inside a -@code{BEGINFILE} rule, but not inside an @code{ENDFILE} rule. +@code{BEGINFILE} rule, not inside an @code{ENDFILE} rule. @cindex @code{getline} statement, @code{BEGINFILE}/@code{ENDFILE} patterns and The @code{getline} statement (@pxref{Getline}) is restricted inside @@ -13004,7 +12906,6 @@ awk '@{ print $1 @}' mail-list @noindent prints the first field of every record. -@c ENDOFRANGE pat @node Using Shell Variables @section Using Shell Variables in Programs @@ -13034,11 +12935,11 @@ awk "/$pattern/ "'@{ nmatches++ @} @noindent The @command{awk} program consists of two pieces of quoted text that are concatenated together to form the program. -The first part is double quoted, which allows substitution of +The first part is double-quoted, which allows substitution of the @code{pattern} shell variable inside the quotes. -The second part is single quoted. +The second part is single-quoted. -Variable substitution via quoting works, but can be potentially +Variable substitution via quoting works, but can potentially be messy. It requires a good understanding of the shell's quoting rules (@pxref{Quoting}), and it's often difficult to correctly @@ -13153,11 +13054,8 @@ For deleting array elements. @node Statements @section Control Statements in Actions -@c STARTOFRANGE csta @cindex control statements -@c STARTOFRANGE acs @cindex statements, control, in actions -@c STARTOFRANGE accs @cindex actions, control statements in @dfn{Control statements}, such as @code{if}, @code{while}, and so on, @@ -13300,13 +13198,13 @@ The body of this loop is a compound statement enclosed in braces, containing two statements. The loop works in the following manner: first, the value of @code{i} is set to one. Then, the @code{while} statement tests whether @code{i} is less than or equal to -three. This is true when @code{i} equals one, so the @code{i}-th +three. This is true when @code{i} equals one, so the @code{i}th field is printed. Then the @samp{i++} increments the value of @code{i} and the loop repeats. The loop terminates when @code{i} reaches four. A newline is not required between the condition and the body; however, using one makes the program clearer unless the body is a -compound statement or else is very simple. The newline after the open-brace +compound statement or else is very simple. The newline after the open brace that begins the compound statement is not required either, but the program is harder to read without it. @@ -13336,9 +13234,9 @@ while (@var{condition}) @end example @noindent -This statement does not execute @var{body} even once if the @var{condition} -is false to begin with. -The following is an example of a @code{do} statement: +This statement does not execute the @var{body} even once if the +@var{condition} is false to begin with. The following is an example of +a @code{do} statement: @example @{ @@ -13405,7 +13303,7 @@ their assignments as separate statements preceding the @code{for} loop.) The same is true of the @var{increment} part. Incrementing additional variables requires separate statements at the end of the loop. The C compound expression, using C's comma operator, is useful in -this context but it is not supported in @command{awk}. +this context, but it is not supported in @command{awk}. Most often, @var{increment} is an increment expression, as in the previous example. But this is not required; it can be any expression @@ -13496,7 +13394,7 @@ default: Control flow in the @code{switch} statement works as it does in C. Once a match to a given case is made, the case statement bodies execute until a @code{break}, -@code{continue}, @code{next}, @code{nextfile} or @code{exit} is encountered, +@code{continue}, @code{next}, @code{nextfile}, or @code{exit} is encountered, or the end of the @code{switch} statement itself. For example: @example @@ -13670,7 +13568,12 @@ body of a loop. Historical versions of @command{awk} treated a @code{continue} statement outside a loop the same way they treated a @code{break} statement outside a loop: as if it were a @code{next} statement +@ifset FOR_PRINT +(discussed in the following section). +@end ifset +@ifclear FOR_PRINT (@pxref{Next Statement}). +@end ifclear @value{DARKCORNER} Recent versions of BWK @command{awk} no longer work this way, nor does @command{gawk}. @@ -13798,7 +13701,7 @@ See @uref{http://austingroupbugs.net/view.php?id=607, the Austin Group website}. @cindex @code{nextfile} statement, user-defined functions and @cindex Brian Kernighan's @command{awk} @cindex @command{mawk} utility -The current version of BWK @command{awk}, and @command{mawk} +The current version of BWK @command{awk} and @command{mawk} also support @code{nextfile}. However, they don't allow the @code{nextfile} statement inside function bodies (@pxref{User-defined}). @command{gawk} does; a @code{nextfile} inside a function body reads the @@ -13836,7 +13739,7 @@ any @code{ENDFILE} rules; they do not execute. In such a case, if you don't want the @code{END} rule to do its job, set a variable -to nonzero before the @code{exit} statement and check that variable in +to a nonzero value before the @code{exit} statement and check that variable in the @code{END} rule. @DBXREF{Assert Function} for an example that does this. @@ -13875,15 +13778,10 @@ Negative values, and values of 127 or greater, may not produce consistent results across different operating systems. @end quotation -@c ENDOFRANGE csta -@c ENDOFRANGE acs -@c ENDOFRANGE accs @node Built-in Variables @section Predefined Variables -@c STARTOFRANGE bvar @cindex predefined variables -@c STARTOFRANGE varb @cindex variables, predefined Most @command{awk} variables are available to use for your own @@ -13909,10 +13807,8 @@ their areas of activity. @end menu @node User-modified -@subsection Built-In Variables That Control @command{awk} -@c STARTOFRANGE bvaru +@subsection Built-in Variables That Control @command{awk} @cindex predefined variables, user-modifiable -@c STARTOFRANGE nmbv @cindex user-modifiable variables The following is an alphabetical list of variables that you can change to @@ -14139,17 +14035,11 @@ marked string constants in the source text, as well as for the (@pxref{Internationalization}). The default value of @code{TEXTDOMAIN} is @code{"messages"}. @end table -@c ENDOFRANGE bvar -@c ENDOFRANGE varb -@c ENDOFRANGE bvaru -@c ENDOFRANGE nmbv @node Auto-set @subsection Built-In Variables That Convey Information -@c STARTOFRANGE bvconi @cindex predefined variables, conveying information -@c STARTOFRANGE vbconi @cindex variables, predefined conveying information The following is an alphabetical list of variables that @command{awk} sets automatically on certain occasions in order to provide @@ -14571,8 +14461,6 @@ implementation issues.} neither @code{FUNCTAB} nor @code{SYMTAB} are available as elements within the @code{SYMTAB} array. @end quotation @end table -@c ENDOFRANGE bvconi -@c ENDOFRANGE vbconi @sidebar Changing @code{NR} and @code{FNR} @cindex @code{NR} variable, changing @@ -14819,7 +14707,6 @@ control how @command{awk} will process the provided @value{DF}s. @node Arrays @chapter Arrays in @command{awk} -@c STARTOFRANGE arrs @cindex arrays An @dfn{array} is a table of values called @dfn{elements}. The @@ -14941,9 +14828,7 @@ Only the values are stored; the indices are implicit from the order of the values. Here, 8 is the value at index zero, because 8 appears in the position with zero elements before it. -@c STARTOFRANGE arrin @cindex arrays, indexing -@c STARTOFRANGE inarr @cindex indexing arrays @cindex associative arrays @cindex arrays, associative @@ -15146,8 +15031,6 @@ that array's indices are consecutive integers starting at one. @command{awk}'s arrays are efficient---the time to access an element is independent of the number of elements in the array. -@c ENDOFRANGE arrin -@c ENDOFRANGE inarr @node Reference to Elements @subsection Referring to an Array Element @@ -16200,14 +16083,11 @@ element is itself a subarray. @end itemize -@c ENDOFRANGE arrs @node Functions @chapter Functions -@c STARTOFRANGE funcbi @cindex functions, built-in -@c STARTOFRANGE bifunc @cindex built-in functions This @value{CHAPTER} describes @command{awk}'s built-in functions, which fall into three categories: numeric, string, and I/O. @@ -17770,13 +17650,9 @@ you would see the latter (undesirable) output. @subsection Time Functions @cindex time functions -@c STARTOFRANGE tst @cindex timestamps -@c STARTOFRANGE logftst @cindex log files, timestamps in -@c STARTOFRANGE filogtst @cindex files, log@comma{} timestamps in -@c STARTOFRANGE gawtst @cindex @command{gawk}, timestamps @cindex POSIX @command{awk}, timestamps and @code{awk} programs are commonly used to process log files @@ -17854,7 +17730,6 @@ is out of range, @code{mktime()} returns @minus{}1. @cindex @command{gawk}, @code{PROCINFO} array in @cindex @code{PROCINFO} array @item @code{strftime(}[@var{format} [@code{,} @var{timestamp} [@code{,} @var{utc-flag}] ] ]@code{)} -@c STARTOFRANGE strf @cindexgawkfunc{strftime} @cindex format time string Format the time specified by @var{timestamp} @@ -18103,7 +17978,6 @@ The time as a decimal timestamp in seconds since the epoch. The date in VMS format (e.g., @samp{20-JUN-1991}). @end ignore @end table -@c ENDOFRANGE strf Additionally, the alternative representations are recognized but their normal representations are used. @@ -18154,23 +18028,14 @@ gawk 'BEGIN @{ exit exitval @}' "$@@" @end example -@c ENDOFRANGE tst -@c ENDOFRANGE logftst -@c ENDOFRANGE filogtst -@c ENDOFRANGE gawtst @node Bitwise Functions @subsection Bit-Manipulation Functions @cindex bit-manipulation functions -@c STARTOFRANGE bit @cindex bitwise, operations -@c STARTOFRANGE and @cindex AND bitwise operation -@c STARTOFRANGE oro @cindex OR bitwise operation -@c STARTOFRANGE xor @cindex XOR bitwise operation -@c STARTOFRANGE opbit @cindex operations, bitwise @quotation @i{I can explain it for you, but I can't understand it for you.} @@ -18462,11 +18327,6 @@ decimal and octal values for the same numbers (@pxref{Nondecimal-numbers}), and then demonstrates the results of the @code{compl()}, @code{lshift()}, and @code{rshift()} functions. -@c ENDOFRANGE bit -@c ENDOFRANGE and -@c ENDOFRANGE oro -@c ENDOFRANGE xor -@c ENDOFRANGE opbit @node Type Functions @subsection Getting Type Information @@ -18546,15 +18406,11 @@ variant of the same message. The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. The default value for @var{category} is @code{"LC_MESSAGES"}. @end table -@c ENDOFRANGE funcbi -@c ENDOFRANGE bifunc @node User-defined @section User-Defined Functions -@c STARTOFRANGE udfunc @cindex user-defined functions -@c STARTOFRANGE funcud @cindex functions, user-defined Complicated @command{awk} programs can often be simplified by defining your own functions. User-defined functions can be called just like @@ -18579,7 +18435,6 @@ variable definitions is appallingly awful.} @author Brian Kernighan @end quotation -@c STARTOFRANGE fdef @cindex functions, defining Definitions of functions can appear anywhere between the rules of an @command{awk} program. Thus, the general form of an @command{awk} program is @@ -18826,12 +18681,10 @@ You might think that @code{ctime()} could use @code{PROCINFO["strftime"]} for its format string. That would be a mistake, because @code{ctime()} is supposed to return the time formatted in a standard fashion, and user-level code could have changed @code{PROCINFO["strftime"]}. -@c ENDOFRANGE fdef @node Function Caveats @subsection Calling User-Defined Functions -@c STARTOFRANGE fudc @cindex functions, user-defined, calling @dfn{Calling a function} means causing the function to run and do its job. A function call is an expression and its value is the value returned by @@ -19123,7 +18976,6 @@ or the @code{nextfile} statement @end ifnotdocbook inside a user-defined function. @command{gawk} does not have this limitation. -@c ENDOFRANGE fudc @node Return Statement @subsection The @code{return} Statement @@ -19251,7 +19103,6 @@ does report the second error. Usually, such things aren't a big issue, but it's worth being aware of them. -@c ENDOFRANGE udfunc @node Indirect Calls @section Indirect Function Calls @@ -19744,7 +19595,6 @@ program. This is equivalent to function pointers in C and C++. @end itemize -@c ENDOFRANGE funcud @ifnotinfo @part @value{PART2}Problem Solving with @command{awk} @@ -19766,11 +19616,8 @@ It contains the following chapters: @node Library Functions @chapter A Library of @command{awk} Functions -@c STARTOFRANGE libf @cindex libraries of @command{awk} functions -@c STARTOFRANGE flib @cindex functions, library -@c STARTOFRANGE fudlib @cindex functions, user-defined, library of @DBREF{User-defined} describes how to write @@ -20093,13 +19940,9 @@ be tested with @command{gawk} and the results compared to the built-in @node Assert Function @subsection Assertions -@c STARTOFRANGE asse @cindex assertions -@c STARTOFRANGE assef @cindex @code{assert()} function (C library) -@c STARTOFRANGE libfass @cindex libraries of @command{awk} functions, assertions -@c STARTOFRANGE flibass @cindex functions, library, assertions @cindex @command{awk} programs, lengthy, assertions When writing large programs, it is often useful to know @@ -20215,10 +20058,6 @@ most likely causing the program to hang as it waits for input. There is a simple workaround to this: make sure that such a @code{BEGIN} rule always ends with an @code{exit} statement. -@c ENDOFRANGE asse -@c ENDOFRANGE assef -@c ENDOFRANGE flibass -@c ENDOFRANGE libfass @node Round Function @subsection Rounding Numbers @@ -20776,11 +20615,8 @@ function shell_quote(s, # parameter @node Data File Management @section @value{DDF} Management -@c STARTOFRANGE dataf @cindex files, managing -@c STARTOFRANGE libfdataf @cindex libraries of @command{awk} functions, managing, data files -@c STARTOFRANGE flibdataf @cindex functions, library, managing data files This @value{SECTION} presents functions that are useful for managing command-line @value{DF}s. @@ -21143,22 +20979,14 @@ The use of @code{No_command_assign} allows you to disable command-line assignments at invocation time, by giving the variable a true value. When not set, it is initially zero (i.e., false), so the command-line arguments are left alone. -@c ENDOFRANGE dataf -@c ENDOFRANGE flibdataf -@c ENDOFRANGE libfdataf @node Getopt Function @section Processing Command-Line Options -@c STARTOFRANGE libfclo @cindex libraries of @command{awk} functions, command-line options -@c STARTOFRANGE flibclo @cindex functions, library, command-line options -@c STARTOFRANGE clop @cindex command-line options, processing -@c STARTOFRANGE oclp @cindex options, command-line, processing -@c STARTOFRANGE clibf @cindex functions, library, C library @cindex arguments, processing Most utilities on POSIX-compatible systems take options on @@ -21510,21 +21338,13 @@ further options Several of the sample programs presented in @ref{Sample Programs}, use @code{getopt()} to process their arguments. -@c ENDOFRANGE libfclo -@c ENDOFRANGE flibclo -@c ENDOFRANGE clop -@c ENDOFRANGE oclp @node Passwd Functions @section Reading the User Database -@c STARTOFRANGE libfudata @cindex libraries of @command{awk} functions, user database, reading -@c STARTOFRANGE flibudata @cindex functions, library, user database@comma{} reading -@c STARTOFRANGE udatar @cindex user database@comma{} reading -@c STARTOFRANGE dataur @cindex database, users@comma{} reading @cindex @code{PROCINFO} array The @code{PROCINFO} array @@ -21871,21 +21691,13 @@ and such a change would clutter up the code. The @command{id} program in @DBREF{Id Program} uses these functions. -@c ENDOFRANGE libfudata -@c ENDOFRANGE flibudata -@c ENDOFRANGE udatar -@c ENDOFRANGE dataur @node Group Functions @section Reading the Group Database -@c STARTOFRANGE libfgdata @cindex libraries of @command{awk} functions, group database, reading -@c STARTOFRANGE flibgdata @cindex functions, library, group database@comma{} reading -@c STARTOFRANGE gdatar @cindex group database, reading -@c STARTOFRANGE datagr @cindex database, group, reading @cindex @code{PROCINFO} array, and group membership @cindex @code{getgrent()} function (C library) @@ -22208,7 +22020,6 @@ function getgrent() @} @c endfile @end example -@c ENDOFRANGE clibf @cindex @code{endgrent()} function (C library) The @code{endgrent()} function resets @code{_gr_count} to zero so that @code{getgrent()} can @@ -22297,10 +22108,6 @@ $ @kbd{gawk -f walk_array.awk} @print{} a[4][2] = 42 @end example -@c ENDOFRANGE libfgdata -@c ENDOFRANGE flibgdata -@c ENDOFRANGE gdatar -@c ENDOFRANGE libf @node Library Functions Summary @section Summary @@ -22414,13 +22221,9 @@ output identical to that of the original version. @end enumerate @c EXCLUDE END -@c ENDOFRANGE flib -@c ENDOFRANGE fudlib -@c ENDOFRANGE datagr @node Sample Programs @chapter Practical @command{awk} Programs -@c STARTOFRANGE awkpex @cindex @command{awk} programs, examples of @c FULLXREF ON @@ -22490,7 +22293,6 @@ cut.awk -- -c1-8 myfiles > results @node Clones @section Reinventing Wheels for Fun and Profit -@c STARTOFRANGE posimawk @cindex POSIX, programs@comma{} implementing in @command{awk} This @value{SECTION} presents a number of POSIX utilities implemented in @@ -22521,11 +22323,8 @@ The programs are presented in alphabetical order. @subsection Cutting Out Fields and Columns @cindex @command{cut} utility -@c STARTOFRANGE cut @cindex @command{cut} utility -@c STARTOFRANGE ficut @cindex fields, cutting -@c STARTOFRANGE colcut @cindex columns, cutting The @command{cut} utility selects, or ``cuts,'' characters or fields from its standard input and sends them to its standard output. @@ -22833,21 +22632,14 @@ other @command{awk} implementations to use @code{substr()} it is also extremely painful. The @code{FIELDWIDTHS} variable supplies an elegant solution to the problem of picking the input line apart by characters. -@c ENDOFRANGE cut -@c ENDOFRANGE ficut -@c ENDOFRANGE colcut @node Egrep Program @subsection Searching for Regular Expressions in Files -@c STARTOFRANGE regexps @cindex regular expressions, searching for -@c STARTOFRANGE sfregexp @cindex searching, files for regular expressions -@c STARTOFRANGE fsregexp @cindex files, searching for regular expressions -@c STARTOFRANGE egrep @cindex @command{egrep} utility The @command{egrep} utility searches files for patterns. It uses regular expressions that are almost identical to those available in @command{awk} @@ -23115,17 +22907,12 @@ function usage() @c endfile @end example -@c ENDOFRANGE regexps -@c ENDOFRANGE sfregexp -@c ENDOFRANGE fsregexp -@c ENDOFRANGE egrep @node Id Program @subsection Printing Out User Information @cindex printing, user information @cindex users, information about, printing -@c STARTOFRANGE id @cindex @command{id} utility The @command{id} utility lists a user's real and effective user ID numbers, real and effective group ID numbers, and the user's group set, if any. @@ -23254,16 +23041,13 @@ code that is used repeatedly, making the whole program shorter and cleaner. In particular, moving the check for the empty string into this function saves several lines of code. -@c ENDOFRANGE id @node Split Program @subsection Splitting a Large File into Pieces @c FIXME: One day, update to current POSIX version of split -@c STARTOFRANGE filspl @cindex files, splitting -@c STARTOFRANGE split @cindex @code{split} utility The @command{split} program splits large text files into smaller pieces. Usage is as follows:@footnote{This is the traditional usage. The @@ -23398,15 +23182,12 @@ You might want to consider how to eliminate the use of way as to solve the EBCDIC issue as well. @end ifset -@c ENDOFRANGE filspl -@c ENDOFRANGE split @node Tee Program @subsection Duplicating Output into Multiple Files @cindex files, multiple@comma{} duplicating output into @cindex output, duplicating into files -@c STARTOFRANGE tee @cindex @code{tee} utility The @code{tee} program is known as a ``pipe fitting.'' @code{tee} copies its standard input to its standard output and also duplicates it to the @@ -23519,18 +23300,14 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE tee @node Uniq Program @subsection Printing Nonduplicated Lines of Text @c FIXME: One day, update to current POSIX version of uniq -@c STARTOFRANGE prunt @cindex printing, unduplicated lines of text -@c STARTOFRANGE tpul @cindex text@comma{} printing, unduplicated lines of -@c STARTOFRANGE uniq @cindex @command{uniq} utility The @command{uniq} utility reads sorted lines of data on its standard input, and by default removes duplicate lines. In other words, it only @@ -23799,26 +23576,17 @@ suggestion. @end ifset -@c ENDOFRANGE prunt -@c ENDOFRANGE tpul -@c ENDOFRANGE uniq @node Wc Program @subsection Counting Things @c FIXME: One day, update to current POSIX version of wc -@c STARTOFRANGE count @cindex counting -@c STARTOFRANGE infco @cindex input files, counting elements in -@c STARTOFRANGE woco @cindex words, counting -@c STARTOFRANGE chco @cindex characters, counting -@c STARTOFRANGE lico @cindex lines, counting -@c STARTOFRANGE wc @cindex @command{wc} utility The @command{wc} (word count) utility counts lines, words, and characters in one or more input files. Its usage is as follows: @@ -23988,13 +23756,6 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE count -@c ENDOFRANGE infco -@c ENDOFRANGE lico -@c ENDOFRANGE woco -@c ENDOFRANGE chco -@c ENDOFRANGE wc -@c ENDOFRANGE posimawk @node Miscellaneous Programs @section A Grab Bag of @command{awk} Programs @@ -24125,9 +23886,7 @@ Aharon Robbins <arnold@skeeve.com> wrote: @author Erik Quanstrom @end quotation -@c STARTOFRANGE tialarm @cindex time, alarm clock example program -@c STARTOFRANGE alaex @cindex alarm clock example program The following program is a simple ``alarm clock'' program. You give it a time of day and an optional message. At the specified time, @@ -24279,15 +24038,11 @@ seconds are necessary: @} @c endfile @end example -@c ENDOFRANGE tialarm -@c ENDOFRANGE alaex @node Translate Program @subsection Transliterating Characters -@c STARTOFRANGE chtra @cindex characters, transliterating -@c STARTOFRANGE tr @cindex @command{tr} utility The system @command{tr} utility transliterates characters. For example, it is often used to map uppercase letters into lowercase for further processing: @@ -24435,15 +24190,11 @@ such as @samp{a-z}, as allowed by the @command{tr} utility. Look at the code for @file{cut.awk} (@pxref{Cut Program}) for inspiration. -@c ENDOFRANGE chtra -@c ENDOFRANGE tr @node Labels Program @subsection Printing Mailing Labels -@c STARTOFRANGE prml @cindex printing, mailing labels -@c STARTOFRANGE mlprint @cindex mailing labels@comma{} printing Here is a ``real world''@footnote{``Real world'' is defined as ``a program actually used to get something done.''} @@ -24507,7 +24258,6 @@ that there are two blank lines at the top and two blank lines at the bottom. The @code{END} rule arranges to flush the final page of labels; there may not have been an even multiple of 20 labels in the data: -@c STARTOFRANGE labels @cindex @code{labels.awk} program @example @c file eg/prog/labels.awk @@ -24572,14 +24322,10 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE prml -@c ENDOFRANGE mlprint -@c ENDOFRANGE labels @node Word Sorting @subsection Generating Word-Usage Counts -@c STARTOFRANGE worus @cindex words, usage counts@comma{} generating When working with large amounts of text, it can be interesting to know @@ -24641,7 +24387,6 @@ to remove punctuation characters. Finally, we solve the third problem by using the system @command{sort} utility to process the output of the @command{awk} script. Here is the new version of the program: -@c STARTOFRANGE wordfreq @cindex @code{wordfreq.awk} program @example @c file eg/prog/wordfreq.awk @@ -24706,13 +24451,10 @@ This way of sorting must be used on systems that do not have true pipes at the command-line (or batch-file) level. See the general operating system documentation for more information on how to use the @command{sort} program. -@c ENDOFRANGE worus -@c ENDOFRANGE wordfreq @node History Sorting @subsection Removing Duplicates from Unsorted Text -@c STARTOFRANGE lidu @cindex lines, duplicate@comma{} removing The @command{uniq} program (@pxref{Uniq Program}), @@ -24737,7 +24479,6 @@ Each element of @code{lines} is a unique command, and the indices of The @code{END} rule simply prints out the lines, in order: @cindex Rakitzis, Byron -@c STARTOFRANGE histsort @cindex @code{histsort.awk} program @example @c file eg/prog/histsort.awk @@ -24780,15 +24521,11 @@ print data[lines[i]], lines[i] @noindent This works because @code{data[$0]} is incremented each time a line is seen. -@c ENDOFRANGE lidu -@c ENDOFRANGE histsort @node Extract Program @subsection Extracting Programs from Texinfo Source Files -@c STARTOFRANGE texse @cindex Texinfo, extracting programs from source files -@c STARTOFRANGE fitex @cindex files, Texinfo@comma{} extracting programs from @ifnotinfo Both this chapter and the previous chapter @@ -24892,7 +24629,6 @@ The first rule handles calling @code{system()}, checking that a command is given (@code{NF} is at least three) and also checking that the command exits with a zero exit status, signifying OK: -@c STARTOFRANGE extract @cindex @code{extract.awk} program @example @c file eg/prog/extract.awk @@ -25038,9 +24774,6 @@ END @{ @} @c endfile @end example -@c ENDOFRANGE texse -@c ENDOFRANGE fitex -@c ENDOFRANGE extract @node Simple Sed @subsection A Simple Stream Editor @@ -25070,7 +24803,6 @@ additional arguments are treated as @value{DF} names to process. If none are provided, the standard input is used: @cindex Brennan, Michael -@c STARTOFRANGE awksed @cindex @command{awksed.awk} program @c @cindex simple stream editor @c @cindex stream editor, simple @@ -25147,14 +24879,11 @@ The @code{usage()} function prints an error message and exits. Finally, the single rule handles the printing scheme outlined earlier, using @code{print} or @code{printf} as appropriate, depending upon the value of @code{RT}. -@c ENDOFRANGE awksed @node Igawk Program @subsection An Easy Way to Use Library Functions -@c STARTOFRANGE libfex @cindex libraries of @command{awk} functions, example program for using -@c STARTOFRANGE flibex @cindex functions, library, example program for using In @ref{Include Files}, we saw how @command{gawk} provides a built-in file-inclusion capability. However, this is a @command{gawk} extension. @@ -25293,7 +25022,6 @@ program. The program is as follows: -@c STARTOFRANGE igawk @cindex @code{igawk.sh} program @example @c file eg/prog/igawk.sh @@ -25618,10 +25346,6 @@ features to a program; they can often be layered on top.@footnote{@command{gawk} does @code{@@include} processing itself in order to support the use of @command{awk} programs as Web CGI scripts.} -@c ENDOFRANGE libfex -@c ENDOFRANGE flibex -@c ENDOFRANGE awkpex -@c ENDOFRANGE igawk @node Anagram Program @subsection Finding Anagrams from a Dictionary @@ -25645,7 +25369,6 @@ The following program uses arrays of arrays to bring together words with the same signature and array sorting to print the words in sorted order: -@c STARTOFRANGE anagram @cindex @code{anagram.awk} program @example @c file eg/prog/anagram.awk @@ -25754,7 +25477,6 @@ babery yabber @dots{} @end example -@c ENDOFRANGE anagram @node Signature Program @subsection And Now for Something Completely Different @@ -26074,9 +25796,7 @@ It contains the following chapters: @node Advanced Features @chapter Advanced Features of @command{gawk} -@c STARTOFRANGE gawadv @cindex @command{gawk}, features, advanced -@c STARTOFRANGE advgaw @cindex advanced features, @command{gawk} @ignore Contributed by: Peter Langston <pud!psl@bellcore.bellcore.com> @@ -26786,7 +26506,6 @@ using regular pipes. @section Using @command{gawk} for Network Programming @cindex advanced features, network programming @cindex networks, programming -@c STARTOFRANGE tcpip @cindex TCP/IP @cindex @code{/inet/@dots{}} special files (@command{gawk}) @cindex files, @code{/inet/@dots{}} (@command{gawk}) @@ -26903,13 +26622,10 @@ which comes as part of the @command{gawk} distribution, for a much more complete introduction and discussion, as well as extensive examples. -@c ENDOFRANGE tcpip @node Profiling @section Profiling Your @command{awk} Programs -@c STARTOFRANGE awkp @cindex @command{awk} programs, profiling -@c STARTOFRANGE proawk @cindex profiling @command{awk} programs @cindex @code{awkprof.out} file @cindex files, @code{awkprof.out} @@ -27236,9 +26952,6 @@ that the profiling output does. This makes it easy to pretty-print your code once development is completed, and then use the result as the final version of your program. -@c ENDOFRANGE awkp -@c ENDOFRANGE proawk - @node Advanced Features Summary @section Summary @@ -27284,8 +26997,6 @@ the program, but that will change in the next major release. @end itemize -@c ENDOFRANGE advgaw -@c ENDOFRANGE gawadv @node Internationalization @chapter Internationalization with @command{gawk} @@ -27298,7 +27009,6 @@ countries, they were able to sell more systems. As a result, internationalization and localization of programs and software systems became a common practice. -@c STARTOFRANGE inloc @cindex internationalization, localization @cindex @command{gawk}, internationalization and, See internationalization @cindex internationalization, localization, @command{gawk} and @@ -27343,7 +27053,6 @@ monetary values are printed and read. @section GNU @command{gettext} @cindex internationalizing a program -@c STARTOFRANGE gettex @cindex @command{gettext} library @command{gawk} uses GNU @command{gettext} to provide its internationalization features. @@ -27395,7 +27104,6 @@ lookup of the translations. @cindex @code{.po} files @cindex files, @code{.po} -@c STARTOFRANGE portobfi @cindex portable object files @cindex files, portable object @item @@ -27407,7 +27115,6 @@ For example, there might be a @file{fr.po} for a French translation. @cindex @code{.gmo} files @cindex files, @code{.gmo} @cindex message object files -@c STARTOFRANGE portmsgfi @cindex files, message object @item Each language's @file{.po} file is converted into a binary @@ -27535,11 +27242,9 @@ before or after the day in a date, local month abbreviations, and so on. @item LC_ALL All of the above. (Not too useful in the context of @command{gettext}.) @end table -@c ENDOFRANGE gettex @node Programmer i18n @section Internationalizing @command{awk} Programs -@c STARTOFRANGE inap @cindex @command{awk} programs, internationalizing @command{gawk} provides the following variables and functions for @@ -27772,8 +27477,6 @@ to provide you translations that you can also then distribute. @DBXREF{I18N Example} for the full list of steps to go through to create and test translations for @command{guide}. -@c ENDOFRANGE portobfi -@c ENDOFRANGE portmsgfi @node Printf Ordering @subsection Rearranging @code{printf} Arguments @@ -27949,7 +27652,6 @@ However, because the positional specifications are primarily for use in @emph{translated} format strings, and because non-GNU @command{awk}s never retrieve the translated string, this should not be a problem in practice. @end itemize -@c ENDOFRANGE inap @node I18N Example @section A Simple Internationalization Example @@ -28100,8 +27802,8 @@ complete detail in @cite{GNU gettext tools}}.) @end ifnotinfo As of this writing, the latest version of GNU @command{gettext} is -@uref{ftp://ftp.gnu.org/gnu/gettext/gettext-0.19.3.tar.gz, -@value{PVERSION} 0.19.3}. +@uref{ftp://ftp.gnu.org/gnu/gettext/gettext-0.19.4.tar.gz, +@value{PVERSION} 0.19.4}. If a translation of @command{gawk}'s messages exists, then @command{gawk} produces usage messages, warnings, @@ -28145,7 +27847,6 @@ a number of translations for its messages. @end itemize -@c ENDOFRANGE inloc @node Debugger @chapter Debugging @command{awk} Programs @@ -29749,7 +29450,7 @@ is available like so: @example $ @kbd{gawk --version} @print{} GNU Awk 4.1.2, API: 1.1 (GNU MPFR 3.1.0-p3, GNU MP 5.0.2) -@print{} Copyright (C) 1989, 1991-2014 Free Software Foundation. +@print{} Copyright (C) 1989, 1991-2015 Free Software Foundation. @dots{} @end example @@ -30403,7 +30104,7 @@ When asked about the algorithm used, Katie replied: @quotation It's not that well known but it's not that obscure either. It's Euler's modification to Newton's method for calculating pi. -Take a look at lines (23) - (25) here: @uref{http://mathworld.wolfram.com/PiFormulas.htm}. +Take a look at lines (23) - (25) here: @uref{http://mathworld.wolfram.com/PiFormulas.html}. The algorithm I wrote simply expands the multiply by 2 and works from the innermost expression outwards. I used this to program HP calculators @@ -34691,9 +34392,7 @@ online documentation}. @node V7/SVR3.1 @appendixsec Major Changes Between V7 and SVR3.1 -@c STARTOFRANGE gawkv @cindex @command{awk}, versions of -@c STARTOFRANGE gawkv1 @cindex @command{awk}, versions of, changes between V7 and SVR3.1 The @command{awk} language evolved considerably between the release of @@ -34780,7 +34479,6 @@ Multiple @code{BEGIN} and @code{END} rules Multidimensional arrays (@pxref{Multidimensional}). @end itemize -@c ENDOFRANGE gawkv1 @node SVR4 @appendixsec Changes Between SVR3.1 and SVR4 @@ -34895,7 +34593,6 @@ not permitted by the POSIX standard. The 2008 POSIX standard can be found online at @url{http://www.opengroup.org/onlinepubs/9699919799/}. -@c ENDOFRANGE gawkv @node BTL @appendixsec Extensions in Brian Kernighan's @command{awk} @@ -34941,11 +34638,8 @@ available in his @command{awk}. @node POSIX/GNU @appendixsec Extensions in @command{gawk} Not in POSIX @command{awk} -@c STARTOFRANGE fripls @cindex compatibility mode (@command{gawk}), extensions -@c STARTOFRANGE exgnot @cindex extensions, in @command{gawk}, not in POSIX @command{awk} -@c STARTOFRANGE posnot @cindex POSIX, @command{gawk} extensions not included in The GNU implementation, @command{gawk}, adds a large number of features. They can all be disabled with either the @option{--traditional} or @@ -35259,9 +34953,6 @@ Support for MirBSD was removed at @command{gawk} @value{PVERSION} 4.2. @c XXX ADD MORE STUFF HERE -@c ENDOFRANGE fripls -@c ENDOFRANGE exgnot -@c ENDOFRANGE posnot @c This does not need to be in the formal book. @ifclear FOR_PRINT @@ -36310,9 +36001,7 @@ the appropriate credit where credit is due. @c last two commas are part of see also @cindex operating systems, See Also GNU/Linux@comma{} PC operating systems@comma{} Unix -@c STARTOFRANGE gligawk @cindex @command{gawk}, installing -@c STARTOFRANGE ingawk @cindex installing @command{gawk} This appendix provides instructions for installing @command{gawk} on the various platforms that are supported by the developers. The primary @@ -36422,7 +36111,6 @@ a local expert. @node Distribution contents @appendixsubsec Contents of the @command{gawk} Distribution -@c STARTOFRANGE gawdis @cindex @command{gawk}, distribution The @command{gawk} distribution has a number of C source files, @@ -36621,7 +36309,6 @@ directory to run your version of @command{gawk} against the test suite. If @command{gawk} successfully passes @samp{make check}, then you can be confident of a successful port. @end table -@c ENDOFRANGE gawdis @node Unix Installation @appendixsec Compiling and Installing @command{gawk} on Unix-Like Systems @@ -37086,9 +36773,7 @@ multibyte functionality is not available. @node PC Using @appendixsubsubsec Using @command{gawk} on PC Operating Systems -@c STARTOFRANGE opgawx @cindex operating systems, PC, @command{gawk} on -@c STARTOFRANGE pcgawon @cindex PC operating systems, @command{gawk} on Under MS-DOS and MS-Windows, the Cygwin and MinGW environments support @@ -37596,8 +37281,6 @@ $ @kbd{gawk :== $sys$common:[syshlp.examples.tcpip.snmp]gawk.exe} This is apparently @value{PVERSION} 2.15.6, which is extremely old. We recommend compiling and using the current version. -@c ENDOFRANGE opgawx -@c ENDOFRANGE pcgawon @node Bugs @appendixsec Reporting Problems and Bugs @@ -37608,9 +37291,7 @@ recommend compiling and using the current version. @end quotation @c the radio show, not the book. :-) -@c STARTOFRANGE dbugg @cindex debugging @command{gawk}, bug reports -@c STARTOFRANGE tblgawb @cindex troubleshooting, @command{gawk}, bug reports If you have problems with @command{gawk} or think that you have found a bug, report it to the developers; we cannot promise to do anything @@ -37707,12 +37388,9 @@ The people maintaining the various @command{gawk} ports are: If your bug is also reproducible under Unix, send a copy of your report to the @EMAIL{bug-gawk@@gnu.org,bug-gawk at gnu dot org} email list as well. -@c ENDOFRANGE dbugg -@c ENDOFRANGE tblgawb @node Other Versions @appendixsec Other Freely Available @command{awk} Implementations -@c STARTOFRANGE awkim @cindex @command{awk}, implementations @ignore From: emory!amc.com!brennan (Michael Brennan) @@ -37772,7 +37450,7 @@ git clone git://github.com/onetrueawk/awk bwkawk @end example @noindent -This command creates a copy of the @uref{http://www.git-scm.com, Git} +This command creates a copy of the @uref{http://git-scm.com, Git} repository in a directory named @file{bwkawk}. If you leave that argument off the @command{git} command line, the repository copy is created in a directory named @file{awk}. @@ -37837,7 +37515,7 @@ To get @command{awka}, go to @url{http://sourceforge.net/projects/awka}. @c andrewsumner@@yahoo.net The project seems to be frozen; no new code changes have been made -since approximately 2003. +since approximately 2001. @cindex Beebe, Nelson H.F.@: @cindex @command{pawk} (profiling version of Brian Kernighan's @command{awk}) @@ -37933,7 +37611,6 @@ See also the ``Versions and implementations'' section of the Wikipedia article} for information on additional versions. @end table -@c ENDOFRANGE awkim @node Installation summary @appendixsec Summary @@ -37971,15 +37648,11 @@ implementations. Many are POSIX compliant; others are less so. @end itemize -@c ENDOFRANGE gligawk -@c ENDOFRANGE ingawk @ifclear FOR_PRINT @node Notes @appendix Implementation Notes -@c STARTOFRANGE gawii @cindex @command{gawk}, implementation issues -@c STARTOFRANGE impis @cindex implementation issues, @command{gawk} This appendix contains information mainly of interest to implementers and @@ -38055,7 +37728,7 @@ However, if you want to modify @command{gawk} and contribute back your changes, you will probably wish to work with the development version. To do so, you will need to access the @command{gawk} source code repository. The code is maintained using the -@uref{http://git-scm.com/, Git distributed version control system}. +@uref{http://git-scm.com, Git distributed version control system}. You will need to install it if your system doesn't have it. Once you have done so, use the command: @@ -38084,11 +37757,8 @@ that has a Git plug-in for working with Git repositories. @node Adding Code @appendixsubsec Adding New Features -@c STARTOFRANGE adfgaw @cindex adding, features to @command{gawk} -@c STARTOFRANGE fadgaw @cindex features, adding to @command{gawk} -@c STARTOFRANGE gawadf @cindex @command{gawk}, features, adding You are free to add any new features you like to @command{gawk}. However, if you want your changes to be incorporated into the @command{gawk} @@ -38123,7 +37793,7 @@ for information on getting the latest version of @command{gawk}.) @item @ifnotinfo -Follow the @uref{http://www.gnu.org/prep/standards/, @cite{GNU Coding Standards}}. +Follow the @cite{GNU Coding Standards}. @end ifnotinfo @ifinfo See @inforef{Top, , Version, standards, GNU Coding Standards}. @@ -38132,7 +37802,7 @@ This document describes how GNU software should be written. If you haven't read it, please do so, preferably @emph{before} starting to modify @command{gawk}. (The @cite{GNU Coding Standards} are available from the GNU Project's -@uref{http://www.gnu.org/prep/standards_toc.html, website}. +@uref{http://www.gnu.org/prep/standards/, website}. Texinfo, Info, and DVI versions are also available.) @cindex @command{gawk}, coding style in @@ -38255,9 +37925,6 @@ Although this sounds like a lot of work, please remember that while you may write the new code, I have to maintain it and support it. If it isn't possible for me to do that with a minimum of extra work, then I probably will not. -@c ENDOFRANGE adfgaw -@c ENDOFRANGE gawadf -@c ENDOFRANGE fadgaw @node New Ports @appendixsubsec Porting @command{gawk} to a New Operating System @@ -38391,7 +38058,6 @@ coding style and brace layout that suits your taste. @node Derived Files @appendixsubsec Why Generated Files Are Kept In Git -@c STARTOFRANGE gawkgit @cindex Git, use of for @command{gawk} source code @c From emails written March 22, 2012, to the gawk developers list. @@ -38580,7 +38246,6 @@ wget http://git.savannah.gnu.org/cgit/gawk.git/snapshot/gawk-@var{branchname}.ta @noindent to retrieve a snapshot of the given branch. -@c ENDOFRANGE gawkgit @node Future Extensions @appendixsec Probable Future Extensions @@ -38961,13 +38626,10 @@ of @command{gawk}, but it @emph{will} be removed in the next major release. @end itemize -@c ENDOFRANGE impis -@c ENDOFRANGE gawii @node Basic Concepts @appendix Basic Programming Concepts @cindex programming, concepts -@c STARTOFRANGE procon @cindex programming, concepts This @value{APPENDIX} attempts to define some of the basic concepts @@ -39205,7 +38867,6 @@ standard for C. This standard became an ISO standard in 1990. In 1999, a revised ISO C standard was approved and released. Where it makes sense, POSIX @command{awk} is compatible with 1999 ISO C. -@c ENDOFRANGE procon @node Glossary @unnumbered Glossary @@ -39256,6 +38917,21 @@ languages. These standards often become international standards as well. See also ``ISO.'' +@item Argument +An argument can be two different things. It can be an option or a +@value{FN} passed to a command while invoking it from the command line, or +it can be something passed to a @dfn{function} inside a program, e.g. +inside @command{awk}. + +In the latter case, an argument can be passed to a function in two ways. +Either it is given to the called function by value, i.e., a copy of the +value of the variable is made available to the called function, but the +original variable cannot be modified by the function itself; or it is +given by reference, i.e., a pointer to the interested variable is passed to +the function, which can then directly modify it. In @command{awk} +scalars are passed by value, and arrays are passed by reference. +See ``Pass By Value/Reference.'' + @item Array A grouping of multiple values under the same name. Most languages just provide sequential arrays. @@ -39297,6 +38973,25 @@ The GNU version of the standard shell @end ifinfo See also ``Bourne Shell.'' +@item Binary +Base-two notation, where the digits are @code{0}--@code{1}. Since +electronic circuitry works ``naturally'' in base 2 (just think of Off/On), +everything inside a computer is calculated using base 2. Each digit +represents the presence (or absence) of a power of 2 and is called a +@dfn{bit}. So, for example, the base-two number @code{10101} is +the same as decimal 21, ((1 x 16) + (1 x 4) + (1 x 1)). + +Since base-two numbers quickly become +very long to read and write, they are usually grouped by 3 (i.e., they are +read as octal numbers), or by 4 (i.e., they are read as hexadecimal +numbers). There is no direct way to insert base 2 numbers in a C program. +If need arises, such numbers are usually inserted as octal or hexadecimal +numbers. The number of base-two digits that fit into registers used for +representing integer numbers in computers is a rough indication of the +computing power of the computer itself. Most computers nowadays use 64 +bits for representing integer numbers in their registers, but 32-bit, +16-bit and 8-bit registers have been widely used in the past. +@xref{Nondecimal-numbers}. @item Bit Short for ``Binary Digit.'' All values in computer memory ultimately reduce to binary digits: values @@ -39328,6 +39023,19 @@ The characters @samp{@{} and @samp{@}}. Braces are used in @command{awk} for delimiting actions, compound statements, and function bodies. +@item Bracket Expression +Inside a @dfn{regular expression}, an expression included in square +brackets, meant to designate a single character as belonging to a +specified character class. A bracket expression can contain a list of one +or more characters, like @samp{[abc]}, a range of characters, like +@samp{[A-Z]}, or a name, delimited by @samp{:}, that designates a known set +of characters, like @samp{[:digit:]}. The form of bracket expression +enclosed between @samp{:} is independent of the underlying representation +of the character themselves, which could utilize the ASCII, ECBDIC, or +Unicode codesets, depending on the architecture of the computer system, and on +localization. +See also ``Regular Expression.'' + @item Built-in Function The @command{awk} language provides built-in functions that perform various numerical, I/O-related, and string computations. Examples are @@ -39381,9 +39089,25 @@ points out similarities between @command{awk} and C when appropriate. In general, @command{gawk} attempts to be as similar to the 1990 version of ISO C as makes sense. +@item C Shell +The C Shell (@command{csh} or its improved version, @command{tcsh}) is a Unix shell that was +created by Bill Joy in the late 1970s. The C shell was differentiated from +other shells by its interactive features and overall style, which +looks more like C. The C Shell is not backward compatible with the Bourne +Shell, so special attention is required when converting scripts +written for other Unix shells to the C shell, especially with regard to the management of +shell variables. +See also ``Bourne Shell.'' + @item C++ A popular object-oriented programming language derived from C. +@item Character Class +See ``Bracket Expression.'' + +@item Character List +See ``Bracket Expression.'' + @cindex ASCII @cindex ISO 8859-1 @cindex ISO Latin-1 @@ -39407,7 +39131,7 @@ A preprocessor for @command{pic} that reads descriptions of molecules and produces @command{pic} input for drawing them. It was written in @command{awk} by Brian Kernighan and Jon Bentley, and is available from -@uref{http://netlib.sandia.gov/netlib/typesetting/chem.gz}. +@uref{http://netlib.org/typesetting/chem}. @item Comparison Expression A relation that is either true or false, such as @samp{a < b}. @@ -39423,11 +39147,23 @@ machine-executable object code. The object code is then executed directly by the computer. See also ``Interpreter.'' +@item Complemented Bracket Expression +The negation of a @dfn{bracket expression}. All that is @emph{not} +described by a given bracket expression. The symbol @samp{^} precedes +the negated bracket expression. E.g.: @samp{[[^:digit:]} +designates whatever character is not a digit. @samp{[^bad]} +designates whatever character is not one of the letters @samp{b}, @samp{a}, +or @samp{d}. +See ``Bracket Expression.'' + @item Compound Statement A series of @command{awk} statements, enclosed in curly braces. Compound statements may be nested. (@xref{Statements}.) +@item Computed Regexps +See ``Dynamic Regular Expressions.'' + @item Concatenation Concatenating two strings means sticking them together, one after another, producing a new string. For example, the string @samp{foo} concatenated with @@ -39442,6 +39178,13 @@ expression is the value of @var{expr2}; otherwise the value is @var{expr3}. In either case, only one of @var{expr2} and @var{expr3} is evaluated. (@xref{Conditional Exp}.) +@item Control Statement +A control statement is an instruction to perform a given operation or a set +of operations inside an @command{awk} program, if a given condition is +true. Control statements are: @code{if}, @code{for}, @code{while}, and +@code{do} +(@pxref{Statements}). + @cindex McIlroy, Doug @cindex cookie @item Cookie @@ -39596,6 +39339,11 @@ Format strings control the appearance of output in the are controlled by the format strings contained in the predefined variables @code{CONVFMT} and @code{OFMT}. (@xref{Control Letters}.) +@item Fortran +Shorthand for FORmula TRANslator, one of the first programming languages +available for scientific calculations. It was created by John Backus, +and has been available since 1957. It is still in use today. + @item Free Documentation License This document describes the terms under which this @value{DOCUMENT} is published and may be copied. (@xref{GNU Free Documentation License}.) @@ -39613,10 +39361,21 @@ Emacs editor. GNU Emacs is the most widely used version of Emacs today. See ``Free Software Foundation.'' @item Function -A specialized group of statements used to encapsulate general -or program-specific tasks. @command{awk} has a number of built-in -functions, and also allows you to define your own. -(@xref{Functions}.) +A part of an @command{awk} program that can be invoked from every point of +the program, to perform a task. @command{awk} has several built-in +functions. +Users can define their own functions in every part of the program. +Function can be recursive, i.e., they may invoke themselves. +@xref{Functions}. +In @command{gawk} it is also possible to have functions shared +among different programs, and included where required using the +@code{@@include} directive +(@pxref{Include Files}). +In @command{gawk} the name of the function that should be invoked +can be generated at run time, i.e., dynamically. +The @command{gawk} extension API provides constructor functions +(@pxref{Constructor Functions}). + @item @command{gawk} The GNU implementation of @command{awk}. @@ -39740,6 +39499,12 @@ meaning. Keywords are reserved and may not be used as variable names. and @code{while}. +@item Korn Shell +The Korn Shell (@command{ksh}) is a Unix shell which was developed by David Korn at Bell +Laboratories in the early 1980s. The Korn Shell is backward-compatible with the Bourne +shell and includes many features of the C shell. +See also ``Bourne Shell.'' + @cindex LGPL (Lesser General Public License) @cindex Lesser General Public License (LGPL) @cindex GNU Lesser General Public License @@ -39779,6 +39544,14 @@ Characters used within a regexp that do not stand for themselves. Instead, they denote regular expression operations, such as repetition, grouping, or alternation. +@item Nesting +Nesting is where information is organized in layers, or where objects +contain other similar objects. +In @command{gawk} the @code{@@include} +directive can be nested. The ``natural'' nesting of arithmetic and +logical operations can be changed using parentheses +(@pxref{Precedence}). + @item No-op An operation that does nothing. @@ -39799,6 +39572,11 @@ Octal numbers are written in C using a leading @samp{0}, to indicate their base. Thus, @code{013} is 11 ((1 x 8) + 3). @xref{Nondecimal-numbers}. +@item Output Record +A single chunk of data that is written out by @command{awk}. Usually, an +@command{awk} output record consists of one or more lines of text. +@xref{Records}. + @item Pattern Patterns tell @command{awk} which input records are interesting to which rules. @@ -39813,6 +39591,9 @@ An acronym describing what is possibly the most frequent source of computer usage problems. (Problem Exists Between Keyboard And Chair.) +@item Plug-in +See ``Extensions.'' + @item POSIX The name for a series of standards that specify a Portable Operating System interface. The ``IX'' denotes @@ -39837,6 +39618,9 @@ A sequence of consecutive lines from the input file(s). A pattern can specify ranges of input lines for @command{awk} to process or it can specify single lines. (@xref{Pattern Overview}.) +@item Record +See ``Input record'' and ``Output record.'' + @item Recursion When a function calls itself, either directly or indirectly. If this is clear, stop, and proceed to the next entry. @@ -39854,6 +39638,15 @@ operators. (@xref{Getline}, and @ref{Redirection}.) +@item Reference Counts +An internal mechanism in @command{gawk} to minimize the amount of memory +needed to store the value of string variables. If the value assumed by +a variable is used in more than one place, only one copy of the value +itself is kept, and the associated reference count is increased when the +same value is used by an additional variable, and decresed when the related +variable is no longer in use. When the reference count goes to zero, +the memory space used to store the value of the variable is freed. + @item Regexp See ``Regular Expression.'' @@ -39871,6 +39664,15 @@ slashes, such as @code{/foo/}. This regular expression is chosen when you write the @command{awk} program and cannot be changed during its execution. (@xref{Regexp Usage}.) +@item Regular Expression Operators +See ``Metacharacters.'' + +@item Rounding +Rounding the result of an arithmetic operation can be tricky. +More than one way of rounding exists, and in @command{gawk} +it is possible to choose which method should be used in a program. +@xref{Setting the rounding mode}. + @item Rule A segment of an @command{awk} program that specifies how to process single input records. A rule consists of a @dfn{pattern} and an @dfn{action}. @@ -39930,6 +39732,12 @@ A @value{FN} interpreted internally by @command{gawk}, instead of being handed directly to the underlying operating system---for example, @file{/dev/stderr}. (@xref{Special Files}.) +@item Statement +An expression inside an @command{awk} program in the action part +of a pattern--action rule, or inside an +@command{awk} function. A statement can be a variable assignment, +an array operation, a loop, etc. + @item Stream Editor A program that reads records from an input stream and processes them one or more at a time. This is in contrast with batch programs, which may @@ -39980,9 +39788,14 @@ This is standard time in Greenwich, England, which is used as a reference time for day and date calculations. See also ``Epoch'' and ``GMT.'' +@item Variable +A name for a value. In @command{awk}, variables may be either scalars +or arrays. + @item Whitespace A sequence of space, TAB, or newline characters occurring inside an input record or a string. + @end table @end ifclear |