diff options
| author | Indrajith K L | 2022-12-03 17:00:20 +0530 |
|---|---|---|
| committer | Indrajith K L | 2022-12-03 17:00:20 +0530 |
| commit | f5c4671bfbad96bf346bd7e9a21fc4317b4959df (patch) | |
| tree | 2764fc62da58f2ba8da7ed341643fc359873142f /coreutils-5.3.0-bin/man/cat1/gawk.1.txt | |
| download | cli-tools-windows-master.tar.gz cli-tools-windows-master.tar.bz2 cli-tools-windows-master.zip | |
Diffstat (limited to 'coreutils-5.3.0-bin/man/cat1/gawk.1.txt')
| -rw-r--r-- | coreutils-5.3.0-bin/man/cat1/gawk.1.txt | 1972 |
1 files changed, 1972 insertions, 0 deletions
diff --git a/coreutils-5.3.0-bin/man/cat1/gawk.1.txt b/coreutils-5.3.0-bin/man/cat1/gawk.1.txt new file mode 100644 index 0000000..a431e7b --- /dev/null +++ b/coreutils-5.3.0-bin/man/cat1/gawk.1.txt @@ -0,0 +1,1972 @@ +GAWK(1) Utility Commands GAWK(1) + + + +NAME + gawk - pattern scanning and processing language + +SYNOPSIS + gawk [ POSIX or GNU style options ] -f program-file [ -- + ] file ... + gawk [ POSIX or GNU style options ] [ -- ] program-text + file ... + + pgawk [ POSIX or GNU style options ] -f program-file [ + -- ] file ... + pgawk [ POSIX or GNU style options ] [ -- ] program-text + file ... + +DESCRIPTION + Gawk is the GNU Project's implementation of the AWK pro- + gramming language. It conforms to the definition of the + language in the POSIX 1003.1 Standard. This version in + turn is based on the description in The AWK Programming + Language, by Aho, Kernighan, and Weinberger, with the + additional features found in the System V Release 4 ver- + sion of UNIX awk. Gawk also provides more recent Bell + Laboratories awk extensions, and a number of GNU-spe- + cific extensions. + + Pgawk is the profiling version of gawk. It is identical + in every way to gawk, except that programs run more + slowly, and it automatically produces an execution pro- + file in the file awkprof.out when done. See the --pro- + file option, below. + + The command line consists of options to gawk itself, the + AWK program text (if not supplied via the -f or --file + options), and values to be made available in the ARGC + and ARGV pre-defined AWK variables. + +OPTION FORMAT + Gawk options may be either traditional POSIX one letter + options, or GNU-style long options. POSIX options start + with a single "-", while long options start with "--". + Long options are provided for both GNU-specific features + and for POSIX-mandated features. + + Following the POSIX standard, gawk-specific options are + supplied via arguments to the -W option. Multiple -W + options may be supplied Each -W option has a correspond- + ing long option, as detailed below. Arguments to long + options are either joined with the option by an = sign, + with no intervening spaces, or they may be provided in + the next command line argument. Long options may be + abbreviated, as long as the abbreviation remains unique. + +OPTIONS + Gawk accepts the following options, listed by frequency. + + -F fs + --field-separator fs + Use fs for the input field separator (the value + of the FS predefined variable). + + -v var=val + --assign var=val + Assign the value val to the variable var, before + execution of the program begins. Such variable + values are available to the BEGIN block of an AWK + program. + + -f program-file + --file program-file + Read the AWK program source from the file pro- + gram-file, instead of from the first command line + argument. Multiple -f (or --file) options may be + used. + + -mf NNN + -mr NNN + Set various memory limits to the value NNN. The + f flag sets the maximum number of fields, and the + r flag sets the maximum record size. These two + flags and the -m option are from an earlier ver- + sion of the Bell Laboratories research version of + UNIX awk. They are ignored by gawk, since gawk + has no pre-defined limits. + + -W compat + -W traditional + --compat + --traditional + Run in compatibility mode. In compatibility + mode, gawk behaves identically to UNIX awk; none + of the GNU-specific extensions are recognized. + The use of --traditional is preferred over the + other forms of this option. See GNU EXTENSIONS, + below, for more information. + + -W copyleft + -W copyright + --copyleft + --copyright + Print the short version of the GNU copyright + information message on the standard output and + exit successfully. + + -W dump-variables[=file] + --dump-variables[=file] + Print a sorted list of global variables, their + types and final values to file. If no file is + provided, gawk uses a file named awkvars.out in + the current directory. + Having a list of all the global variables is a + good way to look for typographical errors in your + programs. You would also use this option if you + have a large program with a lot of functions, and + you want to be sure that your functions don't + inadvertently use global variables that you meant + to be local. (This is a particularly easy mis- + take to make with simple variable names like i, + j, and so on.) + + -W exec file + --exec file + Similar to -f, however, this is option is the + last one processed. This should be used with #! + scripts, particularly for CGI applications, to + avoid passing in options or source code (!) on + the command line from a URL. This option dis- + ables command-line variable assignments. + + -W gen-po + --gen-po + Scan and parse the AWK program, and generate a + GNU .po format file on standard output with + entries for all localizable strings in the pro- + gram. The program itself is not executed. See + the GNU gettext distribution for more information + on .po files. + + -W help + -W usage + --help + --usage + Print a relatively short summary of the available + options on the standard output. (Per the GNU + Coding Standards, these options cause an immedi- + ate, successful exit.) + + -W lint[=value] + --lint[=value] + Provide warnings about constructs that are dubi- + ous or non-portable to other AWK implementations. + With an optional argument of fatal, lint warnings + become fatal errors. This may be drastic, but + its use will certainly encourage the development + of cleaner AWK programs. With an optional argu- + ment of invalid, only warnings about things that + are actually invalid are issued. (This is not + fully implemented yet.) + + -W lint-old + --lint-old + Provide warnings about constructs that are not + portable to the original version of Unix awk. + + -W non-decimal-data + --non-decimal-data + Recognize octal and hexadecimal values in input + data. Use this option with great caution! + + -W posix + --posix + This turns on compatibility mode, with the fol- + lowing additional restrictions: + + · \x escape sequences are not recognized. + + · Only space and tab act as field separators when + FS is set to a single space, newline does not. + + · You cannot continue lines after ? and :. + + · The synonym func for the keyword function is + not recognized. + + · The operators ** and **= cannot be used in + place of ^ and ^=. + + · The fflush() function is not available. + + -W profile[=prof_file] + --profile[=prof_file] + Send profiling data to prof_file. The default is + awkprof.out. When run with gawk, the profile is + just a "pretty printed" version of the program. + When run with pgawk, the profile contains execu- + tion counts of each statement in the program in + the left margin and function call counts for each + user-defined function. + + -W re-interval + --re-interval + Enable the use of interval expressions in regular + expression matching (see Regular Expressions, + below). Interval expressions were not tradition- + ally available in the AWK language. The POSIX + standard added them, to make awk and egrep con- + sistent with each other. However, their use is + likely to break old AWK programs, so gawk only + provides them if they are requested with this + option, or when --posix is specified. + + -W source program-text + --source program-text + Use program-text as AWK program source code. + This option allows the easy intermixing of + library functions (used via the -f and --file + options) with source code entered on the command + line. It is intended primarily for medium to + large AWK programs used in shell scripts. + + -W use-lc-numeric + --use-lc-numeric + This forces gawk to use the locale's decimal + point character when parsing input data. + Although the POSIX standard requires this behav- + ior, and gawk does so when --posix is in effect, + the default is to follow traditional behavior and + use a period as the decimal point, even in + locales where the period is not the decimal point + character. This option overrides the default + behavior, without the full draconian strictness + of the --posix option. + + -W version + --version + Print version information for this particular + copy of gawk on the standard output. This is + useful mainly for knowing if the current copy of + gawk on your system is up to date with respect to + whatever the Free Software Foundation is dis- + tributing. This is also useful when reporting + bugs. (Per the GNU Coding Standards, these + options cause an immediate, successful exit.) + + -- Signal the end of options. This is useful to + allow further arguments to the AWK program itself + to start with a "-". This provides consistency + with the argument parsing convention used by most + other POSIX programs. + In compatibility mode, any other options are flagged as + invalid, but are otherwise ignored. In normal opera- + tion, as long as program text has been supplied, unknown + options are passed on to the AWK program in the ARGV + array for processing. This is particularly useful for + running AWK programs via the "#!" executable interpreter + mechanism. +AWK PROGRAM EXECUTION + An AWK program consists of a sequence of pattern-action + statements and optional function definitions. + pattern { action statements } + function name(parameter list) { statements } + Gawk first reads the program source from the program- + file(s) if specified, from arguments to --source, or + from the first non-option argument on the command line. + The -f and --source options may be used multiple times + on the command line. Gawk reads the program text as if + all the program-files and command line source texts had + been concatenated together. This is useful for building + libraries of AWK functions, without having to include + them in each new AWK program that uses them. It also + provides the ability to mix library functions with com- + mand line programs. + The environment variable AWKPATH specifies a search path + to use when finding source files named with the -f + option. If this variable does not exist, the default + path is ".:/usr/local/share/awk". (The actual directory + may vary, depending upon how gawk was built and + installed.) If a file name given to the -f option con- + tains a "/" character, no path search is performed. + Gawk executes AWK programs in the following order. + First, all variable assignments specified via the -v + option are performed. Next, gawk compiles the program + into an internal form. Then, gawk executes the code in + the BEGIN block(s) (if any), and then proceeds to read + each file named in the ARGV array. If there are no + files named on the command line, gawk reads the standard + input. + If a filename on the command line has the form var=val + it is treated as a variable assignment. The variable + var will be assigned the value val. (This happens after + any BEGIN block(s) have been run.) Command line vari- + able assignment is most useful for dynamically assigning + values to the variables AWK uses to control how input is + broken into fields and records. It is also useful for + controlling state if multiple passes are needed over a + single data file. + If the value of a particular element of ARGV is empty + (""), gawk skips over it. + For each record in the input, gawk tests to see if it + matches any pattern in the AWK program. For each pat- + tern that the record matches, the associated action is + executed. The patterns are tested in the order they + occur in the program. + Finally, after all the input is exhausted, gawk executes + the code in the END block(s) (if any). +VARIABLES, RECORDS AND FIELDS + AWK variables are dynamic; they come into existence when + they are first used. Their values are either floating- + point numbers or strings, or both, depending upon how + they are used. AWK also has one dimensional arrays; + arrays with multiple dimensions may be simulated. Sev- + eral pre-defined variables are set as a program runs; + these are described as needed and summarized below. + Records + Normally, records are separated by newline characters. + You can control how records are separated by assigning + values to the built-in variable RS. If RS is any single + character, that character separates records. Otherwise, + RS is a regular expression. Text in the input that + matches this regular expression separates the record. + However, in compatibility mode, only the first character + of its string value is used for separating records. If + RS is set to the null string, then records are separated + by blank lines. When RS is set to the null string, the + newline character always acts as a field separator, in + addition to whatever value FS may have. + Fields + As each input record is read, gawk splits the record + into fields, using the value of the FS variable as the + field separator. If FS is a single character, fields + are separated by that character. If FS is the null + string, then each individual character becomes a sepa- + rate field. Otherwise, FS is expected to be a full reg- + ular expression. In the special case that FS is a sin- + gle space, fields are separated by runs of spaces and/or + tabs and/or newlines. (But see the section POSIX COM- + PATIBILITY, below). NOTE: The value of IGNORECASE (see + below) also affects how fields are split when FS is a + regular expression, and how records are separated when + RS is a regular expression. + If the FIELDWIDTHS variable is set to a space separated + list of numbers, each field is expected to have fixed + width, and gawk splits up the record using the specified + widths. The value of FS is ignored. Assigning a new + value to FS overrides the use of FIELDWIDTHS, and + restores the default behavior. + Each field in the input record may be referenced by its + position, $1, $2, and so on. $0 is the whole record. + Fields need not be referenced by constants: + n = 5 + print $n + prints the fifth field in the input record. + The variable NF is set to the total number of fields in + the input record. + References to non-existent fields (i.e. fields after + $NF) produce the null-string. However, assigning to a + non-existent field (e.g., $(NF+2) = 5) increases the + value of NF, creates any intervening fields with the + null string as their value, and causes the value of $0 + to be recomputed, with the fields being separated by the + value of OFS. References to negative numbered fields + cause a fatal error. Decrementing NF causes the values + of fields past the new value to be lost, and the value + of $0 to be recomputed, with the fields being separated + by the value of OFS. + Assigning a value to an existing field causes the whole + record to be rebuilt when $0 is referenced. Similarly, + assigning a value to $0 causes the record to be resplit, + creating new values for the fields. + Built-in Variables + Gawk's built-in variables are: + ARGC The number of command line arguments (does + not include options to gawk, or the program + source). + ARGIND The index in ARGV of the current file being + processed. + ARGV Array of command line arguments. The array + is indexed from 0 to ARGC - 1. Dynamically + changing the contents of ARGV can control + the files used for data. + BINMODE On non-POSIX systems, specifies use of + "binary" mode for all file I/O. Numeric + values of 1, 2, or 3, specify that input + files, output files, or all files, respec- + tively, should use binary I/O. String val- + ues of "r", or "w" specify that input files, + or output files, respectively, should use + binary I/O. String values of "rw" or "wr" + specify that all files should use binary + I/O. Any other string value is treated as + "rw", but generates a warning message. + CONVFMT The conversion format for numbers, "%.6g", + by default. + ENVIRON An array containing the values of the cur- + rent environment. The array is indexed by + the environment variables, each element + being the value of that variable (e.g., ENV- + IRON["HOME"] might be /home/arnold). Chang- + ing this array does not affect the environ- + ment seen by programs which gawk spawns via + redirection or the system() function. + ERRNO If a system error occurs either doing a + redirection for getline, during a read for + getline, or during a close(), then ERRNO + will contain a string describing the error. + The value is subject to translation in non- + English locales. + FIELDWIDTHS A white-space separated list of fieldwidths. + When set, gawk parses the input into fields + of fixed width, instead of using the value + of the FS variable as the field separator. + FILENAME The name of the current input file. If no + files are specified on the command line, the + value of FILENAME is "-". However, FILENAME + is undefined inside the BEGIN block (unless + set by getline). + FNR The input record number in the current input + file. + FS The input field separator, a space by + default. See Fields, above. + IGNORECASE Controls the case-sensitivity of all regular + expression and string operations. If + IGNORECASE has a non-zero value, then string + comparisons and pattern matching in rules, + field splitting with FS, record separating + with RS, regular expression matching with ~ + and !~, and the gensub(), gsub(), index(), + match(), split(), and sub() built-in func- + tions all ignore case when doing regular + expression operations. NOTE: Array sub- + scripting is not affected. However, the + asort() and asorti() functions are affected. + Thus, if IGNORECASE is not equal to zero, + /aB/ matches all of the strings "ab", "aB", + "Ab", and "AB". As with all AWK variables, + the initial value of IGNORECASE is zero, so + all regular expression and string operations + are normally case-sensitive. Under Unix, + the full ISO 8859-1 Latin-1 character set is + used when ignoring case. As of gawk 3.1.4, + the case equivalencies are fully locale- + aware, based on the C <ctype.h> facilities + such as isalpha(), and toupper(). + LINT Provides dynamic control of the --lint + option from within an AWK program. When + true, gawk prints lint warnings. When false, + it does not. When assigned the string value + "fatal", lint warnings become fatal errors, + exactly like --lint=fatal. Any other true + value just prints warnings. + NF The number of fields in the current input + record. + NR The total number of input records seen so + far. + OFMT The output format for numbers, "%.6g", by + default. + OFS The output field separator, a space by + default. + ORS The output record separator, by default a + newline. + PROCINFO The elements of this array provide access to + information about the running AWK program. + On some systems, there may be elements in + the array, "group1" through "groupn" for + some n, which is the number of supplementary + groups that the process has. Use the in + operator to test for these elements. The + following elements are guaranteed to be + available: + PROCINFO["egid"] the value of the gete- + gid(2) system call. + PROCINFO["euid"] the value of the + geteuid(2) system call. + PROCINFO["FS"] "FS" if field splitting + with FS is in effect, or + "FIELDWIDTHS" if field + splitting with FIELD- + WIDTHS is in effect. + PROCINFO["gid"] the value of the get- + gid(2) system call. + PROCINFO["pgrpid"] the process group ID of + the current process. + PROCINFO["pid"] the process ID of the + current process. + PROCINFO["ppid"] the parent process ID of + the current process. + PROCINFO["uid"] the value of the + getuid(2) system call. + PROCINFO["version"] + The version of gawk. + This is available from + version 3.1.4 and later. + RS The input record separator, by default a + newline. + RT The record terminator. Gawk sets RT to the + input text that matched the character or + regular expression specified by RS. + RSTART The index of the first character matched by + match(); 0 if no match. (This implies that + character indices start at one.) + RLENGTH The length of the string matched by match(); + -1 if no match. + SUBSEP The character used to separate multiple sub- + scripts in array elements, by default + "\034". + TEXTDOMAIN The text domain of the AWK program; used to + find the localized translations for the pro- + gram's strings. + Arrays + Arrays are subscripted with an expression between square + brackets ([ and ]). If the expression is an expression + list (expr, expr ...) then the array subscript is a + string consisting of the concatenation of the (string) + value of each expression, separated by the value of the + SUBSEP variable. This facility is used to simulate mul- + tiply dimensioned arrays. For example: + i = "A"; j = "B"; k = "C" + x[i, j, k] = "hello, world\n" + assigns the string "hello, world\n" to the element of + the array x which is indexed by the string + "A\034B\034C". All arrays in AWK are associative, i.e. + indexed by string values. + The special operator in may be used to test if an array + has an index consisting of a particular value. + if (val in array) + print array[val] + If the array has multiple subscripts, use (i, j) in + array. + The in construct may also be used in a for loop to iter- + ate over all the elements of an array. + An element may be deleted from an array using the delete + statement. The delete statement may also be used to + delete the entire contents of an array, just by specify- + ing the array name without a subscript. + Variable Typing And Conversion + Variables and fields may be (floating point) numbers, or + strings, or both. How the value of a variable is inter- + preted depends upon its context. If used in a numeric + expression, it will be treated as a number; if used as a + string it will be treated as a string. + To force a variable to be treated as a number, add 0 to + it; to force it to be treated as a string, concatenate + it with the null string. + When a string must be converted to a number, the conver- + sion is accomplished using strtod(3). A number is con- + verted to a string by using the value of CONVFMT as a + format string for sprintf(3), with the numeric value of + the variable as the argument. However, even though all + numbers in AWK are floating-point, integral values are + always converted as integers. Thus, given + CONVFMT = "%2.2f" + a = 12 + b = a "" + the variable b has a string value of "12" and not + "12.00". + When operating in POSIX mode (such as with the --posix + command line option), beware that locale settings may + interfere with the way decimal numbers are treated: the + decimal separator of the numbers you are feeding to gawk + must conform to what your locale would expect, be it a + comma (,) or a period (.). + Gawk performs comparisons as follows: If two variables + are numeric, they are compared numerically. If one + value is numeric and the other has a string value that + is a "numeric string," then comparisons are also done + numerically. Otherwise, the numeric value is converted + to a string and a string comparison is performed. Two + strings are compared, of course, as strings. + Note that string constants, such as "57", are not + numeric strings, they are string constants. The idea of + "numeric string" only applies to fields, getline input, + FILENAME, ARGV elements, ENVIRON elements and the ele- + ments of an array created by split() that are numeric + strings. The basic idea is that user input, and only + user input, that looks numeric, should be treated that + way. + Uninitialized variables have the numeric value 0 and the + string value "" (the null, or empty, string). + Octal and Hexadecimal Constants + Starting with version 3.1 of gawk , you may use C-style + octal and hexadecimal constants in your AWK program + source code. For example, the octal value 011 is equal + to decimal 9, and the hexadecimal value 0x11 is equal to + decimal 17. + String Constants + String constants in AWK are sequences of characters + enclosed between double quotes ("). Within strings, + certain escape sequences are recognized, as in C. These + are: + \\ A literal backslash. + \a The "alert" character; usually the ASCII BEL char- + acter. + \b backspace. + \f form-feed. + \n newline. + \r carriage return. + \t horizontal tab. + \v vertical tab. + \xhex digits + The character represented by the string of hexadec- + imal digits following the \x. As in ANSI C, all + following hexadecimal digits are considered part of + the escape sequence. (This feature should tell us + something about language design by committee.) + E.g., "\x1B" is the ASCII ESC (escape) character. + \ddd The character represented by the 1-, 2-, or 3-digit + sequence of octal digits. E.g., "\033" is the + ASCII ESC (escape) character. + \c The literal character c. + The escape sequences may also be used inside constant + regular expressions (e.g., /[ \t\f\n\r\v]/ matches + whitespace characters). + In compatibility mode, the characters represented by + octal and hexadecimal escape sequences are treated lit- + erally when used in regular expression constants. Thus, + /a\52b/ is equivalent to /a\*b/. +PATTERNS AND ACTIONS + AWK is a line-oriented language. The pattern comes + first, and then the action. Action statements are + enclosed in { and }. Either the pattern may be missing, + or the action may be missing, but, of course, not both. + If the pattern is missing, the action is executed for + every single record of input. A missing action is + equivalent to + { print } + which prints the entire record. + Comments begin with the "#" character, and continue + until the end of the line. Blank lines may be used to + separate statements. Normally, a statement ends with a + newline, however, this is not the case for lines ending + in a ",", {, ?, :, &&, or ||. Lines ending in do or + else also have their statements automatically continued + on the following line. In other cases, a line can be + continued by ending it with a "\", in which case the + newline will be ignored. + Multiple statements may be put on one line by separating + them with a ";". This applies to both the statements + within the action part of a pattern-action pair (the + usual case), and to the pattern-action statements them- + selves. + Patterns + AWK patterns may be one of the following: + BEGIN + END + /regular expression/ + relational expression + pattern && pattern + pattern || pattern + pattern ? pattern : pattern + (pattern) + ! pattern + pattern1, pattern2 + BEGIN and END are two special kinds of patterns which + are not tested against the input. The action parts of + all BEGIN patterns are merged as if all the statements + had been written in a single BEGIN block. They are exe- + cuted before any of the input is read. Similarly, all + the END blocks are merged, and executed when all the + input is exhausted (or when an exit statement is exe- + cuted). BEGIN and END patterns cannot be combined with + other patterns in pattern expressions. BEGIN and END + patterns cannot have missing action parts. + For /regular expression/ patterns, the associated state- + ment is executed for each input record that matches the + regular expression. Regular expressions are the same as + those in egrep(1), and are summarized below. + A relational expression may use any of the operators + defined below in the section on actions. These gener- + ally test whether certain fields match certain regular + expressions. + The &&, ||, and ! operators are logical AND, logical + OR, and logical NOT, respectively, as in C. They do + short-circuit evaluation, also as in C, and are used for + combining more primitive pattern expressions. As in + most languages, parentheses may be used to change the + order of evaluation. + The ?: operator is like the same operator in C. If the + first pattern is true then the pattern used for testing + is the second pattern, otherwise it is the third. Only + one of the second and third patterns is evaluated. + The pattern1, pattern2 form of an expression is called a + range pattern. It matches all input records starting + with a record that matches pattern1, and continuing + until a record that matches pattern2, inclusive. It + does not combine with any other sort of pattern expres- + sion. + Regular Expressions + Regular expressions are the extended kind found in + egrep. They are composed of characters as follows: + c matches the non-metacharacter c. + \c matches the literal character c. + . matches any character including newline. + ^ matches the beginning of a string. + $ matches the end of a string. + [abc...] character list, matches any of the characters + abc.... + [^abc...] negated character list, matches any character + except abc.... + r1|r2 alternation: matches either r1 or r2. + r1r2 concatenation: matches r1, and then r2. + r+ matches one or more r's. + r* matches zero or more r's. + r? matches zero or one r's. + (r) grouping: matches r. + r{n} + r{n,} + r{n,m} One or two numbers inside braces denote an + interval expression. If there is one number + in the braces, the preceding regular expres- + sion r is repeated n times. If there are two + numbers separated by a comma, r is repeated n + to m times. If there is one number followed + by a comma, then r is repeated at least n + times. + Interval expressions are only available if + either --posix or --re-interval is specified + on the command line. + + \y matches the empty string at either the begin- + ning or the end of a word. + + \B matches the empty string within a word. + + \< matches the empty string at the beginning of + a word. + + \> matches the empty string at the end of a + word. + + \w matches any word-constituent character (let- + ter, digit, or underscore). + + \W matches any character that is not word-con- + stituent. + + \` matches the empty string at the beginning of + a buffer (string). + + \' matches the empty string at the end of a + buffer. + + The escape sequences that are valid in string constants + (see below) are also valid in regular expressions. + + Character classes are a feature introduced in the POSIX + standard. A character class is a special notation for + describing lists of characters that have a specific + attribute, but where the actual characters themselves + can vary from country to country and/or from character + set to character set. For example, the notion of what + is an alphabetic character differs in the USA and in + France. + + A character class is only valid in a regular expression + inside the brackets of a character list. Character + classes consist of [:, a keyword denoting the class, and + :]. The character classes defined by the POSIX standard + are: + + [:alnum:] Alphanumeric characters. + + [:alpha:] Alphabetic characters. + + [:blank:] Space or tab characters. + + [:cntrl:] Control characters. + + [:digit:] Numeric characters. + + [:graph:] Characters that are both printable and visi- + ble. (A space is printable, but not visible, + while an a is both.) + + [:lower:] Lower-case alphabetic characters. + + [:print:] Printable characters (characters that are not + control characters.) + + [:punct:] Punctuation characters (characters that are + not letter, digits, control characters, or + space characters). + + [:space:] Space characters (such as space, tab, and + formfeed, to name a few). + + [:upper:] Upper-case alphabetic characters. + + [:xdigit:] Characters that are hexadecimal digits. + + For example, before the POSIX standard, to match + alphanumeric characters, you would have had to write + /[A-Za-z0-9]/. If your character set had other alpha- + betic characters in it, this would not match them, and + if your character set collated differently from ASCII, + this might not even match the ASCII alphanumeric charac- + ters. With the POSIX character classes, you can write + /[[:alnum:]]/, and this matches the alphabetic and + numeric characters in your character set, no matter what + it is. + + Two additional special sequences can appear in character + lists. These apply to non-ASCII character sets, which + can have single symbols (called collating elements) that + are represented with more than one character, as well as + several characters that are equivalent for collating, or + sorting, purposes. (E.g., in French, a plain "e" and a + grave-accented "`" are equivalent.) + + Collating Symbols + A collating symbol is a multi-character collating + element enclosed in [. and .]. For example, if + ch is a collating element, then [[.ch.]] is a + regular expression that matches this collating + element, while [ch] is a regular expression that + matches either c or h. + + Equivalence Classes + An equivalence class is a locale-specific name + for a list of characters that are equivalent. + The name is enclosed in [= and =]. For example, + the name e might be used to represent all of "e," + "´," and "`." In this case, [[=e=]] is a regular + expression that matches any of e, ´, or `. + + These features are very valuable in non-English speaking + locales. The library functions that gawk uses for regu- + lar expression matching currently only recognize POSIX + character classes; they do not recognize collating sym- + bols or equivalence classes. + + The \y, \B, \<, \>, \w, \W, \`, and \' operators are + specific to gawk; they are extensions based on facili- + ties in the GNU regular expression libraries. + + The various command line options control how gawk inter- + prets characters in regular expressions. + + No options + In the default case, gawk provide all the facili- + ties of POSIX regular expressions and the GNU + regular expression operators described above. + However, interval expressions are not supported. + + --posix + Only POSIX regular expressions are supported, the + GNU operators are not special. (E.g., \w matches + a literal w). Interval expressions are allowed. + + --traditional + Traditional Unix awk regular expressions are + matched. The GNU operators are not special, + interval expressions are not available, and nei- + ther are the POSIX character classes ([[:alnum:]] + and so on). Characters described by octal and + hexadecimal escape sequences are treated liter- + ally, even if they represent regular expression + metacharacters. + + --re-interval + Allow interval expressions in regular expres- + sions, even if --traditional has been provided. + + Actions + Action statements are enclosed in braces, { and }. + Action statements consist of the usual assignment, con- + ditional, and looping statements found in most lan- + guages. The operators, control statements, and + input/output statements available are patterned after + those in C. + + Operators + The operators in AWK, in order of decreasing precedence, + are + + + (...) Grouping + + $ Field reference. + + ++ -- Increment and decrement, both prefix and + postfix. + + ^ Exponentiation (** may also be used, and **= + for the assignment operator). + + + - ! Unary plus, unary minus, and logical nega- + tion. + + * / % Multiplication, division, and modulus. + + + - Addition and subtraction. + + space String concatenation. + + | |& Piped I/O for getline, print, and printf. + + < > + <= >= + != == The regular relational operators. + + ~ !~ Regular expression match, negated match. + NOTE: Do not use a constant regular expres- + sion (/foo/) on the left-hand side of a ~ or + !~. Only use one on the right-hand side. + The expression /foo/ ~ exp has the same + meaning as (($0 ~ /foo/) ~ exp). This is + usually not what was intended. + + in Array membership. + + && Logical AND. + + || Logical OR. + + ?: The C conditional expression. This has the + form expr1 ? expr2 : expr3. If expr1 is + true, the value of the expression is expr2, + otherwise it is expr3. Only one of expr2 + and expr3 is evaluated. + + = += -= + *= /= %= ^= Assignment. Both absolute assignment (var = + value) and operator-assignment (the other + forms) are supported. + + Control Statements + The control statements are as follows: + + if (condition) statement [ else statement ] + while (condition) statement + do statement while (condition) + for (expr1; expr2; expr3) statement + for (var in array) statement + break + continue + delete array[index] + delete array + exit [ expression ] + { statements } + + I/O Statements + The input/output statements are as follows: + + + close(file [, how]) Close file, pipe or co-process. + The optional how should only be + used when closing one end of a + two-way pipe to a co-process. It + must be a string value, either + "to" or "from". + + getline Set $0 from next input record; set + NF, NR, FNR. + + getline <file Set $0 from next record of file; + set NF. + + getline var Set var from next input record; + set NR, FNR. + + getline var <file Set var from next record of file. + + command | getline [var] + Run command piping the output + either into $0 or var, as above. + + command |& getline [var] + Run command as a co-process piping + the output either into $0 or var, + as above. Co-processes are a gawk + extension. (command can also be a + socket. See the subsection Spe- + cial File Names, below.) + + next Stop processing the current input + record. The next input record is + read and processing starts over + with the first pattern in the AWK + program. If the end of the input + data is reached, the END block(s), + if any, are executed. + + nextfile Stop processing the current input + file. The next input record read + comes from the next input file. + FILENAME and ARGIND are updated, + FNR is reset to 1, and processing + starts over with the first pattern + in the AWK program. If the end of + the input data is reached, the END + block(s), if any, are executed. + + print Prints the current record. The + output record is terminated with + the value of the ORS variable. + + print expr-list Prints expressions. Each expres- + sion is separated by the value of + the OFS variable. The output + record is terminated with the + value of the ORS variable. + + print expr-list >file Prints expressions on file. Each + expression is separated by the + value of the OFS variable. The + output record is terminated with + the value of the ORS variable. + + printf fmt, expr-list Format and print. + + printf fmt, expr-list >file + Format and print on file. + + system(cmd-line) Execute the command cmd-line, and + return the exit status. (This may + not be available on non-POSIX sys- + tems.) + + fflush([file]) Flush any buffers associated with + the open output file or pipe file. + If file is missing, then standard + output is flushed. If file is the + null string, then all open output + files and pipes have their buffers + flushed. + + Additional output redirections are allowed for print and + printf. + + print ... >> file + Appends output to the file. + + print ... | command + Writes on a pipe. + + print ... |& command + Sends data to a co-process or socket. (See also + the subsection Special File Names, below.) + + The getline command returns 0 on end of file and -1 on + an error. Upon an error, ERRNO contains a string + describing the problem. + + NOTE: If using a pipe, co-process, or socket to getline, + or from print or printf within a loop, you must use + close() to create new instances of the command or + socket. AWK does not automatically close pipes, sock- + ets, or co-processes when they return EOF. + + The printf Statement + The AWK versions of the printf statement and sprintf() + function (see below) accept the following conversion + specification formats: + + %c An ASCII character. If the argument used for %c + is numeric, it is treated as a character and + printed. Otherwise, the argument is assumed to + be a string, and the only first character of + that string is printed. + + %d, %i A decimal number (the integer part). + + %e, %E A floating point number of the form + [-]d.dddddde[+-]dd. The %E format uses E + instead of e. + + %f, %F A floating point number of the form + [-]ddd.dddddd. If the system library supports + it, %F is available as well. This is like %f, + but uses capital letters for special "not a num- + ber" and "infinity" values. If %F is not avail- + able, gawk uses %f. + + %g, %G Use %e or %f conversion, whichever is shorter, + with nonsignificant zeros suppressed. The %G + format uses %E instead of %e. + + %o An unsigned octal number (also an integer). + + %u An unsigned decimal number (again, an integer). + + %s A character string. + + %x, %X An unsigned hexadecimal number (an integer). + The %X format uses ABCDEF instead of abcdef. + + %% A single % character; no argument is converted. + + NOTE: When using the integer format-control letters for + values that are outside the range of a C long integer, + gawk switches to the %0f format specifier. If --lint is + provided on the command line gawk warns about this. + Other versions of awk may print invalid values or do + something else entirely. + + Optional, additional parameters may lie between the % + and the control letter: + + count$ Use the count'th argument at this point in the + formatting. This is called a positional speci- + fier and is intended primarily for use in trans- + lated versions of format strings, not in the + original text of an AWK program. It is a gawk + extension. + + - The expression should be left-justified within + its field. + + space For numeric conversions, prefix positive values + with a space, and negative values with a minus + sign. + + + The plus sign, used before the width modifier + (see below), says to always supply a sign for + numeric conversions, even if the data to be for- + matted is positive. The + overrides the space + modifier. + + # Use an "alternate form" for certain control let- + ters. For %o, supply a leading zero. For %x, + and %X, supply a leading 0x or 0X for a nonzero + result. For %e, %E, %f and %F, the result always + contains a decimal point. For %g, and %G, trail- + ing zeros are not removed from the result. + + 0 A leading 0 (zero) acts as a flag, that indicates + output should be padded with zeroes instead of + spaces. This applies even to non-numeric output + formats. This flag only has an effect when the + field width is wider than the value to be + printed. + + width The field should be padded to this width. The + field is normally padded with spaces. If the 0 + flag has been used, it is padded with zeroes. + + .prec A number that specifies the precision to use when + printing. For the %e, %E, %f and %F, formats, + this specifies the number of digits you want + printed to the right of the decimal point. For + the %g, and %G formats, it specifies the maximum + number of significant digits. For the %d, %o, + %i, %u, %x, and %X formats, it specifies the min- + imum number of digits to print. For %s, it spec- + ifies the maximum number of characters from the + string that should be printed. + + The dynamic width and prec capabilities of the ANSI C + printf() routines are supported. A * in place of either + the width or prec specifications causes their values to + be taken from the argument list to printf or sprintf(). + To use a positional specifier with a dynamic width or + precision, supply the count$ after the * in the format + string. For example, "%3$*2$.*1$s". + + Special File Names + When doing I/O redirection from either print or printf + into a file, or via getline from a file, gawk recognizes + certain special filenames internally. These filenames + allow access to open file descriptors inherited from + gawk's parent process (usually the shell). These file + names may also be used on the command line to name data + files. The filenames are: + + /dev/stdin The standard input. + + /dev/stdout The standard output. + + /dev/stderr The standard error output. + + /dev/fd/n The file associated with the open file + descriptor n. + + These are particularly useful for error messages. For + example: + + print "You blew it!" > "/dev/stderr" + + whereas you would otherwise have to use + + print "You blew it!" | "cat 1>&2" + + The following special filenames may be used with the |& + co-process operator for creating TCP/IP network connec- + tions. + + /inet/tcp/lport/rhost/rport File for TCP/IP connection + on local port lport to + remote host rhost on remote + port rport. Use a port of + 0 to have the system pick a + port. + + /inet/udp/lport/rhost/rport Similar, but use UDP/IP + instead of TCP/IP. + + /inet/raw/lport/rhost/rport Reserved for future use. + + Other special filenames provide access to information + about the running gawk process. These filenames are now + obsolete. Use the PROCINFO array to obtain the informa- + tion they provide. The filenames are: + + /dev/pid Reading this file returns the process ID of + the current process, in decimal, terminated + with a newline. + + /dev/ppid Reading this file returns the parent process + ID of the current process, in decimal, ter- + minated with a newline. + + /dev/pgrpid Reading this file returns the process group + ID of the current process, in decimal, ter- + minated with a newline. + + /dev/user Reading this file returns a single record + terminated with a newline. The fields are + separated with spaces. $1 is the value of + the getuid(2) system call, $2 is the value + of the geteuid(2) system call, $3 is the + value of the getgid(2) system call, and $4 + is the value of the getegid(2) system call. + If there are any additional fields, they are + the group IDs returned by getgroups(2). + Multiple groups may not be supported on all + systems. + + Numeric Functions + AWK has the following built-in arithmetic functions: + + + atan2(y, x) Returns the arctangent of y/x in radians. + + cos(expr) Returns the cosine of expr, which is in + radians. + + exp(expr) The exponential function. + + int(expr) Truncates to integer. + + log(expr) The natural logarithm function. + + rand() Returns a random number N, between 0 and + 1, such that 0 <= N < 1. + + sin(expr) Returns the sine of expr, which is in + radians. + + sqrt(expr) The square root function. + + srand([expr]) Uses expr as a new seed for the random + number generator. If no expr is provided, + the time of day is used. The return value + is the previous seed for the random number + generator. + + String Functions + Gawk has the following built-in string functions: + + + asort(s [, d]) Returns the number of elements + in the source array s. The con- + tents of s are sorted using + gawk's normal rules for compar- + ing values, and the indices of + the sorted values of s are + replaced with sequential inte- + gers starting with 1. If the + optional destination array d is + specified, then s is first + duplicated into d, and then d is + sorted, leaving the indices of + the source array s unchanged. + + asorti(s [, d]) Returns the number of elements + in the source array s. The + behavior is the same as that of + asort(), except that the array + indices are used for sorting, + not the array values. When + done, the array is indexed + numerically, and the values are + those of the original indices. + The original values are lost; + thus provide a second array if + you wish to preserve the origi- + nal. + + gensub(r, s, h [, t]) Search the target string t for + matches of the regular expres- + sion r. If h is a string begin- + ning with g or G, then replace + all matches of r with s. Other- + wise, h is a number indicating + which match of r to replace. If + t is not supplied, $0 is used + instead. Within the replacement + text s, the sequence \n, where n + is a digit from 1 to 9, may be + used to indicate just the text + that matched the n'th parenthe- + sized subexpression. The + sequence \0 represents the + entire matched text, as does the + character &. Unlike sub() and + gsub(), the modified string is + returned as the result of the + function, and the original tar- + get string is not changed. + + gsub(r, s [, t]) For each substring matching the + regular expression r in the + string t, substitute the string + s, and return the number of sub- + stitutions. If t is not sup- + plied, use $0. An & in the + replacement text is replaced + with the text that was actually + matched. Use \& to get a lit- + eral &. (This must be typed as + "\\&"; see GAWK: Effective AWK + Programming for a fuller discus- + sion of the rules for &'s and + backslashes in the replacement + text of sub(), gsub(), and gen- + sub().) + + index(s, t) Returns the index of the string + t in the string s, or 0 if t is + not present. (This implies that + character indices start at one.) + + length([s]) Returns the length of the string + s, or the length of $0 if s is + not supplied. Starting with + version 3.1.5, as a non-standard + extension, with an array argu- + ment, length() returns the num- + ber of elements in the array. + + match(s, r [, a]) Returns the position in s where + the regular expression r occurs, + or 0 if r is not present, and + sets the values of RSTART and + RLENGTH. Note that the argument + order is the same as for the ~ + operator: str ~ re. If array a + is provided, a is cleared and + then elements 1 through n are + filled with the portions of s + that match the corresponding + parenthesized subexpression in + r. The 0'th element of a con- + tains the portion of s matched + by the entire regular expression + r. Subscripts a[n, "start"], + and a[n, "length"] provide the + starting index in the string and + length respectively, of each + matching substring. + + split(s, a [, r]) Splits the string s into the + array a on the regular expres- + sion r, and returns the number + of fields. If r is omitted, FS + is used instead. The array a is + cleared first. Splitting + behaves identically to field + splitting, described above. + + sprintf(fmt, expr-list) Prints expr-list according to + fmt, and returns the resulting + string. + + strtonum(str) Examines str, and returns its + numeric value. If str begins + with a leading 0, strtonum() + assumes that str is an octal + number. If str begins with a + leading 0x or 0X, strtonum() + assumes that str is a hexadeci- + mal number. + + sub(r, s [, t]) Just like gsub(), but only the + first matching substring is + replaced. + + substr(s, i [, n]) Returns the at most n-character + substring of s starting at i. + If n is omitted, the rest of s + is used. + + tolower(str) Returns a copy of the string + str, with all the upper-case + characters in str translated to + their corresponding lower-case + counterparts. Non-alphabetic + characters are left unchanged. + + toupper(str) Returns a copy of the string + str, with all the lower-case + characters in str translated to + their corresponding upper-case + counterparts. Non-alphabetic + characters are left unchanged. + + As of version 3.1.5, gawk is multibyte aware. This + means that index(), length(), substr() and match() all + work in terms of characters, not bytes. + + Time Functions + Since one of the primary uses of AWK programs is pro- + cessing log files that contain time stamp information, + gawk provides the following functions for obtaining time + stamps and formatting them. + + + mktime(datespec) + Turns datespec into a time stamp of the same + form as returned by systime(). The datespec + is a string of the form YYYY MM DD HH MM SS[ + DST]. The contents of the string are six or + seven numbers representing respectively the + full year including century, the month from 1 + to 12, the day of the month from 1 to 31, the + hour of the day from 0 to 23, the minute from + 0 to 59, and the second from 0 to 60, and an + optional daylight saving flag. The values of + these numbers need not be within the ranges + specified; for example, an hour of -1 means 1 + hour before midnight. The origin-zero Grego- + rian calendar is assumed, with year 0 preced- + ing year 1 and year -1 preceding year 0. The + time is assumed to be in the local timezone. + If the daylight saving flag is positive, the + time is assumed to be daylight saving time; if + zero, the time is assumed to be standard time; + and if negative (the default), mktime() + attempts to determine whether daylight saving + time is in effect for the specified time. If + datespec does not contain enough elements or + if the resulting time is out of range, + mktime() returns -1. + + strftime([format [, timestamp[, utc-flag]]]) + Formats timestamp according to the specifica- + tion in format. If utc-flag is present and is + non-zero or non-null, the result is in UTC, + otherwise the result is in local time. The + timestamp should be of the same form as + returned by systime(). If timestamp is miss- + ing, the current time of day is used. If for- + mat is missing, a default format equivalent to + the output of date(1) is used. See the speci- + fication for the strftime() function in ANSI C + for the format conversions that are guaranteed + to be available. + + systime() Returns the current time of day as the number + of seconds since the Epoch (1970-01-01 + 00:00:00 UTC on POSIX systems). + + Bit Manipulations Functions + Starting with version 3.1 of gawk, the following bit + manipulation functions are available. They work by con- + verting double-precision floating point values to + uintmax_t integers, doing the operation, and then con- + verting the result back to floating point. The func- + tions are: + + and(v1, v2) Return the bitwise AND of the values + provided by v1 and v2. + + compl(val) Return the bitwise complement of + val. + + lshift(val, count) Return the value of val, shifted + left by count bits. + + or(v1, v2) Return the bitwise OR of the values + provided by v1 and v2. + + rshift(val, count) Return the value of val, shifted + right by count bits. + + xor(v1, v2) Return the bitwise XOR of the values + provided by v1 and v2. + + + Internationalization Functions + Starting with version 3.1 of gawk, the following func- + tions may be used from within your AWK program for + translating strings at run-time. For full details, see + GAWK: Effective AWK Programming. + + bindtextdomain(directory [, domain]) + Specifies the directory where gawk looks for the + .mo files, in case they will not or cannot be + placed in the ``standard'' locations (e.g., dur- + ing testing). It returns the directory where + domain is ``bound.'' + The default domain is the value of TEXTDOMAIN. + If directory is the null string (""), then bind- + textdomain() returns the current binding for the + given domain. + + dcgettext(string [, domain [, category]]) + Returns the translation of string in text domain + domain for locale category category. The default + value for domain is the current value of TEXTDO- + MAIN. The default value for category is "LC_MES- + SAGES". + If you supply a value for category, it must be a + string equal to one of the known locale cate- + gories described in GAWK: Effective AWK Program- + ming. You must also supply a text domain. Use + TEXTDOMAIN if you want to use the current domain. + + dcngettext(string1 , string2 , number [, domain [, cate- + gory]]) + Returns the plural form used for number of the + translation of string1 and string2 in text domain + domain for locale category category. The default + value for domain is the current value of TEXTDO- + MAIN. The default value for category is "LC_MES- + SAGES". + If you supply a value for category, it must be a + string equal to one of the known locale cate- + gories described in GAWK: Effective AWK Program- + ming. You must also supply a text domain. Use + TEXTDOMAIN if you want to use the current domain. + +USER-DEFINED FUNCTIONS + Functions in AWK are defined as follows: + + function name(parameter list) { statements } + + Functions are executed when they are called from within + expressions in either patterns or actions. Actual + parameters supplied in the function call are used to + instantiate the formal parameters declared in the func- + tion. Arrays are passed by reference, other variables + are passed by value. + + Since functions were not originally part of the AWK lan- + guage, the provision for local variables is rather + clumsy: They are declared as extra parameters in the + parameter list. The convention is to separate local + variables from real parameters by extra spaces in the + parameter list. For example: + + function f(p, q, a, b) # a and b are local + { + ... + } + + /abc/ { ... ; f(1, 2) ; ... } + + The left parenthesis in a function call is required to + immediately follow the function name, without any inter- + vening white space. This avoids a syntactic ambiguity + with the concatenation operator. This restriction does + not apply to the built-in functions listed above. + + Functions may call each other and may be recursive. + Function parameters used as local variables are initial- + ized to the null string and the number zero upon func- + tion invocation. + + Use return expr to return a value from a function. The + return value is undefined if no value is provided, or if + the function returns by "falling off" the end. + + If --lint has been provided, gawk warns about calls to + undefined functions at parse time, instead of at run + time. Calling an undefined function at run time is a + fatal error. + + The word func may be used in place of function. + +DYNAMICALLY LOADING NEW FUNCTIONS + Beginning with version 3.1 of gawk, you can dynamically + add new built-in functions to the running gawk inter- + preter. The full details are beyond the scope of this + manual page; see GAWK: Effective AWK Programming for the + details. + + + extension(object, function) + Dynamically link the shared object file named by + object, and invoke function in that object, to + perform initialization. These should both be + provided as strings. Returns the value returned + by function. + + This function is provided and documented in GAWK: Effec- + tive AWK Programming, but everything about this feature + is likely to change eventually. We STRONGLY recommend + that you do not use this feature for anything that you + aren't willing to redo. + +SIGNALS + pgawk accepts two signals. SIGUSR1 causes it to dump a + profile and function call stack to the profile file, + which is either awkprof.out, or whatever file was named + with the --profile option. It then continues to run. + SIGHUP causes pgawk to dump the profile and function + call stack and then exit. + +EXAMPLES + Print and sort the login names of all users: + + BEGIN { FS = ":" } + { print $1 | "sort" } + + Count lines in a file: + + { nlines++ } + END { print nlines } + + Precede each line by its number in the file: + + { print FNR, $0 } + + Concatenate and line number (a variation on a theme): + + { print NR, $0 } + Run an external command for particular lines of data: + + tail -f access_log | + awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }' + +INTERNATIONALIZATION + String constants are sequences of characters enclosed in + double quotes. In non-English speaking environments, it + is possible to mark strings in the AWK program as + requiring translation to the native natural language. + Such strings are marked in the AWK program with a lead- + ing underscore ("_"). For example, + + gawk 'BEGIN { print "hello, world" }' + + always prints hello, world. But, + + gawk 'BEGIN { print _"hello, world" }' + + might print bonjour, monde in France. + + There are several steps involved in producing and run- + ning a localizable AWK program. + + 1. Add a BEGIN action to assign a value to the TEXTDO- + MAIN variable to set the text domain to a name asso- + ciated with your program. + + BEGIN { TEXTDOMAIN = "myprog" } + + This allows gawk to find the .mo file associated with + your program. Without this step, gawk uses the messages + text domain, which likely does not contain translations + for your program. + + 2. Mark all strings that should be translated with + leading underscores. + + 3. If necessary, use the dcgettext() and/or bindtextdo- + main() functions in your program, as appropriate. + + 4. Run gawk --gen-po -f myprog.awk > myprog.po to gen- + erate a .po file for your program. + + 5. Provide appropriate translations, and build and + install the corresponding .mo files. + + The internationalization features are described in full + detail in GAWK: Effective AWK Programming. + +POSIX COMPATIBILITY + A primary goal for gawk is compatibility with the POSIX + standard, as well as with the latest version of UNIX + awk. To this end, gawk incorporates the following user + visible features which are not described in the AWK + book, but are part of the Bell Laboratories version of + awk, and are in the POSIX standard. + + The book indicates that command line variable assignment + happens when awk would otherwise open the argument as a + file, which is after the BEGIN block is executed. How- + ever, in earlier implementations, when such an assign- + ment appeared before any file names, the assignment + would happen before the BEGIN block was run. Applica- + tions came to depend on this "feature." When awk was + changed to match its documentation, the -v option for + assigning variables before program execution was added + to accommodate applications that depended upon the old + behavior. (This feature was agreed upon by both the + Bell Laboratories and the GNU developers.) + + The -W option for implementation specific features is + from the POSIX standard. + + When processing arguments, gawk uses the special option + "--" to signal the end of arguments. In compatibility + mode, it warns about but otherwise ignores undefined + options. In normal operation, such arguments are passed + on to the AWK program for it to process. + + The AWK book does not define the return value of + srand(). The POSIX standard has it return the seed it + was using, to allow keeping track of random number + sequences. Therefore srand() in gawk also returns its + current seed. + + Other new features are: The use of multiple -f options + (from MKS awk); the ENVIRON array; the \a, and \v escape + sequences (done originally in gawk and fed back into the + Bell Laboratories version); the tolower() and toupper() + built-in functions (from the Bell Laboratories version); + and the ANSI C conversion specifications in printf (done + first in the Bell Laboratories version). + +HISTORICAL FEATURES + There are two features of historical AWK implementations + that gawk supports. First, it is possible to call the + length() built-in function not only with no argument, + but even without parentheses! Thus, + + a = length # Holy Algol 60, Batman! + + is the same as either of + + a = length() + a = length($0) + + This feature is marked as "deprecated" in the POSIX + standard, and gawk issues a warning about its use if + --lint is specified on the command line. + + The other feature is the use of either the continue or + the break statements outside the body of a while, for, + or do loop. Traditional AWK implementations have + treated such usage as equivalent to the next statement. + Gawk supports this usage if --traditional has been spec- + ified. + +GNU EXTENSIONS + Gawk has a number of extensions to POSIX awk. They are + described in this section. All the extensions described + here can be disabled by invoking gawk with the --tradi- + tional or --posix options. + + The following features of gawk are not available in + POSIX awk. + + · No path search is performed for files named via the -f + option. Therefore the AWKPATH environment variable is + not special. + + · The \x escape sequence. (Disabled with --posix.) + + · The fflush() function. (Disabled with --posix.) + + · The ability to continue lines after ? and :. (Dis- + abled with --posix.) + + · Octal and hexadecimal constants in AWK programs. + + · The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN + variables are not special. + + · The IGNORECASE variable and its side-effects are not + available. + + · The FIELDWIDTHS variable and fixed-width field split- + ting. + + · The PROCINFO array is not available. + + · The use of RS as a regular expression. + + · The special file names available for I/O redirection + are not recognized. + + · The |& operator for creating co-processes. + + · The ability to split out individual characters using + the null string as the value of FS, and as the third + argument to split(). + + · The optional second argument to the close() function. + + · The optional third argument to the match() function. + + · The ability to use positional specifiers with printf + and sprintf(). + + · The ability to pass an array to length(). + + · The use of delete array to delete the entire contents + of an array. + + · The use of nextfile to abandon processing of the cur- + rent input file. + + · The and(), asort(), asorti(), bindtextdomain(), + compl(), dcgettext(), dcngettext(), gensub(), + lshift(), mktime(), or(), rshift(), strftime(), str- + tonum(), systime() and xor() functions. + + · Localizable strings. + + · Adding new built-in functions dynamically with the + extension() function. + + The AWK book does not define the return value of the + close() function. Gawk's close() returns the value from + fclose(3), or pclose(3), when closing an output file or + pipe, respectively. It returns the process's exit sta- + tus when closing an input pipe. The return value is -1 + if the named file, pipe or co-process was not opened + with a redirection. + + When gawk is invoked with the --traditional option, if + the fs argument to the -F option is "t", then FS is set + to the tab character. Note that typing gawk -F\t ... + simply causes the shell to quote the "t," and does not + pass "\t" to the -F option. Since this is a rather ugly + special case, it is not the default behavior. This + behavior also does not occur if --posix has been speci- + fied. To really get a tab character as the field sepa- + rator, it is best to use single quotes: gawk -F'\t' .... + + If gawk is configured with the --enable-switch option to + the configure command, then it accepts an additional + control-flow statement: + switch (expression) { + case value|regex : statement + ... + [ default: statement ] + } + + If gawk is configured with the --disable-directories- + fatal option, then it will silently skip directories + named on the command line. Otherwise, it will do so + only if invoked with the --traditional option. + +ENVIRONMENT VARIABLES + The AWKPATH environment variable can be used to provide + a list of directories that gawk searches when looking + for files named via the -f and --file options. + + If POSIXLY_CORRECT exists in the environment, then gawk + behaves exactly as if --posix had been specified on the + command line. If --lint has been specified, gawk issues + a warning message to this effect. + +SEE ALSO + egrep(1), getpid(2), getppid(2), getpgrp(2), getuid(2), + geteuid(2), getgid(2), getegid(2), getgroups(2) + + The AWK Programming Language, Alfred V. Aho, Brian W. + Kernighan, Peter J. Weinberger, Addison-Wesley, 1988. + ISBN 0-201-07981-X. + + GAWK: Effective AWK Programming, Edition 3.0, published + by the Free Software Foundation, 2001. The current ver- + sion of this document is available online at + http://www.gnu.org/software/gawk/manual. + +BUGS + The -F option is not necessary given the command line + variable assignment feature; it remains only for back- + wards compatibility. + + Syntactically invalid single character programs tend to + overflow the parse stack, generating a rather unhelpful + message. Such programs are surprisingly difficult to + diagnose in the completely general case, and the effort + to do so really is not worth it. + +AUTHORS + The original version of UNIX awk was designed and imple- + mented by Alfred Aho, Peter Weinberger, and Brian + Kernighan of Bell Laboratories. Brian Kernighan contin- + ues to maintain and enhance it. + + Paul Rubin and Jay Fenlason, of the Free Software Foun- + dation, wrote gawk, to be compatible with the original + version of awk distributed in Seventh Edition UNIX. + John Woods contributed a number of bug fixes. David + Trueman, with contributions from Arnold Robbins, made + gawk compatible with the new version of UNIX awk. + Arnold Robbins is the current maintainer. + + The initial DOS port was done by Conrad Kwok and Scott + Garfinkle. Scott Deifik is the current DOS maintainer. + Pat Rankin did the port to VMS, and Michal Jaegermann + did the port to the Atari ST. The port to OS/2 was done + by Kai Uwe Rommel, with contributions and help from Dar- + rel Hankerson. Juan M. Guerrero now maintains the OS/2 + port. Fred Fish supplied support for the Amiga, and + Martin Brown provided the BeOS port. Stephen Davies + provided the original Tandem port, and Matthew Woehlke + provided changes for Tandem's POSIX-compliant systems. + +VERSION INFORMATION + This man page documents gawk, version 3.1.6. + +BUG REPORTS + If you find a bug in gawk, please send electronic mail + to bug-gawk@gnu.org. Please include your operating sys- + tem and its revision, the version of gawk (from gawk + --version), what C compiler you used to compile it, and + a test program and data that are as small as possible + for reproducing the problem. + + Before sending a bug report, please do the following + things. First, verify that you have the latest version + of gawk. Many bugs (usually subtle ones) are fixed at + each release, and if yours is out of date, the problem + may already have been solved. Second, please see if + setting the environment variable LC_ALL to LC_ALL=C + causes things to behave as you expect. If so, it's a + locale issue, and may or may not really be a bug. + Finally, please read this man page and the reference + manual carefully to be sure that what you think is a bug + really is, instead of just a quirk in the language. + + Whatever you do, do NOT post a bug report in + comp.lang.awk. While the gawk developers occasionally + read this newsgroup, posting bug reports there is an + unreliable way to report bugs. Instead, please use the + electronic mail addresses given above. + + If you're using a GNU/Linux system or BSD-based system, + you may wish to submit a bug report to the vendor of + your distribution. That's fine, but please send a copy + to the official email address as well, since there's no + guarantee that the bug will be forwarded to the gawk + maintainer. + +ACKNOWLEDGEMENTS + Brian Kernighan of Bell Laboratories provided valuable + assistance during testing and debugging. We thank him. + +COPYING PERMISSIONS + Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, + 1997, 1998, 1999, 2001, 2002, 2003, 2004, 2005, 2007 + Free Software Foundation, Inc. + + Permission is granted to make and distribute verbatim + copies of this manual page provided the copyright notice + and this permission notice are preserved on all copies. + + Permission is granted to copy and distribute modified + versions of this manual page under the conditions for + verbatim copying, provided that the entire resulting + derived work is distributed under the terms of a permis- + sion notice identical to this one. + + Permission is granted to copy and distribute transla- + tions of this manual page into another language, under + the above conditions for modified versions, except that + this permission notice may be stated in a translation + approved by the Foundation. + + + +Free Software Foundation Oct 19 2007 GAWK(1) |