# phpman > man > awk(1) > **TLDR:** A versatile programming language for working on files. > - Print the fifth column (a.k.a. field) in a space-separated file: `awk '{print $5}' {{path/to/file}}` - Print the second column of the lines containing "foo" in a space-separated file: `awk '/{{foo}}/ {print $2}' {{path/to/file}}` - Print the last column of each line in a file, using a comma (instead of space) as a field separator: `awk -F ',' '{print $NF}' {{path/to/file}}` - Sum the values in the first column of a file and print the total: `awk '{s+=$1} END {print s}' {{path/to/file}}` - Print every third line starting from the first line: `awk 'NR%3==1' {{path/to/file}}` - Print different values based on conditions: `awk '{if ($1 == "foo") print "Exact match foo"; else if ($1 ~ "bar") print "Partial match bar"; else print "Baz"}' {{path/to/file}}` - Print all the lines which the 10th column value is between a min and a max: `awk '($10 >= {{min_value}} && $10 <= {{max_value}})' {{path/to/file}}` - Print table of users with UID >=1000 with header and formatted output, using colon as separator (`%-20s` mean: 20 left-align string characters, `%6s` means: 6 right-align string characters): `awk 'BEGIN {FS=":";printf "%-20s %6s %25s\n", "Name", "UID", "Shell"} $4 >= 1000 {printf "%-20s %6d %25s\n", $1, $4, $7}' /etc/passwd` *Source: tldr-pages* --- [GAWK(1)](https://www.chedong.com/phpMan.php/man/GAWK/1/markdown) Utility Commands [GAWK(1)](https://www.chedong.com/phpMan.php/man/GAWK/1/markdown) ## 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 ... ## DESCRIPTION _Gawk_ is the GNU Project's implementation of the AWK programming 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. _Gawk_ provides the additional features found in the current version of Brian Kernighan's _awk_ and numerous GNU-specific extensions. The command line consists of options to _gawk_ itself, the AWK program text (if not supplied via the **-f** or **--include** options), and values to be made available in the **ARGC** and **ARGV** pre- defined AWK variables. When _gawk_ is invoked with the **--profile** option, it starts gathering profiling statistics from the execution of the program. _Gawk_ runs more slowly in this mode, and automatically produces an execution profile in the file **awkprof.out** when done. See the **--profile** option, below. _Gawk_ also has an integrated debugger. An interactive debugging session can be started by sup‐ plying the **--debug** option to the command line. In this mode of execution, _gawk_ loads the AWK source code and then prompts for debugging commands. _Gawk_ can only debug AWK program source provided with the **-f** and **--include** options. The debugger is documented in _GAWK:_ _Effective_ _AWK_ _Programming_. ## OPTION FORMAT _Gawk_ options may be either traditional POSIX-style one letter options, or GNU-style long op‐ tions. POSIX options start with a single “-”, while long options start with “--”. Long op‐ tions are provided for both GNU-specific features and for POSIX-mandated features. _Gawk_-specific options are typically used in long-option form. Arguments to long options are either joined with the option by an **=** sign, with no intervening spaces, or they may be pro‐ vided in the next command line argument. Long options may be abbreviated, as long as the ab‐ breviation remains unique. Additionally, every long option has a corresponding short option, so that the option's func‐ tionality may be used from within **#!** executable scripts. ## OPTIONS _Gawk_ accepts the following options. Standard options are listed first, followed by options for _gawk_ extensions, listed alphabetically by short option. ### -f **--file** _program-file_ Read the AWK program source from the file _program-file_, instead of from the first com‐ mand line argument. Multiple **-f** (or **--file**) options may be used. Files read with **-f** are treated as if they begin with an implicit **@namespace** **"awk"** statement. ### -F **--field-separator** _fs_ Use _fs_ for the input field separator (the value of the **FS** predefined variable). ### -v **--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** rule of an AWK program. ### -b ### --characters-as-bytes Treat all input data as single-byte characters. In other words, don't pay any atten‐ tion to the locale information when attempting to process strings as multibyte charac‐ ters. The **--posix** option overrides this one. ### -c ### --traditional Run in _compatibility_ mode. In compatibility mode, _gawk_ behaves identically to Brian Kernighan's _awk_; none of the GNU-specific extensions are recognized. See **GNU** **EXTEN**‐‐ **SIONS**, below, for more information. ### -C ### --copyright Print the short version of the GNU copyright information message on the standard out‐ put and exit successfully. ### -d **--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 er‐ rors 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 inadver‐ tently use global variables that you meant to be local. (This is a particularly easy mistake to make with simple variable names like **i**, **j**, and so on.) ### -D **--debug**[**=**_file_] Enable debugging of AWK programs. By default, the debugger reads commands interac‐ tively from the keyboard (standard input). The optional _file_ argument specifies a file with a list of commands for the debugger to execute non-interactively. ### -e **--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 **--include** options) with source code entered on the command line. It is intended primarily for medium to large AWK programs used in shell scripts. Each argument supplied via **-e** is treated as if it begins with an implicit **@namespace** **"awk"** statement. ### -E **--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 disables command-line variable assignments. ### -g ### --gen-pot Scan and parse the AWK program, and generate a GNU **.pot** (Portable Object Template) 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 **.pot** files. ### -h **--help** Print a relatively short summary of the available options on the standard output. (Per the _GNU_ _Coding_ _Standards_, these options cause an immediate, successful exit.) ### -i **--include** _include-file_ Load an awk source library. This searches for the library using the **AWKPATH** environ‐ ment variable. If the initial search fails, another attempt will be made after ap‐ pending the **.awk** suffix. The file will be loaded only once (i.e., duplicates are eliminated), and the code does not constitute the main program source. Files read with **--include** are treated as if they begin with an implicit **@namespace** **"awk"** state‐ ment. ### -l **--load** _lib_ Load a _gawk_ extension from the shared library _lib_. This searches for the library us‐ ing the **AWKLIBPATH** environment variable. If the initial search fails, another attempt will be made after appending the default shared library suffix for the platform. The library initialization routine is expected to be named **dl**___**load()**. ### -L **--lint**[**=**_value_] Provide warnings about constructs that are dubious or non-portable to other AWK imple‐ mentations. 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 argument of **invalid**, only warnings about things that are actually invalid are issued. (This is not fully implemented yet.) With an op‐ tional argument of **no-ext**, warnings about _gawk_ extensions are disabled. ### -M ### --bignum Force arbitrary precision arithmetic on numbers. This option has no effect if _gawk_ is not compiled to use the GNU MPFR and GMP libraries. (In such a case, _gawk_ issues a warning.) ### -n ### --non-decimal-data Recognize octal and hexadecimal values in input data. _Use_ _this_ _option_ _with_ _great_ _cau__‐ _tion!_ ### -N ### --use-lc-numeric Force _gawk_ to use the locale's decimal point character when parsing input data. Al‐ though the POSIX standard requires this behavior, 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 op‐ tion overrides the default behavior, without the full draconian strictness of the **--posix** option. ### -o **--pretty-print**[**=**_file_] Output a pretty printed version of the program to _file_. If no _file_ is provided, _gawk_ uses a file named **awkprof.out** in the current directory. This option implies **--no-op**‐‐ **timize**. ### -O ### --optimize Enable _gawk_'s default optimizations upon the internal representation of the program. Currently, this just includes simple constant folding. This option is on by default. ### -p **--profile**[**=**_prof-file_] Start a profiling session, and send the profiling data to _prof-file_. The default is **awkprof.out**. The profile contains execution counts of each statement in the program in the left margin and function call counts for each user-defined function. This op‐ tion implies **--no-optimize**. ### -P ### --posix This turns on _compatibility_ mode, with the following additional restrictions: • **\x** escape sequences are not recognized. • 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 **^=**. ### -r ### --re-interval Enable the use of _interval_ _expressions_ in regular expression matching (see **Regular** **Ex**‐‐ **pressions**, below). Interval expressions were not traditionally available in the AWK language. The POSIX standard added them, to make _awk_ and _egrep_ consistent with each other. They are enabled by default, but this option remains for use together with **--traditional**. ### -s ### --no-optimize Disable _gawk_'s default optimizations upon the internal representation of the program. ### -S ### --sandbox Run _gawk_ in sandbox mode, disabling the **system()** function, input redirection with **get**‐‐ **line**, output redirection with **print** and **printf**, and loading dynamic extensions. Com‐ mand execution (through pipelines) is also disabled. This effectively blocks a script from accessing local resources, except for the files specified on the command line. ### -t ### --lint-old Provide warnings about constructs that are not portable to the original version of UNIX _awk_. ### -V ### --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 distributing. 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 pro‐ gram 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 operation, 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. For POSIX compatibility, the **-W** option may be used, followed by the name of a long option. ## AWK PROGRAM EXECUTION An AWK program consists of a sequence of optional directives, pattern-action statements, and optional function definitions. **@include** **"**_filename_**"** **@load** **"**_filename_**"** **@namespace** **"**_name_**"** _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** op‐ tions may be used multiple times on the command line. _Gawk_ reads the program text as if all the _program-file_s and command line source texts had been concatenated together. This is use‐ ful 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 command line programs. In addition, lines beginning with **@include** may be used to include other source files into your program, making library use even easier. This is equivalent to using the **--include** op‐ tion. Lines beginning with **@load** may be used to load extension functions into your program. This is equivalent to using the **--load** option. The environment variable **AWKPATH** specifies a search path to use when finding source files named with the **-f** and **--include** options. 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 contains a “/” character, no path search is performed. The environment variable **AWKLIBPATH** specifies a search path to use when finding source files named with the **--load** option. If this variable does not exist, the default path is **"/usr/lo**‐‐ **cal/lib/gawk"**. (The actual directory may vary, depending upon how _gawk_ was built and in‐ stalled.) _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** rule(s) (if any), and then proceeds to read each file named in the **ARGV** array (up to **ARGV[ARGC-1]**). If there are no files named on the com‐ mand line, _gawk_ reads the standard input. If a filename on the command line has the form _var_**=**_val_ it is treated as a variable assign‐ ment. The variable _var_ will be assigned the value _val_. (This happens after any **BEGIN** rule(s) have been run.) Command line variable assignment is most useful for dynamically as‐ signing 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 input file, if a **BEGINFILE** rule exists, _gawk_ executes the associated code before processing the contents of the file. Similarly, _gawk_ executes the code associated with **END**‐‐ **FILE** after processing the file. For each record in the input, _gawk_ tests to see if it matches any _pattern_ in the AWK program. For each pattern that the record matches, _gawk_ executes the associated _action_. 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** rule(s) (if any). ### Command Line Directories According to POSIX, files named on the _awk_ command line must be text files. The behavior is ``undefined'' if they are not. Most versions of _awk_ treat a directory on the command line as a fatal error. Starting with version 4.0 of _gawk_, a directory on the command line produces a warning, but is otherwise skipped. If either of the **--posix** or **--traditional** options is given, then _gawk_ re‐ verts to treating directories on the command line as a fatal error. ### 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. Ad‐ ditionally, _gawk_ allows variables to have regular-expression type. AWK also has one dimen‐ sional arrays; arrays with multiple dimensions may be simulated. _Gawk_ provides true arrays of arrays; see **Arrays**, below. Several 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 sepa‐ rated 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 empty 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 separate field. Otherwise, **FS** is expected to be a full regular expression. In the special case that **FS** is a single space, fields are separated by runs of spaces and/or tabs and/or newlines. **NOTE**: The value of **IGNORECASE** (see below) also affects how fields are split when **FS** is a reg‐ ular 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 ex‐ pected to have fixed width, and _gawk_ splits up the record using the specified widths. Each field width may optionally be preceded by a colon-separated value specifying the number of characters to skip before the field starts. The value of **FS** is ignored. Assigning a new value to **FS** or **FPAT** overrides the use of **FIELDWIDTHS**. Similarly, if the **FPAT** variable is set to a string representing a regular expression, each field is made up of text that matches that regular expression. In this case, the regular ex‐ pression describes the fields themselves, instead of the text that separates the fields. As‐ signing a new value to **FS** or **FIELDWIDTHS** overrides the use of **FPAT**. Each field in the input record may be referenced by its position: **$1**, **$2**, and so on. **$0** is the whole record, including leading and trailing whitespace. Fields need not be referenced by constants: **n** **=** **5** **print** **$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 values, and causes the value of **$0** to be re‐ computed, with the fields being separated by the value of **OFS**. References to negative num‐ bered 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 ref‐ erenced. 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. Dy‐ namically 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, re‐ spectively, should use binary I/O. String values of **"r"**, or **"w"** specify that in‐ put 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 current environment. The array is indexed by the environment variables, each element being the value of that variable (e.g., **ENVIRON["HOME"]** might be **"/home/arnold"**). In POSIX mode, changing this array does not affect the environment seen by pro‐ grams which _gawk_ spawns via redirection or the **system()** function. Otherwise, _gawk_ updates its real environment so that programs it spawns see the changes. **ERRNO** If a system error occurs either doing a redirection for **getline**, during a read for **getline**, or during a **close()**, then **ERRNO** is set to a string describing the error. The value is subject to translation in non-English locales. If the string in **ERRNO** corresponds to a system error in the [_errno_(3)](https://www.chedong.com/phpMan.php/man/errno/3/markdown) variable, then the numeric value can be found in **PROCINFO["errno"].** For non-system errors, **PROCINFO["errno"]** will be zero. **FIELDWIDTHS** A whitespace-separated list of field widths. When set, _gawk_ parses the input into fields of fixed width, instead of using the value of the **FS** variable as the field separator. Each field width may optionally be preceded by a colon-sepa‐ rated value specifying the number of characters to skip before the field starts. See **Fields**, above. **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** rule (unless set by **getline**). **FNR** The input record number in the current input file. **FPAT** A regular expression describing the contents of the fields in a record. When set, _gawk_ parses the input into fields, where the fields match the regular ex‐ pression, instead of using the value of **FS** as the field separator. See **Fields**, above. **FS** The input field separator, a space by default. See **Fields**, above. **FUNCTAB** An array whose indices and corresponding values are the names of all the user-de‐ fined or extension functions in the program. **NOTE**: You may not use the **delete** statement with the **FUNCTAB** array. **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** and **FPAT**, record separating with **RS**, regular expression matching with **~** and **!~**, and the **gensub()**, **gsub()**, **index()**, **match()**, **patsplit()**, **split()**, and **sub()** built-in functions all ignore case when doing reg‐ ular expression operations. **NOTE**: Array subscripting 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-sensi‐ tive. **LINT** Provides dynamic control of the **--lint** option from within an AWK program. When true, _gawk_ prints lint warnings. When false, it does not. The values allowed for the **--lint** option may also be assigned to **LINT**, with the same effects. 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. **PREC** The working precision of arbitrary precision floating-point numbers, 53 by de‐ fault. **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 **"group**_n_**"** 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["argv"]** The command line arguments as received by _gawk_ at the C-lan‐ guage level. The subscripts start from zero. **PROCINFO["egid"]** The value of the [_getegid_(2)](https://www.chedong.com/phpMan.php/man/getegid/2/markdown) system call. **PROCINFO["errno"]** The value of [_errno_(3)](https://www.chedong.com/phpMan.php/man/errno/3/markdown) when **ERRNO** is set to the associated error message. **PROCINFO["euid"]** The value of the [_geteuid_(2)](https://www.chedong.com/phpMan.php/man/geteuid/2/markdown) system call. **PROCINFO["FS"]** **"FS"** if field splitting with **FS** is in effect, **"FPAT"** if field splitting with **FPAT** is in effect, **"FIELDWIDTHS"** if field splitting with **FIELDWIDTHS** is in effect, or **"API"** if API input parser field splitting is in effect. **PROCINFO["gid"]** The value of the [_getgid_(2)](https://www.chedong.com/phpMan.php/man/getgid/2/markdown) system call. **PROCINFO["identifiers"]** A subarray, indexed by the names of all identifiers used in the text of the AWK program. The values indicate what _gawk_ knows about the identifiers after it has finished parsing the program; they are _not_ updated while the program runs. For each identifier, the value of the element is one of the following: **"array"** The identifier is an array. **"builtin"** The identifier is a built-in function. **"extension"** The identifier is an extension function loaded via **@load** or **--load**. **"scalar"** The identifier is a scalar. **"untyped"** The identifier is untyped (could be used as a scalar or array, _gawk_ doesn't know yet). **"user"** The identifier is a user-defined function. **PROCINFO["pgrpid"]** The value of the [_getpgrp_(2)](https://www.chedong.com/phpMan.php/man/getpgrp/2/markdown) system call. **PROCINFO["pid"]** The value of the [_getpid_(2)](https://www.chedong.com/phpMan.php/man/getpid/2/markdown) system call. **PROCINFO["platform"]** A string indicating the platform for which _gawk_ was com‐ piled. It is one of: **"djgpp"**, **"mingw"** Microsoft Windows, using either DJGPP, or MinGW, re‐ spectively. **"os2"** OS/2. **"posix"** GNU/Linux, Cygwin, Mac OS X, and legacy Unix systems. **"vms"** OpenVMS or Vax/VMS. **PROCINFO["ppid"]** The value of the [_getppid_(2)](https://www.chedong.com/phpMan.php/man/getppid/2/markdown) system call. **PROCINFO["strftime"]** The default time format string for **strftime()**. Changing its value affects how **strftime()** formats time values when called with no arguments. **PROCINFO["uid"]** The value of the [_getuid_(2)](https://www.chedong.com/phpMan.php/man/getuid/2/markdown) system call. **PROCINFO["version"]** The version of _gawk_. The following elements are present if loading dynamic extensions is available: **PROCINFO["api**___**major"]** The major version of the extension API. **PROCINFO["api**___**minor"]** The minor version of the extension API. The following elements are available if MPFR support is compiled into _gawk_: **PROCINFO["gmp**___**version"]** The version of the GNU GMP library used for arbitrary precision number support in _gawk_. **PROCINFO["mpfr**___**version"]** The version of the GNU MPFR library used for arbitrary precision number support in _gawk_. **PROCINFO["prec**___**max"]** The maximum precision supported by the GNU MPFR library for arbitrary pre‐ cision floating-point numbers. **PROCINFO["prec**___**min"]** The minimum precision allowed by the GNU MPFR library for arbitrary preci‐ sion floating-point numbers. The following elements may set by a program to change _gawk_'s behavior: **PROCINFO["NONFATAL"]** If this exists, then I/O errors for all redirections become nonfatal. **PROCINFO["**_name_**",** **"NONFATAL"]** Make I/O errors for _name_ be nonfatal. **PROCINFO["**_command_**",** **"pty"]** Use a pseudo-tty for two-way communication with _command_ instead of setting up two one-way pipes. **PROCINFO["**_input_**",** **"READ**___**TIMEOUT"]** The timeout in milliseconds for reading data from _input_, where _input_ is a redirection string or a filename. A value of zero or less than zero means no timeout. **PROCINFO["**_input_**",** **"RETRY"]** If an I/O error that may be retried occurs when reading data from _input_, and this array entry exists, then **getline** returns -2 instead of following the default behavior of returning -1 and configuring _input_ to return no further data. An I/O error that may be retried is one where [_errno_(3)](https://www.chedong.com/phpMan.php/man/errno/3/markdown) has the value EAGAIN, EWOULDBLOCK, EINTR, or ETIMEDOUT. This may be useful in conjunction with **PROCINFO["**_input_**",** **"READ**___**TIMEOUT"]** or in situations where a file descriptor has been configured to behave in a non-blocking fashion. **PROCINFO["sorted**___**in"]** If this element exists in **PROCINFO**, then its value controls the order in which array elements are traversed in **for** loops. Supported values are **"@ind**___**str**___**asc"**, **"@ind**___**num**___**asc"**, **"@val**___**type**___**asc"**, **"@val**___**str**___**asc"**, **"@val**___**num**___**asc"**, **"@ind**___**str**___**desc"**, **"@ind**___**num**___**desc"**, **"@val**___**type**___**desc"**, **"@val**___**str**___**desc"**, **"@val**___**num**___**desc"**, and **"@unsorted"**. The value can also be the name (as a _string_) of any comparison function defined as follows: **function** **cmp**___**func(i1,** **v1,** **i2,** **v2)** where _i1_ and _i2_ are the indices, and _v1_ and _v2_ are the corresponding val‐ ues of the two elements being compared. It should return a number less than, equal to, or greater than 0, depending on how the elements of the array are to be ordered. **ROUNDMODE** The rounding mode to use for arbitrary precision arithmetic on numbers, by de‐ fault **"N"** (IEEE-754 roundTiesToEven mode). The accepted values are: **"A"** or **"a"** for rounding away from zero. These are only available if your version of the GNU MPFR library supports rounding away from zero. **"D"** or **"d"** for roundTowardNegative. **"N"** or **"n"** for roundTiesToEven. **"U"** or **"u"** for roundTowardPositive. **"Z"** or **"z"** for roundTowardZero. **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 im‐ plies that character indices start at one.) **RLENGTH** The length of the string matched by **match()**; -1 if no match. **SUBSEP** The string used to separate multiple subscripts in array elements, by default **"\034"**. **SYMTAB** An array whose indices are the names of all currently defined global variables and arrays in the program. The array may be used for indirect access to read or write the value of a variable: **foo** **=** **5** **SYMTAB["foo"]** **=** **4** **print** **foo** **#** **prints** **4** The **typeof()** function may be used to test if an element in **SYMTAB** is an array. You may not use the **delete** statement with the **SYMTAB** array, nor assign to ele‐ ments with an index that is not a variable name. **TEXTDOMAIN** The text domain of the AWK program; used to find the localized translations for the program's strings. ### Arrays Arrays are subscripted with an expression between square brackets (**[** and **]**). If the expres‐ sion 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 multiply dimensioned arrays. For exam‐ ple: **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 particu‐ lar 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 iterate over all the elements of an array. However, the **(i,** **j)** **in** **array** construct only works in tests, not in **for** loops. 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 specifying the array name without a subscript. _gawk_ supports true multidimensional arrays. It does not require that such arrays be ``rectan‐ gular'' as in C or C++. For example: **a[1]** **=** **5** **a[2][1]** **=** **6** **a[2][2]** **=** **7** **NOTE**: You may need to tell _gawk_ that an array element is really a subarray in order to use it where _gawk_ expects an array (such as in the second argument to **split()**). You can do this by creating an element in the subarray and then deleting it with the **delete** statement. ### Namespaces _Gawk_ provides a simple _namespace_ facility to help work around the fact that all variables in AWK are global. A _qualified_ _name_ consists of a two simple identifiers joined by a double colon (**::**). The left-hand identifier represents the namespace and the right-hand identifier is the variable within it. All simple (non-qualified) names are considered to be in the ``current'' name‐ space; the default namespace is **awk**. However, simple identifiers consisting solely of upper‐ case letters are forced into the **awk** namespace, even if the current namespace is different. You change the current namespace with an **@namespace** **"**_name_**"** directive. The standard predefined builtin function names may not be used as namespace names. The names of additional functions provided by _gawk_ may be used as namespace names or as simple identi‐ fiers in other namespaces. For more details, see _GAWK:_ _Effective_ _AWK_ _Programming_. ### Variable Typing And Conversion Variables and fields may be (floating point) numbers, or strings, or both. They may also be regular expressions. How the value of a variable is interpreted 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 zero to it; to force it to be treated as a string, concatenate it with the null string. Uninitialized variables have the numeric value zero and the string value "" (the null, or empty, string). When a string must be converted to a number, the conversion is accomplished using [_strtod_(3)](https://www.chedong.com/phpMan.php/man/strtod/3/markdown). A number is converted to a string by using the value of **CONVFMT** as a format string for [_sprintf_(3)](https://www.chedong.com/phpMan.php/man/sprintf/3/markdown), 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"**. **NOTE**: When operating in POSIX mode (such as with the **--posix** option), beware that locale set‐ tings 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 numeri‐ cally. 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 elements of an array created by **split()** or **patsplit()** that are nu‐ meric strings. The basic idea is that _user_ _input_, and only user input, that looks numeric, should be treated that way. ### Octal and Hexadecimal Constants You may use C-style octal and hexadecimal constants in your AWK program source code. For ex‐ ample, 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 (like **"value"**). Within strings, certain _escape_ _sequences_ are recognized, as in C. These are: **\\** A literal backslash. **\a** The “alert” character; usually the ASCII BEL character. **\b** Backspace. **\f** Form-feed. **\n** Newline. **\r** Carriage return. **\t** Horizontal tab. **\v** Vertical tab. **\x**_hex_ _digits_ The character represented by the string of hexadecimal digits following the **\x**. Up to two following hexadecimal digits are considered part of the escape sequence. 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_. In compatibility mode, the characters represented by octal and hexadecimal escape sequences are treated literally when used in regular expression constants. Thus, **/a\52b/** is equivalent to **/a\*b/**. ### Regexp Constants A regular expression constant is a sequence of characters enclosed between forward slashes (like **/value/**). Regular expression matching is described more fully below; see **Regular** **Ex**‐‐ **pressions**. The escape sequences described earlier may also be used inside constant regular expressions (e.g., **/[** **\t\f\n\r\v]/** matches whitespace characters). _Gawk_ provides _strongly_ _typed_ regular expression constants. These are written with a leading **@** symbol (like so: **@/value/**). Such constants may be assigned to scalars (variables, array ele‐ ments) and passed to user-defined functions. Variables that have been so assigned have regu‐ lar expression type. ## 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 executes 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. Empty 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 comma, **{**, **?**, **:**, **&&**, 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 is ignored. How‐ ever, a “\” after a **#** is not special. 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 themselves. ### Patterns AWK patterns may be one of the following: **BEGIN** **END** **BEGINFILE** **ENDFILE** **/**_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** rule. They are executed before any of the input is read. Similarly, all the **END** rules are merged, and executed when all the input is exhausted (or when an **exit** statement is executed). **BEGIN** and **END** patterns cannot be combined with other patterns in pattern ex‐ pressions. **BEGIN** and **END** patterns cannot have missing action parts. **BEGINFILE** and **ENDFILE** are additional special patterns whose actions are executed before read‐ ing the first record of each command-line input file and after reading the last record of each file. Inside the **BEGINFILE** rule, the value of **ERRNO** is the empty string if the file was opened successfully. Otherwise, there is some problem with the file and the code should use **nextfile** to skip it. If that is not done, _gawk_ produces its usual fatal error for files that cannot be opened. For **/**_regular_ _expression_**/** patterns, the associated statement is executed for each input record that matches the regular expression. Regular expressions are the same as those in [_egrep_(1)](https://www.chedong.com/phpMan.php/man/egrep/1/markdown), and are summarized below. A _relational_ _expression_ may use any of the operators defined below in the section on actions. These generally 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 primi‐ tive 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 pat‐ tern used for testing is the second pattern, otherwise it is the third. Only one of the sec‐ ond 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 expression. ### 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..._**]** A character list: matches any of the characters _abc..._. You may include a range of characters by separating them with a dash. To include a literal dash in the list, put it first or last. **[^**_abc..._**]** A 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 expression _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. **\y** Matches the empty string at either the beginning 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. **\s** Matches any whitespace character. **\S** Matches any nonwhitespace character. **\w** Matches any word-constituent character (letter, digit, or underscore). **\W** Matches any character that is not word-constituent. **\`** 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 **String** **Constants**) 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 visible. (A space is printable, but not visible, while an **a** is both.) **[:lower:]** Lowercase alphabetic characters. **[:print:]** Printable characters (characters that are not control characters.) **[:punct:]** Punctuation characters (characters that are not letter, digits, control charac‐ ters, or space characters). **[:space:]** Space characters (such as space, tab, and formfeed, to name a few). **[:upper:]** Uppercase 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 alphabetic 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 characters. 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 repre‐ sented 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”, “e´”, and “**`**”. In this case, **[[=e=]]** is a regular expression that matches any of **e**, **e**´´, or **`**. These features are very valuable in non-English speaking locales. The library functions that _gawk_ uses for regular expression matching currently only recognize POSIX character classes; they do not recognize collating symbols or equivalence classes. The **\y**, **\B**, **\<**, **\>**, **\s**, **\S**, **\w**, **\W**, **\`**, and **\'** operators are specific to _gawk_; they are ex‐ tensions based on facilities in the GNU regular expression libraries. The various command line options control how _gawk_ interprets characters in regular expres‐ sions. No options In the default case, _gawk_ provides all the facilities of POSIX regular expressions and the GNU regular expression operators described above. ### --posix Only POSIX regular expressions are supported, the GNU operators are not special. (E.g., **\w** matches a literal **w**). ### --traditional Traditional UNIX _awk_ regular expressions are matched. The GNU operators are not spe‐ cial, and interval expressions are not available. Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regular ex‐ pression metacharacters. ### --re-interval Allow interval expressions in regular expressions, even if **--traditional** has been pro‐ vided. ### Actions Action statements are enclosed in braces, **{** and **}**. Action statements consist of the usual assignment, conditional, and looping statements found in most languages. The operators, con‐ trol 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 negation. ***** **/** **%** 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 ex‐ pression (**/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 you want. **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_ **}** **switch** **(**_expression_**)** **{** **case** _value_**|**_regex_ **:** _statement_ _..._ [ **default:** _statement_ ] **}** ### I/O Statements The input/output statements are as follows: **close(**_file_ [**,** _how_]**)** Close file, pipe or coprocess. The optional _how_ should only be used when closing one end of a two-way pipe to a coprocess. It must be a string value, either **"to"** or **"from"**. **getline** Set **$0** from the next input record; set **NF**, **NR**, **FNR**, **RT**. **getline** **<**_file_ Set **$0** from the next record of _file_; set **NF**, **RT**. **getline** _var_ Set _var_ from the next input record; set **NR**, **FNR**, **RT**. **getline** _var_ **<**_file_ Set _var_ from the next record of _file_; set **RT**. _command_ **|** **getline** [_var_] Run _command_, piping the output either into **$0** or _var_, as above, and **RT**. _command_ **|&** **getline** [_var_] Run _command_ as a coprocess piping the output either into **$0** or _var_, as above, and **RT**. Coprocesses are a _gawk_ extension. (The _command_ can also be a socket. See the subsection **Special** **File** **Names**, below.) **next** Stop processing the current input record. Read the next input record and start processing over with the first pattern in the AWK program. Upon reaching the end of the input data, execute any **END** rule(s). **nextfile** Stop processing the current input file. The next input record read comes from the next input file. Update **FILENAME** and **ARGIND**, reset **FNR** to 1, and start processing over with the first pattern in the AWK pro‐ gram. Upon reaching the end of the input data, execute any **ENDFILE** and **END** rule(s). **print** Print the current record. The output record is terminated with the value of **ORS**. **print** _expr-list_ Print expressions. Each expression is separated by the value of **OFS**. The output record is terminated with the value of **ORS**. **print** _expr-list_ **>**_file_ Print expressions on _file_. Each expression is separated by the value of **OFS**. The output record is terminated with the value of **ORS**. **printf** _fmt,_ _expr-list_ Format and print. See **The** _printf_ **Statement**, below. **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 systems.) See _GAWK:_ _Effective_ _AWK_ _Pro__‐ _gramming_ for the full details on the exit status. **fflush(**[_file_]**)** Flush any buffers associated with the open output file or pipe _file_. If _file_ is missing or if it is the null string, then flush all open output files and pipes. Additional output redirections are allowed for **print** and **printf**. **print** **...** **>>** _file_ Append output to the _file_. **print** **...** **|** _command_ Write on a pipe. **print** **...** **|&** _command_ Send data to a coprocess or socket. (See also the subsection **Special** **File** **Names**, be‐ low.) The **getline** command returns 1 on success, zero on end of file, and -1 on an error. If the [_errno_(3)](https://www.chedong.com/phpMan.php/man/errno/3/markdown) value indicates that the I/O operation may be retried, and **PROCINFO["**_input_**",** **"RETRY"]** is set, then -2 is returned instead of -1, and further calls to **getline** may be at‐ tempted. Upon an error, **ERRNO** is set to a string describing the problem. **NOTE**: Failure in opening a two-way socket results in a non-fatal error being returned to the calling function. If using a pipe, coprocess, 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, sockets, or coprocesses when they return EOF. **The** _printf_ **Statement** The AWK versions of the **printf** statement and **sprintf()** function (see below) accept the fol‐ lowing conversion specification formats: **%a**, **%A** A floating point number of the form [**-**]**0x**_h_**.**_hhhh_**p+-**_dd_ (C99 hexadecimal floating point format). For **%A**, uppercase letters are used instead of lowercase ones. **%c** A single character. If the argument used for **%c** is numeric, it is treated as a char‐ acter 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_**.**_dddddd_**e**[**+-**]_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 number” and “infinity” values. If **%F** is not available, _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. 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 _posi__‐ _tional_ _specifier_ and is intended primarily for use in translated 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 formatted is positive. The **+** overrides the space modifier. **#** Use an “alternate form” for certain control letters. 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**, trailing zeros are not removed from the result. **0** A leading **0** (zero) acts as a flag, indicating that output should be padded with zeroes instead of spaces. This applies only to the numeric output formats. This flag only has an effect when the field width is wider than the value to be printed. **'** A single quote character instructs _gawk_ to insert the locale's thousands-separator character into decimal numbers, and to also use the locale's decimal point character with floating point formats. This requires correct locale support in the C library and in the definition of the current locale. _width_ The field should be padded to this width. The field is normally padded with spaces. With the **0** flag, 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 signif‐ icant digits. For the **%d**, **%i**, **%o**, **%u**, **%x**, and **%X** formats, it specifies the minimum number of digits to print. For the **%s** format, it specifies the maximum number of characters from the string that should be printed. The dynamic _width_ and _prec_ capabilities of the ISO C **printf()** routines are supported. A ***** in place of either the _width_ or _prec_ specifications causes their values to be taken from the ar‐ gument 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: **-** The standard input. **/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 **|&** coprocess operator for creating TCP/IP network connections: **/inet/tcp/**_lport_**/**_rhost_**/**_rport_ **/inet4/tcp/**_lport_**/**_rhost_**/**_rport_ **/inet6/tcp/**_lport_**/**_rhost_**/**_rport_ Files for a 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. Use **/inet4** to force an IPv4 connection, and **/inet6** to force an IPv6 connection. Plain **/inet** uses the system de‐ fault (most likely IPv4). Usable only with the **|&** two-way I/O operator. **/inet/udp/**_lport_**/**_rhost_**/**_rport_ **/inet4/udp/**_lport_**/**_rhost_**/**_rport_ **/inet6/udp/**_lport_**/**_rhost_**/**_rport_ Similar, but use UDP/IP instead of TCP/IP. ### Numeric Functions AWK has the following built-in arithmetic functions: **atan2(**_y_**,** _x_**)** Return the arctangent of _y/x_ in radians. **cos(**_expr_**)** Return the cosine of _expr_, which is in radians. **exp(**_expr_**)** The exponential function. **int(**_expr_**)** Truncate to integer. **log(**_expr_**)** The natural logarithm function. **rand()** Return a random number _N_, between zero and one, such that 0 ≤ _N_ < 1. **sin(**_expr_**)** Return the sine of _expr_, which is in radians. **sqrt(**_expr_**)** Return the square root of _expr_. **srand(**[_expr_]**)** Use _expr_ as the new seed for the random number generator. If no _expr_ is pro‐ vided, use the time of day. Return the previous seed for the random number generator. ### String Functions _Gawk_ has the following built-in string functions: **asort(**_s_ [**,** _d_ [**,** _how_] ]**)** Return the number of elements in the source array _s_. Sort the con‐ tents of _s_ using _gawk_'s normal rules for comparing values, and re‐ place the indices of the sorted values _s_ with sequential integers starting with 1. If the optional destination array _d_ is specified, first duplicate _s_ into _d_, and then sort _d_, leaving the indices of the source array _s_ unchanged. The optional string _how_ controls the direc‐ tion and the comparison mode. Valid values for _how_ are any of the strings valid for **PROCINFO["sorted**___**in"]**. It can also be the name of a user-defined comparison function as described in **PROCINFO["sorted**___**in"]**. **asorti(**_s_ [**,** _d_ [**,** _how_] ]**)** Return 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 original. The purpose of the optional string _how_ is the same as described previously for **asort()**. **gensub(**_r_**,** _s_**,** _h_ [**,** _t_]**)** Search the target string _t_ for matches of the regular expression _r_. If _h_ is a string beginning with **g** or **G**, then replace all matches of _r_ with _s_. Otherwise, _h_ is a number indicating which match of _r_ to re‐ place. If _t_ is not supplied, use **$0** 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 parenthesized subex‐ pression. 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 target 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 substitutions. If _t_ is not supplied, use **$0**. An **&** in the replacement text is replaced with the text that was actually matched. Use **\&** to get a literal **&**. (This must be typed as **"\\&"**; see _GAWK:_ _Effective_ _AWK_ _Programming_ for a fuller discussion of the rules for ampersands and backslashes in the replacement text of **sub()**, **gsub()**, and **gensub()**.) **index(**_s_**,** _t_**)** Return the index of the string _t_ in the string _s_, or zero if _t_ is not present. (This implies that character indices start at one.) It is a fatal error to use a regexp constant for _t_. **length(**[_s_]**)** Return the length of the string _s_, or the length of **$0** if _s_ is not supplied. As a non-standard extension, with an array argument, **length()** returns the number of elements in the array. **match(**_s_**,** _r_ [**,** _a_]**)** Return the position in _s_ where the regular expression _r_ occurs, or zero if _r_ is not present, and set 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 zero'th element of _a_ contains the portion of _s_ matched by the entire regular expression _r_. Sub‐ scripts **a[**_n_**,** **"start"]**, and **a[**_n_**,** **"length"]** provide the starting index in the string and length respectively, of each matching substring. **patsplit(**_s_**,** _a_ [**,** _r_ [**,** _seps_] ]**)** Split the string _s_ into the array _a_ and the separators array _seps_ on the regular expression _r_, and return the number of fields. Element values are the portions of _s_ that matched _r_. The value of **seps[**_i_**]** is the possibly null separator that appeared after **a[**_i_**]**. The value of **seps[0]** is the possibly null leading separator. If _r_ is omitted, **FPAT** is used instead. The arrays _a_ and _seps_ are cleared first. Splitting behaves identically to field splitting with **FPAT**, described above. **split(**_s_**,** _a_ [**,** _r_ [**,** _seps_] ]**)** Split the string _s_ into the array _a_ and the separators array _seps_ on the regular expression _r_, and return the number of fields. If _r_ is omitted, **FS** is used instead. The arrays _a_ and _seps_ are cleared first. **seps[**_i_**]** is the field separator matched by _r_ between **a[**_i_**]** and **a[**_i_**+1]**. If _r_ is a single space, then leading whitespace in _s_ goes into the extra array element **seps[0]** and trailing whitespace goes into the extra array element **seps[**_n_**]**, where _n_ is the return value of **split(**_s_**,** _a_**,** _r_**,** _seps_**)**. Splitting behaves identically to field split‐ ting, described above. In particular, if _r_ is a single-character string, that string acts as the separator, even if it happens to be a regular expression metacharacter. **sprintf(**_fmt_**,** _expr-list_**)** Print _expr-list_ according to _fmt_, and return the resulting string. **strtonum(**_str_**)** Examine _str_, and return its numeric value. If _str_ begins with a leading **0**, treat it as an octal number. If _str_ begins with a leading **0x** or **0X**, treat it as a hexadecimal number. Otherwise, assume it is a decimal number. **sub(**_r_**,** _s_ [**,** _t_]**)** Just like **gsub()**, but replace only the first matching substring. Re‐ turn either zero or one. **substr(**_s_**,** _i_ [**,** _n_]**)** Return the at most _n_-character substring of _s_ starting at _i_. If _n_ is omitted, use the rest of _s_. **tolower(**_str_**)** Return a copy of the string _str_, with all the uppercase characters in _str_ translated to their corresponding lowercase counterparts. Non- alphabetic characters are left unchanged. **toupper(**_str_**)** Return a copy of the string _str_, with all the lowercase characters in _str_ translated to their corresponding uppercase counterparts. Non- alphabetic characters are left unchanged. _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 processing log files that contain time stamp information, _gawk_ provides the following functions for obtaining time stamps and formatting them. **mktime(**_datespec_ [**,** _utc-flag_]**)** Turn _datespec_ into a time stamp of the same form as returned by **systime()**, and re‐ turn the result. 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, 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 mid‐ night. The origin-zero Gregorian calendar is assumed, with year 0 preceding year 1 and year -1 preceding year 0. If _utc-flag_ is present and is non-zero or non-null, the time is assumed to be in the UTC time zone; otherwise, the time is assumed to be in the local time zone. If the _DST_ 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 day‐ light saving time is in effect for the specified time. If _datespec_ does not con‐ tain enough elements or if the resulting time is out of range, **mktime()** returns -1. **strftime(**[_format_ [**,** _timestamp_[**,** _utc-flag_]]]**)** Format _timestamp_ according to the specification 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 _time__‐ _stamp_ is missing, the current time of day is used. If _format_ is missing, a default format equivalent to the output of [_date_(1)](https://www.chedong.com/phpMan.php/man/date/1/markdown) is used. The default format is avail‐ able in **PROCINFO["strftime"]**. See the specification for the **strftime()** function in ISO C for the format conversions that are guaranteed to be available. **systime()** Return 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 _Gawk_ supplies the following bit manipulation functions. They work by converting double-pre‐ cision floating point values to **uintmax**___**t** integers, doing the operation, and then converting the result back to floating point. **NOTE**: Passing negative operands to any of these functions causes a fatal error. The functions are: **and(**_v1_**,** _v2_ [, ...]**)** Return the bitwise AND of the values provided in the argument list. There must be at least two. **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 in the argument list. There must be at least two. **rshift(**_val_**,** _count_**)** Return the value of _val_, shifted right by _count_ bits. **xor(**_v1_**,** _v2_ [, ...]**)** Return the bitwise XOR of the values provided in the argument list. There must be at least two. ### Type Functions The following functions provide type related information about their arguments. **isarray(**_x_**)** Return true if _x_ is an array, false otherwise. This function is mainly for use with the elements of multidimensional arrays and with function parameters. **typeof(**_x_**)** Return a string indicating the type of _x_. The string will be one of **"array"**, **"number"**, **"regexp"**, **"string"**, **"strnum"**, **"unassigned"**, or **"undefined"**. ### Internationalization Functions The following functions 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_]**)** Specify the directory where _gawk_ looks for the **.gmo** files, in case they will not or cannot be placed in the ``standard'' locations (e.g., during testing). It returns the directory where _domain_ is ``bound.'' The default _domain_ is the value of **TEXTDOMAIN**. If _directory_ is the null string (**""**), then **bindtextdomain()** returns the current binding for the given _domain_. **dcgettext(**_string_ [**,** _domain_ [**,** _category_]]**)** Return the translation of _string_ in text domain _domain_ for locale category _category_. The default value for _domain_ is the current value of **TEXTDOMAIN**. The default value for _category_ is **"LC**___**MESSAGES"**. If you supply a value for _category_, it must be a string equal to one of the known lo‐ cale categories described in _GAWK:_ _Effective_ _AWK_ _Programming_. You must also supply a text domain. Use **TEXTDOMAIN** if you want to use the current domain. **dcngettext(**_string1_**,** _string2_**,** _number_ [**,** _domain_ [**,** _category_]]**)** Return 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 **TEXTDOMAIN**. The default value for _category_ is **"LC**___**MESSAGES"**. If you supply a value for _category_, it must be a string equal to one of the known lo‐ cale categories described in _GAWK:_ _Effective_ _AWK_ _Programming_. 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 execute 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 function. Arrays are passed by reference, other variables are passed by value. Since functions were not originally part of the AWK language, the provision for local vari‐ ables 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 parame‐ ter 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 intervening whitespace. 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 vari‐ ables are initialized to the null string and the number zero upon function 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. As a _gawk_ extension, functions may be called indirectly. To do this, assign the name of the function to be called, as a string, to a variable. Then use the variable as if it were the name of a function, prefixed with an **@** sign, like so: **function** **myfunc()** **{** **print** **"myfunc** **called"** **...** **}** **{** **...** **the**___**func** **=** **"myfunc"** **@the**___**func()** **#** **call** **through** **the**___**func** **to** **myfunc** **...** **}** As of version 4.1.2, this works with user-defined functions, built-in functions, and exten‐ sion functions. If **--lint** has been provided, _gawk_ warns about calls to undefined functions at parse time, in‐ stead 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**, although this is deprecated. ## DYNAMICALLY LOADING NEW FUNCTIONS You can dynamically add new functions written in C or C++ to the running _gawk_ interpreter with the **@load** statement. The full details are beyond the scope of this manual page; see _GAWK:_ _Effective_ _AWK_ _Programming_. ## SIGNALS The _gawk_ profiler 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 _gawk_ to dump the profile and function call stack and then exit. ## 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 trans‐ lation to the local 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 running a localizable AWK program. 1. Add a **BEGIN** action to assign a value to the **TEXTDOMAIN** variable to set the text domain to a name associated with your program: **BEGIN** **{** **TEXTDOMAIN** **=** **"myprog"** **}** This allows _gawk_ to find the **.gmo** 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 **bindtextdomain()** functions in your program, as appropriate. 4. Run **gawk** **--gen-pot** **-f** **myprog.awk** **>** **myprog.pot** to generate a **.pot** file for your program. 5. Provide appropriate translations, and build and install the corresponding **.gmo** files. The internationalization features are described in full detail in _GAWK:_ _Effective_ _AWK_ _Pro__‐ _gramming_. ## POSIX COMPATIBILITY A primary goal for _gawk_ is compatibility with the POSIX standard, as well as with the latest version of Brian Kernighan's _awk_. To this end, _gawk_ incorporates the following user visible features which are not described in the AWK book, but are part of the Brian Kernighan's ver‐ sion 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** rule is executed. However, in earlier implementations, when such an assignment appeared before any file names, the assignment would happen _before_ the **BEGIN** rule was run. Applications came to depend on this “feature.” When _awk_ was changed to match its documentation, the **-v** option for assigning variables before pro‐ gram execution was added to accommodate applications that depended upon the old behavior. (This feature was agreed upon by both the Bell Laboratories developers and the GNU develop‐ ers.) 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 op‐ eration, 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 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 ver‐ sion); the **tolower()** and **toupper()** built-in functions (from the Bell Laboratories version); and the ISO C conversion specifications in **printf** (done first in the Bell Laboratories ver‐ sion). ## HISTORICAL FEATURES There is one feature of historical AWK implementations that _gawk_ supports: 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)** Using this feature is poor practice, and _gawk_ issues a warning about its use if **--lint** is specified on the command line. ## GNU EXTENSIONS _Gawk_ has a too-large 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 **--traditional** 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** envi‐ ronment variable is not special. • There is no facility for doing file inclusion (_gawk_'s **@include** mechanism). • There is no facility for dynamically adding new functions written in C (_gawk_'s **@load** mecha‐ nism). • The **\x** escape sequence. • The ability to continue lines after **?** and **:**. • Octal and hexadecimal constants in AWK programs. • The **ARGIND**, **BINMODE**, **ERRNO**, **LINT**, **PREC**, **ROUNDMODE**, **RT** and **TEXTDOMAIN** variables are not spe‐ cial. • The **IGNORECASE** variable and its side-effects are not available. • The **FIELDWIDTHS** variable and fixed-width field splitting. • The **FPAT** variable and field splitting based on field values. • The **FUNCTAB**, **SYMTAB**, and **PROCINFO** arrays are 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 coprocesses. • The **BEGINFILE** and **ENDFILE** special patterns are not available. • The ability to split out individual characters using the null string as the value of **FS**, and as the third argument to **split()**. • An optional fourth argument to **split()** to receive the separator texts. • 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 **and()**, **asort()**, **asorti()**, **bindtextdomain()**, **compl()**, **dcgettext()**, **dcngettext()**, **gen**‐‐ **sub()**, **lshift()**, **mktime()**, **or()**, **patsplit()**, **rshift()**, **strftime()**, **strtonum()**, **systime()** and **xor()** functions. • Localizable strings. • Non-fatal I/O. • Retryable I/O. The AWK book does not define the return value of the **close()** function. _Gawk_'s **close()** re‐ turns the value from [_fclose_(3)](https://www.chedong.com/phpMan.php/man/fclose/3/markdown), or [_pclose_(3)](https://www.chedong.com/phpMan.php/man/pclose/3/markdown), when closing an output file or pipe, respec‐ tively. It returns the process's exit status when closing an input pipe. The return value is -1 if the named file, pipe or coprocess 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 specified. To really get a tab character as the field separator, it is best to use single quotes: **gawk** **-F'\t'** **...**. ## 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**, **--file**, **-i** and **--include** options, and the **@include** directive. If the initial search fails, the path is searched again after appending **.awk** to the filename. The **AWKLIBPATH** environment variable can be used to provide a list of directories that _gawk_ searches when looking for files named via the **-l** and **--load** options. The **GAWK**___**READ**___**TIMEOUT** environment variable can be used to specify a timeout in milliseconds for reading input from a terminal, pipe or two-way communication including sockets. For connection to a remote host via socket, **GAWK**___**SOCK**___**RETRIES** controls the number of retries, and **GAWK**___**MSEC**___**SLEEP** the interval between retries. The interval is in milliseconds. On sys‐ tems that do not support [_usleep_(3)](https://www.chedong.com/phpMan.php/man/usleep/3/markdown), the value is rounded up to an integral number of seconds. 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 mes‐ sage to this effect. ## EXIT STATUS If the **exit** statement is used with a value, then _gawk_ exits with the numeric value given to it. Otherwise, if there were no problems during execution, _gawk_ exits with the value of the C constant **EXIT**___**SUCCESS**. This is usually zero. If an error occurs, _gawk_ exits with the value of the C constant **EXIT**___**FAILURE**. This is usu‐ ally one. If _gawk_ exits because of a fatal error, the exit status is 2. On non-POSIX systems, this value may be mapped to **EXIT**___**FAILURE**. ## VERSION INFORMATION This man page documents _gawk_, version 5.1. ## AUTHORS The original version of UNIX _awk_ was designed and implemented by Alfred Aho, Peter Wein‐ berger, and Brian Kernighan of Bell Laboratories. Brian Kernighan continues to maintain and enhance it. Paul Rubin and Jay Fenlason, of the Free Software Foundation, 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_ com‐ patible with the new version of UNIX _awk_. Arnold Robbins is the current maintainer. See _GAWK:_ _Effective_ _AWK_ _Programming_ for a full list of the contributors to _gawk_ and its docu‐ mentation. See the **README** file in the _gawk_ distribution for up-to-date information about maintainers and which ports are currently supported. ## BUG REPORTS If you find a bug in _gawk_, please send electronic mail to ****. Please include your operating system and its revision, the version of _gawk_ (from **gawk** **--version**), which 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 set‐ ting 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 occa‐ sionally read this newsgroup, posting bug reports there is an unreliable way to report bugs. Similarly, do **NOT** use a web forum (such as Stack Overflow) for reporting bugs. Instead, please use the electronic mail addresses given above. Really. If you're using a GNU/Linux 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 ad‐ dress as well, since there's no guarantee that the bug report will be forwarded to the _gawk_ maintainer. ## BUGS The **-F** option is not necessary given the command line variable assignment feature; it remains only for backwards compatibility. ## SEE ALSO [_egrep_(1)](https://www.chedong.com/phpMan.php/man/egrep/1/markdown), [_sed_(1)](https://www.chedong.com/phpMan.php/man/sed/1/markdown), [_getpid_(2)](https://www.chedong.com/phpMan.php/man/getpid/2/markdown), [_getppid_(2)](https://www.chedong.com/phpMan.php/man/getppid/2/markdown), [_getpgrp_(2)](https://www.chedong.com/phpMan.php/man/getpgrp/2/markdown), [_getuid_(2)](https://www.chedong.com/phpMan.php/man/getuid/2/markdown), [_geteuid_(2)](https://www.chedong.com/phpMan.php/man/geteuid/2/markdown), [_getgid_(2)](https://www.chedong.com/phpMan.php/man/getgid/2/markdown), _gete__‐ [_gid_(2)](https://www.chedong.com/phpMan.php/man/gid/2/markdown), [_getgroups_(2)](https://www.chedong.com/phpMan.php/man/getgroups/2/markdown), [_printf_(3)](https://www.chedong.com/phpMan.php/man/printf/3/markdown), [_strftime_(3)](https://www.chedong.com/phpMan.php/man/strftime/3/markdown), [_usleep_(3)](https://www.chedong.com/phpMan.php/man/usleep/3/markdown) _The_ _AWK_ _Programming_ _Language_, Alfred V. Aho, Brian W. Kernighan, Peter J. Weinberger, Addi‐ son-Wesley, 1988. ISBN 0-201-07981-X. _GAWK:_ _Effective_ _AWK_ _Programming_, Edition 5.1, shipped with the _gawk_ source. The current ver‐ sion of this document is available online at ****. The GNU **gettext** documentation, available online at ****. ## 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")** **}'** ## ACKNOWLEDGEMENTS Brian Kernighan 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, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 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 distrib‐ uted under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual page into another language, under the above conditions for modified versions, except that this permission no‐ tice may be stated in a translation approved by the Foundation. Free Software Foundation Mar 23 2020 [GAWK(1)](https://www.chedong.com/phpMan.php/man/GAWK/1/markdown)