# man > awk > **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. ## PREFACE This manual page is intentionally as terse as possible. Full details are provided in _GAWK:_ _Effective_ _AWK_ _Programming_, and you should look there for the full story on any specific fea‐ ture. Where possible, links to the online version of the manual are provided. ## 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 _ Read the AWK program source from the file _program-file_, instead of from the first com‐ mand line argument. Multiple **-f **options may be used. Files read with **-f **are treated as if they begin with an implicit **@namespace "awk" **statement. ### -F _ --field-separator _ Use _fs_ for the input field separator (the value of the **FS **predefined variable). ### -v _ --assign _ 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. 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. ### -C --copyright Print the short version of the GNU copyright information message on the standard out‐ put and exit successfully. ### -d --dump-variables Print a sorted list of global variables, their types and final values to _file_. The default file is **awkvars.out **in the current directory. ### -D --debug 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. In this mode of execution, _gawk_ loads the AWK source code and then prompts for debug‐ ging commands. _Gawk_ can only debug AWK program source provided with the **-f **and **--in‐** **clude **options. The debugger is documented in _GAWK:_ _Effective_ _AWK_ _Programming_; see _. ### -e _ --source _ Use _program-text_ as AWK program source code. Each argument supplied via **-e **is treated as if it begins with an implicit **@namespace "awk" **statement. ### -E _ --exec _ 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. ### -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 _ 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. ### -I --trace Print the internal byte code names as they are executed when running the program. The trace is printed to standard error. Each ``op code'' is preceded by a **+ **sign in the output. ### -l _ --load _ 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 Provide warnings about constructs that are dubious or non-portable to other AWK imple‐ mentations. See _‐_ _tions_ for the list of possible values for _value_. ### -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.) **NOTE: **This feature is _on_ _parole_. The primary _gawk_ maintainer is no longer supporting it, although there is a member of the development team who is. If this situation changes, the feature will be removed from _gawk_. ### -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. ### -o --pretty-print Output a pretty printed version of the program to _file_. The default file is **awkprof.out **in the current directory. This option implies **--no-optimize**. ### -O --optimize Enable _gawk_'s default optimizations upon the internal representation of the program. This option is on by default. ### -p --profile Start a profiling session, and send the profiling data to _prof-file_. The default is **awkprof.out **in the current directory. The profile contains execution counts of each statement in the program in the left margin and function call counts for each user-de‐ fined function. _Gawk_ runs more slowly in this mode. This option implies **--no-opti‐** **mize**. ### -P --posix This turns on _compatibility_ mode, and disables a number of common extensions. ### -r --re-interval Enable the use of _interval_ _expressions_ in regular expression matching. Interval ex‐ pressions are enabled by default, but this option remains for backwards compatibility. ### -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. ### -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 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 “-”. 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. 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. In addition, lines beginning with **@include **may be used to include other source files into your program. This is equivalent to using the **--include **option. 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.) 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 **rules 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. For _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_ reverts to treating direc‐ tories 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. However, _gawk_ provides true arrays of arrays. Several pre-defined variables are set as a program runs; these are de‐ scribed 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**. See _‐_ _ware/gawk/manual/html_node/Records.html_ for the details. ### Fields As each input record is read, _gawk_ splits the record into _fields_, using the value of the **FS** variable as the field separator. Additionally, **FIELDWIDTHS **and **FPAT **may be used to control input field splitting. See the details, starting at _‐_ _ual/html_node/Fields.html_. Each field in the input record may be referenced by its position: **$1**, **$2**, and so on. **$0 **is the whole record, including leading and trailing whitespace. The variable **NF **is set to the total number of fields in the input record. References to non-existent fields (i.e., fields after **$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 listed below. This list is purposely terse. For details, see _. **ARGC **The number of command line arguments. **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. **BINMODE **On non-POSIX systems, specifies use of “binary” mode for all file I/O. See _ for the details. **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. **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. **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. **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. **FS **The input field separator, a space by default. See _‐_ _ware/gawk/manual/html_node/Field-Separators.html_ for the details. **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. See _ for details. **LINT **Provides dynamic control of the **--lint **option from within an AWK program. **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. See _ for the details. **ROUNDMODE **The rounding mode to use for arbitrary precision arithmetic on numbers, by de‐ fault **"N" **(IEEE-754 roundTiesToEven mode). See _‐_ _ware/gawk/manual/html_node/Setting-the-rounding-mode_ for the details. **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. **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. You may not use the **delete **statement with the **SYMTAB** array, nor assign to elements 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++. See _ for details. ### 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 _‐_ _ual/html_node/Namespaces.html#Namespaces_. ### 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. _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. See _ for the details. ### Regexp Constants A regular expression constant is a sequence of characters enclosed between forward slashes (like **/value/**). The escape sequences described in the manual may also be used inside constant regular expres‐ sions (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 essentially the same as those in [_egrep_(1)](https://www.chedong.com/phpMan.php/man/egrep/1/markdown). See _ for the de‐ tails on regular expressions. 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. ### 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. **+ - ! **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. **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 an open 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**. (The _command_ can also be a socket. See the subsection **Special File Names**, below.) **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. **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. **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 _‐_ _ware/gawk/manual/html_node/I_002fO-Functions.html#I_002fO-Functions_ for the full details on the exit status. 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 AWK versions of the **printf **statement and **sprintf() **function are similar to those of C. For details, see _. ### 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_. 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; details are provided in _. **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 described in _‐_ _tions.html#String-Functions_. _s_ and _d_ are allowed to be the same ar‐ ray; this only makes sense when supplying the third argument as well. **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 for **asort()**. Here too, _s_ and _d_ are allowed to be the same array; this only makes sense when supplying the third argument as well. **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 _‐_ _ware/gawk/manual/html_node/Gory-Details.html#Gory-Details_ 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.) **length(**[_s_]**) **Return the length of the string _s_, or the length of **$0 **if _s_ is not supplied. With an array argument, **length() **returns the number of el‐ ements 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_. See _ _Functions.html#String-Functions_ for a description of how the array _a_ is filled if it is provided. **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**. **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]**. Splitting behaves identically to field splitting. **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 _Gawk_ provides the following functions for obtaining time stamps and formatting them. Details are provided in _. **mktime(_**datespec_ [**, _**utc-flag_]**)** Turn _datespec_ into a time stamp of the same form as returned by **systime()**, and re‐ turn the result. 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 lo‐ cal time zone. If _datespec_ does not contain enough elements or if the resulting time is out of range, **mktime() **returns -1. See _‐_ _ware/gawk/manual/html_node/Time-Functions.html#Time-Functions_ for the details of _datespec_. **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. 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. **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 _ _Functions.html#I18N-Functions_. **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. 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"**. **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"**. ### Boolean Valued Functions You can create special Boolean-typed values; see the manual for how they work and why they exist. **mkbool(_**expression_**)** Based on the boolean value of _expression_ return either a true value or a false value. True values have numeric value one. False values have numeric value zero. ## 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. Local variables are declared as extra parameters in the parameter list. The convention is to separate local variables from real parameters by extra spaces in the parameter list. For ex‐ ample: **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 restriction does not apply to the built-in func‐ tions 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. 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, pre‐ fixed with an **@ **sign, like so: **function myfunc()** **{** **print "myfunc called"** **...** **}** **{ ...** **the_func = "myfunc"** **@the_func() # call through the_func to myfunc** **...** **}** 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. ## 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 _‐_ _sions_. ## 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. See _‐_ _ual/html_node/Internationalization.html#Internationalization_ for the steps involved in pro‐ ducing and running a localizable AWK program. ## GNU EXTENSIONS _Gawk_ has a too-large number of extensions to POSIX _awk_. They are described in _. All the extensions can be disabled by invoking _gawk_ with the **--traditional **or **--posix **options. ## 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_PERSIST_FILE **environment variable, if present, specifies a file to use as the back‐ ing store for persistent memory. _This_ _is_ _an_ _experimental_ _feature_. See _GAWK:_ _Effective_ _AWK_ _Programming_ for the details. 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 5.2. ## 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 use the [_gawkbug_(1)](https://www.chedong.com/phpMan.php/man/gawkbug/1/markdown) program to report it. Full instructions for reporting a bug are provided in _‐_ _ual/html_node/Bugs.html_. _Please_ carefully read and follow the instructions given there. This will make bug reporting and resolution much easier for everyone involved. Really. ## BUGS The **-F **option is not necessary given the command line variable assignment feature; it remains only for backwards compatibility. This manual page is too long; _gawk_ has too many features. ## 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), [_gawkbug_(1)](https://www.chedong.com/phpMan.php/man/gawkbug/1/markdown), [_printf_(3)](https://www.chedong.com/phpMan.php/man/printf/3/markdown), and [_strftime_(3)](https://www.chedong.com/phpMan.php/man/strftime/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 5.2, 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") }'** ## 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, 2021, 2022 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 Jun 09 2022 [_GAWK_(1)](https://www.chedong.com/phpMan.php/man/GAWK/1/markdown)