gawk(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | PREFACE | OPTION FORMAT | OPTIONS | AWK PROGRAM EXECUTION | VARIABLES, RECORDS AND FIELDS | PATTERNS AND ACTIONS | USER-DEFINED FUNCTIONS | DYNAMICALLY LOADING NEW FUNCTIONS | SIGNALS | INTERNATIONALIZATION | GNU EXTENSIONS | ENVIRONMENT VARIABLES | EXIT STATUS | VERSION INFORMATION | AUTHORS | BUG REPORTS | BUGS | SEE ALSO | EXAMPLES | COPYING PERMISSIONS | COLOPHON

GAWK(1)                     Utility Commands                     GAWK(1)

NAME         top

       gawk - pattern scanning and processing language

SYNOPSIS         top

       gawk [ POSIX or GNU style options ] -f program-file [ -- ] file
       ...
       gawk [ POSIX or GNU style options ] [ -- ] program-text file ...

DESCRIPTION         top

       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         top

       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 feature.
       Where possible, links to the online version of the manual are
       provided.

OPTION FORMAT         top

       Gawk options may be either traditional POSIX-style one letter
       options, or GNU-style long options.  POSIX options start with a
       single “-”, while long options start with “--”.  Long options are
       provided for both GNU-specific features and for POSIX-mandated
       features.

       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 provided in
       the next command line argument.  Long options may be abbreviated,
       as long as the abbreviation remains unique.

       Additionally, every long option has a corresponding short option,
       so that the option's functionality may be used from within #!
       executable scripts.

OPTIONS         top

       Gawk accepts the following options.  Standard options are listed
       first, followed by options for gawk extensions, listed
       alphabetically by short option.

       -f program-file, --file program-file
              Read the AWK program source from the file program-file,
              instead of from the first command 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 fs, --field-separator fs
              Use fs for the input field separator (the value of the FS
              predefined variable).

       -v var=val, --assign var=val
              Assign the value val to the variable var, before execution
              of the program begins.  Such variable values are available
              to the BEGIN 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 output and exit successfully.

       -d[file], --dump-variables[=file]
              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[file], --debug[=file]
              Enable debugging of AWK programs.  By default, the
              debugger reads commands interactively 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 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; see
              https://www.gnu.org/software/gawk/manual/html_node/Debugger.html#Debugger .

       -e program-text, --source program-text
              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 file, --exec file
              Similar to -f, however, this 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 program.
              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-file, --include include-file
              Load an awk source library.  This searches for the library
              using the AWKPATH environment variable.  If the initial
              search fails, another attempt will be made after appending
              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" statement.

       -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.

       -k, --csv
              Enable CSV special processing.  See Comma Separated
              Values, below, for more detail.

       -l lib, --load lib
              Load a gawk extension from the shared library lib.  This
              searches for the library using 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 [value], --lint[=value]
              Provide warnings about constructs that are dubious or non-
              portable to other AWK implementations.  See
              https://www.gnu.org/software/gawk/manual/html_node/Options.html#Options 
              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 caution!

       -N, --use-lc-numeric
              Force gawk to use the locale's decimal point character
              when parsing input data.

       -o[file], --pretty-print[=file]
              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[prof-file], --profile[=prof-file]
              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-defined function.  Gawk runs
              more slowly in this mode.  This option implies
              --no-optimize.

       -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 expressions 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 getline, output redirection with
              print and printf, and loading dynamic extensions.  Command
              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 program 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         top

       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 options
       may be used multiple times on the command line.  Gawk reads the
       program text as if all the program-files and command line source
       texts had been concatenated together.

       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/local/lib/gawk".  (The actual directory may vary, depending
       upon how gawk was built and installed.)

       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 command line,
       gawk reads the standard input.

       If a filename on the command line has the form var=val it is
       treated as a variable assignment.  The variable var will be
       assigned the value val.  (This happens after any BEGIN 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 ENDFILE 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 directories on
       the command line as a fatal error.

VARIABLES, RECORDS AND FIELDS         top

       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.
       Additionally, gawk allows variables to have regular-expression
       type.  AWK also has one dimensional 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 described as needed and summarized below.

   Records
       Normally, records are separated by newline characters.  You can
       control how records are separated by assigning values to the
       built-in variable RS.  See
       https://www.gnu.org/software/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
       https://www.gnu.org/software/gawk/manual/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 recomputed, with the fields being
       separated by the value of OFS.  References to negative numbered
       fields cause a fatal error.  Decrementing NF causes the values of
       fields past the new value to be lost, and the value of $0 to be
       recomputed, with the fields being separated by the value of OFS.

       Assigning a value to an existing field causes the whole record to
       be rebuilt when $0 is referenced.  Similarly, assigning a value
       to $0 causes the record to be resplit, creating new values for
       the fields.

   Comma Separated Values
       When invoked with either the -k or the --csv option, gawk does
       not use regular record determination and field splitting as
       described above.  Instead, records are terminated by unquoted
       newlines, and fields are separated by commas.  Double-quotes may
       be used to enclose fields containing commas, newlines, or doubled
       double-quotes.  See
       https://www.gnu.org/software/gawk/manual/html_node/Comma-Separated-Fields.html 
       for more details.

   Built-in Variables
       Gawk's built-in variables are listed below.  This list is
       purposely terse. For details, see
       https://www.gnu.org/software/gawk/manual/html_node/Built_002din-Variables .

       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
              https://www.gnu.org/software/gawk/manual/html_node/PC-Using.html 
              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-separated 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 expression, instead of
              using the value of FS as the field separator.

       FS     The input field separator, a space by default.  See
              https://www.gnu.org/software/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-defined 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
              https://www.gnu.org/software/gawk/manual/html_node/Case_002dsensitivity.html 
              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 default.

       PROCINFO
              The elements of this array provide access to information
              about the running AWK program.  See
              https://www.gnu.org/software/gawk/manual/html_node/Auto_002dset 
              for the details.

       ROUNDMODE
              The rounding mode to use for arbitrary precision
              arithmetic on numbers, by default "N" (IEEE-754
              roundTiesToEven mode).  See
              https://www.gnu.org/software/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 expression is an expression list (expr, expr
       ...)  then the array subscript is a string consisting of the
       concatenation of the (string) value of each expression, separated
       by the value of the SUBSEP variable.  This facility is used to
       simulate multiply dimensioned arrays.  For example:

              i = "A"; j = "B"; k = "C"
              x[i, j, k] = "hello, world\n"

       assigns the string "hello, world\n" to the element of the array x
       which is indexed by the string "A\034B\034C".  All arrays in AWK
       are associative, i.e., indexed by string values.

       The special operator in may be used to test if an array has an
       index consisting of a particular value:

              if (val in array)
                   print array[val]

       If the array has multiple subscripts, use (i, j) in array.

       The in construct may also be used in a for loop to 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 ``rectangular'' as in C or C++.  See
       https://www.gnu.org/software/gawk/manual/html_node/Arrays  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'' namespace; the default namespace is awk.  However,
       simple identifiers consisting solely of uppercase 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 identifiers in
       other namespaces.  For more details, see
       https://www.gnu.org/software/gawk/manual/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).  A number is converted to a string
       by using the value of CONVFMT as a format string for sprintf(3),
       with the numeric value of the variable as the argument.  However,
       even though all numbers in AWK are floating-point, integral
       values are always converted as integers.

       Gawk performs comparisons as follows: If two variables are
       numeric, they are compared numerically.  If one value is numeric
       and the other has a string value that is a “numeric string,” then
       comparisons are also done numerically.  Otherwise, the numeric
       value is converted to a string and a string comparison is
       performed.  Two strings are compared, of course, as strings.

       Note that string constants, such as "57", are not numeric
       strings, they are string constants.  The idea of “numeric string”
       only applies to fields, getline input, FILENAME, ARGV elements,
       ENVIRON elements and the elements of an array created by split()
       or patsplit() that are numeric 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 example, the octal value 011 is equal
       to decimal 9, and the hexadecimal value 0x11 is equal to decimal
       17.

   String Constants
       String constants in AWK are sequences of characters enclosed
       between double quotes (like "value").  Within strings, certain
       escape sequences are recognized, as in C.  See
       https://www.gnu.org/software/gawk/manual/html_node/Escape-Sequences 
       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 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 elements)
       and passed to user-defined functions. Variables that have been so
       assigned have regular expression type.

PATTERNS AND ACTIONS         top

       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.  However, 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 expressions.  BEGIN and END patterns cannot have missing
       action parts.

       BEGINFILE and ENDFILE are additional special patterns whose
       actions are executed before reading 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).  See
       https://www.gnu.org/software/gawk/manual/html_node/Regexp.html 
       for the details 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
       primitive pattern expressions.  As in most languages, parentheses
       may be used to change the order of evaluation.

       The ?: operator is like the same operator in C.  If the first
       pattern is true then the pattern used for testing is the second
       pattern, otherwise it is the third.  Only one of the second and
       third patterns is evaluated.

       The pattern1, pattern2 form of an expression is called a range
       pattern.  It matches all input records starting with a record
       that matches pattern1, and continuing until a record that matches
       pattern2, inclusive.  It does not combine with any other sort of
       pattern 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,
       control statements, and input/output statements available are
       patterned after those in C.

   Operators
       The operators in AWK, in order of decreasing precedence, are:

       (...)  Grouping

       $      Field reference.

       ++ --  Increment and decrement, both prefix and postfix.

       ^      Exponentiation.

       + - !  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 program.  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
              https://www.gnu.org/software/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, below.)

       The getline command returns 1 on success, zero on end of file,
       and -1 on an error.  If the errno(3) 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 attempted.  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
       https://www.gnu.org/software/gawk/manual/html_node/Printf.html .

   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 default (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 provided, 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
       https://www.gnu.org/software/gawk/manual/html_node/String-Functions .

       asort(s [, d [, how] ])
              Return the number of elements in the source array s.  Sort
              the contents of s using gawk's normal rules for comparing
              values, and replace 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
              direction and the comparison mode.  Valid values for how
              are described in
              https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions .
              s and d are allowed to be the same array; 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 replace.  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 subexpression.  The sequence \0 represents
              the entire matched text, as does the character &.  Unlike
              sub() and gsub(), the modified string is returned as the
              result of the function, and the original 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
              https://www.gnu.org/software/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 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.  See
              https://www.gnu.org/software/gawk/manual/html_node/String-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.  Return 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
       https://www.gnu.org/software/gawk/manual/html_node/Time-Functions .

       mktime(datespec [, utc-flag])
              Turn datespec into a time stamp of the same form as
              returned by systime(), and return 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 local time zone.  If datespec does
              not contain enough elements or if the resulting time is
              out of range, mktime() returns -1.  See
              https://www.gnu.org/software/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 timestamp is missing, the current time of
              day is used.  If format is missing, a default format
              equivalent to the output of date(1) is used.  The default
              format is available 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-precision 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
       https://www.gnu.org/software/gawk/manual/html_node/I18N-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         top

       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 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 restriction does not apply to the built-in
       functions listed above.

       Functions may call each other and may be recursive.  Function
       parameters used as local variables are 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, prefixed
       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, instead of at run time.  Calling an
       undefined function at run time is a fatal error.

DYNAMICALLY LOADING NEW FUNCTIONS         top

       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
       https://www.gnu.org/software/gawk/manual/html_node/Dynamic-Extensions.html#Dynamic-Extensions .

SIGNALS         top

       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         top

       String constants are sequences of characters enclosed in double
       quotes.  In non-English speaking environments, it is possible to
       mark strings in the AWK program as requiring translation to the
       local natural language. Such strings are marked in the AWK
       program with a leading 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
       https://www.gnu.org/software/gawk/manual/html_node/Internationalization.html#Internationalization 
       for the steps involved in producing and running a localizable AWK
       program.

GNU EXTENSIONS         top

       Gawk has a too-large number of extensions to POSIX awk.  They are
       described in
       https://www.gnu.org/software/gawk/manual/html_node/POSIX_002fGNU.html .
       All the extensions can be disabled by invoking gawk with the
       --traditional or --posix options.

ENVIRONMENT VARIABLES         top

       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 backing 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 systems
       that do not support usleep(3), 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 message to this
       effect.

EXIT STATUS         top

       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 usually 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         top

       This man page documents gawk, version 5.3.

AUTHORS         top

       The original version of UNIX awk was designed and implemented by
       Alfred Aho, Peter Weinberger, and Brian Kernighan of Bell
       Laboratories.  Ozan Yigit is the the current maintainer.  Brian
       Kernighan occasionally dabbles in its development.

       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 compatible 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 documentation.

       See the README file in the gawk distribution for up-to-date
       information about maintainers and which ports are currently
       supported.

BUG REPORTS         top

       If you find a bug in gawk, please use the gawkbug(1) program to
       report it.

       Full instructions for reporting a bug are provided in
       https://www.gnu.org/software/gawk/manual/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         top

       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         top

       egrep(1), sed(1), gawkbug(1), printf(3), and strftime(3).

       The AWK Programming Language, second edition, Alfred V. Aho,
       Brian W. Kernighan, Peter J. Weinberger, Addison-Wesley, 2023.
       ISBN 9-780138-269722.

       GAWK: Effective AWK Programming, Edition 5.3, shipped with the
       gawk source.  The current version of this document is available
       online at https://www.gnu.org/software/gawk/manual .

       The GNU gettext documentation, available online at
       https://www.gnu.org/software/gettext .

EXAMPLES         top

       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         top

       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, 2023
       Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim copies of
       this manual page provided the copyright notice and this
       permission notice are preserved on all copies.

       Permission is granted to copy and distribute modified versions of
       this manual page under the conditions for verbatim copying,
       provided that the entire resulting derived work is distributed
       under the terms of a 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 notice may be
       stated in a translation approved by the Foundation.

COLOPHON         top

       This page is part of the gawk (GNU awk) project.  Information
       about the project can be found at 
       ⟨http://www.gnu.org/software/gawk/⟩.  If you have a bug report for
       this manual page, see
       ⟨http://pkg-shadow.alioth.debian.org/getinvolved.php⟩.  This page
       was obtained from the project's upstream Git repository
       ⟨git://git.savannah.gnu.org/gawk.git⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-14.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Free Software Foundation       Nov 02 2023                       GAWK(1)