NAME

mawk - pattern scanning and text processing language

SYNOPSIS

mawk [-W option] [-F value] [-v var=value] [- -] 'program text' [file
...]
mawk [-W option] [-F value] [-v var=value] [-f program-file] [- -] [file
...]

DESCRIPTION

mawk is an interpreter for the AWK Programming Language. The AWK
language is useful for manipulation of data files, text retrieval and
processing, and for prototyping and experimenting with algorithms. mawk
is a new awk meaning it implements the AWK language as defined in Aho,
Kernighan and Weinberger, The AWK Programming Language, Addison-Wesley
Publishing, 1988 (hereafter referred to as the AWK book.) mawk conforms
to the POSIX 1003.2 (draft 11.3) definition of the AWK language which
contains a few features not described in the AWK book, and mawk provides
a small number of extensions.

An AWK program is a sequence of pattern {action} pairs and function
definitions. Short programs are entered on the command line usually
enclosed in ' ' to avoid shell interpretation. Longer programs can be
read in from a file with the -f option. Data input is read from the list
of files on the command line or from standard input when the list is
empty. The input is broken into records as determined by the record
separator variable, RS. Initially, RS = \n and records are synonymous
with lines. Each record is compared against each pattern and if it
matches, the program text for {action} is executed.

OPTIONS

-F value

    sets the field separator, FS, to value.

-f file

    Program text is read from file instead of from the command line.
    Multiple -f options are allowed.

-v var=value

    assigns value to program variable var.

- -

    indicates the unambiguous end of options.

The above options will be available with any POSIX compatible
implementation of AWK. Implementation specific options are prefaced with
-W. mawk provides these:

-W dump

    writes an assembler like listing of the internal representation of
    the program to stdout and exits 0 (on successful compilation).

-W exec file

    Program text is read from file and this is the last option.

    This is a useful alternative to -f on systems that support the #!
    magic number convention for executable scripts. Those implicitly
    pass the pathname of the script itself as the final parameter, and
    expect no more than one - option on the #! line. Because mawk can
    combine multiple -W options separated by commas, you can use this
    option when an additional -W option is needed.

-W help

    prints a usage message to stderr and exits (same as -W usage).

-W interactive

    changes the buffering of stdout and stdin to make it more responsive
    in interactive use.

    Normally mawk does not change the standard streams buffering, which
    uses line-buffering stdin and stdout if they are connected to a
    terminal, and block-buffering otherwise (e.g., if mawk is run in a
    pipe).

    When opening a pipe, a special file (such as -), or one of the stdio
    devices, mawk first opens a file descriptor. Mawk then decides
    whether to use buffered I/O by checking if the file descriptor is
    for a terminal, and if RS is currently set to the single character
    \n (newline). As a special case, file descriptor zero (0) is
    assigned to stdin, while fdopen handles other file descriptors.

    The interactive option bypasses both checks in deciding to use
    buffered I/O (is a terminal, and RS is \n). The interactive option
    also changes stdout to unbuffered (like stderr).

    Mawk changes streams to unbuffered I/O in a few other cases:

    - if a file is created or appended to, i.e., using > or >> mawk
      treats this differently from opening pipes, first opening it as a
      stream (block buffered) and then changing it to unbuffered if it
      happens to be a terminal.

    - if the standard output is connected to a terminal and the the
      interactive option was not given, mawk changes it to unbuffered.

-W posix

    modifies mawk's behavior to be more POSIX-compliant:

    - forces mawk not to consider '\n' to be space.

      The original posix_space is recognized, but deprecated.

    - Allow hexadecimal, inf (infinity) and nan (not-a-number).

      The Open Group Base Specifications Issue 8 allows but does not
      require these features.

-W random=num

    calls srand with the given parameter (and overrides the auto-seeding
    behavior).

-W sprintf=num

    adjusts the size of mawk's internal sprintf buffer to num bytes.
    More than rare use of this option indicates mawk should be
    recompiled.

-W traditional

    Omit features such as interval expressions which were not supported
    by traditional awk.

-W usage

    prints a usage message to stderr and exits (same as -W help).

-W version

    mawk writes its version and copyright to stdout and compiled limits
    to stderr and exits 0.

mawk accepts abbreviations for any of these options, e.g., -W v and -Wv
both tell mawk to show its version.

mawk allows multiple -W options to be combined by separating the options
with commas, e.g., -Wsprint=2000,posix. This is useful for executable #!
magic number invocations in which only one argument is supported, e.g.,
-Winteractive,exec.

THE AWK LANGUAGE

1. Program structure

An AWK program is a sequence of pattern {action} pairs and user function
definitions.

A pattern can be:

    BEGIN
    END
    expression
    expression , expression

One, but not both, of pattern {action} can be omitted. If {action} is
omitted it is implicitly { print }. If pattern is omitted, then it is
implicitly matched. BEGIN and END patterns require an action.

Statements are terminated by newlines, semi-colons or both. Groups of
statements such as actions or loop bodies are blocked via { ... } as in
C. The last statement in a block doesn't need a terminator. Blank lines
have no meaning; an empty statement is terminated with a semi-colon.
Long statements can be continued with a backslash, \ . A statement can
be broken without a backslash after a comma, left brace, &&, ||, do,
else, the right parenthesis of an if, while or for statement, and the
right parenthesis of a function definition. A comment starts with # and
extends to, but does not include the end of line.

The following statements control program flow inside blocks.

  if ( expr ) statement

  if ( expr ) statement else statement

  while ( expr ) statement

  do statement while ( expr )

  for ( opt_expr ; opt_expr ; opt_expr ) statement

  for ( var in array ) statement

  continue

  break

2. Data types, conversion and comparison

There are two basic data types, numeric and string. Numeric constants
can be integer like -2, decimal like 1.08, or in scientific notation
like -1.1e4 or .28E-3. All numbers are represented internally and all
computations are done in floating point arithmetic. So for example, the
expression 0.2e2 == 20 is true and true is represented as 1.0.

String constants are enclosed in double quotes.

"This is a string with a newline at the end.\n"

Strings can be continued across a line by escaping (\) the newline. The
following escape sequences are recognized.


    	\\		\
    	\"		"
    	\a		alert, ascii 7
    	\b		backspace, ascii 8
    	\t		tab, ascii 9
    	\n		newline, ascii 10
    	\v		vertical tab, ascii 11
    	\f		formfeed, ascii 12
    	\r		carriage return, ascii 13
    	\ddd		1, 2 or 3 octal digits for ascii ddd
    	\xhh		1 or 2 hex digits for ascii  hh

If you escape any other character \c, you get \c, i.e., mawk ignores the
escape.

There are really three basic data types; the third is number and string
which has both a numeric value and a string value at the same time. User
defined variables come into existence when first referenced and are
initialized to null, a number and string value which has numeric value 0
and string value "". Non-trivial number and string typed data come from
input and are typically stored in fields. (See section 4).

The type of an expression is determined by its context and automatic
type conversion occurs if needed. For example, to evaluate the
statements


    	y = x + 2  ;  z = x  "hello"

The value stored in variable y will be typed numeric. If x is not
numeric, the value read from x is converted to numeric before it is
added to 2 and stored in y. The value stored in variable z will be typed
string, and the value of x will be converted to string if necessary and
concatenated with "hello". (Of course, the value and type stored in x is
not changed by any conversions.) A string expression is converted to
numeric using its longest numeric prefix as with atof(3). A numeric
expression is converted to string by replacing expr with
sprintf(CONVFMT, expr), unless expr can be represented on the host
machine as an exact integer then it is converted to sprintf("%d", expr).
Sprintf() is an AWK built-in that duplicates the functionality of
sprintf(3), and CONVFMT is a built-in variable used for internal
conversion from number to string and initialized to "%.6g". Explicit
type conversions can be forced, expr "" is string and expr+0 is numeric.

To evaluate, expr1 rel-op expr2, if both operands are numeric or number
and string then the comparison is numeric; if both operands are string
the comparison is string; if one operand is string, the non-string
operand is converted and the comparison is string. The result is
numeric, 1 or 0.

In boolean contexts such as, if ( expr ) statement, a string expression
evaluates true if and only if it is not the empty string ""; numeric
values if and only if not numerically zero.

3. Regular expressions

In the AWK language, records, fields and strings are often tested for
matching a regular expression. Regular expressions are enclosed in
slashes, and


    	expr ~ /r/

is an AWK expression that evaluates to 1 if expr matches r, which means
a substring of expr is in the set of strings defined by r. With no match
the expression evaluates to 0; replacing ~ with the not match operator,
!~ , reverses the meaning. As pattern-action pairs,


    	/r/ { action }   and   $0 ~ /r/ { action }

are the same, and for each input record that matches r, action is
executed. In fact, /r/ is an AWK expression that is equivalent to ($0 ~
/r/) anywhere except when on the right side of a match operator or
passed as an argument to a built-in function that expects a regular
expression argument.

AWK uses extended regular expressions as with the -E option of grep(1).
The regular expression metacharacters, i.e., those with special meaning
in regular expressions are


    	\ ^ $ . [ ] | ( ) * + ? { }

If the command line option -W traditional is used, these are omitted:


    	{ }

are also regular expression metacharacters, and in this mode, require
escaping to be a literal character.

Regular expressions are built up from characters as follows:

  

  c

      matches any non-metacharacter c.

  \c

      matches a character defined by the same escape sequences used in
      string constants or the literal character c if \c is not an escape
      sequence.

  .

      matches any character (including newline).

  ^

      matches the front of a string.

  $

      matches the back of a string.

  [c1c2c3...]

      matches any character in the class c1c2c3... . An interval of
      characters is denoted c1-c2 inside a class [...].

  [^c1c2c3...]

      matches any character not in the class c1c2c3...

Regular expressions are built up from other regular expressions as
follows:

  

  r1r2

      matches r1 followed immediately by r2 (concatenation).

  r1 | r2

      matches r1 or r2 (alternation).

  r*

      matches r repeated zero or more times.

  r+

      matches r repeated one or more times.

  r?

      matches r zero or once. (repetition).

  (r)

      matches r (grouping).

  r{n}

      matches r exactly n times.

  r{n,}

      matches r repeated n or more times.

  r{n,m}

      matches r repeated n to m (inclusive) times.

  r{,m}

      matches r repeated 0 to m times (a non-standard option).

The increasing precedence of operators is:


    alternation concatenation repetition grouping

For example,


    	/^[_a-zA-Z][_a-zA-Z0-9]*$/  and
    	/^[-+]?([0-9]+\ .?|\ .[0-9])[0-9]*([eE][-+]?[0-9]+)?$/

are matched by AWK identifiers and AWK numeric constants respectively.
Note that . has to be escaped to be recognized as a decimal point, and
that metacharacters are not special inside character classes.

Any expression can be used on the right hand side of the ~ or !~
operators or passed to a built-in that expects a regular expression. If
needed, it is converted to string, and then interpreted as a regular
expression. For example,


    	BEGIN { identifier = "[_a-zA-Z][_a-zA-Z0-9]*" }

    	$0 ~ "^" identifier

prints all lines that start with an AWK identifier.

mawk recognizes the empty regular expression, // , which matches the
empty string and hence is matched by any string at the front, back and
between every character. For example,


    	echo  abc | mawk '{ gsub(//, "X")' ; print }
    	XaXbXcX

4. Records and fields

Records are read in one at a time, and stored in the field variable $0.
The record is split into fields which are stored in $1, $2, ..., $NF.
The built-in variable NF is set to the number of fields, and NR and FNR
are incremented by 1. Fields above $NF are set to "".

Assignment to $0 causes the fields and NF to be recomputed. Assignment
to NF or to a field causes $0 to be reconstructed by concatenating the
$i's separated by OFS. Assignment to a field with index greater than NF,
increases NF and causes $0 to be reconstructed.

Data input stored in fields is string, unless the entire field has
numeric form and then the type is number and string. For example,

    	echo 24 24E |
    	mawk '{ print($1>100, $1>"100", $2>100, $2>"100") }'
    	0 1 1 1

$0 and $2 are string and $1 is number and string. The first comparison
is numeric, the second is string, the third is string (100 is converted
to "100"), and the last is string.

5. Expressions and operators

The expression syntax is similar to C. Primary expressions are numeric
constants, string constants, variables, fields, arrays and function
calls. The identifier for a variable, array or function can be a
sequence of letters, digits and underscores, that does not start with a
digit. Variables are not declared; they exist when first referenced and
are initialized to null.

New expressions are composed with the following operators in order of
increasing precedence.

  assignment		=  +=  -=  *=  /=  %=  ^=
      conditional		?  :
      logical or		||
      logical and		&&
      array membership	in
      matching		~   !~
      relational		<  >   <=  >=  ==  !=
      concatenation		(no explicit operator)
      add ops			+  -
      mul ops			*  /  %
      unary			+  -
      logical not		!
      exponentiation		^
      inc and dec		++ - - (both post and pre)
      field			$

  Assignment, conditional and exponentiation associate right to left;
  the other operators associate left to right. Any expression can be
  parenthesized.

6. Arrays

Awk provides one-dimensional arrays. Array elements are expressed as
array[expr]. Expr is internally converted to string type, so, for
example, A[1] and A["1"] are the same element and the actual index is
"1". Arrays indexed by strings are called associative arrays. Initially
an array is empty; elements exist when first accessed. An expression,
expr in array evaluates to 1 if array[expr] exists, else to 0.

There is a form of the for statement that loops over each index of an
array.


    	for ( var in array ) statement

sets var to each index of array and executes statement. The order that
var transverses the indices of array is not defined.

The statement, delete array[expr], causes array[expr] not to exist. mawk
supports the delete array feature, which deletes all elements of array.

Multidimensional arrays are synthesized with concatenation using the
built-in variable SUBSEP. array[expr1, expr2] is equivalent to
array[expr1 SUBSEP expr2]. Testing for a multidimensional element uses a
parenthesized index, such as

    	if ( (i, j) in A )  print A[i, j]

7. Builtin-variables

The following variables are built-in and initialized before program
execution.

  

  ARGC

      number of command line arguments.

  ARGV

      array of command line arguments, 0..ARGC-1.

  CONVFMT

      format for internal conversion of numbers to string, initially =
      "%.6g".

  ENVIRON

      array indexed by environment variables. An environment string,
      var=value is stored as ENVIRON[var] = value.

  FILENAME

      name of the current input file.

  FNR

      current record number in FILENAME.

  FS

      splits records into fields as a regular expression.

  NF

      number of fields in the current record.

  NR

      current record number in the total input stream.

  OFMT

      format for printing numbers; initially = "%.6g".

  OFS

      inserted between fields on output, initially = " ".

  ORS

      terminates each record on output, initially = "\n".

  RLENGTH

      length set by the last call to the built-in function, match().

  RS

      input record separator, initially = "\n".

  RSTART

      index set by the last call to match().

  SUBSEP

      used to build multiple array subscripts, initially = "\034".

8. Built-in functions

String functions

  

  gsub(r,s,t) gsub(r,s)

      Global substitution, every match of regular expression r in
      variable t is replaced by string s. The number of replacements is
      returned. If t is omitted, $0 is used. An & in the replacement
      string s is replaced by the matched substring of t. \& and \\ put
      literal & and \, respectively, in the replacement string.

  index(s,t)

      If t is a substring of s, then the position where t starts is
      returned, else 0 is returned. The first character of s is in
      position 1.

  length(s)

      Returns the length of string or array s.

  match(s,r)

      Returns the index of the first longest match of regular expression
      r in string s. Returns 0 if no match. As a side effect, RSTART is
      set to the return value. RLENGTH is set to the length of the match
      or -1 if no match. If the empty string is matched, RLENGTH is set
      to 0, and 1 is returned if the match is at the front, and
      length(s)+1 is returned if the match is at the back.

  split(s,A,r) split(s,A)

      String s is split into fields by regular expression r and the
      fields are loaded into array A. The number of fields is returned.
      See section 11 below for more detail. If r is omitted, FS is used.

  sprintf(format,expr-list)

      Returns a string constructed from expr-list according to format.
      See the description of printf() below.

  sub(r,s,t) sub(r,s)

      Single substitution, same as gsub() except at most one
      substitution.

  substr(s,i,n) substr(s,i)

      Returns the substring of string s, starting at index i, of length
      n. If n is omitted, the suffix of s, starting at i is returned.

  tolower(s)

      Returns a copy of s with all upper case characters converted to
      lower case.

  toupper(s)

      Returns a copy of s with all lower case characters converted to
      upper case.

Time functions

These are available on systems which support the corresponding C mktime
and strftime functions:

  

  mktime(specification)

      converts a date specification to a timestamp with the same units
      as systime. The date specification is a string containing the
      components of the date as decimal integers:

      YYYY

          the year, e.g., 2012

      MM

          the month of the year starting at 1

      DD

          the day of the month starting at 1

      HH

          hour (0-23)

      MM

          minute (0-59)

      SS

          seconds (0-59)

      DST

          tells how to treat timezone versus daylight savings time:

          positive

              DST is in effect

          zero (default)

              DST is not in effect

          negative

              mktime() should (use timezone information and system
              databases to) attempt to determine whether DST is in
              effect at the specified time.

  strftime([format [, timestamp [, utc ]]])

      formats the given timestamp using the format (passed to the C
      strftime function):

      - If the format parameter is missing, "%c" is used.

      - If the timestamp parameter is missing, the current value from
        systime is used.

      - If the utc parameter is present and nonzero, the result is in
        UTC. Otherwise local time is used.

  systime()

      returns the current time of day as the number of seconds since the
      Epoch (1970-01-01 00:00:00 UTC on POSIX systems).

Arithmetic functions

  

  atan2(y,x)

      Arctan of y/x between -pi and pi.

  cos(x)

      Cosine function, x in radians.

  exp(x)

      Exponential function.

  int(x)

      Returns x truncated towards zero.

  log(x)

      Natural logarithm.

  rand()

      Returns a random number between zero and one.

  sin(x)

      Sine function, x in radians.

  sqrt(x)

      Returns square root of x.

  srand(expr)

      

      srand()

          Seeds the random number generator, using the clock if expr is
          omitted, and returns the value of the previous seed.
          Srand(expr) is useful for repeating pseudo random sequences.

          Note: mawk is normally configured to seed the random number
          generator from the clock at startup, making it unnecessary to
          call srand(). This feature can be suppressed via conditional
          compile, or overridden using the -Wrandom option.

9. Input and output

There are two output statements, print and printf.

  

  print

      writes $0 ORS to standard output.

  print expr1, expr2, ..., exprn

      writes expr1 OFS expr2 OFS ... exprn ORS to standard output.
      Numeric expressions are converted to string with OFMT.

  printf format, expr-list

      duplicates the printf C library function writing to standard
      output. The complete ANSI C format specifications are recognized
      with conversions %c, %d, %e, %E, %f, %g, %G, %i, %o, %s, %u, %x,
      %X and %%, and conversion qualifiers h and l.

The argument list to print or printf can optionally be enclosed in
parentheses. Print formats numbers using OFMT or "%d" for exact
integers. "%c" with a numeric argument prints the corresponding 8 bit
character, with a string argument it prints the first character of the
string. The output of print and printf can be redirected to a file or
command by appending > file, >> file or | command to the end of the
print statement. Redirection opens file or command only once, subsequent
redirections append to the already open stream. By convention, mawk
associates the filename

  - "/dev/stderr" with stderr,

  - "/dev/stdout" with stdout,

  - "-" and "/dev/stdin" with stdin.

The association with stderr is especially useful because it allows print
and printf to be redirected to stderr. These names can also be passed to
functions.

The input function getline has the following variations.

  

  getline

      reads into $0, updates the fields, NF, NR and FNR.

  getline < file

      reads into $0 from file, updates the fields and NF.

  getline var

      reads the next record into var, updates NR and FNR.

  getline var < file

      reads the next record of file into var.

  command | getline

      pipes a record from command into $0 and updates the fields and NF.

  command | getline var

      pipes a record from command into var.

Getline returns 0 on end-of-file, -1 on error, otherwise 1.

Commands on the end of pipes are executed by /bin/sh.

The function close(expr) closes the file or pipe associated with expr.
Close returns 0 if expr is an open file, the exit status if expr is a
piped command, and -1 otherwise. Close is used to reread a file or
command, make sure the other end of an output pipe is finished or
conserve file resources.

The function fflush(expr) flushes the output file or pipe associated
with expr. Fflush returns 0 if expr is an open output stream else -1.
Fflush without an argument flushes stdout. Fflush with an empty argument
("") flushes all open output.

The function system(expr) uses the C runtime system call to execute expr
and returns the corresponding wait status of the command as follows:

- if the system call failed, setting the status to -1, mawk returns that
  value.

- if the command exited normally, mawk returns its exit-status.

- if the command exited due to a signal such as SIGHUP, mawk returns the
  signal number plus 256.

Changes made to the ENVIRON array are not passed to commands executed
with system or pipes.

10. User defined functions

The syntax for a user defined function is


    	function name( args ) { statements }

The function body can contain a return statement


    	return opt_expr

A return statement is not required. Function calls may be nested or
recursive. Functions are passed expressions by value and arrays by
reference. Extra arguments serve as local variables and are initialized
to null. For example, csplit(s, A) puts each character of s into array A
and returns the length of s.


    	function csplit(s, A,	n, i)
    	{
    	  n = length(s)
    	  for( i = 1 ; i <= n ; i++ ) A[i] = substr(s, i, 1)
    	  return n
    	}

Putting extra space between passed arguments and local variables is
conventional. Functions can be referenced before they are defined, but
the function name and the '(' of the arguments must touch to avoid
confusion with concatenation.

A function parameter is normally a scalar value (number or string). If
there is a forward reference to a function using an array as a
parameter, the function's corresponding parameter will be treated as an
array.

11. Splitting strings, records and files

Awk programs use the same algorithm to split strings into arrays with
split(), and records into fields on FS. mawk uses essentially the same
algorithm to split files into records on RS.

Split(expr, A, sep) works as follows:

  

  (1)

      If sep is omitted, it is replaced by FS. Sep can be an expression
      or regular expression. If it is an expression of non-string type,
      it is converted to string.

  (2)

      If sep = " " (a single space), then <SPACE> is trimmed from the
      front and back of expr, and sep becomes <SPACE>. mawk defines
      <SPACE> as the regular expression /[ \t\n]+/. Otherwise sep is
      treated as a regular expression, except that meta-characters are
      ignored for a string of length 1, e.g., split(x, A, "*") and
      split(x, A, /\*/) are the same.

  (3)

      If expr is not string, it is converted to string. If expr is then
      the empty string "", split() returns 0 and A is set empty.
      Otherwise, all non-overlapping, non-null and longest matches of
      sep in expr, separate expr into fields which are loaded into A.
      The fields are placed in A[1], A[2], ..., A[n] and split() returns
      n, the number of fields which is the number of matches plus one.
      Data placed in A that looks numeric is typed number and string.

Splitting records into fields works the same except the pieces are
loaded into $1, $2,..., $NF. If $0 is empty, NF is set to 0 and all $i
to "".

mawk splits files into records by the same algorithm, but with the
slight difference that RS is really a terminator instead of a separator.
(ORS is really a terminator too).

  E.g., if FS = :+ and $0 = a::b: , then NF = 3 and $1 = a, $2 = b and
  $3 = "", but if a::b: is the contents of an input file and RS = :+,
  then there are two records a and b.

RS = " " is not special.

If FS = "", then mawk breaks the record into individual characters, and,
similarly, split(s,A,"") places the individual characters of s into A.

12. Multi-line records

Since mawk interprets RS as a regular expression, multi-line records are
easy. Setting RS = "\n\n+", makes one or more blank lines separate
records. If FS = " " (the default), then single newlines, by the rules
for <SPACE> above, become space and single newlines are field
separators.

  For example, if

  - a file is "a b\nc\n\n",

  - RS = "\n\n+" and

  - FS = " ",

  then there is one record a b\nc with three fields a, b and c:

  - using FS = \n, gives two fields a b and c;

  - using FS = , gives one field identical to the record.

If you want lines with spaces or tabs to be considered blank, set RS =
\n([ \t]*\n)+. For compatibility with other awks, setting RS = "" has
the same effect as if blank lines are stripped from the front and back
of files and then records are determined as if RS = \n\n+. POSIX
requires that \n always separates records when RS = "" regardless of the
value of FS. mawk does not support this convention, because defining \n
as <SPACE> makes it unnecessary.

Most of the time when you change RS for multi-line records, you will
also want to change ORS to \n\n so the record spacing is preserved on
output.

13. Program execution

This section describes the order of program execution. First ARGC is set
to the total number of command line arguments passed to the execution
phase of the program.

- ARGV[0] is set to the name of the AWK interpreter and

- ARGV[1] ... ARGV[ARGC-1] holds the remaining command line arguments
  exclusive of options and program source.

For example, with


    	mawk  -f  prog  v=1  A  t=hello  B

ARGC = 5 with

  ARGV[0] = "mawk",
  ARGV[1] = "v=1",
  ARGV[2] = "A",
  ARGV[3] = "t=hello" and
  ARGV[4] = "B".

Next, each BEGIN block is executed in order. If the program consists
entirely of BEGIN blocks, then execution terminates, else an input
stream is opened and execution continues. If ARGC equals 1, the input
stream is set to stdin, else the command line arguments ARGV[1] ...
ARGV[ARGC-1] are examined for a file argument.

The command line arguments divide into three sets: file arguments,
assignment arguments and empty strings "". An assignment has the form
var=string. When an ARGV[i] is examined as a possible file argument, if
it is empty it is skipped; if it is an assignment argument, the
assignment to var takes place and i skips to the next argument; else
ARGV[i] is opened for input. If it fails to open, execution terminates
with exit code 2. If no command line argument is a file argument, then
input comes from stdin. Getline in a BEGIN action opens input. - as a
file argument denotes stdin.

Once an input stream is open, each input record is tested against each
pattern, and if it matches, the associated action is executed. An
expression pattern matches if it is boolean true (see the end of section
2). A BEGIN pattern matches before any input has been read, and an END
pattern matches after all input has been read. A range pattern,
expr1, expr2 , matches every record between the match of expr1 and the
match expr2 inclusively.

When end of file occurs on the input stream, the remaining command line
arguments are examined for a file argument, and if there is one it is
opened, else the END pattern is considered matched and all END actions
are executed.

In the example, the assignment v=1 takes place after the BEGIN actions
are executed, and the data placed in v is typed number and string. Input
is then read from file A. On end of file A, t is set to the string
"hello", and B is opened for input. On end of file B, the END actions
are executed.

Program flow at the pattern {action} level can be changed with the


    	next
    	nextfile
    	exit  opt_expr

statements:

- A next statement causes the next input record to be read and pattern
  testing to restart with the first pattern {action} pair in the
  program.

- A nextfile statement tells mawk to stop processing the current input
  file. It then updates FILENAME to the next file listed on the command
  line, and resets FNR to 1.

- An exit statement causes immediate execution of the END actions or
  program termination if there are none or if the exit occurs in an END
  action. The opt_expr sets the exit value of the program unless
  overridden by a later exit or subsequent error.

ENVIRONMENT

Mawk recognizes these variables:

  

  MAWKBINMODE

      (see COMPATIBILITY)

  MAWK_LONG_OPTIONS

      If this is set, mawk uses its value to decide what to do with
      GNU-style long options:

      allow

          Mawk allows the option to be checked against the (small) set
          of long options it recognizes.

          The long names from the -W option are recognized, e.g.,
          --version is derived from -Wversion.

      error

          Mawk prints an error message and exits. This is the default.

      ignore

          Mawk ignores the option, unless it happens to be one of the
          one it recognizes.

      warn

          Print an warning message and otherwise ignore the option.

      If the variable is unset, mawk prints an error message and exits.

  WHINY_USERS

      This is a gawk 3.1.0 feature, removed in the 4.0.0 release. It
      tells mawk to sort array indices before it starts to iterate over
      the elements of an array.

COMPATIBILITY

MAWK 1.3.3 versus POSIX 1003.2 Draft 11.3

The POSIX 1003.2(draft 11.3) definition of the AWK language is AWK as
described in the AWK book with a few extensions that appeared in
SystemVR4 nawk. The extensions are:

  - New functions: toupper() and tolower().

  - New variables: ENVIRON[ ] and CONVFMT.

  - ANSI C conversion specifications for printf() and sprintf().

  - New command options: -v var=value, multiple -f options and
    implementation options as arguments to -W.

  - For systems (MS-DOS or Windows) which provide a setmode function, an
    environment variable MAWKBINMODE and a built-in variable BINMODE.
    The bits of the BINMODE value tell mawk how to modify the RS and ORS
    variables:

    0

        set standard input to binary mode, and if BIT-2 is unset, set RS
        to "\r\n" (CR/LF) rather than "\n" (LF).

    1

        set standard output to binary mode, and if BIT-2 is unset, set
        ORS to "\r\n" (CR/LF) rather than "\n" (LF).

    2

        suppress the assignment to RS and ORS of CR/LF, making it
        possible to run scripts and generate output compatible with Unix
        line-endings.

POSIX AWK is oriented to operate on files a line at a time. RS can be
changed from "\n" to another single character, but it is hard to find
any use for this — there are no examples in the AWK book. By convention,
RS = "", makes one or more blank lines separate records, allowing
multi-line records. When RS = "", "\n" is always a field separator
regardless of the value in FS.

mawk, on the other hand, allows RS to be a regular expression. When "\n"
appears in records, it is treated as space, and FS always determines
fields.

Removing the line at a time paradigm can make some programs simpler and
can often improve performance. For example, redoing example 3 from
above,


    	BEGIN { RS = "[^A-Za-z]+" }

    	{ word[ $0 ] = "" }

    	END { delete  word[ "" ]
    	  for( i in word )  cnt++
    	  print cnt
    	}

counts the number of unique words by making each word a record. On
moderate size files, mawk executes twice as fast, because of the
simplified inner loop.

The following program replaces each comment by a single space in a C
program file,


    	BEGIN {
    	  RS = "/ \*([^*] | \*+[^/*])*\*+/"
    		# comment is record separator
    	  ORS = " "
    	  getline  hold
           }

           { print hold ; hold = $0 }

           END { printf "%s" , hold }

Buffering one record is needed to avoid terminating the last record with
a space.

With mawk, the following are all equivalent,


    	x ~ /a\+b/    x ~ "a\+b"     x ~ "a\\+b"

The strings get scanned twice, once as string and once as regular
expression. On the string scan, mawk ignores the escape on non-escape
characters while the AWK book advocates \c be recognized as c which
necessitates the double escaping of meta-characters in strings. POSIX
explicitly declines to define the behavior which passively forces
programs that must run under a variety of awks to use the more portable
but less readable, double escape.

POSIX AWK does not recognize "/dev/std{in,out,err}". Some systems
provide an actual device for this, allowing AWKs which do not implement
the feature directly to support it.

POSIX AWK does not recognize \x hex escape sequences in strings. Unlike
ANSI C, mawk limits the number of digits that follows \x to two as the
current implementation only supports 8 bit characters.

POSIX explicitly leaves the behavior of FS = "" undefined, and mentions
splitting the record into characters as a possible interpretation, but
currently this use is not portable across implementations.

Some features were not part of the POSIX standard until long after their
introduction in mawk and other implementations. These were published in
IEEE 1003.1-2024 (The Open Group Base Specifications Issue 8):

- The built-in fflush first appeared in a 1993 AT&T awk released to
  netlib. It was approved for the POSIX standard in 2012.

- The built-in nextfile first appeared in gawk in 1988, was adopted by
  BWK in 1996, and by mawk in 2012. It was approved for the POSIX
  standard in 2012.

- Aggregate deletion with delete array was approved in 2018.

Random numbers

POSIX does not prescribe a method for initializing random numbers at
startup.

In practice, most implementations do nothing special, which makes srand
and rand follow the C runtime library, making the initial seed value 1.
Some implementations (Solaris XPG4 and Tru64) return 0 from the first
call to srand, although the results from rand behave as if the initial
seed is 1. Other implementations return 1.

While mawk can call srand at startup with no parameter (initializing
random numbers from the clock), this feature may be suppressed using
conditional compilation.

Extensions added for compatibility for GAWK and BWK

Mktime, strftime and systime are gawk extensions.

The "/dev/stdin" feature was added to mawk after 1.3.4, for
compatibility with gawk and BWK awk. The corresponding "-" (alias for
/dev/stdin) was present in mawk 1.3.3.

Interval expressions, e.g., a range {m,n} in Extended Regular
Expressions (EREs), were not supported in awk (or even the original
nawk):

- Gawk provided this feature in 1991 (and later, in 1998, options for
  turning it off, for compatibility with traditional awk).

- Interval expressions, were introduced into awk regular expressions in
  IEEE 1003.1-2001 (also known as Unix 03), along with some
  internationalization features.

- Apple modified its copy of the original awk in April 2006, making this
  version of awk support interval expressions.

  The updated source provides for compatibility with older legacy
  versions using an environment variable, making this Unix 2003 feature
  (perhaps meant as Unix 03) the default.

- NetBSD developers copied this change in January 2018, omitting the
  compatibility option, and then applied it to BWK awk.

- The interval expression implementation in mawk is based on changes
  proposed by James Parkinson in April 2016.

Mawk also recognizes a few gawk-specific command line options for script
compatibility:

  --help, --posix, -r, --re-interval, --traditional, --version

Subtle Differences not in POSIX or the AWK Book

Finally, here is how mawk handles exceptional cases not discussed in the
AWK book or the POSIX draft. It is unsafe to assume consistency across
awks and safe to skip to the next section.

  - substr(s, i, n) returns the characters of s in the intersection of
    the closed interval [1, length(s)] and the half-open interval [i,
    i+n). When this intersection is empty, the empty string is returned;
    so substr("ABC", 1, 0) = "" and substr("ABC", -4, 6) = "A".

  - Every string, including the empty string, matches the empty string
    at the front so, s ~ // and s ~ "", are always 1 as is match(s, //)
    and match(s, ""). The last two set RLENGTH to 0.

  - index(s, t) is always the same as match(s, t1) where t1 is the same
    as t with metacharacters escaped. Hence consistency with match
    requires that index(s, "") always returns 1. Also the condition,
    index(s,t) != 0 if and only t is a substring of s, requires
    index("","") = 1.

  - If getline encounters end of file, getline var, leaves var
    unchanged. Similarly, on entry to the END actions, $0, the fields
    and NF have their value unaltered from the last record.

BUGS

mawk implements printf() and sprintf() using the C library functions,
printf and sprintf, so full ANSI compatibility requires an ANSI C
library. In practice this means the h conversion qualifier may not be
available.

Also mawk inherits any bugs or limitations of the library functions.

Implementors of the AWK language have shown a consistent lack of
imagination when naming their programs.

EXAMPLES

    1. emulate cat.

    	{ print }

    2. emulate wc.

    	{ chars += length($0) + 1  # add one for the \n
    	  words += NF
    	}

    	END{ print NR, words, chars }

    3. count the number of unique real words.

    	BEGIN { FS = "[^A-Za-z]+" }

    	{ for(i = 1 ; i <= NF ; i++)  word[$i] = "" }

    	END { delete word[""]
    	      for ( i in word )  cnt++
    	      print cnt
    	}

4. sum the second field of every record based on the first field.


    	$1 ~ /credit | gain/ { sum += $2 }
    	$1 ~ /debit | loss/  { sum -= $2 }

    	END { print sum }

    5. sort a file, comparing as string

    	{ line[NR] = $0 "" }  # make sure of comparison type
    			      # in case some lines look numeric

    	END {  isort(line, NR)
    	  for(i = 1 ; i <= NR ; i++) print line[i]
    	}

    	#insertion sort of A[1..n]
    	function isort( A, n,	i, j, hold)
    	{
    	  for( i = 2 ; i <= n ; i++)
    	  {
    	    hold = A[j = i]
    	    while ( A[j-1] > hold )
    	    { j- - ; A[j+1] = A[j] }
    	    A[j] = hold
    	  }
    	  # sentinel A[0] = "" will be created if needed
    	}

AUTHORS

Mike Brennan (brennan@whidbey.com).
Thomas E. Dickey <dickey@invisible-island.net>.

SEE ALSO

grep(1)

Aho, Kernighan and Weinberger, The AWK Programming Language,
Addison-Wesley Publishing, 1988, (the AWK book), defines the language,
opening with a tutorial and advancing to many interesting programs that
delve into issues of software design and analysis relevant to
programming in any language.

The GAWK Manual, The Free Software Foundation, 1991, is a tutorial and
language reference that does not attempt the depth of the AWK book and
assumes the reader may be a novice programmer. The section on AWK arrays
is excellent. It also discusses POSIX requirements for AWK.

mawk-arrays(7) discusses mawk's implementation of arrays.

mawk-code(7) gives more information on the -W dump option.

awk – pattern scanning and processing language
The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
https://pubs.opengroup.org/onlinepubs/9799919799/utilities/awk.html
