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NAME    [Toc]    [Back]

       mawk - pattern scanning and text processing language

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

       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    [Toc]    [Back]

       -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,  and implementation specific options are prefaced with
       -W.  mawk provides six:

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

       -W dump	      writes  an assembler like listing of the internal representation
 of the program to stdout and exits 0 (on  successful

       -W interactive sets unbuffered writes to stdout and line buffered reads
		      from stdin.  Records from stdin are lines regardless  of
		      the value of RS.

       -W exec file   Program  text  is  read  from  file and this is the last
		      option. Useful on systems that support  the  #!	"magic
		      number" convention for executable scripts.

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

       The  short  forms  -W[vdiesp] are recognized and on some systems -We is
       mandatory to avoid command line length limitations.

THE AWK LANGUAGE    [Toc]    [Back]

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

       A pattern can be:
	      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  semicolon.
  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



   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

       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 egrep(1).  The regular
       expression metacharacters, i.e., those with special meaning in  regular
       expressions are

	     ^ $ . [ ] | ( ) * + ?

       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.

	      (r)	   matches r, providing grouping.

       The  increasing	precedence  of operators is alternation, concatenation
       and unary (*, + or ?).

       For example,

	    /^[_a-zA-Z][_a-zA-Z0-9]*$/	and

       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 }

   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

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

	    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 an extension, delete array, which deletes all elements of

       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

	      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]  =

	      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,

	      RS	input record separator, initially = "\n".

	      RSTART	index set by the last call to match().

	      SUBSEP	used to build multiple array subscripts,  initially  =

   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.

		     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.

		     Returns the length of string s.

		     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.

		     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

	      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.

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

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

       Arithmetic functions

	      atan2(y,x)     Arctan of y/x between -n and n.

	      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.   mawk  seeds  the random number generator from the
		     clock at startup  so  there  is  no  real	need  to  call
		     srand().  Srand(expr) is useful for repeating pseudo random

   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

	      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  which	allows
       print  and printf to be redirected to stderr.  mawk also associates "-"
       and "/dev/stdout" with stdin and stdout which allows these  streams  to
       be passed to functions.

       The input function getline has the following variations.

		     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 /bin/sh to execute expr and returns the
       exit status of the command expr.  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.

   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

       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".  Changing FS = "\n", gives two  fields  "a  b"  and
	      "c";  changing 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

   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 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

	    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.  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.

EXAMPLES    [Toc]    [Back]

       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


       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.

       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

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

	    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{out,err}"  or \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.	The built-in fflush first appeared in a recent	(1993)
       AT&T  awk  released  to	netlib, and is not part of the posix standard.
       Aggregate deletion with delete array is not part of the posix standard.

       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.

       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) =

	      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.

SEE ALSO    [Toc]    [Back]


       Aho,  Kernighan	and Weinberger, The AWK Programming Language, AddisonWesley
 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.

BUGS    [Toc]    [Back]

       mawk cannot handle ascii NUL \0 in the source or data files.   You  can
       output  NUL  using  printf  with  %c,  and any other 8 bit character is
       acceptable input.

       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

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

AUTHOR    [Toc]    [Back]

       Mike Brennan (brennan@whidbey.com).

Version 1.2			  Dec 22 1994			       MAWK(1)
[ Back ]
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