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mawk(1) [opendarwin man page]

MAWK(1) 							   USER COMMANDS							   MAWK(1)

       mawk - pattern scanning and text processing language

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

       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 = "
" and records are synonymous with lines.  Each record is compared against  each  pattern
       and if it matches, the program text for {action} is executed.

       -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 compila-

       -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

       -W posix_space forces mawk not to consider '
' to be space.

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

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

       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 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



   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.

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

	    "	      "
	    a	      alert, ascii 7
	    	      backspace, ascii 8
	    		      tab, ascii 9
	      newline, ascii 10
	    v	      vertical tab, ascii 11
	    f	      formfeed, ascii 12
	      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

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

	    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  neces-
       sary 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  conver-
       sion 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 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 con-
       verted 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

   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.   Ini-
       tially  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 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 an extension, delete array, 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 = "

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

	      RS	input record separator, initially = "

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

	      SUBSEP	used to build multiple array subscripts, initially = "34".

   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 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

		     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 -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.   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 sequences.

   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  recog-
		     nized 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 inte-
       gers.  "%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 /[ 	
]+/.  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 = "

+", makes one or more blank  lines  sepa-
       rate  records.  If FS = " " (the default), then single newlines, by the rules for <SPACE> above, become space and single newlines are field

	      For example, if a file is "a b

", RS = "

+" and FS = " ", then there is one record "a b
c" with three fields "a", "b"  and
	      "c".  Changing FS = "
", 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 = "
([ 	]*
)+".	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  =  "

       Posix  requires	that  "
"  always  separates  records when RS = "" regardless of the value of FS.  mawk does not support this convention,
       because defining "
" 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 "

" 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 exe-
       cution 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 termi-
       nates 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.

       1. emulate cat.

	    { print }

       2. emulate wc.

	    { chars += length($0) + 1  # add one for the 

	      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 Sys-
       temVR4 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 "
" 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 = "", "
" is always a field separator regardless of the value in FS.

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

       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  sim-
       plified 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  stan-

       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) = "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.


       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  cannot  handle  ascii  NUL  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 functions.

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

       Mike Brennan (

Version 1.2							    Dec 22 1994 							   MAWK(1)
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