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Linux 2.6 - man page for mawk (linux section 1)

MAWK(1) 				  USER COMMANDS 				  MAWK(1)

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 experi-
       menting	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	interpre-
       tation.	 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,  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 pro-
		      gram to stdout and exits 0 (on successful compilation).

       -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  sys-
		      tems 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
   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 def-
       inition.  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 exis-
       tence  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 nec-
       essary  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  long-
       est  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 egrep(1).	The regular expression	metachar-
       acters, 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 charac-
			   ters 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]*$/	and
	    /^[-+]?([0-9]+\.?|\.[0-9])[0-9]*([eE][-+]?[0-9]+)?$/

       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.   Assign-
       ment  to  a  field  with  index	greater  than NF, increases NF and causes $0 to be recon-
       structed.

       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  prece-
       dence.

	      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 ele-
       ment 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 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 = "\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 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.

       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 gener-
		     ator  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 recognized  with  conversions  %c,
		     %d, %e, %E, %f, %g, %G, %i, %o, %s, %u, %x, %X and %%, and conversion quali-
		     fiers 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 char-
       acter  of  the string.  The output of print and printf can be redirected to a file or com-
       mand by appending > file, >> file or | command to the end of the print  statement.   Redi-
       rection	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.

	      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 /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.   Func-
       tions  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  regu-
		     lar  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-over-
		     lapping, 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".	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 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 the name of the AWK interpreter and ARGV[1] ...  ARGV[ARGC-1] holds the remaining com-
       mand 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  argu-
       ment,  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 com-
       mand  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 bool-
       ean 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  inclu-
       sively.

       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
	    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
       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
	    }

COMPATIBILITY ISSUES
       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 exam-
       ples 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{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.  Aggre-
       gate 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 porta-
       ble 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 intersec-
	      tion is empty, the empty string is returned; so substr("ABC", 1, 0) = ""	and  sub-
	      str("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.

SEE ALSO
       egrep(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.

BUGS
       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  con-
       version 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.

AUTHOR
       Mike Brennan (brennan@whidbey.com).

Version 1.2				   Dec 22 1994					  MAWK(1)


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