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       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  =  "\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.


       -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 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 systems that support  the  #!   "magic
                      number" convention for executable scripts.

       -W sprintf=num adjusts  the  size  of mawks 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.


   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

       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

            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

              r1r2         matches    r1    followed    immediately    by   r2

              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
       $is  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

   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] = 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,

              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 -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

              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

              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

            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.


       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 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
       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.



       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 \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.


       Mike Brennan (