http://invisible-island.net/mawk/


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 lan-
       guage is useful for manipulation of data files, text retrieval and pro-
       cessing,  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  con-
       forms  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 synony-
       mous 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 com-
                      mand 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 implemen-
       tation  of  AWK.  Implementation specific options are prefaced with -W.
       mawk provides these:

       -W dump        writes an assembler like listing of the internal  repre-
                      sentation  of the program to stdout and exits 0 (on suc-
                      cessful compilation).

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

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

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

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

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

       -W random=num  calls srand with the given parameter (and overrides  the
                      auto-seeding behavior).

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

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

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

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

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

THE AWK LANGUAGE

1. Program structure

       An  AWK  program is a sequence of pattern {action} pairs and user func-
       tion 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 state-
       ment  can  be broken without a backslash after a comma, left brace, &&,
       ||, do, else, the right parenthesis of an if, while or  for  statement,
       and  the  right parenthesis of a function definition.  A comment starts
       with # and extends to, but does not include the end of line.

       The following statements control program flow inside blocks.

              if ( expr ) statement

              if ( expr ) statement else statement

              while ( expr ) statement

              do statement while ( expr )

              for ( opt_expr ; opt_expr ; opt_expr ) statement

              for ( var in array ) statement

              continue

              break

2. Data types, conversion and comparison

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

       String constants are enclosed in double quotes.

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

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

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

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

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

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

            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
       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 op-
       erand 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  exe-
       cuted.   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 fol-
       lows:

              r1r2         matches  r1  followed immediately by r2 (concatena-
                           tion).

              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 !~ opera-
       tors or passed to a built-in that expects  a  regular  expression.   If
       needed,  it  is  converted to string, and then interpreted as a regular
       expression.  For example,

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

            $0 ~ "^" identifier

       prints all lines that start with an AWK identifier.

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

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

4. Records and fields

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

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

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

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

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

5. Expressions and operators

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

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

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

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

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
       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  environ-
                        ment  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  char-
                     acter of s is in position 1.

              length(s)
                     Returns the length of string or array.  s.

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

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

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

              sub(r,s,t)  sub(r,s)
                     Single  substitution,  same  as gsub() except at most one
                     substitution.

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

              tolower(s)
                     Returns a copy of s with all upper case  characters  con-
                     verted to lower case.

              toupper(s)
                     Returns  a  copy of s with all lower case characters con-
                     verted to upper case.

       Time functions

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

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

                     YYYY
                        the year, e.g., 2012

                     MM the month of the year starting at 1

                     DD the day of the month starting at 1

                     HH hour (0-23)

                     MM minute (0-59)

                     SS seconds (0-59)

                     DST
                        tells how to treat timezone  versus  daylight  savings
                        time:

                        positive
                           DST is in effect

                        zero (default)
                           DST is not in effect

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

              strftime([format [, timestamp [, utc ]]])
                     formats  the  given timestamp using the format (passed to
                     the C strftime function):

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

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

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

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

       Arithmetic functions

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

              cos(x)         Cosine function, x in radians.

              exp(x)         Exponential function.

              int(x)         Returns x truncated towards zero.

              log(x)         Natural logarithm.

              rand()         Returns a random number between zero and one.

              sin(x)         Sine function, x in radians.

              sqrt(x)        Returns square root of x.

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

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

9. Input and output

       There are two output statements, print and printf.

              print  writes $0  ORS to standard output.

              print expr1, expr2, ..., exprn
                     writes expr1 OFS expr2 OFS ... exprn ORS to standard out-
                     put.  Numeric expressions are converted  to  string  with
                     OFMT.

              printf format, expr-list
                     duplicates the printf C library function writing to stan-
                     dard 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  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, subse-
       quent redirections append to the already open stream.   By  convention,
       mawk associates the filename

          o   "/dev/stderr" with stderr,

          o   "/dev/stdout" with stdout,

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

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

       The input function getline has the following variations.

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

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

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

              getline var < file
                     reads the next record of file into var.

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

               command | getline var
                     pipes a record from command into var.

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

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

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

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

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

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

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

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

10. User defined functions

       The syntax for a user defined function is

            function name( args ) { statements }

       The function body can contain a return statement

            return opt_expr

       A return statement is not required.  Function calls may  be  nested  or
       recursive.   Functions  are  passed  expressions by value and arrays by
       reference.  Extra arguments serve as local variables and  are  initial-
       ized  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 con-
       fusion with concatenation.

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

11. Splitting strings, records and files

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

       Split(expr,A,sep) works as follows:

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

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

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

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

       mawk splits files into records by the  same  algorithm,  but  with  the
       slight  difference  that RS is really a terminator instead of a separa-
       tor.  (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 separa-
       tors.

              For example, if

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

              o   RS = "\n\n+" and

              o   FS = " ",

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

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

              o   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 = "" regard-
       less 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  execu-
       tion  phase  of the program.  ARGV[0] is set the name of the AWK inter-
       preter and ARGV[1] ...  ARGV[ARGC-1] holds the remaining  command  line
       arguments exclusive of options and program source.  For example with

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

       ARGC = 5 with ARGV[0] = "mawk", ARGV[1] = "v=1", ARGV[2] = "A", ARGV[3]
       = "t=hello" and ARGV[4] = "B".

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

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

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

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

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

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

            next
            nextfile
            exit  opt_expr

       statements:

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

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

       o   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

MAWK 1.3.3 versus POSIX 1003.2 Draft 11.3

       The POSIX 1003.2(draft 11.3) definition of the AWK language is  AWK  as
       described  in  the AWK book with a few extensions that appeared in Sys-
       temVR4 nawk.  The extensions are:

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

          o   New variables: ENVIRON[] and CONVFMT.

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

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

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

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

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

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

       POSIX AWK is oriented to operate on files a line at a time.  RS can  be
       changed  from  "\n" to another single character, but it is hard to find
       any use for this -- there are no examples in the AWK book.  By  conven-
       tion, 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  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
       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  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 pro-
       grams that must run under a variety of awks to use  the  more  portable
       but less readable, double escape.

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

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

Random numbers

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

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

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

Extensions added for compatibility for GAWK and BWK

       Nextfile  is a gawk extension (also implemented by BWK awk), is not yet
       part of the POSIX standard (as of October 2012), although it  has  been
       accepted for the next revision of the standard.

       Mktime, strftime and systime are gawk extensions.

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

Subtle Differences not in POSIX or the AWK Book

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

          o   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".

          o   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.

          o   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.

          o   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.

ENVIRONMENT VARIABLES

       Mawk recognizes these variables:

          MAWKBINMODE
             (see COMPATIBILITY ISSUES)

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

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

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

             ignore Mawk ignores the option.

             warn   Print an warning message and otherwise ignore the option.

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

          WHINY_USERS
             This is an undocumented gawk feature.   It  tells  mawk  to  sort
             array indices before it starts to iterate over the elements of an
             array.

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  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 imagi-
       nation when naming their programs.

AUTHOR

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

Version 1.3.4                     2016-09-18                           MAWK(1)