mawk

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 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  op-
                      tion.

                      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  op-
       tions  with commas, e.g., -Wsprint=2000,posix.  This is useful for exe-
       cutable #!  "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 nu-
       meric, 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(CON-
       VFMT,  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 nu-
       meric, 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 ex-
       pression argument.

       AWK uses extended regular expressions as with the -E option of grep(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 se-
                         quences used in string constants or the literal char-
                         acter 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 nu-
       meric 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  se-
       quence  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 ex-
       ample, 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  ex-
       pression,  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 ar-
       ray[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 ex-
       ecution.

            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 replace-
                   ments is returned.  If t is omitted, $0 is used.  An  &  in
                   the  replacement  string  s is replaced by the matched sub-
                   string 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 or array.  s.

            match(s,r)
                   Returns the index of the first longest match of regular ex-
                   pression 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 sub-
                   stitution.

            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  con-
                   taining 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 systems).

       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  se-
                   quences.

                   Note: mawk is normally configured to seed the random number
                   generator from the clock at startup, making it  unnecessary
                   to call srand().  This feature can be suppressed via condi-
                   tional 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 qualifiers h and
                   l.

       The argument list to print or printf  can  optionally  be  enclosed  in
       parentheses.   Print formats numbers using OFMT or "%d" for exact inte-
       gers.  "%c" with a numeric argument  prints  the  corresponding  8  bit
       character,  with a string argument it prints the first character of the
       string.  The output of print and printf can be redirected to a file  or
       command  by  appending  >  file, >> file or | command to the end of the
       print statement.  Redirection opens file or command only  once,  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  ar-
       ray.

   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()  re-
               turns  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, be-
       cause 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, as-
       signment 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  as-
       signment  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  ex-
       pression  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.  In-
       put 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  in-
           put  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 im-
              plementation 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
                 possible 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 re-
       gardless 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  ex-
       pression.   On  the  string scan, mawk ignores the escape on non-escape
       characters while the AWK book advocates \c be recognized as c which ne-
       cessitates  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.   Un-
       like 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  un-
              changed.  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 de-
                      fault.

               ignore Mawk ignores the option.

               warn   Print  an  warning  message and otherwise ignore the op-
                      tion.

             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  ar-
             ray  indices  before it starts to iterate over the elements of an
             array.

SEE ALSO
       grep(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  ar-
       rays 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  li-
       brary.   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                     2019-12-31                           MAWK(1)
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