mawk - pattern scanning and text processing language


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


       mawk  is  an  interpreter  for  the  AWK Programming Language.  The AWK
       language is useful for manipulation of data files, text  retrieval  and
       processing,  and  for  prototyping  and  experimenting with algorithms.
       mawk is a new awk meaning it implements the AWK language as defined  in
       Aho,  Kernighan  and Weinberger, The AWK Programming Language, Addison-
       Wesley Publishing, 1988 (hereafter referred to as the AWK book.)   mawk
       conforms  to  the  POSIX  1003.2  (draft  11.3)  definition  of the AWK
       language which contains a few features not described in the  AWK  book,
       and mawk provides a small number of extensions.

       An  AWK  program  is  a sequence of pattern {action} pairs and function
       definitions.  Short programs are entered on the  command  line  usually
       enclosed  in ' ' to avoid shell interpretation.  Longer programs can be
       read in from a file with the -f option.  Data  input is read  from  the
       list  of files on the command line or from standard input when the list
       is empty.  The input is broken into records as determined by the record
       separator   variable,  RS.   Initially,  RS  =  "\n"  and  records  are
       synonymous with lines.  Each record is compared  against  each  pattern
       and if it matches, the program text for {action} is executed.


       -F value       sets the field separator, FS, to value.

       -f file        Program  text  is  read  from  file  instead of from the
                      command line.  Multiple -f options are allowed.

       -v var=value   assigns value to program variable var.

       --             indicates the unambiguous end of options.

       The  above  options  will  be  available  with  any  POSIX   compatible
       implementation  of  AWK.   Implementation specific options are prefaced
       with -W.  mawk provides these:

       -W dump
              writes an assembler like listing of the internal  representation
              of   the   program   to   stdout  and  exits  0  (on  successful

       -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  support  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

       -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

       -W posix
              modifies mawk's behavior to be more POSIX-compliant:

              o   forces mawk not to consider '\n' to be space.

              The original "posix_space" is recognized, but deprecated.

       -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

       -W traditional
              Omit  features  such  as  interval  expressions  which  were not
              supported by traditional awk.

       -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  compiled
              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.


1. Program structure

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

       A pattern can be:
            expression , expression

       One, but not both, of pattern {action} can be omitted.  If {action}  is
       omitted  it is implicitly { print }.  If pattern is omitted, then it is
       implicitly matched.  BEGIN and END patterns require an action.

       Statements are terminated by newlines, semi-colons or both.  Groups  of
       statements such as actions or loop bodies are blocked via { ... } as in
       C.  The last statement in a block doesn't  need  a  terminator.   Blank
       lines  have  no  meaning; an empty statement is terminated with a semi-
       colon.  Long statements can  be  continued  with  a  backslash,  \.   A
       statement  can be broken without a backslash after a comma, left brace,
       &&, ||, do, else,  the  right  parenthesis  of  an  if,  while  or  for
       statement,  and  the  right  parenthesis  of  a function definition.  A
       comment starts with # and extends to, but does not include the  end  of

       The following statements control program flow inside blocks.

            if ( expr ) statement

            if ( expr ) statement else statement

            while ( expr ) statement

            do statement while ( expr )

            for ( opt_expr ; opt_expr ; opt_expr ) statement

            for ( var in array ) statement



2. Data types, conversion and comparison

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

       String constants are enclosed in double quotes.

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

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

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

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

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

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

            y = x + 2  ;  z = x  "hello"

       The value stored in variable y will be typed  numeric.   If  x  is  not
       numeric,  the  value  read  from x is converted to numeric before it is
       added to 2 and stored in y.  The value stored in  variable  z  will  be
       typed  string,  and  the  value  of  x  will  be converted to string if
       necessary and concatenated with "hello".  (Of  course,  the  value  and
       type  stored  in  x  is  not  changed  by  any  conversions.)  A string
       expression is converted to numeric using its longest numeric prefix  as
       with atof(3).  A numeric expression is converted to string by replacing
       expr with sprintf(CONVFMT, expr), unless expr can be represented on the
       host  machine as an exact integer then it is converted to sprintf("%d",
       expr).  Sprintf() is an AWK built-in that duplicates the  functionality
       of  sprintf(3),  and  CONVFMT  is a built-in variable used for internal
       conversion from number to string and initialized to  "%.6g".   Explicit
       type  conversions  can  be  forced,  expr  ""  is  string and expr+0 is

       To evaluate, expr1 rel-op expr2, if both operands are numeric or number
       and  string then the comparison is numeric; if both operands are string
       the comparison is string; if one  operand  is  string,  the  non-string
       operand  is  converted  and  the  comparison  is string.  The result is
       numeric, 1 or 0.

       In boolean contexts such as, if ( expr ) statement, a string expression
       evaluates  true  if  and only if it is not the empty string ""; numeric
       values if and only if not numerically zero.

3. Regular expressions

       In the AWK language, records, fields and strings are often  tested  for
       matching  a  regular  expression.   Regular expressions are enclosed in
       slashes, and

            expr ~ /r/

       is an AWK expression that evaluates to 1 if  expr  "matches"  r,  which
       means  a substring of expr is in the set of strings defined by r.  With
       no match the expression evaluates to  0;  replacing  ~  with  the  "not
       match" operator, !~ , reverses the meaning.  As  pattern-action pairs,

            /r/ { action }   and   $0 ~ /r/ { action }

       are  the  same,  and  for  each  input record that matches r, action is
       executed.  In fact, /r/ is an AWK expression that is equivalent to  ($0
       ~  /r/)  anywhere  except when on the right side of a match operator or
       passed as an argument to a built-in function  that  expects  a  regular
       expression argument.

       AWK uses extended regular expressions as with the -E option of grep(1).
       The regular expression metacharacters, i.e., those with special meaning
       in regular expressions are

            \ ^ $ . [ ] | ( ) * + ? { }

       If the command line option -W traditional is used, these are omitted:

            { }

       are also regular expression metacharacters, and in this mode,
       require escaping to be a literal character.

       Regular expressions are built up from characters as follows:

            c            matches any non-metacharacter

            \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

       Regular expressions are built up from other regular expressions
       as follows:

            r1r2         matches
                         followed immediately by

            r1 | r2      matches
                         r1 or

            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

            r{n}         matches r exactly n times.

            r{n,}        matches r repeated n or more times.

            r{n,m}       matches r repeated n to m (inclusive) times.

            r{,m}        matches r repeated 0 to m times (a non-standard option).

       The increasing precedence of operators is:

       alternation concatenation repetition grouping

       For example,

            /^[_a-zA-Z][_a-zA-Z0-9]*$/  and

       are  matched by AWK identifiers and AWK numeric constants respectively.
       Note that "." has to be escaped to be recognized as  a  decimal  point,
       and that metacharacters are not special inside character classes.

       Any  expression  can  be  used  on  the  right hand side of the ~ or !~
       operators or passed to a built-in that expects  a  regular  expression.
       If needed, it is converted to string, and then interpreted as a regular
       expression.  For example,

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

            $0 ~ "^" identifier

       prints all lines that start with an AWK identifier.

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

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

4. Records and fields

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

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

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

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

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

5. Expressions and operators

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

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

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

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

6. Arrays

       Awk  provides  one-dimensional arrays.  Array elements are expressed as
       array[expr].  Expr is internally converted  to  string  type,  so,  for
       example,  A[1]  and A["1"] are the same element and the actual index is
       "1".   Arrays  indexed  by  strings  are  called  associative   arrays.
       Initially  an  array  is empty; elements exist when first accessed.  An
       expression, expr in array evaluates to 1 if array[expr] exists, else to

       There  is  a form of the for statement that loops over each index of an

            for ( var in array ) statement

       sets var to each index of array and executes statement.  The order that
       var transverses the indices of array is not defined.

       The  statement,  delete  array[expr],  causes array[expr] not to exist.
       mawk supports the delete array feature, which deletes all  elements  of

       Multidimensional  arrays  are  synthesized with concatenation using the
       built-in  variable  SUBSEP.   array[expr1,expr2]   is   equivalent   to
       array[expr1 SUBSEP expr2].  Testing for a multidimensional element uses
       a parenthesized index, such as

            if ( (i, j) in A )  print A[i, j]

7. Builtin-variables

       The following variables are built-in  and  initialized  before  program

            ARGC   number of command line arguments.

            ARGV   array of command line arguments, 0..ARGC-1.

                   format  for  internal  conversion  of  numbers  to  string,
                   initially = "%.6g".

                   array indexed by  environment  variables.   An  environment
                   string, var=value is stored as ENVIRON[var] = value.

                   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".

                   length  set  by  the  last  call  to the built-in function,

            RS     input record separator, initially = "\n".

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

            SUBSEP used  to  build  multiple  array  subscripts,  initially  =

8. Built-in functions

       String functions

            gsub(r,s,t)  gsub(r,s)
                   Global substitution, every match of regular expression r in
                   variable  t  is  replaced  by  string  s.   The  number  of
                   replacements is returned.  If t is omitted, $0 is used.  An
                   & in the replacement string s is replaced  by  the  matched
                   substring   of  t.   \&  and  \\  put   literal  &  and  \,
                   respectively, in the replacement string.

                   If t is a substring of s, then the position where t  starts
                   is  returned, else 0 is returned.  The first character of s
                   is in position 1.

                   Returns the length of string or array s.

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

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

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

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

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

                   Returns  a  copy  of  s  with  all  upper  case  characters
                   converted to lower case.

                   Returns  a  copy  of  s  with  all  lower  case  characters
                   converted to upper case.

       Time functions

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

                   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:

                      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)

                      tells how to  treat  timezone  versus  daylight  savings

                           DST is in effect

                        zero (default)
                           DST is not in effect

                           mktime()   should  (use  timezone  information  and
                           system 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.

                   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

                   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.

                   Returns square root of x.


                   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

                   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
                   conditional  compile,  or  overridden  using  the  -Wrandom

9. Input and output

       There are two output statements, print and printf.

            print  writes $0  ORS to standard output.

            print expr1, expr2, ..., exprn
                   writes expr1 OFS  expr2  OFS  ...  exprn  ORS  to  standard
                   output.   Numeric  expressions are converted to string with

            printf format, expr-list
                   duplicates  the  printf  C  library  function  writing   to
                   standard output.  The complete ANSI C format specifications
                   are recognized with conversions %c, %d, %e, %E, %f, %g, %G,
                   %i,  %o, %s, %u, %x, %X and %%, and conversion qualifiers h
                   and l.

       The argument list to print or printf  can  optionally  be  enclosed  in
       parentheses.   Print  formats  numbers  using  OFMT  or  "%d" for exact
       integers.  "%c" with a numeric argument prints the corresponding 8  bit
       character,  with a string argument it prints the first character of the
       string.  The output of print and printf can be redirected to a file  or
       command  by  appending  >  file, >> file or | command to the end of the
       print  statement.   Redirection  opens  file  or  command  only   once,
       subsequent   redirections  append  to  the  already  open  stream.   By
       convention, mawk associates the filename

          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.

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

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

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

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

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

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

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

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

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

       The  function  fflush(expr)  flushes the output file or pipe associated
       with expr.  Fflush returns 0 if expr is an open output stream else  -1.
       Fflush  without  an  argument  flushes  stdout.   Fflush  with an empty
       argument ("") flushes all open output.

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

       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
       initialized to null.  For example, csplit(s,A) puts each character of s
       into array A and returns the length of s.

            function csplit(s, A,    n, i)
              n = length(s)
              for( i = 1 ; i <= n ; i++ ) A[i] = substr(s, i, 1)
              return n

       Putting  extra  space  between  passed arguments and local variables is
       conventional.  Functions can be referenced before they are defined, but
       the  function  name  and  the  '(' of the arguments must touch to avoid
       confusion with concatenation.

       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
       parameter, the function's corresponding parameter will be treated as an

11. Splitting strings, records and files

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

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

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

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

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

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

       mawk  splits  files  into  records  by the same algorithm, but with the
       slight  difference  that  RS  is  really  a  terminator  instead  of  a
       separator.  (ORS is really a terminator too).

            E.g., if FS = ":+" and $0 = "a::b:" , then NF = 3 and $1 = "a", $2
            = "b" and $3 = "", but if "a::b:" is the contents of an input file
            and RS = ":+", then there are two records "a" and "b".

       RS = " " is not special.

       If  FS  =  "",  then mawk breaks the record into individual characters,
       and, similarly, split(s,A,"") places the  individual  characters  of  s
       into A.

12. Multi-line records

       Since  mawk  interprets  RS as a regular expression, multi-line records
       are easy.  Setting RS = "\n\n+", makes one or more blank lines separate
       records.  If FS = " " (the default), then single newlines, by the rules
       for  <SPACE>  above,  become  space  and  single  newlines  are   field

            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

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

            o   using FS = "", gives one field identical to the record.

       If you want lines with spaces or tabs to be considered blank, set RS  =
       "\n([ \t]*\n)+".   For  compatibility  with other awks, setting RS = ""
       has the same effect as if blank lines are stripped from the  front  and
       back  of  files  and  then  records  are determined as if RS = "\n\n+".
       POSIX requires  that  "\n"  always  separates  records  when  RS  =  ""
       regardless  of the value of FS.  mawk does not support this convention,
       because defining "\n" as <SPACE> makes it unnecessary.

       Most of the time when you change RS for multi-line  records,  you  will
       also want to change ORS to "\n\n" so the record spacing is preserved on

13. Program execution

       This section describes the order of program execution.  First  ARGC  is
       set  to  the  total  number  of  command  line  arguments passed to the
       execution phase of the program.

       o   ARGV[0] is set to the name of the AWK interpreter and

       o   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
       section 2).  A BEGIN pattern matches before any input  has  been  read,
       and  an  END  pattern  matches  after all input has been read.  A range
       pattern, expr1,expr2 , matches every record between the match of  expr1
       and the match expr2 inclusively.

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

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

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

            exit  opt_expr


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

       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.


       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


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
       SystemVR4 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
              function,  an  environment  variable  MAWKBINMODE and a built-in
              variable 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
       convention, RS = "", makes one or more blank  lines  separate  records,
       allowing  multi-line  records.   When  RS  = "", "\n" is always a field
       separator regardless of the value in FS.

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

       Removing the line at a time paradigm can make some programs simpler and
       can  often  improve  performance.   For example, redoing example 3 from

            BEGIN { RS = "[^A-Za-z]+" }

            { word[ $0 ] = "" }

            END { delete  word[ "" ]
              for( i in word )  cnt++
              print cnt

       counts the number of unique words by making each  word  a  record.   On
       moderate  size  files,  mawk  executes  twice  as  fast, because of the
       simplified inner loop.

       The following program replaces each comment by a single space  in  a  C
       program file,

            BEGIN {
              RS = "/\*([^*]|\*+[^/*])*\*+/"
                 # comment is record separator
              ORS = " "
              getline  hold

              { print hold ; hold = $0 }

              END { printf "%s" , hold }

       Buffering  one  record  is  needed to avoid terminating the last record
       with a space.

       With mawk, the following are all equivalent,

            x ~ /a\+b/    x ~ "a\+b"     x ~ "a\\+b"

       The strings get scanned twice, once  as  string  and  once  as  regular
       expression.   On the string scan, mawk ignores the escape on non-escape
       characters while the AWK book advocates \c be  recognized  as  c  which
       necessitates  the double escaping of meta-characters in strings.  POSIX
       explicitly declines to  define  the  behavior  which  passively  forces
       programs that must run under a variety of awks to use the more portable
       but less readable, double escape.

       POSIX AWK does  not  recognize  "/dev/std{in,out,err}".   Some  systems
       provide 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.

       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.

       Some features were not part of the  POSIX  standard  until  long  after
       their  introduction in mawk and other implementations.  These have been
       approved, though still (as of July 2020), are not part of  a  published

       o   The  built-in  fflush first appeared in a 1993 AT&T awk released to
           netlib.  It was approved for the POSIX standard in 2012.

       o   Aggregate deletion with delete array was approved in 2018.

Random numbers

       POSIX does not prescribe a method for initializing  random  numbers  at

       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).  It was
       approved for the POSIX standard in September 2012, and is  expected  to
       be part of 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
       compatibility with gawk and BWK awk.  The corresponding "-" (alias  for
       /dev/stdin) was present in mawk 1.3.3.

       Interval   expressions,   e.g.,  a  range  {m,n}  in  Extended  Regular
       Expressions (EREs), were not supported in awk  (or  even  the  original

       o   Gawk provided this feature in 1991 (and later, in 1998, options for
           turning it off, for compatibility with "traditional awk").

       o   Interval expressions, were introduced into awk regular  expressions
           in  IEEE  1003.1-2001  (also  known  as  Unix  03), along with some
           internationalization features.

       o   Apple modified its copy of the original awk in April  2006,  making
           this version of awk support interval expressions.

           The  updated  source provides for compatibility with older "legacy"
           versions using an environment variable,  making  this  "Unix  2003"
           feature (perhaps meant as Unix 03) the default.

       o   NetBSD  developers copied this change in January 2018, omitting the
           compatibility option, and then applied it to BWK awk.

       o   The interval expression implementation in mawk is based on  changes
           proposed by James Parkinson in April 2016.

       Mawk  also  recognizes  a  few  gawk-specific  command line options for
       script compatibility:

            --help, --posix, -r, --re-interval, --traditional, --version

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) =

          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.


       Mawk recognizes these variables:

             (see COMPATIBILITY ISSUES)

             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.

                      The long names from the -W option are recognized,  e.g.,
                      --version is derived from -Wversion.

               error  Mawk prints an error message and exits.  This is the de-

               ignore Mawk ignores the option, unless it happens to be one  of
                      the one it recognizes.

               warn   Print  an  warning  message and otherwise ignore the op-

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

             This is a gawk 3.1.0 feature, removed in the 4.0.0  release.   It
             tells mawk to sort array indices before it starts to iterate over
             the elements of an array.



       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.

       mawk-arrays(7) discusses mawk's implementation of arrays.

       mawk-code(7) gives more information on the -W dump option.


       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

       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.


       Mike Brennan (
       Thomas E. Dickey <>.

Version 1.3.4                     2023-04-04                           MAWK(1)