     MAWK(1)                                                             MAWK(1)
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     NAME
          mawk - pattern scanning and text processing language

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

     DESCRIPTION
          mawk is an interpreter for the AWK Programming Language.  The AWK
          language is useful for manipulation of data files, text retrieval and
          processing, and for prototyping and 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.

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

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

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

          --             indicates the unambiguous end of options.

          The above options will be available with any Posix compatible
          implementation of AWK, and implementation specific options are
          prefaced with -W.  mawk provides six:

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

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

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

          -W exec file   Program text is read from file and this is the last
                         option. Useful on systems that support the #! "magic
                         number" convention for executable scripts.

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

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

          The short forms -W[vdiesp] are recognized and on some systems -We is
          mandatory to avoid command line length limitations.

          mawk allows multiple -W options to be combined by separating the
          options with commas, e.g., -Wsprint=2000,posix.

     THE AWK LANGUAGE
        1. Program structure
          An AWK program is a sequence of pattern {action} pairs and user
          function definitions.

          A pattern can be:
               BEGIN
               END
               expression
               expression , expression

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

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

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               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).

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

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

          The value stored in variable y will be typed numeric.  If x is not
          numeric, the value read from x is converted to numeric before it is
          added to 2 and stored in y.  The value stored in variable z will be
          typed string, and the value of x will be converted to string if
          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 numeric.

          To evaluate, expr
                           1 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.

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          AWK uses extended regular expressions as with egrep(1).  The regular
          expression metacharacters, i.e., those with special meaning in regular
          expressions are

                ^ $ . [ ] | ( ) * + ?

          Regular expressions are built up from characters as follows:

               c            matches any non-metacharacter c.

               \c           matches a character defined by the same escape
                            sequences used in string constants or the literal
                            character c if \c is not an escape sequence.

               .            matches any character (including newline).

               ^            matches the front of a string.

               $            matches the back of a string.

               [c
                 1c2c3...]  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
          follows:

               r1r2         matches r1 followed immediately by r2
                            (concatenation).

               r1 | r2      matches r1 or r2 (alternation).

               r*           matches r repeated zero or more times.

               r+           matches r repeated one or more times.

               r?           matches r zero or once.

               (r)          matches r, providing grouping.

          The increasing precedence of operators is alternation, concatenation
          and unary (*, + or ?).

          For example,

               /^[_a-zA-Z][_a-zA-Z0-9]*$/  and
               /^[-+]?([0-9]+\.?|\.[0-9])[0-9]*([eE][-+]?[0-9]+)?$/

          are matched by AWK identifiers and AWK numeric constants respectively.

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          Note that . has to be escaped to be recognized as a decimal point, and
          that metacharacters are not special inside character classes.

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

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

               $0 ~ "^" identifier

          prints all lines that start with an AWK identifier.

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

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

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

          Assignment to $0 causes the fields and NF to be recomputed.
          Assignment to NF or to a field causes $0 to be reconstructed by
          concatenating the $i's separated by OFS.  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.

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          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
          parenthesized.

        6. Arrays
          Awk provides one-dimensional arrays.  Array elements are expressed as
          array[expr].  Expr is internally converted to string type, so, for
          example, A[1] and A["1"] are the same 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 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[expr
                                               1,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]

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        7. Builtin-variables
          The following variables are built-in and initialized before program
          execution.

               ARGC      number of command line arguments.

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

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

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

               FILENAME  name of the current input file.

               FNR       current record number in FILENAME.

               FS        splits records into fields as a regular expression.

               NF        number of fields in the current record.

               NR        current record number in the total input stream.

               OFMT      format for printing numbers; initially = "%.6g".

               OFS       inserted between fields on output, initially = " ".

               ORS       terminates each record on output, initially = "\n".

               RLENGTH   length set by the last call to the built-in function,
                         match().

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

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

               SUBSEP    used to build multiple array subscripts, initially =
                         "\034".

        8. Built-in functions
          String functions

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

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

               length(s)
                    Returns the length of string s.

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

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

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

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

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

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

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

          Arithmetic functions

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

               cos(x)         Cosine function, x in radians.

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               exp(x)         Exponential function.

               int(x)         Returns x truncated towards zero.

               log(x)         Natural logarithm.

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

               sin(x)         Sine function, x in radians.

               sqrt(x)        Returns square root of x.

               srand(expr)  srand()
                    Seeds the random number generator, using the clock if expr
                    is omitted, and returns the value of the previous seed.
                    mawk seeds the random number generator from the clock at
                    startup so there is no real need to call srand().
                    Srand(expr) is useful for repeating pseudo random sequences.

        9. Input and output
          There are two output statements, print and printf.

               print
                    writes $0  ORS to standard output.

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

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

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

          The input function getline has the following variations.

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

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

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

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

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

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

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

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

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

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

          The function system(expr) uses /bin/sh to execute expr and returns the
          exit status of the command expr.  Changes made to the ENVIRON array
          are not passed to commands executed with system or pipes.

        10. User defined functions
          The syntax for a user defined function is

               function name( args ) { statements }

          The function body can contain a return statement

               return opt_expr

          A return statement is not required. Function calls may be nested or
          recursive.  Functions are passed expressions by value and arrays by
          reference.  Extra arguments serve as local variables and are
          initialized to null.  For example, csplit(s,A) puts each character of

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          s into array A and returns the length of s.

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

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

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

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

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

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

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

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               file and RS = ":+", then there are two records "a" and "b".

          RS = " " is not special.

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

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

               For example, if a file is "a b\nc\n\n", RS = "\n\n+" and FS =
               " ", then there is one record "a b\nc" with three fields "a", "b"
               and "c".  Changing FS = "\n", gives two fields "a b" and "c";
               changing FS = "", gives one field identical to the record.

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

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

        13. Program execution
          This section describes the order of program execution.  First ARGC is
          set to the total number of command line arguments passed to the
          execution phase of the program.  ARGV[0] is set the name of the AWK
          interpreter and ARGV[1] ... ARGV[ARGC-1] holds the remaining 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.

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          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

               next
               exit  opt_expr

          statements.  A next statement causes the next input record to be read
          and pattern testing to restart with the first pattern {action} pair in
          the program.  An exit statement causes immediate execution of the END
          actions or program termination if there are none or if the exit occurs
          in an END action.  The opt_expr sets the exit value of the program
          unless overridden by a later exit or subsequent error.

     EXAMPLES
          1. emulate cat.

               { print }

          2. emulate wc.

               { chars += length($0) + 1  # add one for the \n
                 words += NF
               }

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     MAWK(1)                                                             MAWK(1)
                                    USER COMMANDS

               END{ print NR, words, chars }

          3. count the number of unique "real words".

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

               { for(i = 1 ; i <= NF ; i++)  word[$i] = "" }

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

          4. sum the second field of every record based on the first field.

               $1 ~ /credit|gain/ { sum += $2 }
               $1 ~ /debit|loss/  { sum -= $2 }

               END { print sum }

          5. sort a file, comparing as string

               { line[NR] = $0 "" }  # make sure of comparison type
                               # in case some lines look numeric

               END {  isort(line, NR)
                 for(i = 1 ; i <= NR ; i++) print line[i]
               }

               #insertion sort of A[1..n]
               function isort( A, n,    i, j, hold)
               {
                 for( i = 2 ; i <= n ; i++)
                 {
                   hold = A[j = i]
                   while ( A[j-1] > hold )
                   { j-- ; A[j+1] = A[j] }
                   A[j] = hold
                 }
                 # sentinel A[0] = "" will be created if needed
               }

     COMPATIBILITY ISSUES
          The Posix 1003.2(draft 11.3) definition of the AWK language is AWK as
          described in the AWK book with a few extensions that appeared in
          SystemVR4 nawk. The extensions are:

               New functions: toupper() and tolower().

               New variables: ENVIRON[] and CONVFMT.

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                                    USER COMMANDS

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

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

               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 above,

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

               { word[ $0 ] = "" }

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

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

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

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                                    USER COMMANDS

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

                 { print hold ; hold = $0 }

                 END { printf "%s" , hold }

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

          With mawk, the following are all equivalent,

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

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

          Posix AWK does not recognize "/dev/std{out,err}" or \x hex escape
          sequences in strings.  Unlike ANSI C, mawk limits the number of digits
          that follows \x to two as the current implementation only supports 8
          bit characters.  The built-in fflush first appeared in a recent (1993)
          AT&T awk released to netlib, and is not part of the posix standard.
          Aggregate deletion with delete array is not part of the posix
          standard.

          Posix explicitly leaves the behavior of FS = "" undefined, and
          mentions splitting the record into characters as a possible
          interpretation, but currently this use is not portable across
          implementations.

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

               substr(s, i, n) returns the characters of s in the intersection
               of the closed interval [1, length(s)] and the half-open interval
               [i, i+n).  When this intersection is empty, the empty string is
               returned; so substr("ABC", 1, 0) = "" and substr("ABC", -4, 6) =
               "A".

               Every string, including the empty string, matches the empty
               string at the front so, s ~ // and s ~ "", are always 1 as is

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     MAWK(1)                                                             MAWK(1)
                                    USER COMMANDS

               match(s, //) and match(s, "").  The last two set RLENGTH to 0.

               index(s, t) is always the same as match(s, t1) where t1 is the
               same as t with metacharacters escaped.  Hence consistency with
               match requires that index(s, "") always returns 1.  Also the
               condition, index(s,t) != 0 if and only t is a substring of s,
               requires index("","") = 1.

               If getline encounters end of file, getline var, leaves var
               unchanged.  Similarly, on entry to the END actions, $0, the
               fields and NF have their value unaltered from the last record.

     SEE ALSO
          egrep(1)

          Aho, Kernighan and Weinberger, The AWK Programming Language, Addison-
          Wesley Publishing, 1988, (the AWK book), defines the language, opening
          with a tutorial and advancing to many interesting programs that delve
          into issues of software design and analysis relevant to programming in
          any language.

          The GAWK Manual, The Free Software Foundation, 1991, is a tutorial and
          language reference that does not attempt the depth of the AWK book and
          assumes the reader may be a novice programmer. The section on AWK
          arrays is excellent.  It also discusses Posix requirements for AWK.

     BUGS
          mawk implements printf() and sprintf() using the C library functions,
          printf and sprintf, so full ANSI compatibility requires an ANSI C
          library.  In practice this means the h conversion qualifier may not be
          available.  Also mawk inherits any bugs or limitations of the library
          functions.

          Implementors of the AWK language have shown a consistent lack of
          imagination when naming their programs.

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

                                       - 18 -          Formatted:  June 28, 2010