packages icon

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      mawk - pattern scanning and text processing language

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

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

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

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

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

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

      --             indicates the unambiguous end of options.

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

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

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

                                    - 1 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      -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.

    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

                                    - 2 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

           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).

                                    - 3 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      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 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.

                                    - 4 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      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.

             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

           r1r2         matches r1 followed immediately by r2

           r1 | r2      matches r1 or r2 (alternation).

           r*           matches r repeated zero or more times.

           r+           matches r repeated one or more times.

           r?           matches r zero or once.

           (r)          matches r, providing grouping.

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

      For example,

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

      are matched by AWK identifiers and AWK numeric constants respectively.

                                    - 5 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      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.

                                    - 6 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      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 0.

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

           for ( var in array ) statement

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

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

                                    - 7 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

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

           ARGC      number of command line arguments.

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

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

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

           FILENAME  name of the current input file.

           FNR       current record number in FILENAME.

           FS        splits records into fields as a regular expression.

           NF        number of fields in the current record.

           NR        current record number in the total input stream.

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

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

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

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

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

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

           SUBSEP    used to build multiple array subscripts, initially =

    8. Built-in functions
      String functions

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

                                    - 8 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

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

                Returns the length of string s.

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

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

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

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

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

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

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

      Arithmetic functions

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

           cos(x)         Cosine function, x in radians.

                                    - 9 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

           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.

                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

      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.

                                   - 10 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

                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

                                   - 11 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

      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

                                   - 12 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

           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

           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.

                                   - 13 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                USER COMMANDS

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

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

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

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

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

           exit  opt_expr

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

      1. emulate cat.

           { print }

      2. emulate wc.

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

                                   - 14 -      Formatted:  February 28, 2024

 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

      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.

                                   - 15 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                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,

                                   - 16 -      Formatted:  February 28, 2024

 MAWK(1)                                                             MAWK(1)
                                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

      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

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

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

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

                                   - 17 -      Formatted:  February 28, 2024

 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.


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

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

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

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

      Mike Brennan (
      Thomas E. Dickey <>.

                                   - 18 -      Formatted:  February 28, 2024