mawk


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

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

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

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

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

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

       --             indicates the unambiguous end of options.

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

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

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

       -W 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

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

       A pattern can be:
              BEGIN
              END
              expression
              expression , expression

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

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

       The following statements control program flow inside blocks.

              if ( expr ) statement

              if ( expr ) statement else statement

              while ( expr ) statement

              do statement while ( expr )

              for ( opt_expr ; opt_expr ; opt_expr ) statement

              for ( var in array ) statement

              continue

              break

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

       String constants are enclosed in double quotes.

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

            \ddd      1, 2 or 3 octal digits for ascii ddd
            \xhh      1 or 2 hex digits for ascii  hh

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

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

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

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

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

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

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

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

            expr ~ /r/

       is an AWK expression that evaluates to 1 if  expr  "matches"  r,  which
       means  a substring of expr is in the set of strings defined by r.  With
       expression metacharacters, i.e., those with special meaning in  regular
       expressions are

             ^ $ . [ ] | ( ) * + ?

       Regular expressions are built up from characters as follows:

              c            matches any non-metacharacter c.

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

              .            matches any character (including newline).

              ^            matches the front of a string.

              $            matches the back of a string.

              [c1c2c3...]  matches  any character in the class c1c2c3... .  An
                           interval of characters is denoted  c1-c2  inside  a
                           class [...].

              [^c1c2c3...] matches any character not in the class c1c2c3...

       Regular expressions are built up from other regular expressions as fol-
       lows:

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

              r1 | r2      matches r1 or r2 (alternation).

              r*           matches r repeated zero or more times.

              r+           matches r repeated one or more times.

              r?           matches r zero or once.

              (r)          matches r, providing grouping.

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

       For example,

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

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

       Any expression can be used on the right hand side of the ~ or !~ opera-
       between every character.  For example,

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


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

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

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

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

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

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

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

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

       0.

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

            for ( var in array ) statement

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

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

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

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


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

              ARGC      number of command line arguments.

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

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

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

              FILENAME  name of the current input file.

              FNR       current record number in FILENAME.

              FS        splits records into fields as a regular expression.

              NF        number of fields in the current record.

              NR        current record number in the total input stream.

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

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

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

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

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

              length(s)
                     Returns the length of string s.

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

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

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

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

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

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

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

       Arithmetic functions

              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 ran-
                     dom sequences.

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

              print  writes $0  ORS to standard output.

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

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

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

              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

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

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

       The  function system(expr) uses /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 initial-
       ized to null.  For example, csplit(s,A) puts each character of  s  into
       array A and returns the length of s.

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

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

   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.

                     fields which are loaded into A.  The fields are placed in
                     A[1],  A[2],  ..., A[n] and split() returns n, the number
                     of fields which is the number of matches plus one.   Data
                     placed  in  A  that  looks  numeric  is  typed number and
                     string.

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

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

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

       RS = " " is not special.

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

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

              For example, if 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 = "" regard-
       less of the value of  FS.   mawk  does  not  support  this  convention,
       because defining "\n" as <SPACE> makes it unnecessary.

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

   13. Program execution
       This  section  describes the order of program execution.  First ARGC is
       set to the total number of command line arguments passed to the  execu-
       tion  phase  of the program.  ARGV[0] is set the name of the AWK inter-
       preter and ARGV[1] ...  ARGV[ARGC-1] holds the remaining  command  line
       arguments exclusive of options and program source.  For example with
       The command line arguments divide  into  three  sets:  file  arguments,
       assignment  arguments and empty strings "".  An assignment has the form
       var=string.  When an ARGV[i] is examined as a possible  file  argument,
       if  it  is  empty  it  is skipped; if it is an assignment argument, the
       assignment to var takes place and i skips to the  next  argument;  else
       ARGV[i] is opened for input.  If it fails to open, execution terminates
       with exit code 2.  If no command line argument is a file argument, then
       input comes from stdin.  Getline in a BEGIN action opens input.  "-" as
       a file argument denotes stdin.

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

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

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

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

            next
            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
            }

            END{ print NR, words, chars }


            $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 Sys-
       temVR4 nawk. The extensions are:

              New functions: toupper() and tolower().

              New variables: ENVIRON[] and CONVFMT.

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

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


       Posix  AWK is oriented to operate on files a line at a time.  RS can be
       changed from "\n" to another single character, but it is hard  to  find
       any  use for this -- there are no examples in the AWK book.  By conven-
       tion, RS = "", makes one or more blank lines separate records, allowing
       multi-line  records.   When  RS  = "", "\n" is always a field separator
       regardless of the value in FS.

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

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

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

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

              { print hold ; hold = $0 }

              END { printf "%s" , hold }

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

       With mawk, the following are all equivalent,

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

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

       Posix AWK does not  recognize  "/dev/std{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) =
              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 cannot handle ascii NUL \0 in the source or data files.   You  can
       output  NUL  using  printf  with  %c,  and any other 8 bit character is
       acceptable input.

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

       Implementors of the AWK language have shown a consistent lack of imagi-
       nation when naming their programs.

AUTHOR
       Mike Brennan (brennan@whidbey.com).



Version 1.2                       Dec 22 1994                          MAWK(1)
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