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        awk - pattern-directed scanning and processing language


        awk [ -F fs ] [ -v var=value ] [ ’prog’ | -f progfile ] [ file ...  ]


        Awk scans each input file for lines that match any of a set of patterns
        specified literally in prog or in one or more  files  specified  as  -f
        progfile.   With  each  pattern  there can be an associated action that
        will be performed when a line of a file matches the pattern.  Each line
        is  matched  against the pattern portion of every pattern-action state‐
        ment; the associated action is performed for each matched pattern.  The
        file  name  - means the standard input.  Any file of the form var=value
        is treated as an assignment, not a filename, and  is  executed  at  the
        time  it  would  have been opened if it were a filename.  The option -v
        followed by var=value is an assignment to be done before prog  is  exe‐
        cuted;  any  number  of  -v  options  may be present.  The -F fs option
        defines the input field separator to be the regular expression fs.
        An input line is normally made up of fields separated by  white  space,
        or by regular expression FS.  The fields are denoted $1, $2, ..., while
        $0 refers to the entire line.  If FS is null, the input line  is  split
        into one field per character.
        A pattern-action statement has the form
               pattern { action }
        A  missing  {  action  } means print the line; a missing pattern always
        matches.  Pattern-action statements are separated by newlines or  semi‐
        An  action  is a sequence of statements.  A statement can be one of the
               if( expression ) statement [ else statement ]
               while( expression ) statement
               for( expression ; expression ; expression ) statement
               for( var in array ) statement
               do statement while( expression )
               { [ statement ... ] }
               expression              # commonly var = expression
               print [ expression-list ] [ > expression ]
               printf format [ , expression-list ] [ > expression ]
               return [ expression ]
               next                    # skip remaining patterns on this input line
               nextfile                # skip rest of this file, open next, start at top
               delete array[ expression ]# delete an array element
               delete array            # delete all elements of array
               exit [ expression ]     # exit immediately; status is expression
        Statements are terminated by semicolons, newlines or right braces.   An
        empty  expression-list stands for $0.  String constants are quoted " ",
        with the usual C escapes recognized within.  Expressions take on string
        or numeric values as appropriate, and are built using the operators + -
        * / % ^ (exponentiation), and concatenation (indicated by white space).
        The  operators  !  ++  -- += -= *= /= %= ^= > >= < <= == != ?: are also
        available in expressions.  Variables may  be  scalars,  array  elements
        (denoted  x[i])  or  fields.   Variables  are  initialized  to the null
        string.  Array subscripts may be any string, not  necessarily  numeric;
        this allows for a form of associative memory.  Multiple subscripts such
        as [i,j,k] are permitted; the constituents are concatenated,  separated
        by the value of SUBSEP.
        The  print statement prints its arguments on the standard output (or on
        a file if >file or >>file is present or on a pipe if |cmd is  present),
        separated  by the current output field separator, and terminated by the
        output record separator.  file and cmd may be literal names  or  paren‐
        thesized  expressions;  identical string values in different statements
        denote the same open file.  The printf statement formats its expression
        list  according  to  the format (see printf(3)).  The built-in function
        close(expr) closes the  file  or  pipe  expr.   The  built-in  function
        fflush(expr) flushes any buffered output for the file or pipe expr.
        The  mathematical  functions  exp,  log,  sqrt, sin, cos, and atan2 are
        built in.  Other built-in functions:
        length the length of its argument taken as a string, or  of  $0  if  no
        rand   random number on (0,1)
        srand  sets seed for rand and returns the previous seed.
        int    truncates to an integer value
        substr(s, m, n)
               the n-character substring of s that begins at position m counted
               from 1.
        index(s, t)
               the position in s where the string t occurs, or  0  if  it  does
        match(s, r)
               the position in s where the regular expression r occurs, or 0 if
               it does not.  The variables RSTART and RLENGTH are  set  to  the
               position and length of the matched string.
        split(s, a, fs)
               splits  the  string s into array elements a[1], a[2], ..., a[n],
               and returns n.  The separation is done with the regular  expres‐
               sion  fs  or with the field separator FS if fs is not given.  An
               empty string as field separator splits the string into one array
               element per character.
        sub(r, t, s)
               substitutes t for the first occurrence of the regular expression
               r in the string s.  If s is not given, $0 is used.
        gsub   same as sub except that all occurrences of the  regular  expres‐
               sion  are  replaced;  sub and gsub return the number of replace‐
        sprintf(fmt, expr, ... )
               the string resulting from formatting expr ...  according to  the
               printf(3) format fmt
               executes cmd and returns its exit status
               returns  a copy of str with all upper-case characters translated
               to their corresponding lower-case equivalents.
               returns a copy of str with all lower-case characters  translated
               to their corresponding upper-case equivalents.
        The ‘‘function’’ getline sets $0 to the next input record from the cur‐
        rent input file; getline <file sets $0 to the next  record  from  file.
        getline  x  sets  variable x instead.  Finally, cmd | getline pipes the
        output of cmd into getline; each call of getline returns the next  line
        of  output  from cmd.  In all cases, getline returns 1 for a successful
        input, 0 for end of file, and -1 for an error.
        Patterns are arbitrary Boolean combinations (with ! || &&)  of  regular
        expressions  and relational expressions.  Regular expressions are as in
        egrep; see grep(1).  Isolated regular expressions in a pattern apply to
        the  entire  line.   Regular  expressions  may also occur in relational
        expressions, using the operators ~ and !~.  /re/ is a constant  regular
        expression;  any string (constant or variable) may be used as a regular
        expression, except in the position of an isolated regular expression in
        a pattern.
        A  pattern  may  consist  of two patterns separated by a comma; in this
        case, the action is performed for all lines from an occurrence  of  the
        first pattern though an occurrence of the second.
        A relational expression is one of the following:
               expression matchop regular-expression
               expression relop expression
               expression in array-name
               (expr,expr,...) in array-name
        where  a  relop  is  any  of  the  six relational operators in C, and a
        matchop is either ~ (matches) or !~ (does not match).  A conditional is
        an  arithmetic expression, a relational expression, or a Boolean combi‐
        nation of these.
        The special patterns BEGIN and END  may  be  used  to  capture  control
        before  the first input line is read and after the last.  BEGIN and END
        do not combine with other patterns.
        Variable names with special meanings:
               conversion format used when converting numbers (default %.6g)
        FS     regular expression used to separate  fields;  also  settable  by
               option -Ffs.
        NF     number of fields in the current record
        NR     ordinal number of the current record
        FNR    ordinal number of the current record in the current file
               the name of the current input file
        RS     input record separator (default newline)
        OFS    output field separator (default blank)
        ORS    output record separator (default newline)
        OFMT   output format for numbers (default %.6g)
        SUBSEP separates multiple subscripts (default 034)
        ARGC   argument count, assignable
        ARGV   argument  array, assignable; non-null members are taken as file‐
               array of environment variables; subscripts are names.
        Functions may be defined (at the position of  a  pattern-action  state‐
        ment) thus:
               function foo(a, b, c) { ...; return x }
        Parameters  are  passed  by  value  if scalar and by reference if array
        name; functions may be called recursively.  Parameters are local to the
        function;  all other variables are global.  Thus local variables may be
        created by providing excess parameters in the function definition.


        length($0) > 72
               Print lines longer than 72 characters.
        { print $2, $1 }
               Print first two fields in opposite order.
        BEGIN { FS = ",[ \t]*|[ \t]+" }
              { print $2, $1 }
               Same, with input fields separated by  comma  and/or  blanks  and
             { s += $1 }
        END  { print "sum is", s, " average is", s/NR }
               Add up first column, print sum and average.
        /start/, /stop/
               Print all lines between start/stop pairs.
        BEGIN     {    # Simulate echo(1)
             for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
             printf "\n"
             exit }
        lex(1), sed(1)
        A.  V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Lan‐
        guage, Addison-Wesley, 1988.  ISBN 0-201-07981-X


        There are no explicit conversions  between  numbers  and  strings.   To
        force  an expression to be treated as a number add 0 to it; to force it
        to be treated as a string concatenate "" to it.
        The scope rules for variables in functions are a botch; the  syntax  is


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