4.3BSD - /usr/man/cat1/awk.0

AWK(1)                                                                  AWK(1)


NAME
       awk - pattern scanning and processing language

SYNOPSIS
       awk [ -Fc ] [ prog ] [ file ] ...

DESCRIPTION
       Awk scans each input file for lines that match any of a set of patterns
       specified in prog.  With each pattern in prog there can be  an  associ‐
       ated  action  that  will be performed when a line of a file matches the
       pattern.  The set of patterns may appear literally as  prog,  or  in  a
       file specified as -f file.

       Files  are  read in order; if there are no files, the standard input is
       read.  The file name ‘-’  means  the  standard  input.   Each  line  is
       matched  against the pattern portion of every pattern-action statement;
       the associated action is performed for each matched pattern.

       An input line is made up of fields separated  by  white  space.   (This
       default  can  be  changed  by  using  FS,  vide infra.)  The fields are
       denoted $1, $2, ... ; $0 refers to the entire line.


       A pattern-action statement has the form

            pattern { action }

       A missing { action } means print the line;  a  missing  pattern  always
       matches.

       An  action  is a sequence of statements.  A statement can be one of the
       following:

            if ( conditional ) statement [ else statement ]
            while ( conditional ) statement
            for ( expression ; conditional ; expression ) statement
            break
            continue
            { [ statement ] ... }
            variable = expression
            print [ expression-list ] [ >expression ]
            printf format [ , expression-list ] [ >expression ]
            next # skip remaining patterns on this input line
            exit # skip the rest of the input

       Statements are terminated by semicolons, newlines or right braces.   An
       empty  expression-list  stands for the whole line.  Expressions take on
       string or numeric values as appropriate, and are built using the opera‐
       tors  +,  -, *, /, %,  and concatenation (indicated by a blank).  The C
       operators ++, --, +=, -=, *=, /=, and %= are also available in  expres‐
       sions.   Variables  may  be  scalars,  array elements (denoted x[i]) or
       fields.  Variables are initialized to  the  null  string.   Array  sub‐
       scripts  may  be any string, not necessarily numeric; this allows for a
       form of associative memory.  String constants are quoted "...".

       The print statement prints its arguments on the standard output (or  on
       a file if >file is present), separated by the current output field sep‐
       arator, and terminated by the  output  record  separator.   The  printf
       statement  formats  its  expression  list  according to the format (see
       printf(3S)).

       The built-in function length returns the length of its  argument  taken
       as  a  string,  or  of  the  whole line if no argument.  There are also
       built-in functions exp, log, sqrt, and int.   The  last  truncates  its
       argument  to  an integer.  substr(s, m, n) returns the n-character sub‐
       string   of   s   that   begins   at   position   m.    The    function
       sprintf(fmt, expr, expr, ...)  formats the expressions according to the
       printf(3S) format given by fmt and returns the resulting string.

       Patterns are arbitrary Boolean combinations (!, ||, &&,  and  parenthe‐
       ses)  of  regular  expressions  and  relational  expressions.   Regular
       expressions must be surrounded by slashes and are as  in  egrep.   Iso‐
       lated regular expressions in a pattern apply to the entire line.  Regu‐
       lar expressions may also occur in relational expressions.

       A pattern may consist of two patterns separated by  a  comma;  in  this
       case,  the  action  is performed for all lines between an occurrence of
       the first pattern and the next occurrence of the second.

       A relational expression is one of the following:

            expression matchop regular-expression
            expression relop expression

       where a relop is any of the  six  relational  operators  in  C,  and  a
       matchop  is  either  ~  (for contains) or !~ (for does not contain).  A
       conditional is an arithmetic expression, a relational expression, or  a
       Boolean combination 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 must  be
       the first pattern, END the last.

       A single character c may be used to separate the fields by starting the
       program with

            BEGIN { FS = "c" }

       or by using the -Fc option.

       Other variable names with special meanings include NF,  the  number  of
       fields  in  the  current  record; NR, the ordinal number of the current
       record; FILENAME, the name of the current input file; OFS,  the  output
       field  separator  (default  blank);  ORS,  the  output record separator
       (default newline); and OFMT, the output  format  for  numbers  (default
       "%.6g").


EXAMPLES
       Print lines longer than 72 characters:

            length > 72

       Print first two fields in opposite order:

            { print $2, $1 }

       Add up first column, print sum and average:

                 { s += $1 }
            END  { print "sum is", s, " average is", s/NR }

       Print fields in reverse order:

            { for (i = NF; i > 0; --i) print $i }

       Print all lines between start/stop pairs:

            /start/, /stop/

       Print all lines whose first field is different from previous one:

            $1 != prev { print; prev = $1 }

SEE ALSO
       lex(1), sed(1)
       A.  V. Aho, B. W. Kernighan, P. J. Weinberger, Awk - a pattern scanning
       and processing language

BUGS
       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.


7th Edition                     April 29, 1985                          AWK(1)