AWK(1)                               BSD                                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 associated
     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 filename - 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 the FS variable name (see below).  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
     operators +, -, *, /, %, and concatenation (indicated by a blank).  The C
     operators ++, --, +=, -=, *=, /=, and %= are also available in
     expressions.  Variables can be scalars, array elements (denoted x[i]) or
     fields.  Initialize variables to the null string.  Array subscripts can
     be any string, not necessarily numeric; this allows for a form of
     associative memory.  Enclose string constants in quotation marks: "...".

     The print statement prints its arguments on the standard output (or on a
     file if >file is present), separated by the current output field
     separator, 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 there is no argument.  There are also
     built-in functions exp, log, sqrt, and int.  int truncates its argument
     to an integer.  substr(s, m, n) returns the n-character substring 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 parentheses)
     of regular expressions and relational expressions.  Regular expressions
     must be surrounded by slashes and 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.

     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.

     You can use the special patterns BEGIN and END to capture control before
     the first input line is read and after the last.  BEGIN must be the first
     pattern; END the last.

     You can use a single character c 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 the first two fields in opposite order:

          { print $2, $1 }

     Add up the first column, print the 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 }


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.

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