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 associated action that will be performed
          when a line of a file matches the pattern.  The set of pat-
          terns 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,

     AWK(1)                                                     AWK(1)

          and are built using the operators +, -, *, /, %,  and con-
          catenation (indicated by a blank).  The C operators ++, --,
          +=, -=, *=, /=, and %= 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.  String con-
          stants 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 separator, and terminated by the output
          record separator.  The printf statement formats its expres-
          sion list according to the format (see printf(3)).

          The built-in function length returns the length of its argu-
          ment 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 substring of s that
          begins at position m. The function
          sprintf(fmt, expr, expr, ...) formats the expressions
          according to the printf(3) format given by fmt and returns
          the resulting string.

          Patterns are arbitrary Boolean combinations (!, oror, &&, and
          parentheses) of regular expressions and relational expres-
          sions.  Regular expressions must be surrounded by slashes
          and are as in egrep. Isolated regular expressions in a pat-
          tern 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.

          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

     AWK(1)                                                     AWK(1)

          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 num-
          ber 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 pat-
          tern 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 concate-
          nate "" to it.