man(1) Manual page archive

     AWK(1)                                                     AWK(1)

          awk - pattern-directed scanning and processing language

          awk [ -Fs ] [ prog ] [ file ] ...

          Awk scans each input file for lines that match any of a set
          of patterns specified literally in prog or in a file speci-
          fied as -f file. With each pattern there can be an associ-
          ated action that will be performed when a line of a file
          matches the pattern.  Each line is matched against the pat-
          tern portion of every pattern-action statement; the associ-
          ated action is performed for each matched pattern.  The file
          name `-' means the standard input.

          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

          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
               for ( var in array ) statement
               { [ statement ] ... }
               expression     # commonly variable = expression
               print [ expression-list ] [ >expression ]
               printf format [ , expression-list ] [ >expression ]
               next      # skip remaining patterns on this input line
               exit [expr]    # skip the rest of the input; exit status is expr

          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 +, -, *, /, %, ^ (exponen-
          tiation), and concatenation (indicated by a blank).  The C
          operators ++, --, +=, -=, *=, /=, %= and ^= are also

     AWK(1)                                                     AWK(1)

          available in expressions.  Variables may be scalars, array
          elements (denoted x[i]) or fields.  Variables are initial-
          ized to the null string.  Array subscripts 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 or on a pipe if
          orcmd 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(3)). The function close closes the
          file or pipe named as its argument.

          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, sin, cos,
          atan2, rand (returns a random number on (0,1)), srand (sets
          seed for rand), and int (truncates its argument to an inte-
          ger).  substr(s, m, n) returns the n-character substring of
          s that begins at position m. index(s, t) returns the posi-
          tion in s where t occurs, or 0 if it does not.  The function
          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 expression fs or with the field separator
          FS if fs is not given.

          The function sub(r, t, s) substitutes t for the first occur-
          rence of the regular expression r in the string s. If s is
          not given, $0 is used.  The function gsub is the same except
          that all occurrences of the regular expression are replaced.
          Sub and gsub return the number of replacements.

          The function sprintf(fmt, expr, expr, ...) formats the
          expressions according to the printf(3) format given by fmt
          and returns the resulting string.

          The function system(cmd) executes cmd and returns its exit
          status The function getline sets $0 to the next input record
          from the current input file; getline <file sets $0 to the
          next record from file. getline x sets variable x instead.
          Finally, cmdorgetline pipes the input 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 (!, oror, &&, and
          parentheses) of regular expressions and relational expres-
          sions.  Regular expressions are as in egrep(1). Isolated
          regular expressions in a pattern apply to the entire line.
          Regular expressions may also occur in relational expres-
          sions, using the operators ~ and !~.  /re/ is a constant

     AWK(1)                                                     AWK(1)

          regular expression; in addition, 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 between
          an occurrence of the first pattern and the next occurrence
          of the second, inclusive.

          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 and END do not combine with other patterns.

          A regular expression r may be used to separate fields, by
          assigning to the variable FS or by means of the -Fs 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; FNR, the ordinal number of the
          current record in the current file; FILENAME, the name of
          the current input file; RS, the input record separator
          (default newline); OFS, the output field separator (default
          blank); ORS, the output record separator (default newline);
          OFMT, the output format for numbers (default "%.6g"); ARGC,
          the argument count; and ARGV, the argument array.  ARGC and
          the ARGV array may be altered; non-null members are taken as

          Functions may be defined (at the position of a pattern-
          action statement) as
               func foo(a, b, c) {...}
          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.
          The return statement may be used to return a value.

          Print lines longer than 72 characters:

               length > 72

          Print first two fields in opposite order:

     AWK(1)                                                     AWK(1)

               { print $2, $1 }

          Same, with input fields separated by comma and/or blanks and
               BEGIN { FS = ",[ \t]*or[ \t]+" }
                    { print $2, $1 }

          Add up first column, print sum and average:

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

          Print all lines between start/stop pairs:

               /start/, /stop/

          Simulate echo(1):

               BEGIN {
                    for (i = 1; i < ARGC; i++)
                         printf "%s ", ARGV[i]
                    printf "\n"

          lex(1), sed(1), sno(1)
          A. V. Aho, B. W. Kernighan, P. J. Weinberger, Awk - a pat-
          tern scanning and processing language: user's manual

          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.

          The scope rules for variables in functions are a botch.