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AWK(1)                     OpenBSD Reference Manual                     AWK(1)

     awk - pattern-directed scanning and processing language

     awk [-F fs] [-v var=value] [-safe] [-mr n] [-mf n] [prog | -f progfile]
         file ...
     nawk ...

     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 statement;
     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 executed; any number
     of -v options may be present.  The -F fs option defines the input field
     separator to be the regular expression fs.  The -safe option disables
     file output (print >, print >>,) process creation (cmd | getline, print
     |, system) and access to the environment (ENVIRON).  This is a first (and
     not very reliable) approximation to a ``safe'' version of awk.

     An input line is normally made up of fields separated by whitespace, 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.

     To compensate for inadequate implementation of storage management, the
     -mr option can be used to set the maximum size of the input record, and
     the -mf option to set the maximum number of fields.

     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
           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 whitespace).  The
     operators ! ++ -- += -= *= /= %= ^= are also available in expressions.
     Variables may be scalars, array elements (denoted x[i]) or fields.  Vari-
     ables 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 con-
     stituents 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 parenthe-
     sized expressions; identical string values in different statements denote
     the same open file.  The printf statement formats its expression list ac-
     cording 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 argument.

     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 not.

     match(s, r)       the position in s where the regular expression r oc-
                       curs, 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 expression fs or with the field separator
                       FS if fs is not given.  An empty string as field sepa-
                       rator splits the string into one array element per

     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

     gsub(r, t, s)     same as sub() except that all occurrences of the regu-
                       lar expression are replaced; sub() and gsub() return
                       the number of replacements.

     sprintf(fmt, expr, ...)
                       the string resulting from formatting expr, ...  accord-
                       ing to the printf(3) format fmt.

     system(cmd)       executes cmd and returns its exit status.

     tolower(str)      returns a copy of str with all upper-case characters
                       translated to their corresponding lower-case equiva-

     toupper(str)      returns a copy of str with all lower-case characters
                       translated to their corresponding upper-case equiva-

     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, 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 ex-
     pressions and relational expressions.  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 expressions, us-
     ing 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 arith-
     metic expression, a relational expression, or a Boolean combination of

     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:

     CONVFMT       conversion format used when converting numbers (default
     FS            regular expression used to separate fields; also settable
                   by option -F fs.
     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
     FILENAME      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
     ENVIRON       array of environment variables; subscripts are names.

     Functions may be defined (at the position of a pattern-action statement)

           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 func-
     tion; all other variables are global.  Thus local variables may be creat-
     ed 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 tabs.

           { 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, and P. J. Weinberger, The AWK Programming
     Language, Addison-Wesley, 1988, ISBN 0-201-07981-X.

     An awk utility appeared in Version 7 AT&T UNIX.

     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

OpenBSD 3.4                      June 29, 1996                               4


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