AWK(1)                       General Commands Manual                      AWK(1)

       awk - pattern-directed scanning and processing language

       awk [ -F fs ] [ -v var=value ] [ 'prog' | -f progfile ] [ file ...  ]

       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.

       An input line is normally made up of fields separated by white space, or
       by the 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.

       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

       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 at top
              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 white space).
       The operators ! ++ -- += -= *= /= %= ^= > >= < <= == != ?: 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.  Multiple subscripts such as [i,j,k]
       are permitted; the constituents 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
       parenthesized expressions; identical string values in different
       statements denote the same open file.  The printf statement formats its
       expression list according 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 atan2, cos, exp, log, sin, and sqrt are built
       in.  Other built-in functions:

            the length of its argument taken as a string, number of elements in
            an array for an array argument, or length of $0 if no argument.
       rand random number on [0,1).
            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.  If no n, use the rest of the string.
       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 occurs, 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 separator 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 used.
       gsub(r, t [, s])
            same as sub except that all occurrences of the regular expression
            are replaced; sub and gsub return the number of replacements.
       sprintf(fmt, expr, ...)
            the string resulting from formatting expr ...  according to the
            printf(3) format fmt.
            executes cmd and returns its exit status. This will be -1 upon
            error, cmd's exit status upon a normal exit, 256 + sig upon death-
            by-signal, where sig is the number of the murdering signal, or 512 +
            sig if there was a core dump.
            returns a copy of str with all upper-case characters translated to
            their corresponding lower-case equivalents.
            returns a copy of str with all lower-case characters translated to
            their corresponding upper-case equivalents.

       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
       expressions and relational expressions.  Regular expressions are as
       defined in re_format(7).  Isolated regular expressions in a pattern apply
       to the entire line.  Regular expressions may also occur in relational
       expressions, using 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

       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
       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.  They may appear multiple times in a program
       and execute in the order they are read by awk.

       Variable names with special meanings:

       ARGC argument count, assignable.
       ARGV argument array, assignable; non-null members are taken as filenames.
            conversion format used when converting numbers (default %.6g).
            array of environment variables; subscripts are names.
            the name of the current input file.
       FNR  ordinal number of the current record in the current file.
       FS   regular expression used to separate fields; also settable by option
       NF   number of fields in the current record.
       NR   ordinal number of the current record.
       OFMT output format for numbers (default %.6g).
       OFS  output field separator (default space).
       ORS  output record separator (default newline).
            the length of a string matched by match.
       RS   input record separator (default newline).  If empty, blank lines
            separate records.  If more than one character long, RS is treated as
            a regular expression, and records are separated by text matching the
            the start position of a string matched by match.
            separates multiple subscripts (default 034).

       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
       function; all other variables are global.  Thus local variables may be
       created by providing excess parameters in the function definition.

       If POSIXLY_CORRECT is set in the environment, then awk follows the POSIX
       rules for sub and gsub with respect to consecutive backslashes and

       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 spaces 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 }

       grep(1), lex(1), sed(1)
       A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming
       Language, Addison-Wesley, 1988.  ISBN 0-201-07981-X.

       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

       Only eight-bit characters sets are handled correctly.

                                   2020-11-24                             AWK(1)