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AWK(1)                      General Commands Manual                     AWK(1)

     awk - pattern-directed scanning and processing language

     awk [-F fs] [-v var=value] [-safe] [-d[N]] [prog | -f progfile] file ...
     awk -version

     awk is the Bell Labs' implementation of the AWK programming language as
     described in the The AWK Programming Language by A.V. Aho,
     B.W. Kernighan, P.J. Weinberger.

     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 options are as follows:

     -d[N]       Set debug level to specified number N.  If the number is
                 omitted, debug level is set to 1.

     -f filename
                 Read the AWK program source from specified file filename,
                 instead of the first command line argument.  Multiple -f
                 options may be specified.

     -F fs       Set the input field separator FS to the regular expression

     -mr NNN, -mf NNN
                 Obsolete, no longer needed options.  Set limit on maximum
                 record or fields number.

     -safe       Potentially unsafe functions such as system() make the
                 program abort (with a warning message).

     -v var=value
                 Assign the value value to the variable var before prog is
                 executed.  Any number of -v options may be present.

     -version    Print awk version on standard output and exit.

     An input line is normally made up of fields separated by white space, or
     by the regular expression the built-in variable FS is set to.  If FS is
     null, the input line is split into one field per character.  The fields
     are denoted $1, $2, ..., while $0 refers to the entire line.  Setting any
     other field causes the re-evaluation of $0 Assigning to $0 resets the
     values of all other fields and the NF built-in variable.

     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.  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 (see next subsection).
     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.

     awk operators, in order of decreasing precedence, are:

     (...)       Grouping
     $           Field reference
     ++ --       Increment and decrement, can be used either as postfix or
     ^           Exponentiation (the ** form is also supported, and **= for
                 the assignment operator).
     + - !       Unary plus, unary minus and logical negation.
     * / %       Multiplication, division and modulus.
     + -         Addition and subtraction.
     space       String concatenation.
     < >
     <= >=
     != ==       Regular relational operators
     ~ !~        Regular expression match and not match
     in          Array membership
     &&          Logical AND
     ||          Logical OR
     ?:          C conditional expression.  This is used as expr1 ? expr2 :
                 expr3.  If expr1 is true, the result value is expr2,
                 otherwise it is expr3.  Only one of expr2 and expr3 is
     = += -=
     *= /= %= ^=
                 Assignment and Operator-Assignment

   Control Statements
     The control statements are as follows:

     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

     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 an array

     exit [expression]
                       Exit immediately; status is expression

   I/O Statements
     The input/output statements are as follows:

     close(expr)       Closes the file or pipe expr.  Returns zero on success;
                       otherwise nonzero.

     fflush(expr)      Flushes any buffered output for the file or pipe expr.
                       Returns zero on success; otherwise nonzero.

     getline [var]     Set var (or $0 if var is not specified) to the next
                       input record from the current input file.  getline
                       returns 1 for a successful input, 0 for end of file,
                       and -1 for an error.

     getline [var] < file
                       Set var (or $0 if var is not specified) to the next
                       input record from the specified file file.

     expr | getline    Pipes the output of expr into getline; each call of
                       getline returns the next line of output from expr.

     print [expr-list] [redirection]
                       Print arguments separated by the current output field
                       separator OFS, and terminated by the output record
                       separator ORS.

     printf format[, expr-list] [redirection]
                       Format and print its expression list according to
                       format.  See printf(3) for list of supported formats
                       and their meaning.

     Both print and printf statements write to standard output by default.
     The output is written to the file or pipe specified by redirection if one
     is supplied, as follows: > file,  >> file, or | expr.  Both file and expr
     may be literal names or parenthesized expressions; identical string
     values in different statements denote the same open file.  For that
     purpose the file names /dev/stdin, /dev/stdout, and /dev/stderr refer to
     the program's stdin, stdout, and stderr respectively (and are unrelated
     to the fd(4) devices of the same names).

   Mathematical and Numeric Functions
     AWK has the following mathematical and numerical functions built-in:

     atan2(x, y)       Returns the arctangent of x/y in radians.  See also

     cos(expr)         Computes the cosine of expr, measured in radians.  See
                       also cos(3).

     exp(expr)         Computes the exponential value of the given argument
                       expr.  See also exp(3).

     int(expr)         Truncates expr to integer.

     log(expr)         Computes the value of the natural logarithm of argument
                       expr.  See also log(3).

     rand()            Returns random number between 0 and 1.

     sin(expr)         Computes the sine of expr, measured in radians.  See
                       also sin(3).

     sqrt(expr)        Computes the non-negative square root of expr.  See
                       also sqrt(3).

     srand([expr])     Sets seed for random number generator (rand()) and
                       returns the previous seed.

   String Functions
     AWK has the following string functions built-in:

     gensub(r, s, h [t])
                       Search the target string t for matches of the regular
                       expression r.  If h is a string beginning with `g' or
                       `G', then replace all matches of r with s.  Otherwise,
                       h is a number indicating which match of r to replace.
                       If no t is supplied, $0 is used instead.  Unlike sub()
                       and gsub(), the modified string is returned as the
                       result of the function, and the original target is not
                       changed.  Note that the `\n' sequences within
                       replacement string s supported by GNU awk are not
                       supported at this moment.

     gsub(r, s [t])    Same as sub() except that all occurrences of the
                       regular expression are replaced; sub() and gsub()
                       return the number of replacements.

     index(s, t)       The position in s where the string t occurs, or 0 if it
                       does not.

                       The length of its argument taken as a string, or of $0
                       if no argument.

     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

     sprintf(fmt, expr, ...)
                       Returns the string resulting from formatting expr
                       according to the printf(3) format fmt.

     sub(r, s [t])     Substitutes s for the first occurrence of the regular
                       expression r in the target string t.  If t is not
                       given, $0 is used.

     substr(s, m [n])  Returns the at most n-character substring of s starting
                       at position m, counted from 1.  If n is omitted, the
                       rest of s is returned.

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

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

   Time Functions
     This awk provides the following two functions for obtaining time stamps
     and formatting them:

     systime()         Returns the value of time in seconds since the start of
                       Unix Epoch (midnight, January 1, 1970, Coordinated
                       Universal Time).  See also time(3).

     strftime([format [timestamp]])
                       Formats the time timestamp according to the string
                       format.  timestamp should be in same form as value
                       returned by systime().  If timestamp is missing,
                       current time is used.  If format is missing, a default
                       format equivalent to the output of date(1) would be
                       used.  See the specification of ANSI C strftime(3) for
                       the format conversions which are supported.

   Other built-in functions
     system(cmd)       Executes cmd and returns its exit status.

     Patterns are arbitrary Boolean combinations (with ! || &&) of regular
     expressions 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,
     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 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
     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.

     If an awk program consists of only actions with the pattern BEGIN, and
     the BEGIN action contains no getline statement, awk exits without reading
     its input when the last statement in the last BEGIN action is executed.
     If an awk program consists of only actions with the pattern END or only
     actions with the patterns BEGIN and END, the input is read before the
     statements in the END actions are executed.

   Built-in Variables
     Variable names with special meanings:

     ARGC          argument count, assignable

     ARGV          argument array, assignable; non-null members are taken as

     CONVFMT       conversion format used when converting numbers (default

     ENVIRON       array of environment variables; subscripts are names.

     FILENAME      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 -F fs.

     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 blank)

     ORS           output record separator (default newline)

     RS            input record separator (default newline)

     RSTART        position of the first character matched by match(); 0 if no

     RLENGTH       length of the string matched by match(); -1 if no match.

     SUBSEP        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.

     Print lines longer than 72 characters.  length() defaults to $0 and the
     empty parens can also be omitted in this case:

           length > 72

     Print first two fields in opposite order:

           { print $2, $1 }

     Same, with input fields separated by comma and/or blanks and tabs:

           BEGIN { FS = ",[ \t]*|[ \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%s", ARGV[i], i==ARGC-1?"\n":" ")

     Another way to do the same that demonstrates field assignment and $0 re-

           BEGIN { for (i = 1; i < ARGC; ++i) $i = ARGV[i]; print }

     Print an error message to standard error:

           { print "error!" > "/dev/stderr" }

     egrep(1), lex(1), sed(1), atan2(3), cos(3), exp(3), log(3), sin(3),
     sqrt(3), strftime(3), time(3)

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

     AWK Language Programming, Edition 1.0, published by the Free Software
     Foundation, 1995

     nawk has been the default system awk since NetBSD 2.0, replacing the
     previously used GNU awk.

     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.

NetBSD 10.99                     July 5, 2022                     NetBSD 10.99