awk

AWK(1)                     BSD General Commands Manual                    AWK(1)

NAME
     awk — pattern-directed scanning and processing language

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

DESCRIPTION
     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 options are as follows:

     -d[n]   Debug mode.  Set debug level to n, or 1 if n is not specified.  A
             value greater than 1 causes awk to dump core on fatal errors.

     -F fs   Define the input field separator to be the regular expression fs.

     -f progfile
             Read program code from the specified file progfile instead of from
             the command line.

     -safe   Disable file output (print >, print >>), process creation (cmd |
             getline, print |, system) and access to the environment (ENVIRON;
             see the section on variables below).  This is a first (and not very
             reliable) approximation to a “safe” version of awk.

     -version
             Print the version number of awk to standard output and exit.

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

     The input is normally made up of input lines (records) separated by
     newlines, or by the value of RS.  If RS is null, then any number of blank
     lines are used as the record separator, and newlines are used as field
     separators (in addition to the value of FS).  This is convenient when
     working with multi-line records.

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

     Normally, any number of blanks separate fields.  In order to set the field
     separator to a single blank, use the -F option with a value of ‘[ ]’.  If a
     field separator of ‘t’ is specified, awk treats it as if ‘\t’ had been
     specified and uses ⟨TAB⟩ as the field separator.  In order to use a literal
     ‘t’ as the field separator, use the -F option with a value of ‘[t]’.

     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
     semicolons.

     Newlines are permitted after a terminating statement or following a comma
     (‘,’), an open brace (‘{’), a logical AND (‘&&’), a logical OR (‘||’),
     after the ‘do’ or ‘else’ keywords, or after the closing parenthesis of an
     ‘if’, ‘for’, or ‘while’ statement.  Additionally, a backslash (‘\’) can be
     used to escape a newline between tokens.

     An action is a sequence of statements.  A statement can be one of the
     following:

           if (expression) statement [else statement]
           while (expression) statement
           for (expression; expression; expression) statement
           for (var in array) statement
           do statement while (expression)
           break
           continue
           { [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 (see printf(1) for a complete list of
     these).  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.  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 (see the section on
     variables below).

     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(1)).

     Patterns are arbitrary Boolean combinations (with ! || &&) of regular
     expressions and relational expressions.  awk supports extended regular
     expressions (EREs).  See re_format(7) for more information on regular
     expressions.  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 through 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.

     Variable names with special meanings:

     ARGC       Argument count, assignable.
     ARGV       Argument array, assignable; non-null members are taken as
                filenames.
     CONVFMT    Conversion format when converting numbers (default "%.6g").
     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.  $NF can be used to
                obtain the value of the last field 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).
     RLENGTH    The length of the string matched by the match() function.
     RS         Input record separator (default newline).
     RSTART     The starting position of the string matched by the match()
                function.
     SUBSEP     Separates multiple subscripts (default 034).

FUNCTIONS
     The awk language has a variety of built-in functions: arithmetic, string,
     input/output, general, and bit-operation.

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

           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.

   Arithmetic Functions
     atan2(y, x)  Return the arctangent of y/x in radians.

     cos(x)       Return the cosine of x, where x is in radians.

     exp(x)       Return the exponential of x.

     int(x)       Return x truncated to an integer value.

     log(x)       Return the natural logarithm of x.

     rand()       Return a random number, n, such that 0≤n<1.

     sin(x)       Return the sine of x, where x is in radians.

     sqrt(x)      Return the square root of x.

     srand(expr)  Sets seed for rand() to expr and returns the previous seed.
                  If expr is omitted, the time of day is used instead.

   String Functions
     gsub(r, t, s)    The same as sub() except that all occurrences of the
                      regular expression are replaced.  gsub() returns the
                      number of replacements.

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

     length(s)        The length of s taken as a string, or of $0 if no argument
                      is given.

     match(s, r)      The position in s where the regular expression r occurs,
                      or 0 if it does not.  The variable RSTART is set to the
                      starting position of the matched string (which is the same
                      as the returned value) or zero if no match is found.  The
                      variable RLENGTH is set to the length of the matched
                      string, or -1 if no match is found.

     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 character.

     sprintf(fmt, expr, ...)
                      The string resulting from formatting expr, ... according
                      to the printf(1) format fmt.

     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.  An ampersand (‘&’) in t is replaced in string s
                      with regular expression r.  A literal ampersand can be
                      specified by preceding it with two backslashes (‘\\’).  A
                      literal backslash can be specified by preceding it with
                      another backslash (‘\\’).  sub() returns the number of
                      replacements.

     substr(s, m, n)  Return at most the n-character substring of s that begins
                      at position m counted from 1.  If n is omitted, or if n
                      specifies more characters than are left in the string, the
                      length of the substring is limited by the length of s.

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

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

   Input/Output and General Functions
     close(expr)           Closes the file or pipe expr.  expr should match the
                           string that was used to open the file or pipe.

     cmd | getline [var]   Read a record of input from a stream piped from the
                           output of cmd.  If var is omitted, the variables $0
                           and NF are set.  Otherwise var is set.  If the stream
                           is not open, it is opened.  As long as the stream
                           remains open, subsequent calls will read subsequent
                           records from the stream.  The stream remains open
                           until explicitly closed with a call to close().
                           getline returns 1 for a successful input, 0 for end
                           of file, and -1 for an error.

     fflush([expr])        Flushes any buffered output for the file or pipe
                           expr, or all open files or pipes if expr is omitted.
                           expr should match the string that was used to open
                           the file or pipe.

     getline               Sets $0 to the next input record from the current
                           input file.  This form of getline sets the variables
                           NF, NR, and FNR.  getline returns 1 for a successful
                           input, 0 for end of file, and -1 for an error.

     getline var           Sets $0 to variable var.  This form of getline sets
                           the variables NR and FNR.  getline returns 1 for a
                           successful input, 0 for end of file, and -1 for an
                           error.

     getline [var]  <file  Sets $0 to the next record from file.  If var is
                           omitted, the variables $0 and NF are set.  Otherwise
                           var is set.  If file is not open, it is opened.  As
                           long as the stream remains open, subsequent calls
                           will read subsequent records from file.  file remains
                           open until explicitly closed with a call to close().

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

   Bit-Operation Functions
     compl(x)      Returns the bitwise complement of integer argument x.

     and(v1, v2, ...)
                   Performs a bitwise AND on all arguments provided, as
                   integers.  There must be at least two values.

     or(v1, v2, ...)
                   Performs a bitwise OR on all arguments provided, as integers.
                   There must be at least two values.

     xor(v1, v2, ...)
                   Performs a bitwise Exclusive-OR on all arguments provided, as
                   integers.  There must be at least two values.

     lshift(x, n)  Returns integer argument x shifted by n bits to the left.

     rshift(x, n)  Returns integer argument x shifted by n bits to the right.

EXIT STATUS
     The awk utility exits 0 on success, and >0 if an error occurs.

     But note that the exit expression can modify the exit status.

EXAMPLES
     Print lines longer than 72 characters:

           length($0) > 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 { # Simulate echo(1)
                   for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
                   printf "\n"
                   exit }

     Print an error message to standard error:

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

SEE ALSO
     cut(1), lex(1), printf(1), sed(1), re_format(7)

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

STANDARDS
     The awk utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”)
     specification, except awk does not support {n,m} pattern matching.

     The flags -d, -safe, and -version as well as the commands fflush, compl,
     and, or, xor, lshift, rshift, are extensions to that specification.

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

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 concatenate "" to it.

     The scope rules for variables in functions are a botch; the syntax is
     worse.

BSD                               June 6, 2020                               BSD