| AWK(1) | General Commands Manual | AWK(1) | 
awk —
| awk | [ -Ffs]
      [-vvar=value]
      [-safe]
      [-d[N]]
      [prog |-ffilename] 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, and 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 filename. 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]-f
    filename-f options may be
    specified.-F
    fs-mr
    NNN, -mf
    NNN-safesystem() make
      the program abort (with a warning message).-v
    var=value-v options may be present.-versionawk version on standard output and
    exit.An input line is normally made up of fields separated by white space, 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.
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.
An action is a sequence of statements. Statements are terminated by semicolons, newlines or right braces. An empty expression-list stands for $0. String constants are quoted " ", with the usual C escapes recognized within. Expressions take on string or numeric values as appropriate, and are built using the Operators (see next subsection). Variables may be scalars, array elements (denoted x[i]) or fields. Variables are initialized to the null string. Array subscripts may be any string, not necessarily numeric; this allows for a form of associative memory. Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.
awk operators, in order of decreasing precedence, are:
(...)$++
    --^** form is also supported, and
      **= for the assignment operator).<
    >≤
    ≥!=
    ==~
    !~in&&||?:? expr2
      : expr3 . If
      expr1 is true, the result value is
      expr2, otherwise it is expr3.
      Only one of expr2 and expr3 is
      evaluated.= +=
    -=*=
    /= %= ^=if
    ( expression )
    statement [else
    statement]while
    ( expression )
    statementfor
    ( expression ;
    expression ;
    expression )
    statementfor
    ( var in
    array )
    statementdo
    statement while (
    expression )breakcontinuedelete
    array [expression]delete
    arrayexit
    [expression]return
    [expression]{
    [statement ...] }close(expr)fflush(expr)getline
    [var]getline returns 1 for a
      successful input, 0 for end of file, and -1 for an error.getline
    [var] <
    file| getlinegetline; each call of
      getline returns the next line of output from
      expr.nextnextfileprint
    [expr-list] [>
    file]print statement prints its arguments on the
      standard output (or to a file if > file or to a
      pipe if | expr is present), separated by the current
      output field separator OFS, and terminated by the
      output record separator ORS. Both
      file and expr may be literal
      names or parenthesized expressions; identical string values in different
      statements denote the same open file.printf
    format [,
    expr-list] [>
    file]atan2(x,
    y)/ y in radians. See also
      atan2(3).cos(expr)exp(expr)int(expr)log(expr)rand()sin(expr)sqrt(expr)srand([expr])rand())
      and returns the previous seed.gensub(r,
    s, h,
    [t])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])sub() except that all occurrences of the
      regular expression are replaced; sub() and
      gsub() return the number of replacements.index(s,
    t)length([string])match(s,
    r)split(s,
    a, [fs])sprintf(fmt,
    expr, ...)sub(r,
    s, [t])substr(s,
    m, [n])tolower(str)toupper(str)awk provides the following two functions for
  obtaining time stamps and formatting them:
systime()strftime([format [,
    timestamp]])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.system(cmd)! ||
  &&) 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:
in
    array-name) in array-namewhere 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.
-F fs.match(); 0 if not match.match(); -1 if no
      match.
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.
length($0) > 72Print 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" }
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.
The scope rules for variables in functions are a botch; the syntax is worse.
| May 18, 2017 | NetBSD 9.4 |