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AWK(1)                      General Commands Manual                     AWK(1)



NAME
       awk - pattern-directed scanning and processing language

SYNOPSIS
       awk  [  -F fs ] [ -d ] [ -mf n ] [ -mr n ] [ -safe ] [ -v var=value ] [
       -f progfile | prog ] [ 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  state‐
       ment; 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 file name, and is executed at the time
       it would have been opened if it were a file name.  The option  -v  fol‐
       lowed  by  var=value  is an assignment to be done before the program is
       executed; any number of -v options may be present.  -F  fs  option  de‐
       fines 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 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.

       The -safe option causes awk to run in ``safe mode,'' in which it is not
       allowed  to run shell commands or open files and the environment is not
       made available in the ENVIRON 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 semi‐
       colons.

       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.  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 paren‐
       thesized expressions; identical string values in  different  statements
       denote the same open file.  The printf statement formats its expression
       list according to the format (see fprintf(2)).  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.  If
       expr is omitted or is a null string, all open files are flushed.

       The  mathematical  functions  exp,  log,  sqrt, sin, cos, and atan2 are
       built in.  Other built-in functions:

       length If its argument is a string, the string's  length  is  returned.
              If its argument is an array, the number of subscripts in the ar‐
              ray is returned.  If no argument, the length of $0 is returned.

       rand   random number on (0,1)

       srand  sets seed for rand and returns the previous seed.

       int    truncates to an integer value

       utf    converts its numerical argument, a character number,  to  a  UTF
              string

       substr(s, m, n)
              the n-character substring of s that begins at position m counted
              from 1.  If n is omitted, it is taken to be the length of s from
              m.

       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 expres‐
              sion 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.

       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.  A character
              in t will be replaced by the sub-string of s matched  by  r;  it
              may be escaped with to substitute a literal

       gsub   same  as  sub except that all occurrences of the regular expres‐
              sion are replaced; sub and gsub return the  number  of  replace‐
              ments.

       sprintf(fmt, expr, ...)
              the  string resulting from formatting expr ...  according to the
              printf 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 equivalents.

       toupper(str)
              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 cur‐
       rent  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  in
       regexp(6).   Isolated regular expressions in a pattern apply to the en‐
       tire line.  Regular expressions may also occur  in  relational  expres‐
       sions,  using  the  operators ~ and !~.  /re/ is a constant regular ex‐
       pression; 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  combi‐
       nation of these.

       The  special  patterns BEGIN and END may be used to capture control be‐
       fore 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 %.6g)

       FS     regular expression used to separate fields; also settable by op‐
              tion -Ffs.

       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  file
              names

       ENVIRON
              array of environment variables; subscripts are names.

       Functions  may  be  defined (at the position of a pattern-action state‐
       ment) thus:

              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.

EXAMPLES
       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 }

SOURCE
       /sys/src/cmd/awk

SEE ALSO
       sed(1), regexp(6),
       A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming  Lan‐
       guage, Addison-Wesley, 1988.  ISBN 0-201-07981-X

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.
       UTF is not always dealt with correctly, though awk does make an attempt
       to  do  so.   The split function with an empty string as final argument
       now copes with UTF in the string being split.



                                                                        AWK(1)