NAME

nawk - pattern scanning and processing language

SYNOPSIS

nawk [-F re] [-v var=value] ['prog'] [file...]
nawk [-F re] [-v var=value] [-f progfile] [file...]

DESCRIPTION

nawk scans each input file for lines that match any of a set of patterns specified in prog. The prog string must be enclosed in single quotes (') to protect it from the shell. For each pattern in prog there may be an associated action performed when a line of a file matches the pattern. The set of pattern-action statements may appear literally as prog or in a file specified with the -f progfile option. Input files are read in order; if there are no files, the standard input is read. The file name - means the standard input.

Each input line is matched against the pattern portion of every pattern-action statement; the associated action is performed for each matched pattern. 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, 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.

An input line is normally made up of fields separated by white space. (This default can be changed by using the FS built-in variable or the -F re option.) The fields are denoted $1, $2, ...; $0 refers to the entire line.

A pattern-action statement has the form:

pattern { action }

Either pattern or action may be omitted. If there is no action with a pattern, the matching line is printed. If there is no pattern with an action, the action is performed on every input line. Pattern-action statements are separated by newlines or semicolons.

Patterns are arbitrary Boolean combinations ( !, ||, &&, and
parentheses)  of  relational expressions and regular expres-
sions.  A relational expression is one of the following:

     expression relop expression
     expression matchop regular_expression
     expression in array-name
     (expression,expression, ...  ) in array-name

where a relop is any of the six relational operators in C, and a matchop is either ~ (contains) or !~ (does not contain). An expression is an arithmetic expression, a relational expression, the special expression

var in array

or a Boolean combination of these.

Regular expressions are as in egrep(1). In patterns they must be surrounded by slashes. Isolated regular expressions in a pattern apply to the entire line. Regular expressions may also occur in relational expressions. A pattern may consist of two patterns separated by a comma; in this case, the action is performed for all lines between an occurrence of the first pattern and the next occurrence of the second pattern.

The special patterns BEGIN and END may be used to capture control before the first input line has been read and after the last input line has been read respectively. These keywords do not combine with any other patterns.

A regular expression may be used to separate fields by using the -F re option or by assigning the expression to the built-in variable FS. The default is to ignore leading blanks and to separate fields by blanks and/or tab characters. However, if FS is assigned a value, leading blanks are no longer ignored.

Other built-in variables include:

ARGC command line argument count

ARGV command line argument array

ENVIRON array of environment variables; subscripts are names

FILENAME name of the current input file

FNR ordinal number of the current record in the current file

FS input field separator regular expression (default blank and tab)

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 new-line)

     SUBSEP        separates multiple subscripts (default is
                   034)
An action is a sequence of statements.  A statement  may  be
one of the following:

     if ( expression ) statement [ else statement ]
     while ( expression ) statement
     do statement while ( expression )
     for ( expression ; expression ; expression ) statement
     for ( var in array ) statement
     delete array[subscript] #delete an array element
     break
     continue
     { [ statement ] ... }
     expression     # commonly variable = expression
     print [ expression-list ] [ >expression ]
     printf format [ , expression-list ] [ >expression ]
     next      # skip remaining patterns on this input line
     exit [expr]    # skip the rest of the input; exit status is expr
     return [expr]

Statements are terminated by semicolons, new-lines, or right braces. An empty expression-list stands for the whole input line. Expressions take on string or numeric values as appropriate, and are built using the operators +, -, *, /, %, ^ and concatenation (indicated by a blank). 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 or zero. 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. String constants are quoted (""), with the usual C excapes recognized within.

The print statement prints its  arguments  on  the  standard
output, or on a file if >expression is present, or on a pipe
if | cmd is present.  The arguments  are  separated  by  the
current  output field separator and terminated by the output
record separator.  The printf statement formats its  expres-
sion  list  according  to  the format [see printf(3S) in the
Programmer's  Reference  Manual].   The  built-in   function
close(expr) closes the file or pipe expr.

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

Other built-in functions include:

gsub(for, repl, in)

behaves like sub (see below), except that it replaces successive occurrences of the regular expression (like the ed global substitute command).

index(s, t)

returns the position in string s where string t first occurs, or 0 if it does not occur at all.

int       truncates to an integer value.

length(s) returns the length of  its  argument  taken  as  a
          string,  or of the whole line if there is no argu-
          ment.

match(s, re)

returns the position in string s where the regular expression re occurs, or 0 if it does not occur at all. RSTART is set to the starting position (which is the same as the returned value), and RLENGTH is set to the length of the matched string.

rand      random number on (0, 1).

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.

srand     sets the seed for rand

sprintf(fmt, expr, expr,...)

formats the expressions according to the printf(3S) format given by fmt and returns the resulting string.

sub(for, repl, in)

substitutes the string repl in place of the first instance of the regular expression for in string in and returns the number of substitutions. If in is omitted, nawk substitutes in the current record ($0).

substr(s, m, n)

returns the n-character substring of s that begins at position m. The input/output built-in functions are:

close(filename)

closes the file or pipe named filename.

cmd | getline

pipes the output of cmd into getline; each successive call to getline returns the next line of output from cmd.

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.

getline x <file

sets x from the next record of file.

system(cmd)

executes cmd and returns its exit status. All forms of getline return 1 for successful input, 0 for end of file, and -1 for an error.

nawk also provides user-defined functions. Such functions may be defined (in the pattern position of a pattern-action statement) as

function name(args,...) { stmts }

Function arguments are passed by value if scalar and by reference if array name. Argument names are local to the function; all other variable names are global. Function calls may be nested and functions may be recursive. The return statement may be used to return a value.

EXAMPLES

Print lines longer than 72 characters:

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 fields in reverse order:

{ for (i = NF; i > 0; --i) print $i }

Print all lines between start/stop pairs:

/start/, /stop/

Print all lines whose first field is different from previous one:

     $1 != prev { print; prev = $1 }

Simulate echo(1):

     BEGIN     {
          for (i = 1; i < ARGC; i++)
               printf "%s", ARGV[i]
          printf "\n"
          exit
          }

Print a file, filling in page numbers starting at 5:

/Page/    { $2 = n++; }

     { print }

Assuming this program is in a file named prog, the following command line prints the file input numbering its pages starting at 5: nawk -f prog n=5 input.

SEE ALSO

egrep(1), grep(1), sed(1).
lex(1), printf(3S) in the Programmer's Reference Manual.
The awk chapter in the User's Guide.
A. V. Aho, B. W. Kerninghan, P. J. Weinberger, The AWK  Pro-
gramming Language Addison-Wesley, 1988.

NOTES

nawk is a new version of awk that provides capabilities unavailable in previous versions. This version will become the default version of awk in the next major UNIX system release.

Input white space is not preserved on output if fields are involved.

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 the null string ("") to it.