Input Lines

Each input line is matched against the pattern portion of every pattern-action statement; the associated action is performed for each matched pattern. Any filename 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. Variables assigned in this manner are not available inside a BEGIN rule, and are assigned after previously specified files have been read.

An input line is normally made up of fields separated by white spaces. (This default can be changed by using the FS built-in variable or the -Fc option.) The default is to ignore leading blanks and to separate fields by blanks and/or tab characters. However, if FS is assigned a value that does not include any of the white spaces, then leading blanks are not ignored. The fields are denoted $1, $2, ...; $0 refers to the entire line.

Pattern-action Statements

A pattern-action statement has the form:

pattern { action } 

Either pattern or action can be omitted. If there is no action, the matching line is printed. If there is no pattern, 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 expressions. A relational expression is one of the following:

expression relop expression
expression matchop regular_expression

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 can also occur in relational expressions. A pattern can consist of two patterns separated by a comma; in this case, the action is performed for all lines between the occurrence of the first pattern to the occurrence of the second pattern.

The special patterns BEGIN and END can 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.

Built-in Variables

Built-in variables include:

FILENAME

FS

NF

NR

OFMT

OFS

ORS

RS

An action is a sequence of statements. A statement can 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
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

Statements are terminated by semicolons, newlines, 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 ++, −−, +=, −=, *=, /=, %=, ^=, >, >=, <, <=, ==, !=, and ?: are also available in expressions. Variables can be scalars, array elements (denoted x[i]), or fields. Variables are initialized to the null string or zero. Array subscripts can be any string, not necessarily numeric; this allows for a form of associative memory. String constants are quoted (""), with the usual C escapes 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 output resulted from the print statement is terminated by the output record separator with each argument separated by the current output field separator. The printf statement formats its expression list according to the format (see printf(3C)).

Built-in Functions

The arithmetic functions are as follows:

exp(x)

log(x)

sqrt(x)

int(x)

The string functions are as follows:

index(s, t)

int(s)

length(s)

split(s, a, fs)

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

substr(s, m, n)

The input/output function is as follows:

getline

Large File Behavior

See largefile(7) for the description of the behavior of oawk when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

/usr/bin/oawk