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Church Of The
Swimming Elephant


AWK Usage
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 may be omitted. If there is no action, the matching line is printed. If there is no pat-tern, 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 expressionexpression 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 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 the occurrence of the first pattern to the 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.



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Service Details

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All pages ©1999, 2000, 2001, 2002, 2003 Church of the Swimming Elephant unless otherwise stated
Church of the Swimming Elephant©1999, 2000, 2001, 2002, 2003 is a wholly owned subsidiary of Packetderm, LLC.

Packetderm, LLC
210 Park Ave #308
Worcester, MA 01609