awk patterns may be one of the following:
/regular expression/ relational expression pattern && pattern pattern || pattern pattern ? pattern : pattern (pattern) ! pattern pattern1, pattern2 BEGIN END
END are two special kinds of patterns that are not
tested against the input. The action parts of all
BEGIN rules are
concatenated as if all the statements had been written in a single
rule. They are executed before any of the input is read. Similarly, all the
END rules are concatenated, and executed when all the input is exhausted (or
exit statement is executed).
patterns cannot be combined with other patterns in pattern expressions.
END rules cannot have missing action parts.
/regular-expression/ patterns, the associated statement is
executed for each input record that matches the regular expression. Regular
expressions are summarized below.
A relational expression may use any of the operators defined below in the section on actions. These generally test whether certain fields match certain regular expressions.
The `&&', `||', and `!' operators are logical "and," logical "or," and logical "not," respectively, as in C. They do short-circuit evaluation, also as in C, and are used for combining more primitive pattern expressions. As in most languages, parentheses may be used to change the order of evaluation.
The `?:' operator is like the same operator in C. If the first pattern matches, then the second pattern is matched against the input record; otherwise, the third is matched. Only one of the second and third patterns is matched.
The `pattern1, pattern2' form of a pattern is called a range pattern. It matches all input lines starting with a line that matches pattern1, and continuing until a line that matches pattern2, inclusive. A range pattern cannot be used as an operand of any of the pattern operators.
See section Pattern Elements.
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