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Kinds of Patterns

   Here is a summary of the types of patterns supported in `awk'.

     A regular expression as a pattern.  It matches when the text of the
     input record fits the regular expression.  (*Note Regular
     Expressions as Patterns: Regexp.)

     A single expression.  It matches when its value, converted to a
     number, is nonzero (if a number) or nonnull (if a string).  (
See Expressions as Patterns: Expression Patterns.)

`PAT1, PAT2'
     A pair of patterns separated by a comma, specifying a range of
     records.  (See Specifying Record Ranges with Patterns: Ranges.)

     Special patterns to supply start-up or clean-up information to
     `awk'.  (See `BEGIN' and `END' Special Patterns: BEGIN/END.)

     The empty pattern matches every input record.  (*Note The Empty
     Pattern: Empty.)