Info: (gawk) Pattern Overview

gawk: Pattern Overview

 
 7.1 Pattern Elements
 ====================

 
· Regexp Patterns             Using regexps as patterns.
· Expression Patterns         Any expression can be used as a pattern.
· Ranges                      Pairs of patterns specify record ranges.
· BEGIN/END                   Specifying initialization and cleanup rules.
· BEGINFILE/ENDFILE           Two special patterns for advanced control.
· Empty                       The empty pattern, which matches every record.
 
 Patterns in 'awk' control the execution of rules--a rule is executed
 when its pattern matches the current input record.  The following is a
 summary of the types of 'awk' patterns:
 
 '/REGULAR EXPRESSION/'
      A regular expression.  It matches when the text of the input record
      fits the regular expression.  (Regexp.)
 
 'EXPRESSION'
      A single expression.  It matches when its value is nonzero (if a
      number) or non-null (if a string).  (Expression Patterns.)
 
 'BEGPAT, ENDPAT'
      A pair of patterns separated by a comma, specifying a "range" of
      records.  The range includes both the initial record that matches
      BEGPAT and the final record that matches ENDPAT.  (Ranges.)
 
 'BEGIN'
 'END'
      Special patterns for you to supply startup or cleanup actions for
      your 'awk' program.  (BEGIN/END.)
 
 'BEGINFILE'
 'ENDFILE'
      Special patterns for you to supply startup or cleanup actions to be
      done on a per-file basis.  (BEGINFILE/ENDFILE.)
 
 'EMPTY'
      The empty pattern matches every input record.  (Empty.)

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