Multi-Character Regular Expressions  
 
 

You can use the following rules to build a multi-character regular expressions:

  • Parentheses group parts of regular expressions together into grouped sub-expressions that can be treated as a single unit. For example, (ha)+ matches one or more instances of "ha".
  • A one-character regular expression or grouped sub-expressions followed by an asterisk (*) matches zero or more occurrences of the regular expression. For example, [a-z]* matches zero or more lower-case characters.
  • A one-character regular expression or grouped sub-expressions followed by a plus (+) matches one or more occurrences of the regular expression. For example, [a-z]+ matches one or more lower-case characters.
  • A one-character regular expression or grouped sub-expressions followed by a question mark (?) matches zero or one occurrences of the regular expression. For example, xy?z matches either "xyz" or "xz".
  • The concatenation of regular expressions creates a regular expression that matches the corresponding concatenation of strings. For example, [A-Z][a-z]* matches any capitalized word.
  • The OR character (|) allows a choice between two regular expressions. For example, jell(y|ies) matches either "jelly" or "jellies".
  • Braces ({}) are used to indicate a range of occurrences of a regular expression, in the form {m, n} where m is a positive integer equal to or greater than zero indicating the start of the range and n is equal to or greater than m, indicating the end of the range. For example, (ba){0,3} matches up to three pairs of the expression "ba".
  • An excellent reference on regular expressions is Mastering Regular Expressions, Jeffrey E. F. Friedl. O'Reilly & Associates, Inc., 1997. ISBN: 1-56592-257-3, http://www.oreilly.com.


 
 
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