LYCOS RETRIEVER 
Regular Expression
built 180 days ago
Regular Expressions are a feature of UNIX. They describe a pattern to match, a sequence of characters, not words, within a line of text. Here is a quick summary of the special characters used in the grep tool and their meaning:
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The use of Regular Expressions it beyond the scope of this User Guide... there are many resources on the Internet to help learn how to create Regular Expressions for use in this Validator. Form Master provides 4 built-in expressions which are:
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Basically, Regular Expressions are made up of normal characters and meta characters. Normal characters include upper and lower case letters and digits. The meta characters are special characters and have special meanings. Understanding meta characters really make good use of regular expressions.
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Regular Expressions were never developed to be easy to understand. They are a condensed shorthand that, on preliminary inspection, looks as if someone has repeatedly sat on the keyboard. Even when interpreted, the logic isn't always easy to follow. If you don't agree, then explain this one!
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Grammars describing the syntax of both basic and extended regular expressions are presented in this section. The grammar takes precedence over the text. See the Shell and Utilities volume of IEEEStd1003.1-2001, Section 1.10, Grammar Conventions.
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Using a backreference is how you finally get to witness the real power of regular expressions. Extracting a list of links from a page of source is useful, but nowhere as useful as being able to do something with that data. Parentheses can be used to "remember" a subexpression, and a backreference in the form of \digit is how you refer to that particular group. Parentheses are counted from left to right within the expression, so the first open parentheses group has a backreference of \1, the second has a backreference of \2, and so on. You can use the memory-like functionality of a backreference in a replace string.
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Regular Expression