What is a regular expression?

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Question
What is a regular expression?

Answer
ResponseMailer allows you to specify the method to use when evaluating a filter condition. You can choose to use :
Normal - for simple words and pharses
Wildcards - for words and pharses with missing letters
Regular Expreession - for complex words and phrases


Regular Expression

• A regular expression is a compact way of describing complex patterns in texts.
  
• It is a formula for matching strings that follow some pattern.
  
• A regular expression is a pattern describing a certain amount of text.
  
• A regular expression is a text pattern consisting of a combination of alphanumeric characters and special characters known as metacharacters. A close relative is in fact the wildcard expression which are often used in file
  

Here are a few examples

• |
  A vertical bar separates alternatives. For example, "gray|grey" matches grey or gray.
  
  
• A quantifier after a character specifies how often that character is allowed to occur. The most common quantifiers are +, ?, and *:
  
• +
  The plus sign indicates that the preceding character must be present at least once. For example, "goo+gle" matches the infinite set google, gooogle, goooogle, etc.
  
• ?
  The question mark indicates that the preceding character may be present at most once. For example, "colou?r" matches color and colour.
  
• *
  The asterisk indicates that the preceding character may be present zero, one, or more times. For example, "0*42" matches 42, 042, 0042, etc.
  
  
• ( )
  Parentheses are used to define the scope and precedence of the other operators. For example, "gr(a|e)y" is the same as "gray|grey", and "(grand)?father" matches both father and grandfather.
  

Additional links on Regular Expression
Learning to Use Regular Expressions by Example
A Tao of Regular Expressions
Regular expression, From Wikipedia
Regular Expression Basics
Regular Expressions explained