Regular Expressions - Refactoring HTML: Improving the Design of Existing Web Applications - page 303

Appendix A. Regular Expressions

Regular expressions enable one to search for common patterns in text files. Many tools support regular-
expression-based search and replace. Although there are small differences in syntax from one tool to the next,
most of the syntax and the basic ideas are much the same.

Characters That Match Themselves

The first rule of regular expressions is that most normal characters match themselves. A "normal" character is a
letter, a digit, or a space. Thus, the regular expression "Al Gore was elected president in the year 2000"
matches exactly the string "Al Gore was elected president in the year 2000" and no others. Searching for that
string will find all occurrences of that exact string in the searched document or documents. However, it will not
find even slight variations, such an extra space between the words Al and Gore . Table A.1 shows some more
examples.

Table A.1. Characters That Match Themselves

Pattern Matches Example

Foo The string Foo Foo

foo The string foo Foo

foo bar The string foo bar foo bar

2000 The string 2000 2000

a e The string a e a e

<!DOCTYPE The string <!DOCTYPE <!DOCTYPE

<p> The string <p> <p>

</p> The string </p> </p>

To be specific, the following characters match themselves:

All ASCII letters A-Z and a-z

The ASCII digits 0-9

The space character

All non-ASCII characters: é, ç,... and so on

The following ASCII punctuation characters:

!