The document provides an overview of regular expressions (regex), explaining their purpose, functionality, and advantages. Regex matches patterns within text using characters, metacharacters, and quantifiers, making it useful for various programming languages. Additionally, it highlights the ease of use for non-programmers and its applications in compiler construction.

1. RegEx : Expressions and
Parsing Examples

2. Overview
 What is RegEx
 Purpose of RegEx
 How it Works
 Advantages
 Demonstration
 Q&A
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3. Introduction to RegEx
 RegEx is a sequence of characters for a search to match a
pattern.
 Arose in the 1950 by Stephen Kleene, an American
Mathematician.
 Regular expressions are composed of characters,
metacharacters and quantifiers.
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4. Purpose of RegEx
 To match the pieces of text within a larger document.
 To capture the string.
 RegEx is used in PERL, Java and other programming
languages.
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5. How it Works
 Regular Expressions: Exact Matches
regular expression
cks
rocks.
match
is okay.
no match
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6. How it Works
 Regular Expressions: Multiple Matches
regular expression
a p p l e
Scrapple from the apple.
match 1
match 2
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7. Metacharacters of RegEx
.
- Matches any single character.
 d - Matches a digit character.
 s - Matches any whitespace character including space, tab,
form-feed, etc.
 w - Matches any word character including underscore.
 n
- Matches a newline character.
^
- The beginning of a line
$
- The end of a line
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8. Metacharacters of RegEx
 abc
- Exactly this sequence of three letters
 [abc]
- Any one of the letters a, b, or c
 [^abc]
- Any character except one of the letters a, b, or c
 [a-z]
- Any one character from a through z
 [a-zA-Z0-9]-Any one letter or digit.
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9. Quantifier
Quantifier specify the number of string pattern should
occur in matching string.
*
- Zero or more times.
+
- One or more times.
?
- Zero or one time
 {m,n}
- Matches for atleast m times and atmost n times.
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10. Advantages
 The regular expression syntax is declarative: The pattern
"looks like" what you want to match.
 Easily compatible with different programing languages.
 Easier for non-programmers than code.
 Less error prone than code.
 Use in Compiler Construction.
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