RegEx : Expressions and Parsing Examples

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RegEx Expressions and Parsing Examples
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Overview

• What is RegEx
• Purpose of RegEx
• How it Works
• Advantages
• Demonstration
• QA

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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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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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How it Works

• Regular Expressions Exact Matches

c k s
regular expression
rocks.
match
is okay.
no match
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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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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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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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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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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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Questions ?
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