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RegEx : Expressions and Parsing Examples
| Date post: | 05-Jul-2015 |
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Technology |
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RegEx : Expressions and Parsing Examples
Overview
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What is RegEx
Purpose of RegEx
How it Works
Advantages
Demonstration
Q&A
Introduction to RegEx
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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.
Purpose of RegEx
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To match the pieces of text within a larger document.
To capture the string.
RegEx is used in PERL, Java and other programming languages.
How it Works
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Regular Expressions: Exact Matches
rocks.
match
regular expression c k s
is okay.no match
How it Works
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Regular Expressions: Multiple Matches
Scrapple from the apple.
match 1 match 2
regular expression a p p l e
Metacharacters of RegEx
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. - 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
Metacharacters of RegEx
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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.
Quantifier
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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.
Advantages
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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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