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Regular Expressions What are they and what can they do for you?
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\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2-4}\b
Source: http://www.regular-expressions.info/email.html
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So...what is a regular expression?
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A Regular Expression is a pattern for a string.
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What can you do with Regular Expressions?
Test a stringExtract a stringChange a string
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Creating Regular Expressions
/RegularExpression/
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Scenario #1Testing Strings
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Examples from “Programming Ruby” (PickAxe)
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“dog and cat”
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“dog and cat”
/cat/
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“dog and cat”
/cat/
/cat/ =~ “dog and cat”
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=~/cat/ =~ “dog and cat”
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match/cat/.match(“dog and cat”)
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Valid Emails
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Alternation/Nell | Brandon/
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Metacharacters
any single character
character can appear any number of times
.*
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.*//matches ANYTHING
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Range[a-d] [1-4]
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Shorthand!
\w stands for any word character.
It’s the same as:[a-zA-Z0-9_]
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Metacharacters
character occurs one or more times+
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Scenario #2Extracting Strings
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Shorthand!
\d stands for any digit
\D stands for any non-digit
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Repetition!
\d{3} Looks for exactly 3 digits
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Make It Optional!
?Makes a character
optional. It can occur 0 or 1 time.
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Scenario #3Changing Strings
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“Brandon is the teacher of the class right now. Brandon is teaching about regular expressions.”
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sub(/pattern/, “text”)
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gsub(/pattern/, “text”)
(replace ALL the matches)
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sub and gsub create new strings. sub! and gsub! change the original strings
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Welcome to the wonderful world of Regular Expressions!
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