• By the end of this lesson you should be able to write regular expressions to:

  *

  1) test a string to see whether it matches a pattern.

  *

  2) extract from a string the sections that match all or part of a pattern.

  *

  3) change the string, replacing parts that match a pattern.

• Regular Expressions are a part of many programming languages: Ruby, JS, Perl, Python, Java, unix shell scripts (grep) ...

• Regular Expressions are used for pattern matching, find and replace tasks.

• Good for model validations: valid email format, valid phone format, valid ssn ...

• Regex is real cryptic code. You have to decipher it to understand it.

• The strategy is to only match what you want.

• Each character in a regex is either a metacharacter with special meaning, or a regular character with its literal meaning.

• Exact pattern matches

  *

  Place exact string between to forward slashes: /cat/ matches "cat"

  *

  However, /cat/ also matches "catastrophe" and "scat"

• Use metacharacters to be more specific on what you match.

• Type this sentence into Rubular (http://www.rubular.com/) and follow along.

• Dogs are not dogmatic about dog things unlike Madog the bad dog.

• .match(/regex matcher/, "replacement string")

• "I love my cat.".match(/cat/)

• match[0] => cat

  string = "I love my cat."

  if string.match(/cat/)

  puts "I found a match."
  

  end

• . - wild card, matches any char

• \ - escape a character, turns a metacharacter into a string literal - to match a literal period use \\.

• | - logical or, /cat|dog/ matches "cat" or "dog"

• \s - matches any whitespace

• \S - matches any non-whitespace

• ^ - start of line

• $ - end of line

• /cAt/i - "/i" case insensitive, matches Cat, cAt, CAT, CaT, cat ...

• open "match_string.rb" in sublime, and follow the instructions within

• run using: $ruby match_string.rb string_data

• Type this into Rubular (http://www.rubular.com/) and follow along.

• 2014-03-01

• see file: data_decomp.rb

• (...) - enclosed matches are assigned variable names $1+ that can be reused

• [] - range of characters or numbers to match: [0-9] or [a-z]

• \d - any digit, same as [0-9]

• \D - any non-digit

• {} - exact number of times character or number is repeated, a{2} == "aa"

• + - one or more

• * - zero or more

• ? - zero or one

• open "real_time_data.rb" in sublime, and follow the instructions within

• run using: $ruby read_time_data.rb time_data

• Commands: .sub and .gsub

• .sub substitutes on first match, .gsub substitutes globally all matches

• Syntax: my_string.sub( /sub string to match/ , "replacement sub string" )

• "That is a cute dog.".sub(/dog/, "cat") => "That is a cute cat."

• Can be chained together:

  *

  "Red is my favorite color, I just love red".sub(/red/, "blue").sub(/Red/,"Blue")

• open "find_replace.rb" in sublime, and follow the instructions within

• run using: $ruby find_replace.rb find_replace_data

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