Regular Expressions Are Your Friend

This was a talk given by me at WindyCityRails, its a combined talk with choices to do the basics or advanced. The audience chose the advanced side of the talk.

Regular Expressions help you find that needle in the haystack, where Waldo might be, or the location of Jimmy Hoffa’s body. You’ll find them in most programming languages and tools, but they can do so much more than checking an e-mail address! We’ll go over the basics as well as advanced topics and you’re encouraged to follow along as the examples are shown.

Video here: http://vimeo.com/31204910

Transcript

1. Regular Expressions are your friend
4. Hello
5. Aaron Kalin @martinisoft
7. We’re hiring!
11. Warning (memes ahead!)
12. Interaction!
13. Regular Expressions
14. Regex
15. Pattern
16. /Pattern/
17. Subject
18. Match
19. Editors vim emacs TextMate RubyMine Redcar BBEdit ...
20. Languages perl ruby python lua java javascript ...
21. Meta language
24. Menu
25. history basics good practices ruby tips
26. History
27. A long time ago in a galaxy far, far away...
28. Seriously
29. Ed 1971 ( Ken Thompson )
30. g/re/p
31. g/re/p global regular expression print
32. grep 1973 (Ken Thompson)
33. self.clone! egrep fgrep sed awk lex
34. Perl 1987 ( Larry Wall )
35. Regular Expressions Package 1987 (Henry Spencer)
36. Perl 5 1994
37. PCRE 1994
38. Perl
39. Compatible
40. Regular
41. Expressions
42. Basics
43. Follow Along Rubular (Ruby 1.8 Regex Tester) http://www.rubular.com/ RubyXP (Ruby 1.9 Regex Tester) http://www.rubyxp.com/
44. /^Hello [Ww]orld.?$/
45. Literal Characters
46. Any Letter or Number Including blank space!
47. Metacharacters There are a few
48. [ \ ^ $ . | ? * + ( )
49. // (the construct)
50. Anchor Characters ^ (beginning) $ (end)
51. Character Matchers . (Any Character) \d (Any Number) \s (Any Whitespace) \w (Any Word Character)
52. Quantifiers * (Zero or more) + (One or more) ? (One or None) {n,m} (Only n matches up to m)
53. Quantifiers (part Deux) Changes the number of matches to the left of the quantifier. a* (if there, match a, keep going) a+ (must match a, keep going) a? (if there, match a) a{1,3} (matches a or aa or aaa)
54. Character Classes [] (Matches groups of literal characters) [^] (Don’t match any of these characters)
55. Character Classes (gotcha) [.+*] (Matches a dot, plus or splat) Any meta character inside a character class becomes a literal character
56. Character Classes (part Deux) \w = [A-Za-z0-9_] \W = [^A-Za-z0-9_] \s = [ \t\r\n] The - is a range of literal characters
57. Grouping Combine matches into groups using ( and ) surrounding your matches. (Hello) World Matches Hello World and Hello separately
58. Escaping (from alcatraz) Use \ to turn a metacharacter into a literal . Matches anything \. Matches a period
59. /^Hello [Ww]orld.?$/
60. Break it Down!
61. /^Hello [Ww]orld.?$/
62. /^Hello [Ww]orld.?$/ Beginning End Exact letters H e l l o (including space) Exact letters o r l d Anything Maybe once? Capital or lower-case W
63. /Hello World/ Hello World Hi, Hello World Say Hello World
64. /^Hello World$/ Hello World Hi, Hello World Say Hello World
65. /^Hello World.?$/ Hello World Hello World! Hello, World! Hello, World
66. /^Hello [Ww]orld.?$/ Hello World! Hello world Hello World Hello, world!
67. /^Hello [Ww]orld.?$/
68. /^Hello [Ww]orld.?$/ Beginning End Exact letters H e l l o (including space) Exact letters o r l d Anything Maybe once? Capital or lower-case W
70. Good Practices
71. Be Precise
73. Don’t Be Greedy!
75. Precision Matches exactly what you want
76. Greed Matches everything you don’t want
77. Precision vs Greed Be as specific as you can! Avoid use of the dot . Avoid greedy quantifiers + or .+
78. Precise! /[0-9]{5}(-[0-9]{4})?/ 12345 12345-6789 867-5309
79. Greedy! /[0-9]+(-[0-9]+)?/ 12345 12345-6789 867-5309
80. ruby (the highlights)
82. Basic Regex if /Bacon/ =~ “Chunky Bacon” puts “Bacon!” end => “Bacon!”
83. Match “Chunky Bacon”.match(/Bacon/).to_s => “Bacon”
84. Match (Part Deux) regex = %r{ Bacon }x regex.match(“Chunky Bacon”).to_s => “Bacon”
85. Gsub “Chunky Bacon”.gsub(/Bacon/, “Foo”) => “Chunky Foo”
86. Options Matching options (usually added after the second /) i - case insensitive o - interpolate once (#{}’s) m - multiline mode (‘.’ matches \n) x - extended mode (ignore whitespace)
87. Options (Extended Dvd Edition) “Chunky Bacon”.match(/bacon/i).to_s => “Bacon”
88. 1.9 Only (but possible with Oniguruma gem)
89. POSIX Matchers [:alpha:] = [a-zA-Z] [:alnum:] = [a-zA-Z0-9] Many, many more
90. Arrays? str = “Chunky Bacon” str[/Bacon/] => “Bacon”
91. Assertions (?=) Look Ahead (?!) Negative Look Ahead (?<) Look Behind (?<!) Negative Look Behind (?(if) then | else) Conditional
92. And Many More Checkout Oniguruma Gem
93. Questions?
94. Menu
95. brain.reload assertions
96. Follow Along RubyXP (Ruby 1.9 Regex Tester) http://www.rubyxp.com/ Graffiti (RubyGem) http://rubygems.org/gems/graffiti gem install graffiti
97. brain.reload
98. /^Hello [Ww]orld.?$/
99. /^Hello [Ww]orld.?$/ Beginning End Exact letters H e l l o (including space) Exact letters o r l d Anything Maybe once? Capital or lower-case W
100. Literal Characters
101. Any Character
102. /Chunky Bacon/ Chunky Bacon ChunkyBacon
103. Meta Characters
104. [ \ ^ $ . | ? * + ( )
105. Grouping
106. Grouping Hello world Hello (world) Hello world world
107. Quantifiers
108. Quantifiers * (Zero or more) + (One or more) ? (One or None) {n,m} (Only n matches up to m)
110. Assertions
111. Lookahead
112. Lookbehind
113. Lookaround
114. Zero-Width Assertions
115. IF - ELSE
116. /^Hello [Ww]orld.?$/
117. /^Hello [Ww]orld.?$/ Start Here
118. /^Hello [Ww]orld.?$/ Start Here Walk this way
119. Lookaround
120. Positive
121. Negative
122. Positive = True
123. Negative = False
124. Break it Down!
125. Lookahead
126. Lookahead /b(?=a)/ <- Positive /b(?!a)/ <- Negative
127. Lookahead (positive) /b(?=a)/ bacon beacon
128. Lookahead (positive) /b(?=a)/ Match b
129. Lookahead (positive) /b(?=a)/ Match b If (true)
130. Lookahead (positive) /b(?=a)/ Match b If (true) Followed by a
131. Lookahead (positive) /b(?=a)/ bacon beacon
132. Zero-Width Assertions
133. Lookbehind
134. Lookbehind /(?<=o)l/ <- Positive /(?<!o)l/ <- Negative
135. Lookbehind (positive) /(?<=o)l/ pool peel
136. Lookbehind (positive) /(?<=o)l/ If (true)
137. Lookbehind (positive) /(?<=o)l/ If (true) Preceded by o
138. Lookbehind (positive) /(?<=o)l/ Match L If (true) Preceded by o
140. Examples
141. validates_length_of :title, minimum: 2
142. validates :title, length: { minimum: 2 }
143. /(?=.{2,}).+/
144. /(?=.{2,}).+/ T i t l e
145. /(?=.{2,}).+/ T i t l e
146. /(?=.{2,}).+/ T i t l e
147. /(?=.{2,}).+/ T i t l e
148. /(?=.{2,}).+/ T i t l e
149. /(?=.{2,}).+/ T i t l e
150. /(?=.{2,}).+/ T i t l e
151. MOAR?
152. number_to_currency
153. /(\d)(?=(\d{3})+(?!\d))/
155. “1000000.00”.gsub /(\d)(?=(\d{3})+(?!\d))/, ‘\1,’ 1,000,000.00
156. 1000000.00 /(\d)(?=(\d{3})+(?!\d))/
157. /(\d)(?=(\d{3})+(?!\d))/ Match a number 1000000.00
158. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) 1000000.00
159. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead 1000000.00
160. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more Followed by non-number 1000000.00
161. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1000000.00 Followed by non-number
162. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1000000.00 Followed by non-number
163. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1000000.00 Followed by non-number
164. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
165. /(\d)(?=(\d{3})+(?!\d))/ Match a number 1,000000.00
166. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) 1,000000.00
167. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00
168. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
169. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
170. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
171. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number FALSE
172. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
173. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
174. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number FALSE
175. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
176. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
177. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
178. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000000.00 Followed by non-number
179. /(\d)(?=(\d{3})+(?!\d))/ Match a number If (true) Look for 3 numbers ahead at least once or more 1,000,000.00 Followed by non-number
181. Resources Rubular (Ruby 1.8 Regex Tester) http://www.rubular.com/ Ruby Expressions http://rubyexpressions.com http://regular-expressions.info
182. fin!
183. Thank you! Windy City Rails Organizers! Derek Weathersbee (Franchise Font) http://vurl.me/AZSG Raph Levien (Inconsolata Font) http://vurl.me/AZSH
184. aaron.inspect “web” => martinisoftware.com “twitter” => @martinisoft “github” => martinisoft “spkr8” => spkr8.com/t/8317