Transcript Ruby - Colorado School of Mines

Ruby Regular Expressions
AND OTHER LANGUAGES…
Why Learn Regular Expressions?
 RegEx are part of many programmer’s tools
 vi, grep, PHP, Perl
 They provide powerful search (via pattern matching)
capabilities
 Simple regex are easy, but more advanced patterns
can be created as needed
From: http://www.websiterepairguy.com/articles/re/12_re.html
Regular Expressions in Ruby
 Objects of type Regexp
 Matched using =~ operator
 Constructed as
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/pattern/
/pattern/options
%r{pattern}
%r{pattern}options
Regexp.new
 Options provide additional info about how pattern match
should be done, for example:
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i – ignore case
m – multiline, newline is an ordinary character to match
u,e,s,n – specifies encoding, such as UTF-8 (u)
From: http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UJ
Simple Example
s = "ruby is cool"
s2 = "i love ruby!"
if s =~ /Ruby/i
puts "found Ruby - case
insensitive"
end
if s =~ /[Rr]uby/
puts "found Ruby - Rr option"
end
if s =~ /\Aruby/
puts "found Ruby at beginning"
end
if s2 =~ /\Aruby/
puts "found Ruby at beginning"
else
puts "ruby is not at the beginning"
end
s3 = "I love Java and Ruby and PHP"
if s3 =~ /Java|PHP/
puts "what, another language?"
end
partNum = "aZ2"
if partNum =~ /[a-z][A-Z][0-9]/
puts "part number is lower-case
then upper-case then digit"
end
anotherPart = "A45@"
if anotherPart =~ /.[0-9]+@/
puts "another part is any character,
some digits, @"
end
Play with Regex: rubular.com
Quick Exercise
 Create regex for the following. Use rubular.com to
check it out.
 Phone numbers
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(303) 555-2222
303.555.2222
3035552222
 Date
 nn-nn-nn
 Try some other options
Some Resources
 http://www.bluebox.net/about/blog/2013/02/using
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regular-expressions-in-ruby-part-1-of-3/
http://www.ruby-doc.org/core-2.0.0/Regexp.html
http://rubular.com/
http://coding.smashingmagazine.com/2009/06/01/essent
ial-guide-to-regular-expressions-tools-tutorials-andresources/
http://www.ralfebert.de/archive/ruby/regex_cheat_sheet/
http://stackoverflow.com/questions/577653/differencebetween-a-z-and-in-ruby-regular-expressions (thanks, Austin
and Santi)
Topic Exploration
 http://www.codinghorror.com/blog/2005/02/regex-use-vs-regex-abuse.html
 http://programmers.stackexchange.com/questions/113237/when-you-should
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not-use-regular-expressions
http://coding.smashingmagazine.com/2009/05/06/introduction-toadvanced-regular-expressions/
http://stackoverflow.com/questions/5413165/ruby-generating-new-regexpsfrom-strings
A little more motivation to use…
http://blog.stevenlevithan.com/archives/10-reasons-to-learn-and-use-regularexpressions
http://www.websiterepairguy.com/articles/re/12_re.html
Submit on BB (3 points) and report back: 3-5 things you want to remember
about regex. Include the URL. Feel free to read others not in the list.
In-class Challenge
 Review one of the regex cheat sheets
 Make up a pattern (e.g., part numbers, foreign
telephone numbers, dates, parse an error log, etc.).
Try to use as many aspects of regex as you can. For
example, when I pay VISA online, my confirmation
includes an embedded date and some other
encoding. Create examples of your pattern
 Have your neighbor try to recreate your pattern.
 Nothing to submit.
Is this exercise intended to explore good uses of regex? NO! It’s
just a logic puzzle and refresher (or intro) to regex syntax.