Ruby Regex: Pattern Matching Made Simple
Regular expressions (regex) in Ruby are powerful tools for pattern matching and text manipulation. Let’s dive into the essentials with practical examples you can use immediately.
Basic Syntax
Ruby provides two ways to create regex patterns:
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| # Literal notation
pattern = /hello/
# Constructor method
pattern = Regexp.new("hello")
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Common Matching Methods
match - Returns MatchData object
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| email = "user@example.com"
result = email.match(/@(.+)\.(.+)/)
puts result[1] # "example"
puts result[2] # "com"
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=~ - Returns position of match
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| text = "The price is $25"
position = text =~ /\$\d+/
puts position # 13
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scan - Returns all matches
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| text = "Call me at 123-456-7890 or 987-654-3210"
phones = text.scan(/\d{3}-\d{3}-\d{4}/)
puts phones # ["123-456-7890", "987-654-3210"]
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Essential Patterns
| Pattern |
Meaning |
Example |
\d |
Digit |
/\d{3}/ matches “123” |
\w |
Word character |
/\w+/ matches “hello” |
\s |
Whitespace |
/\s+/ matches spaces |
. |
Any character |
/h.llo/ matches “hello” |
^ |
Start of string |
/^Hello/ |
$ |
End of string |
/world$/ |
Practical Examples
1. Email Validation
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| def valid_email?(email)
email.match?(/\A[\w+\-.]+@[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i)
end
puts valid_email?("test@example.com") # true
puts valid_email?("invalid-email") # false
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| text = "Contact: (555) 123-4567 or 555.987.6543"
phones = text.scan(/\(?\d{3}\)?[\s.-]?\d{3}[\s.-]?\d{4}/)
puts phones # ["(555) 123-4567", "555.987.6543"]
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3. URL Parser
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| url = "https://www.example.com/path?param=value"
match = url.match(/^(https?):\/\/([^\/]+)(\/[^?]*)?\??(.*)$/)
puts "Protocol: #{match[1]}" # https
puts "Domain: #{match[2]}" # www.example.com
puts "Path: #{match[3]}" # /path
puts "Query: #{match[4]}" # param=value
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4. Password Strength Checker
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| def strong_password?(password)
return false if password.length < 8
return false unless password.match?(/[A-Z]/) # uppercase
return false unless password.match?(/[a-z]/) # lowercase
return false unless password.match?(/\d/) # digit
return false unless password.match?(/[!@#$%^&*]/) # special char
true
end
puts strong_password?("MyPass123!") # true
puts strong_password?("weak") # false
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5. Text Cleaning and Replacement
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| # Remove extra whitespace
text = "Too many spaces"
clean = text.gsub(/\s+/, " ")
puts clean # "Too many spaces"
# Extract hashtags
tweet = "Loving #ruby and #programming today!"
hashtags = tweet.scan(/#\w+/)
puts hashtags # ["#ruby", "#programming"]
# Mask credit card numbers
card = "My card number is 1234-5678-9012-3456"
masked = card.gsub(/\d{4}-\d{4}-\d{4}-(\d{4})/, "****-****-****-\\1")
puts masked # "My card number is ****-****-****-3456"
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Modifiers
Add flags after the closing / to modify behavior:
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| # Case insensitive
/hello/i.match("HELLO") # matches
# Multiline mode
/^start/m.match("line1\nstart here") # matches
# Extended mode (ignore whitespace)
pattern = /
\d{3} # area code
- # separator
\d{4} # number
/x
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Quick Tips
- Use
match? for boolean checks - it’s faster than match when you only need true/false
- Escape special characters with backslash:
\., \$, \(
- Use raw strings for complex patterns:
%r{pattern} instead of /pattern/
- Test your regex - use online tools or IRB to verify patterns
Common Gotchas
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| # Wrong: . matches any character
"hello world".match(/hello.world/) # matches "hello world"
# Right: escape the dot
"hello.world".match(/hello\.world/) # matches "hello.world"
# Wrong: greedy matching
"<tag>content</tag>".match(/<.+>/) # matches entire string
# Right: non-greedy matching
"<tag>content</tag>".match(/<.+?>/) # matches "<tag>"
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Ruby’s regex engine is both powerful and intuitive. Start with these examples and gradually build more complex patterns as needed. Remember: readable code is better than clever regex - use them wisely!