Regular Expressions in Ruby

=~ and #match operators

The pattern matching is achieved by =~ and #match operator.

Let us discuss them in detail:

=~ operator 

The first is a regular expression, and the second is a string. The string is matched with the regular expression.

If a match is found, the operator returns the index of the first match; otherwise, it returns nil.
 

For example:
 

# Find the word 'Ninja'
puts "Are you a Ninja?" =~ /Ninja/ 

 

Output 

Explanation

This returns the index of the first occurrence of the matched word, if not matched nil is returned. Henceforth, 10 is returned!

Let us one more example: 
 

# Find the word 'Coder’'
puts "Are you a Ninja?" =~ /Coder/   #nil

 

#match operator 

If a match is found, this operator returns a MatchData object; otherwise, it returns nil.
 

For example:

# Find the word 'Coder'
puts /coder/.match("Are you a coder?")

 

Output

Meta Characters and Escapes 

In a pattern, metacharacters have a specific meaning. They are back slashed (\) or escaped to match a string.

Some meta characters are (,), (.), (?), (+), (-), (*), [,], {,}.
 

When a match is found, it returns the specific string; otherwise, it returns nil.
 

For example:
 

puts /Hello\! I am new here\./.match("Ninja here, Hello! I am new here.")
puts /3 \* 4 \+ 5 = \?/.match("3 * 4 + 5 = ?")
puts /3 * 4 + 5 = ?/.match("3 * 4 + 5 = ?")

 

Output

Characters Classes 

Metacharacters have specific meaning in a pattern. To match a string, they are back slashed (\\\) or escaped.

A character class is encircled within square brackets.

[pq..]

Here, [pq] denotes either p or q. It is the inverse of /pq/, which stands for p and q.

For example:

puts /C[aeivo]ding/.match("Coding Ninjas")
puts /C[aei]ding/.match("Coding Ninjas")

 

Output

[p - s]

 

• Here, [p-s] is equivalent to [pqrs]. 
• The hyphen (-) character class represents a range of characters.
   

For examples:

 

puts /[a-d]/.match("Java")
puts /[p-s]/.match("Pythonista")
puts /[L-P]/.match("Programmer")

 

Output

[^p-s]

The ^ sign represents any other character that is not present in the range.

puts /[^a-rs-z]/.match("Ga")
puts /[^a-fe-p]/.match("Pys")
puts /[^L-P]/.match("Pro")

 

Output

So far we’ve discussed pattern matching for single characters. With the help of repetition metacharacter, we can specify how many times they need to occur. These meta characters are called quantifiers.

Quantifiers

Quantifiers allow you to specify the count of repeated strings.

Check out this problem - Shortest Common Supersequence.

Frequently Asked Questions

What is regex?

The regex or regexp is the acronym for 'regular expression', which is a sequence of characters that describes a search pattern in the text.

What is a delimiter?

One or more characters which divide text strings are known as delimiters. Commas (,), semicolons (;), quotes (", "), braces (), pipes (|), and slashes (/) are common delimiters.

Where are textual patterns utilised?

Textual patterns are typically utilised by string-searching algorithms for input validation or 'find' or 'find-and-replace' operations on strings.

What are Expression and Operator?

An expression is a section of Ruby code that the Ruby interpreter can evaluate to produce a value. An operator is a token or a particular symbol in the Ruby language representing an operation (such as addition or comparison) performed on one or more operands.

What are the uses of regular expressions in Ruby?

A string of characters known as a regular expression defines a search pattern, typically used in string pattern matching. Regular expressions in ruby help us to search for specific patterns within strings. Validation and parsing are two applications of ruby regex.

Conclusion

This article extensively discussed Regular Expressions in Ruby. We started with a brief introduction to regular expression and then learnt about regex literals, regex factory methods, regex syntax and pattern matching with regular expression.

After reading about Regular Expressions in Ruby, are you not feeling excited to read/explore more articles on the topics related to Ruby?. To learn, see History of Ruby, eight reasons why Ruby should be your first language, Ruby vs Python, Documentation of Ruby, Official Ruby FAQ, and Learn Ruby with the Edgecase Ruby Koans.

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