Modifying Regular Expressions in Ruby

Regular expressions are powerful pattern-matching tools. They use a specialized syntax to define search patterns within strings. In Ruby, these patterns are typically written as literals enclosed in slashes (e.g., /pattern/) or, more flexibly, using the %r operator followed by arbitrary delimiters (e.g., %r{pattern}).

Syntax

/pattern/
/pattern/im    # option can be specified
%r!/usr/local! # general delimited regular expression

Example

#!/usr/bin/ruby

line1 = "Cats are smarter than dogs";
line2 = "Dogs also like meat";

if ( line1 =~ /Cats(.*)/ )
   puts "Line1 contains Cats"
end
if ( line2 =~ /Cats(.*)/ )
   puts "Line2 contains  Dogs"
end

This will result in the following outcome:

Line 1 has cats.

Ruby Regex Modifiers

Ruby’s regular expression literals can be fine-tuned using optional modifiers placed after the closing slash. These modifiers, represented by single characters, alter the matching behavior in various ways.

Ruby lets you start regular expressions with %r and then a delimiter of your choice, just like string literals delimited with %Q. When the pattern you are describing has a lot of forward slash characters that you don’t want to escape, this is helpful.

# Following matches a single slash character, no escape required
%r|/|

# Flag characters are allowed with this syntax, too
%r[</(.*)>]i

Understanding Ruby Regex Patterns

Every character matches itself, with the exception of the control characters (+ ? . * ^ $ ( ) [ ] { } | / ). By using a backslash before a control character, you can get out of it.

String Manipulation with Regex in Ruby

Sub, gsub, and their in-place versions sub! are some of the most significant String techniques that make use of regular expressions. as well as gsub.

All of these strategies perform a search-and-replace operation utilizing a Regexp design. The sub & sub! replaces the to begin with event of the design and gsub & gsub! replaces all events.

The sub and gsub returns a unused string, clearing out the unique unmodified whereas sub! and gsub! adjust the string on which they are called.

Here’s an example:

#!/usr/bin/ruby

phone = "2004-959-559 #This is Phone Number"

# Delete Ruby-style comments
phone = phone.sub!(/#.*$/, "")   
puts "Phone Num : #{phone}"

# Remove anything other than digits
phone = phone.gsub!(/\D/, "")    
puts "Phone Num : #{phone}"

This will result in the following outcome –

Phone Num : 2004-959-559
Phone Num : 2004959559

Here’s an example:

#!/usr/bin/ruby

text = "rails are rails, really good Ruby on Rails"

# Change "rails" to "Rails" throughout
text.gsub!("rails", "Rails")

# Capitalize the word "Rails" throughout
text.gsub!(/\brails\b/, "Rails")
puts "#{text}"

The outcome of this will be as follows –

Rails is Rails, and Ruby on Rails is excellent.