How to Use gsub in Ruby: Replace Text Easily

In Ruby, gsub is a method used to replace all occurrences of a pattern in a string with a specified replacement. You call it on a string like string.gsub(pattern, replacement), where pattern can be a string or regular expression, and it returns a new string with replacements.

Syntax

The gsub method replaces all matches of a pattern in a string with a replacement. It does not change the original string but returns a new one.

• string: The original text you want to change.
• pattern: What you want to find. It can be a simple string or a regular expression.
• replacement: The text you want to use instead of the found pattern.

ruby

string.gsub(pattern, replacement)

Example

This example shows how to replace all spaces with dashes in a sentence using gsub. It demonstrates how the method returns a new string with changes but keeps the original string unchanged.

ruby

sentence = "I love ruby programming"
new_sentence = sentence.gsub(" ", "-")
puts new_sentence
puts sentence

Output

I-love-ruby-programming
I love ruby programming

Common Pitfalls

One common mistake is expecting gsub to change the original string. It returns a new string instead. To change the original string, use gsub! with an exclamation mark.

Another mistake is using a string pattern when a regular expression is needed for more complex matching.

ruby

text = "hello world"
text.gsub("world", "Ruby")
puts text  # prints original text, no change

text.gsub!("world", "Ruby")
puts text  # original text changed

Output

hello world
hello Ruby

Quick Reference

Usage	Description
string.gsub(pattern, replacement)	Returns new string with all matches replaced
string.gsub!(pattern, replacement)	Replaces all matches in original string (in-place)
pattern can be String or Regexp	Use Regexp for flexible matching
replacement can be String or block	Block allows dynamic replacement

Key Takeaways

Use gsub to replace all occurrences of a pattern in a string and get a new string.

gsub does not modify the original string; use gsub! to change it in place.

Patterns can be simple strings or powerful regular expressions.

You can use a block with gsub for custom replacement logic.

Remember gsub returns a new string, so assign or use the result.