How to Use gsub with Regex in Ruby: Simple Guide

In Ruby, you can use gsub with a regular expression by passing the regex as the first argument and the replacement string as the second. This method searches the string for all matches of the regex and replaces them with the given replacement.

Syntax

The gsub method replaces all occurrences of a pattern in a string. When using regex, the pattern is a regular expression object.

• string.gsub(/pattern/, 'replacement'): replaces all matches of pattern with replacement.
• The /pattern/ is a regex literal in Ruby.
• The replacement can be a string or a block for dynamic replacements.

ruby

string = "hello 123 world 456"
result = string.gsub(/\d+/, "number")
puts result

Output

hello number world number

Example

This example shows how to replace all digits in a string with the word "number" using gsub and a regex.

ruby

text = "My phone is 555-1234 and my zip is 90210."
new_text = text.gsub(/\d+/, "[digits]")
puts new_text

Output

My phone is [digits]-[digits] and my zip is [digits].

Common Pitfalls

One common mistake is using gsub with a string pattern instead of a regex when you want pattern matching. Also, forgetting to escape special regex characters can cause unexpected results.

Another pitfall is using gsub when you only want to replace the first match; in that case, use sub instead.

ruby

wrong = "abc123".gsub("\d+", "X") # This replaces the literal string "\d+", not digits
correct = "abc123".gsub(/\d+/, "X") # This replaces digits correctly
puts wrong
puts correct

Output

abc123
abcX

Quick Reference

Usage	Description
string.gsub(/pattern/, 'replacement')	Replace all matches of regex pattern with replacement string
string.gsub(/pattern/) { |match| block }	Replace matches using a block for dynamic replacement
string.sub(/pattern/, 'replacement')	Replace only the first match of regex pattern
Escape special chars in regex	Use backslash (\) before special characters like ., *, +, etc.

Key Takeaways

Use gsub with a regex to replace all matching patterns in a string.

Pass the regex as the first argument and the replacement string or block as the second.

Escape special regex characters to avoid unexpected matches.

Use sub instead of gsub if you want to replace only the first match.

You can use a block with gsub for dynamic replacements based on each match.