How to Concatenate Strings in Ruby: Simple Syntax and Examples

In Ruby, you can concatenate strings using the + operator, the << method, or string interpolation with #{}. The + operator creates a new string, while << modifies the original string. String interpolation is a clean way to combine strings and variables.

Syntax

Here are the main ways to concatenate strings in Ruby:

• Using + operator: Joins two strings and returns a new string.
• Using << method: Appends to the original string, modifying it.
• Using string interpolation: Embeds variables or expressions inside a string with #{}.

ruby

str1 = "Hello"
str2 = "World"

# Using + operator
result_plus = str1 + " " + str2

# Using << method
str1_dup = str1.dup
str1_dup << " " << str2

# Using string interpolation
result_interpolation = "#{str1} #{str2}"

Example

This example shows how to concatenate strings using all three methods and prints the results.

ruby

str1 = "Hello"
str2 = "World"

# Using + operator
result_plus = str1 + " " + str2
puts "Using + : #{result_plus}"

# Using << method
str3 = "Hello"
str3 << " " << str2
puts "Using << : #{str3}"

# Using string interpolation
result_interpolation = "#{str1} #{str2}"
puts "Using interpolation : #{result_interpolation}"

Output

Using + : Hello World
Using << : Hello World
Using interpolation : Hello World

Common Pitfalls

Common mistakes when concatenating strings in Ruby include:

• Using + operator repeatedly in a loop, which creates many temporary strings and slows down performance.
• Modifying strings unintentionally with <<, which changes the original string.
• Forgetting to convert non-string values to strings before concatenation, causing errors.

Always ensure variables are strings or use interpolation which handles conversion automatically.

ruby

str = "Hello"

# Wrong: modifies original string
str << " World"
puts str  # Output: Hello World

# If you want to keep original, use +
str = "Hello"
new_str = str + " World"
puts str      # Output: Hello
puts new_str  # Output: Hello World

Output

Hello World
Hello
Hello World

Quick Reference

Method	Description	Modifies Original?	Example
+ operator	Joins strings, returns new string	No	"Hello" + " World" => "Hello World"
<< method	Appends to original string	Yes	"Hello" << " World" => "Hello World" (original changed)
String interpolation	Embeds variables inside strings	No	"#{var1} #{var2}" => combined string

Key Takeaways

Use + to join strings without changing originals.

Use << to append and modify the original string efficiently.

String interpolation is the safest and cleanest way to combine strings and variables.

Avoid using + repeatedly in loops to prevent slow performance.

Always ensure non-string values are converted or use interpolation to avoid errors.