Heredoc syntax for multiline strings in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple heredoc string

What is the output of this Ruby code using heredoc syntax?

Ruby

str = <<-TEXT
Hello,
World!
TEXT
puts str

A Hello,\nWorld!\n

B Hello, World!

C Hello,\nWorld!

D Hello,World!\n

💡 Hint

Remember that heredoc preserves newlines exactly as written.

The heredoc syntax preserves the line breaks and includes a final newline. So the output includes both lines and ends with a newline.

❓ Predict Output

intermediate

Indentation behavior with <<- heredoc

What will this Ruby code print?

Ruby

str = <<-DOC
  Line one
  Line two
DOC
puts str

A Line one\n Line two\n

B Line one\nLine two\n

C owt eniL eno eniL

D Line one Line two

💡 Hint

The <<- syntax allows the end marker to be indented but does not remove indentation inside the string.

The indentation inside the heredoc content is preserved exactly, so the two lines start with two spaces each.

❓ Predict Output

advanced

Difference between <<- and <<~ in heredoc

What is the output of this Ruby code?

Ruby

str = <<~HEREDOC
    Hello
      World
  HEREDOC
puts str

A Hello\nWorld\n

B Hello\n World\n

C Hello\n World\n

D Hello\n World\n"

💡 Hint

The <<~ syntax removes the least common leading whitespace from all lines.

The <<~ removes the smallest indentation common to all lines, so the first line's 4 spaces are removed from both lines, preserving relative indentation.

🧠 Conceptual

advanced

Heredoc with variable interpolation

Given this Ruby code, what will be the output?

Ruby

name = "Alice"
str = <<-TEXT
Hello, #{name}!
Welcome.
TEXT
puts str

A Hello, #{name}!\nWelcome.\n

B Hello, \#{name}!\nWelcome.\n

C Hello, Alice! Welcome.

D Hello, Alice!\nWelcome.\n

💡 Hint

Double-quoted heredocs allow variable interpolation.

The heredoc with <<- uses double quotes by default, so #{name} is replaced with Alice.

🔧 Debug

expert

Why does this heredoc cause a syntax error?

This Ruby code raises a SyntaxError. What is the cause?

Ruby

str = <<HEREDOC
Hello
World
  HEREDOC
puts str

A The heredoc content must be indented to match the ending marker.

B The ending HEREDOC marker is indented, but << without a dash requires it to be at the start of the line.

C The heredoc content must not contain blank lines.

D The heredoc marker must be quoted to avoid errors.

💡 Hint

Check the position of the ending marker when using << without a dash.

When using <

Practice

1. What is the main purpose of using heredoc syntax in Ruby?

easy

A. To declare variables with fixed values

B. To create single-line comments

C. To write multiline strings easily without using escape characters

D. To define methods with multiple parameters

Solution

1. Step 1: Understand what heredoc does

   Heredoc syntax allows writing strings that span multiple lines without needing escape characters like \n.

2. Step 2: Compare options

   Declaring variables with fixed values, creating single-line comments, and defining methods with multiple parameters describe unrelated Ruby features. Only writing multiline strings easily without using escape characters correctly describes heredoc's purpose.

3. Final Answer:

   To write multiline strings easily without using escape characters -> Option C

4. Quick Check:

   Heredoc = multiline strings [OK]

Hint: Heredoc is for easy multiline text, not comments or methods [OK]

Common Mistakes:

• Confusing heredoc with comments
• Thinking heredoc defines methods
• Assuming heredoc is for variables only

2. Which of the following is the correct syntax to start a heredoc string named TEXT in Ruby?

easy

A. << TEXT

B. <TEXT

C.

D. TEXT<<

Solution

1. Step 1: Recall heredoc start syntax

   Heredoc starts with << followed immediately by an identifier, e.g., <

2. Step 2: Check each option

   <<TEXT matches the correct syntax. << TEXT with space is invalid. Arrangements like

3. Final Answer:

   <<TEXT -> Option B

4. Quick Check:

   Start heredoc with <<IDENTIFIER [OK]

Hint: Heredoc starts with << followed by the identifier [OK]

Common Mistakes:

• Putting identifier before <<
• Using incorrect symbols like < or - wrongly
• Confusing heredoc start with end

3. What will be the output of this Ruby code?

text = <<~GREETING
  Hello,
    Welcome to Ruby!
GREETING
puts text

medium

A. Hello,
Welcome to Ruby!

B. Hello,
Welcome to Ruby!

C. Hello,
Welcome to Ruby!

D. !ybuR ot emocleW
,olleH

Solution

1. Step 1: Understand <<~ operator

   The <<~ syntax removes leading spaces common to all lines, aligning text left.

2. Step 2: Analyze the given text

   Original lines have 2 spaces before 'Hello,' and 4 before 'Welcome'. The common indent is 2 spaces, so those are removed.

3. Step 3: Resulting output

   After removing 2 spaces, 'Hello,' starts at column 0, 'Welcome...' starts with 2 spaces.

4. Final Answer:

   Hello, Welcome to Ruby! -> Option A

5. Quick Check:

   <<~ removes common indent [OK]

Hint: <<~ removes common leading spaces from all lines [OK]

Common Mistakes:

• Ignoring <<~ and expecting original indentation
• Confusing \n with actual new lines
• Assuming all spaces are removed

4. Identify the error in this Ruby heredoc code:

message = <

medium

A. The string must be enclosed in quotes

B. The starting identifier should be lowercase

C. The heredoc must use <<~ instead of <<

D. The ending identifier must match exactly and be alone on its line

Solution

1. Step 1: Check heredoc start and end identifiers

   Heredoc must end with the same identifier used to start it, alone on a line with no spaces.

2. Step 2: Analyze given code

   Start identifier is GREETING but end identifier is END, which is incorrect.

3. Final Answer:

   The ending identifier must match exactly and be alone on its line -> Option D

4. Quick Check:

   Start and end identifiers must match [OK]

Hint: End heredoc with the exact same word alone on a line [OK]

Common Mistakes:

• Mismatching start and end identifiers
• Adding spaces after end identifier
• Using lowercase instead of uppercase identifiers

5. You want to create a multiline string with indentation preserved but also want to remove leading spaces common to all lines for neat code. Which heredoc syntax should you use in Ruby?

hard

A. <<~TEXT

B. <<-TEXT

C. <TEXT

D. <<=TEXT

Solution

1. Step 1: Understand heredoc variants

   <<TEXT preserves all spaces; <<-TEXT allows indenting the end marker; <<~TEXT removes common leading spaces from all lines.

2. Step 2: Match requirement

   To keep indentation inside the string but remove common leading spaces for clean code, <<~TEXT is the correct choice.

3. Final Answer:

   <<~TEXT -> Option A

4. Quick Check:

   <<~ trims common indent [OK]

Hint: <<~ removes common indent, use it for clean multiline strings [OK]

Common Mistakes:

• Using <<- which only affects end marker indentation
• Using << which keeps all spaces
• Assuming <<= is valid syntax