Running scripts with ruby command - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a Ruby script run with ruby command

What is the output when running this Ruby script with ruby script.rb?

Ruby

puts "Hello, Ruby!"
puts 5 + 3 * 2

A Hello, Ruby!\n10

B Hello, Ruby!\n16

C Hello, Ruby!\n11

D SyntaxError

💡 Hint

Remember the order of operations in arithmetic.

The script prints the string first, then calculates 5 + (3 * 2) = 11.

❓ Predict Output

intermediate

Effect of command line argument on Ruby script output

What will be the output of this Ruby script when run as ruby greet.rb Alice?

Ruby

name = ARGV[0]
puts "Hello, #{name}!"

A NameError

B Hello, Alice!

C ARGV[0]

D Hello, !

💡 Hint

ARGV holds command line arguments passed to the script.

ARGV[0] is 'Alice', so the script prints 'Hello, Alice!'.

🔧 Debug

advanced

Identify the error when running this Ruby script

What error will occur when running this Ruby script with ruby test.rb?

Ruby

def greet(name)
  puts "Hello, #{name}!"
end

greet()

A ArgumentError: wrong number of arguments (given 0, expected 1)

B SyntaxError: unexpected end-of-input

C NoMethodError: undefined method 'greet' for main:Object

D No error, prints 'Hello, !'

💡 Hint

Check how many arguments the method expects versus what is given.

The method greet requires 1 argument but is called with none, causing ArgumentError.

❓ Predict Output

advanced

Output of a Ruby script using a block with ruby command

What is the output of this Ruby script when run with ruby block.rb?

Ruby

3.times do |i|
  puts i * 2
end

A SyntaxError

B 1\n2\n3

C 0\n1\n2

D 0\n2\n4

💡 Hint

The block variable i starts at 0 and goes up to 2.

3.times runs the block 3 times with i = 0,1,2; output is i*2 each time.

🧠 Conceptual

expert

Understanding Ruby script exit status with ruby command

If a Ruby script ends with exit(3), what will be the exit status code when run with ruby script.rb?

A 3

B nil

C 1

D 0

💡 Hint

The exit method sets the program's exit status code.

Calling exit(3) sets the exit status code to 3, which the OS receives.

Practice

1. What does the ruby command do when used in the terminal?

easy

A. It runs a Ruby script saved in a file.

B. It compiles Ruby code into an executable.

C. It opens the Ruby interactive console.

D. It installs Ruby gems automatically.

Solution

1. Step 1: Understand the purpose of the ruby command

   The ruby command is used to run Ruby scripts saved in files from the terminal.

2. Step 2: Differentiate from other Ruby tools

   It does not compile code, open the console, or install gems automatically.

3. Final Answer:

   It runs a Ruby script saved in a file. -> Option A

4. Quick Check:

   ruby command runs scripts = A [OK]

Hint: ruby command runs saved scripts, not compilers or consoles [OK]

Common Mistakes:

• Confusing ruby command with irb (interactive console)
• Thinking ruby compiles code to executables
• Assuming ruby installs gems automatically

2. Which of the following is the correct way to run a Ruby script named hello.rb from the terminal?

easy

A. run hello.rb

B. start ruby hello.rb

C. execute hello.rb

D. ruby hello.rb

Solution

1. Step 1: Identify the correct command syntax

   The correct syntax to run a Ruby script is ruby filename.rb.

2. Step 2: Check each option

   Only ruby hello.rb matches the correct syntax.

3. Final Answer:

   ruby hello.rb -> Option D

4. Quick Check:

   Use ruby + filename.rb to run scripts [OK]

Hint: Use 'ruby filename.rb' to run scripts in terminal [OK]

Common Mistakes:

• Using 'run' or 'execute' commands which don't exist
• Adding extra words like 'start' before ruby
• Forgetting to include the .rb extension

3. Given a file greet.rb with the following content:

puts "Hello, Ruby!"

What will be the output when you run ruby greet.rb in the terminal?

medium

A. Hello, Ruby!

B. puts "Hello, Ruby!"

C. SyntaxError

D. No output

Solution

1. Step 1: Understand the Ruby code

   The code uses puts to print the string "Hello, Ruby!" to the terminal.

2. Step 2: Predict the output of running the script

   Running ruby greet.rb executes the code and prints the string.

3. Final Answer:

   Hello, Ruby! -> Option A

4. Quick Check:

   puts prints string output = C [OK]

Hint: puts prints text exactly when script runs [OK]

Common Mistakes:

• Thinking puts prints the code itself
• Expecting no output from puts
• Confusing syntax errors with correct code

4. You try to run a Ruby script with ruby myscript.rb but get an error: ruby: command not found. What is the most likely cause?

medium

A. The script file myscript.rb has a syntax error.

B. Ruby is not installed or not in your system's PATH.

C. You forgot to save the script file.

D. You need to add ./ before the filename.

Solution

1. Step 1: Analyze the error message

   The error ruby: command not found means the terminal cannot find the ruby program.

2. Step 2: Identify the cause

   This usually means Ruby is not installed or its location is not in the system PATH environment variable.

3. Final Answer:

   Ruby is not installed or not in your system's PATH. -> Option B

4. Quick Check:

   Command not found means Ruby missing or PATH issue [OK]

Hint: Command not found means Ruby missing or PATH issue [OK]

Common Mistakes:

• Assuming syntax error causes command not found
• Thinking file must be saved to fix this error
• Adding ./ before filename only works for executables, not ruby command

5. You have two Ruby scripts in the same folder: first.rb and second.rb. You want to run second.rb but accidentally type ruby first.rb. How can you avoid this mistake when running scripts?

hard

A. Use ruby run second.rb to specify the script.

B. Rename the files to have different extensions.

C. Always check your current folder and type the exact filename with extension.

D. Run scripts without typing the filename; Ruby will pick the right one.

Solution

1. Step 1: Understand the cause of the mistake

   Typing the wrong filename runs the wrong script because the command requires exact filenames.

2. Step 2: Find the best practice to avoid errors

   Always verify your current folder and type the exact filename with extension to run the correct script.

3. Final Answer:

   Always check your current folder and type the exact filename with extension. -> Option C

4. Quick Check:

   Exact filename avoids running wrong script [OK]

Hint: Double-check filename and folder before running script [OK]

Common Mistakes:

• Thinking Ruby auto-selects the right script
• Trying to run scripts without filenames
• Using incorrect commands like 'ruby run'