IO modes (r, w, a) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using mode 'r'?

Consider this Ruby code that tries to read a file in 'r' mode. What will it output if the file 'example.txt' contains the text 'Hello World'?

Ruby

File.open('example.txt', 'r') do |file|
  puts file.read
end

A Hello World

B File not found error

C Empty output

D Permission denied error

💡 Hint

Mode 'r' opens the file for reading only.

The 'r' mode opens the file for reading. Since the file exists and contains 'Hello World', the program prints that text.

❓ Predict Output

intermediate

What happens when opening a file with mode 'w'?

Given this Ruby code, what will be the content of 'output.txt' after running it?

Ruby

File.open('output.txt', 'w') do |file|
  file.write('First line')
end
File.open('output.txt', 'w') do |file|
  file.write('Second line')
end

A The file contains 'First line'

B The file contains 'First lineSecond line'

C The file is empty

D The file contains 'Second line'

💡 Hint

Mode 'w' overwrites the file each time it opens it.

Each time the file is opened with 'w', it clears the previous content. So after the second write, only 'Second line' remains.

❓ Predict Output

advanced

What is the output after appending text with mode 'a'?

Assuming 'log.txt' initially contains 'Start\n', what will be the content after running this Ruby code?

Ruby

File.open('log.txt', 'a') do |file|
  file.puts('Entry 1')
end
File.open('log.txt', 'a') do |file|
  file.puts('Entry 2')
end
content = File.read('log.txt')
puts content

A

Start

B

Entry 1
Entry 2

C

Start
Entry 1
Entry 2

D

Start
Entry 2

💡 Hint

Mode 'a' adds new content to the end without deleting existing content.

The 'a' mode appends text. So the original 'Start\n' stays, and 'Entry 1' and 'Entry 2' are added on new lines.

❓ Predict Output

advanced

What error occurs when opening a non-existent file in 'r' mode?

What happens when this Ruby code runs and 'missing.txt' does not exist?

Ruby

File.open('missing.txt', 'r') do |file|
  puts file.read
end

A Errno::ENOENT (No such file or directory) error

B Empty output

C Permission denied error

D Creates an empty file named 'missing.txt'

💡 Hint

Mode 'r' requires the file to exist.

Opening a non-existent file in 'r' mode raises an error because the file must exist to read it.

🧠 Conceptual

expert

How do 'w' and 'a' modes differ when writing to a file?

Which statement correctly describes the difference between opening a file in 'w' mode versus 'a' mode in Ruby?

A 'w' mode appends to the file, 'a' mode overwrites the file content

B 'w' mode overwrites the file content, 'a' mode appends to the file without deleting existing content

C 'w' mode only writes if the file exists, 'a' mode creates a new file if it does not exist

D 'w' mode opens the file for reading and writing, 'a' mode opens the file for reading only

💡 Hint

Think about what happens to existing content in each mode.

'w' mode clears the file before writing, while 'a' mode adds new content at the end preserving existing data.