File.open with block (auto-close) in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does File.open with a block do in Ruby?

It opens a file, runs the code inside the block using the file, and then automatically closes the file when the block finishes.

beginner

Why is using File.open with a block safer than opening and closing files manually?

Because it ensures the file is always closed properly, even if an error happens inside the block.

beginner

Show the syntax of File.open with a block to read a file named 'example.txt'.

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

intermediate

What happens if you try to use the file outside the block when using File.open with a block?

The file is already closed, so trying to read or write will cause an error.

beginner

Can you write to a file using File.open with a block? How?

Yes. Open the file with write mode ('w') and use the block to write inside it. Example:

File.open('output.txt', 'w') do |file|
  file.puts 'Hello!'
end

What does File.open('data.txt', 'r') do |f| ... end do?

A Opens 'data.txt' for reading and closes it automatically after the block.

B Opens 'data.txt' for writing and never closes it.

C Creates a new file named 'data.txt'.

D Deletes 'data.txt' after reading.

Using File.open with a block opens the file and closes it automatically after the block finishes.

What happens if an error occurs inside the block passed to File.open?

A The file remains open and causes a leak.

B The program crashes without closing the file.

C The file is still closed automatically.

D The file is deleted.

Ruby ensures the file is closed even if an error happens inside the block.

Which mode should you use with File.open to write new content to a file?

A 'w'

B 'a'

C 'r'

D 'x'

'w' mode opens the file for writing and overwrites existing content.

What will happen if you try to read from the file outside the block after File.open with a block?

A It will read the file normally.

B It will raise an error because the file is closed.

C It will create a new file.

D It will append data to the file.

The file is closed after the block, so reading outside causes an error.

Which of these is a benefit of using File.open with a block?

A It deletes the file after use.

B You must manually close the file.

C The file stays open for the whole program.

D The file is automatically closed after the block.

The block form automatically closes the file, making code safer and cleaner.

Explain how File.open with a block works and why it is useful.

Think about what happens before, during, and after the block.

Write a simple Ruby code snippet using File.open with a block to read and print a file's content.

Use 'r' mode and a block with |file| parameter.