IO modes (r, w, a) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file for reading.

Ruby

file = File.open('example.txt', '[1]')

Drag options to blanks, or click blank then click option'

Aw

Br

Ca

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'w' will erase the file content.

Using 'a' opens the file for appending, not reading.

Use mode 'r' to open a file for reading only.

2fill in blank

medium

Complete the code to open a file for writing (overwriting existing content).

Ruby

file = File.open('output.txt', '[1]')

Drag options to blanks, or click blank then click option'

Aa

Br

Cw

Dr+

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'r' will cause an error if the file does not exist.

Using 'a' will append instead of overwrite.

Use mode 'w' to open a file for writing and overwrite existing content.

3fill in blank

hard

Fix the error in the code to open a file for appending text.

Ruby

file = File.open('log.txt', '[1]')

Drag options to blanks, or click blank then click option'

Aw

Bw+

Cr

Da

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'w' erases the file content.

Using 'r' opens for reading only, no writing allowed.

Use mode 'a' to open a file for appending text at the end.

4fill in blank

hard

Fill both blanks to open a file for reading and writing without erasing content.

Ruby

file = File.open('data.txt', '[1]')
file.write('Hello') if file.[2]

Drag options to blanks, or click blank then click option'

Ar+

Bw

Cwritable?

Dreadable?

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'w' erases the file content.

Checking readable? does not confirm writing permission.

Mode 'r+' opens for reading and writing without erasing. Use writable? to check if writing is allowed.

5fill in blank

hard

Fill all three blanks to open a file for appending, write a line, and close the file.

Ruby

file = File.open('notes.txt', '[1]')
file.[2]('New note\n')
file.[3]

Drag options to blanks, or click blank then click option'

Aa

Bwrite

Cclose

Dread

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'w' erases existing content.

Forgetting to close the file can cause data loss.

Use mode 'a' to append, write to add text, and close to save and close the file.

Practice

1. What does the 'r' mode do when opening a file in Ruby?

easy

A. Opens the file for reading only, without changing its content.

B. Opens the file for writing and erases existing content.

C. Opens the file for appending new content at the end.

D. Creates a new file if it doesn't exist and writes to it.

Solution

1. Step 1: Understand the purpose of 'r' mode

   The 'r' mode is used to open a file only for reading, so the file content is not changed.

2. Step 2: Compare with other modes

   'w' mode writes and erases content, 'a' appends, but 'r' only reads.

3. Final Answer:

   Opens the file for reading only, without changing its content. -> Option A

4. Quick Check:

   'r' = read only [OK]

Hint: Remember 'r' stands for read only, no changes made [OK]

Common Mistakes:

• Confusing 'r' with 'w' and thinking it erases content
• Assuming 'r' can write to the file
• Mixing 'r' with 'a' mode functionality

2. Which of the following is the correct syntax to open a file named data.txt for appending in Ruby?

easy

A. File.open('data.txt', 'x')

B. File.open('data.txt', 'w')

C. File.open('data.txt', 'r')

D. File.open('data.txt', 'a')

Solution

1. Step 1: Identify the mode for appending

   The mode 'a' is used to open a file for appending new content at the end.

2. Step 2: Check the syntax

   The correct syntax is File.open('filename', 'a') to append.

3. Final Answer:

   File.open('data.txt', 'a') -> Option D

4. Quick Check:

   Append mode = 'a' [OK]

Hint: Use 'a' to add content without erasing [OK]

Common Mistakes:

• Using 'r' which is read-only mode
• Using 'w' which erases file content
• Using 'x' which creates a new file and errors if exists

3. What will be the output of this Ruby code if example.txt initially contains "Hello"?

File.open('example.txt', 'w') { |f| f.puts 'World' }
content = File.read('example.txt')
puts content

medium

A. Hello\nWorld

B. Hello

C. World

D. Error: file not found

Solution

1. Step 1: Understand 'w' mode effect

   Opening with 'w' erases existing content and writes new content.

2. Step 2: Analyze the code output

   The file is overwritten with "World" and then read back, so output is "World" with a newline.

3. Final Answer:

   World -> Option C

4. Quick Check:

   'w' erases old content, so output is new content with newline [OK]

Hint: Writing with 'w' erases old content, so only new text shows [OK]

Common Mistakes:

• Thinking 'w' appends instead of overwriting
• Expecting old content to remain
• Confusing output with combined old and new text

4. The following Ruby code is intended to add the line "Goodbye" to the end of log.txt. What is the error?

File.open('log.txt', 'w') do |file|
  file.puts 'Goodbye'
end

medium

A. The file name should be in double quotes, not single quotes.

B. Using 'w' mode erases the file instead of appending.

C. Missing a block parameter for the file object.

D. The method 'puts' cannot be used inside File.open.

Solution

1. Step 1: Identify the mode used

   The code uses 'w' mode which overwrites the file content.

2. Step 2: Understand the intended action

   To add content without erasing, 'a' mode should be used instead of 'w'.

3. Final Answer:

   Using 'w' mode erases the file instead of appending. -> Option B

4. Quick Check:

   Append needs 'a', not 'w' [OK]

Hint: Use 'a' to add lines, 'w' erases file [OK]

Common Mistakes:

• Confusing 'w' with append mode
• Thinking 'w' adds content without erasing
• Believing quotes style affects file opening

5. You want to create a Ruby script that reads a file notes.txt, appends the line "New note added", and then reads the updated content to print it. Which sequence of file modes should you use?

hard

A. Open with 'r' to read, then 'a' to append, then 'r' to read again.

B. Open with 'a' to append, then 'r' to read the updated content.

C. Open with 'w' to write, then 'a' to append, then 'r' to read.

D. Open with 'r' to read, then 'w' to write, then 'r' to read again.

Solution

1. Step 1: Read the original file

   Use 'r' mode to read the existing content without changing it.

2. Step 2: Append the new line

   Use 'a' mode to add "New note added" at the end without erasing.

3. Step 3: Read the updated content

   Open again with 'r' mode to read and print the updated file content.

4. Final Answer:

   Open with 'r' to read, then 'a' to append, then 'r' to read again. -> Option A

5. Quick Check:

   Read, append, read = 'r', 'a', 'r' [OK]

Hint: Read first, append with 'a', then read again [OK]

Common Mistakes:

• Using 'w' which erases content before appending
• Trying to append before reading original content
• Not reopening file to read updated content