File.write for writing in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using File.write?

Consider this Ruby code that writes to a file and then reads it back:

File.write('test.txt', 'Hello')
content = File.read('test.txt')
puts content

What will be printed?

Ruby

File.write('test.txt', 'Hello')
content = File.read('test.txt')
puts content

A test.txt

B nil

C Hello

D Error: file not found

💡 Hint

File.write writes the string to the file, and File.read reads it back.

The File.write method writes the string 'Hello' to 'test.txt'. Then File.read reads the content of the file, which is 'Hello'. So, puts prints 'Hello'.

❓ Predict Output

intermediate

What does File.write return in Ruby?

Look at this Ruby code:

result = File.write('output.txt', 'Data')

What is the value of result after this runs?

Ruby

result = File.write('output.txt', 'Data')

A The number of bytes written (4)

B The string 'Data'

C true

D nil

💡 Hint

File.write returns how many bytes it wrote to the file.

File.write returns the number of bytes written to the file. Since 'Data' has 4 characters, it returns 4.

🔧 Debug

advanced

Why does this File.write code raise an error?

What error does this Ruby code raise?

File.write(123, 'Hello')

Ruby

File.write(123, 'Hello')

A ArgumentError: wrong number of arguments

B TypeError: no implicit conversion of Integer into String

C Errno::ENOENT: No such file or directory

D No error, writes file named '123'

💡 Hint

File.write expects a string filename, not a number.

File.write expects the first argument to be a string (filename). Passing an integer causes a TypeError because Ruby cannot convert Integer to String automatically.

📝 Syntax

advanced

Which option correctly appends text to a file using File.write?

You want to add text to the end of an existing file. Which Ruby code does this correctly?

A File.write('log.txt', 'New entry', append: true)

B File.write('log.txt', 'New entry', 'a')

C File.write('log.txt', 'New entry', flags: 'w')

D File.write('log.txt', 'New entry', mode: 'a')

💡 Hint

File.write accepts options as a hash, and mode: 'a' means append.

To append text, you pass mode: 'a' as an option hash to File.write. Option D is invalid syntax, A uses a wrong option name, and D uses 'w' which overwrites the file.

🚀 Application

expert

How many bytes are written and what is the file content after this code?

Consider this Ruby code:

bytes = File.write('data.txt', "Line1\nLine2\n", mode: 'w')
content = File.read('data.txt')

What are the values of bytes and content?

Ruby

bytes = File.write('data.txt', "Line1\nLine2\n", mode: 'w')
content = File.read('data.txt')

A bytes = 12, content = "Line1\nLine2\n"

B bytes = 11, content = "Line1\nLine2"

C bytes = 12, content = "Line1 Line2"

D bytes = 10, content = "Line1\nLine2\n"

💡 Hint

Count characters including newline characters. File.write returns bytes written exactly.

The string "Line1\nLine2\n" has 12 characters (5 + 1 + 5 + 1). File.write returns 12. The file content includes the newlines exactly as written.

Practice

1. What does the Ruby method File.write do by default when writing to a file?

easy

A. It creates the file if it doesn't exist and overwrites existing content.

B. It appends new content to the end of the file without changing existing content.

C. It only reads the file content without modifying it.

D. It deletes the file before writing new content.

Solution

1. Step 1: Understand File.write default behavior

   By default, File.write creates the file if it does not exist.

2. Step 2: Check how it handles existing files

   If the file exists, it overwrites the entire content with the new data.

3. Final Answer:

   It creates the file if it doesn't exist and overwrites existing content. -> Option A

4. Quick Check:

   File.write overwrites by default = A [OK]

Hint: Remember: File.write overwrites unless mode is changed [OK]

Common Mistakes:

• Thinking File.write appends by default
• Assuming File.write only reads files
• Believing File.write deletes files before writing

2. Which of the following is the correct syntax to write the string "Hello" to a file named "greet.txt" using File.write in Ruby?

easy

A. File.write("greet.txt") { "Hello" }

B. File.write("Hello", "greet.txt")

C. File.write("greet.txt", "Hello")

D. File.write("greet.txt" => "Hello")

Solution

1. Step 1: Identify File.write parameters

   The first argument is the filename, the second is the content string.

2. Step 2: Match correct syntax

   File.write("greet.txt", "Hello") correctly uses File.write("greet.txt", "Hello").

3. Final Answer:

   File.write("greet.txt", "Hello") -> Option C

4. Quick Check:

   File.write(filename, content) = C [OK]

Hint: Filename first, content second in File.write [OK]

Common Mistakes:

• Swapping filename and content arguments
• Using block syntax incorrectly
• Passing a hash instead of arguments

3. What will be the content of the file "data.txt" after running this Ruby code?

File.write("data.txt", "Line 1\n")
File.write("data.txt", "Line 2\n")

medium

A. Line 2\n

B. Line 1\nLine 2\n

C. Line 1\n

D. Line 1\n\nLine 2\n

Solution

1. Step 1: Analyze first File.write call

   It writes "Line 1\n" to "data.txt", creating or overwriting the file.

2. Step 2: Analyze second File.write call

   It overwrites the entire file content with "Line 2\n" because File.write overwrites by default.

3. Final Answer:

   Line 2\n -> Option A

4. Quick Check:

   File.write overwrites, so last write stays = B [OK]

Hint: Each File.write overwrites unless mode 'a' is set [OK]

Common Mistakes:

• Assuming File.write appends by default
• Expecting both lines to be in the file
• Confusing newline characters with extra lines

4. The following Ruby code is intended to append "More text" to the file "notes.txt". What is the error?

File.write("notes.txt", "More text")

medium

A. The filename should be a symbol, not a string.

B. File.write overwrites instead of appending; mode 'a' is missing.

C. The string "More text" must be inside single quotes.

D. File.write cannot write strings, only bytes.

Solution

1. Step 1: Understand File.write default mode

   By default, File.write overwrites the file content.

2. Step 2: Identify how to append

   To append, you must specify mode: File.write("notes.txt", "More text", mode: "a").

3. Final Answer:

   File.write overwrites instead of appending; mode 'a' is missing. -> Option B

4. Quick Check:

   Append needs mode 'a' = A [OK]

Hint: Use mode: 'a' to append with File.write [OK]

Common Mistakes:

• Not specifying mode to append
• Using symbols instead of strings for filename
• Thinking quotes style affects writing
• Believing File.write can't write strings

5. You want to write multiple lines to a file "log.txt" without overwriting existing content. Which Ruby code correctly appends these lines using File.write?

hard

A. File.write("log.txt", "First line\nSecond line\n", append: true)

B. File.write("log.txt", "First line\nSecond line\n")

C. File.write("log.txt", "First line\nSecond line\n", mode: "w")

D. File.write("log.txt", "First line\nSecond line\n", mode: "a")

Solution

1. Step 1: Identify how to append with File.write

   Appending requires mode set to "a" (append mode).

2. Step 2: Check options for correct syntax

   File.write("log.txt", "First line\nSecond line\n", mode: "a") uses mode: "a" correctly to append multiple lines.

3. Final Answer:

   File.write("log.txt", "First line\nSecond line\n", mode: "a") -> Option D

4. Quick Check:

   Append mode is 'a' in File.write = D [OK]

Hint: Use mode: 'a' to append multiple lines safely [OK]

Common Mistakes:

• Omitting mode for append
• Using mode 'w' which overwrites
• Using invalid option 'append: true'