File.write for writing in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does File.write do in Ruby?

File.write writes the given content to a file. If the file doesn't exist, it creates it. If it exists, it overwrites the content.

beginner

How do you write the string "Hello" to a file named "greeting.txt" using File.write?

File.write("greeting.txt", "Hello")

beginner

What happens if you use File.write on an existing file?

The existing file's content is replaced with the new content you provide.

intermediate

Can File.write append content to a file?

No, File.write overwrites the file. To append, you need to use other methods like File.open with append mode.

intermediate

What value does File.write return after writing to a file?

It returns the number of bytes written to the file.

What does File.write('example.txt', 'Hi') do if 'example.txt' does not exist?

A Creates 'example.txt' and writes 'Hi' inside

B Throws an error because the file doesn't exist

C Appends 'Hi' to the file

D Deletes the file

File.write creates the file if it doesn't exist and writes the content.

If 'data.txt' contains 'Old', what will File.write('data.txt', 'New') do?

A Overwrite 'Old' with 'New'

B Append 'New' after 'Old'

C Throw an error

D Create a new file named 'data.txt1'

File.write overwrites existing content.

What does File.write return after writing to a file?

A The file name

B The content written

C Nothing (nil)

D The number of bytes written

It returns the number of bytes written to the file.

Which method should you use to add content to the end of a file instead of overwriting?

A File.write

B File.read

C File.open with append mode

D File.delete

Use File.open with append mode ('a') to add content.

What happens if you pass a non-string object to File.write as content?

A It writes the object as is

B It converts the object to string and writes it

C It throws an error

D It ignores the content

File.write converts the content to string before writing.

Explain how File.write works for writing content to files in Ruby.

Think about what happens if the file exists or not.

Describe the difference between File.write and appending content to a file.

Consider how to keep old content and add new content.

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'