IO modes (r, w, a) in Ruby - Step-by-Step Execution

Concept Flow - IO modes (r, w, a)

Open file with mode

↓

Read (r) mode?

Yes→Read content

↓

Close file

↓

Write (w) mode?

Yes→Overwrite content

↓

Close file

↓

Append (a) mode?

Yes→Add content at end

↓

Close file

↓

Error: Invalid mode

↓

Exit

Open a file in read, write, or append mode, perform the action, then close the file.

Execution Sample

Ruby

File.open("test.txt", "w") do |file|
  file.write("Hello")
end

Open 'test.txt' in write mode and write 'Hello', overwriting existing content.

Execution Table

Step	Action	Mode	File Content Before	File Content After	Notes
1	Open file	w	"Old Data"	""	File opened in write mode
2	Write 'Hello'	w	""	"Hello"	Content overwritten
3	Close file	w	"Hello"	"Hello"	File closed
4	Open file	r	"Hello"	"Hello"	File opened in read mode
5	Read content	r	"Hello"	"Hello"	Content read as 'Hello'
6	Close file	r	"Hello"	"Hello"	File closed
7	Open file	a	"Hello"	"Hello"	File opened in append mode
8	Append ' World'	a	"Hello"	"Hello World"	Content appended
9	Close file	a	"Hello World"	"Hello World"	File closed

💡 All file operations completed successfully

Variable Tracker

Variable	Start	After Step 2	After Step 5	After Step 8	Final
file_content	"Old Data"	"Hello"	"Hello"	"Hello World"	"Hello World"

Key Moments - 3 Insights

Why does opening a file in 'w' mode erase the old content?

Because 'w' mode means write and it clears the file before writing new data, as shown in step 2 where 'Old Data' becomes 'Hello'.

What happens if you try to read a file opened in 'w' mode?

You cannot read in 'w' mode; the file is for writing only. Reading is done in 'r' mode as shown in steps 4-6.

How does 'a' mode differ from 'w' mode?

'a' mode adds new data at the end without erasing existing content, as seen in step 8 where ' World' is added after 'Hello'.

Visual Quiz - 3 Questions

Look at the execution table, what is the file content after step 2?

A "Hello World"

B "Old Data"

C "Hello"

D ""

💡 Hint

Check the 'File Content After' column for step 2 in the execution table.

At which step does the file content become 'Hello World'?

A Step 8

B Step 2

C Step 5

D Step 9

💡 Hint

Look at the 'File Content After' column and find when 'Hello World' appears.

If we open a file in 'r' mode and try to write, what would happen?

A The file content is overwritten

B An error occurs because 'r' mode is read-only

C Content is appended at the end

D The file is deleted

💡 Hint

Recall from key moments and execution table that 'r' mode is for reading only.

Concept Snapshot

IO modes in Ruby:
- 'r': read only, file must exist
- 'w': write only, clears file or creates new
- 'a': append, adds to end or creates new
Open file with File.open(filename, mode) do |file| ... end
Always close file after operation

Full Transcript

This visual trace shows how Ruby handles file input/output modes: read ('r'), write ('w'), and append ('a'). When opening a file in 'w' mode, the old content is erased before writing new data. In 'r' mode, you can only read the content without changing it. In 'a' mode, new data is added to the end without deleting existing content. The execution table walks through opening, reading, writing, appending, and closing the file step-by-step, tracking the file content changes. Key moments clarify common confusions about mode behaviors. The quiz tests understanding by asking about file content at different steps and mode restrictions.