cat (display file contents) in Linux CLI - Step-by-Step Execution

Concept Flow - cat (display file contents)

Start

↓

Run 'cat filename'

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Shell reads file

↓

File contents sent to stdout

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Display contents on screen

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End

The 'cat' command reads a file and shows its contents on the screen step-by-step.

Execution Sample

Linux CLI

cat example.txt

This command shows the contents of 'example.txt' on the screen.

Execution Table

Step	Action	Input	Output	Notes
1	Run command	cat example.txt	None	Command starts
2	Shell opens file	example.txt	File data stream	Reads file contents
3	Send data to stdout	File data stream	Text lines	Data flows to screen
4	Display output	Text lines	Visible file contents	User sees file text
5	End	None	None	Command finishes

💡 File fully read and displayed, command ends

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
file_data	None	File contents loaded	Sent to stdout	Displayed on screen

Key Moments - 2 Insights

Why does 'cat' show the whole file at once instead of line by line?

The execution_table row 3 shows 'cat' reads the entire file data stream before sending it to the screen, so it outputs all content continuously.

What happens if the file does not exist?

The shell cannot open the file (step 2 fails), and 'cat' shows an error message instead of file contents.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at step 3?

A Text lines

B Visible file contents

C None

D Error message

💡 Hint

Check the 'Output' column at step 3 in the execution_table.

At which step does the file contents become visible on the screen?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Notes' column for when the user sees the file text.

If the file is empty, what would the output be at step 4?

A Error message

B Visible file contents with text

C No output (blank screen)

D Partial file contents

💡 Hint

Refer to variable_tracker for file_data state and execution_table step 4 output.

Concept Snapshot

cat filename

- Reads the whole file named 'filename'
- Sends contents to screen (stdout)
- Shows file text exactly as is
- If file missing, shows error
- Useful to quickly view file contents

Full Transcript

The 'cat' command in Linux reads a file and displays its contents on the screen. When you run 'cat filename', the shell opens the file, reads all its data, sends it to the screen, and then finishes. If the file does not exist, an error message appears instead. This command is simple and useful to quickly see what's inside a file.