tee for splitting output in Linux CLI - Step-by-Step Execution

Concept Flow - tee for splitting output

Run command producing output

↓

Output stream sent to tee

↓

Write to file

↓

End of process

The command output is sent to tee, which splits it to both a file and the screen simultaneously.

Execution Sample

Linux CLI

echo "Hello World" | tee output.txt

This command prints 'Hello World' on the screen and saves it to output.txt at the same time.

Execution Table

Step	Action	Input	Output to Screen	Output to File
1	Run echo command	No input	Hello World
2	Pipe output to tee	Hello World	Hello World	Hello World
3	tee writes to file	Hello World	Hello World	Hello World
4	tee outputs to screen	Hello World	Hello World	Hello World
5	Process ends	No input	Hello World displayed	File saved

💡 Command finishes after tee writes output to both screen and file.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Output Stream	empty	Hello World	Hello World	Hello World	Hello World
File output.txt	empty	empty	Hello World	Hello World	Hello World
Screen output	empty	Hello World	Hello World	Hello World	Hello World

Key Moments - 2 Insights

Why do we see the output on the screen even though it is saved to a file?

Because tee duplicates the output stream: it sends the output both to the file and to the screen as shown in execution_table steps 2 to 4.

What happens if the file already exists?

tee overwrites the file by default, replacing its contents with the new output, as implied in step 3 of the execution_table.

Visual Quiz - 3 Questions

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

A No output

B Hello World

C Empty line

D Error message

💡 Hint

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

At which step does tee write the output to the file?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look at the 'Output to File' column in the execution_table.

If we remove tee from the command, what changes in the variable_tracker?

A Output to file is empty

B Output to file remains the same

C Output to screen disappears

D Output stream becomes empty

💡 Hint

Without tee, output is not saved to file, check 'File output.txt' row in variable_tracker.

Concept Snapshot

tee command duplicates output streams.
Syntax: command | tee filename
Outputs go to both screen and file.
Overwrites file by default.
Use -a to append instead of overwrite.

Full Transcript

The tee command in Linux takes the output of a command and splits it so that it goes to both the screen and a file. For example, echo "Hello World" | tee output.txt prints Hello World on the screen and saves it to output.txt at the same time. The flow starts with the command producing output, which is piped to tee. Tee then writes the output to the file and also sends it to the screen. This way, you can see the output live and keep a copy saved. If the file exists, tee overwrites it unless you use the -a option to append. This is useful when you want to log output but still watch it as it happens.