tee

The tee command is used to store and view (pipe) the output of any other command at the same time.

1. Basic Syntax

command | tee [options] [file_name]

Common Usage Examples

Write to a file and see output

Redirect output to a file while still seeing it in the terminal.

ls -l | tee output.txt

Append to an existing file

By default, tee overwrites files. Use -a to append instead.

echo "New log entry" | tee -a log.txt

Write to multiple files

You can broadcast the output to several files at once.

echo "Config update" | tee file1.txt file2.txt file3.txt

Use with sudo

Useful when you need to write to a file that requires root permissions, but the redirection operator > would fail.

echo "127.0.0.1 special.host" | sudo tee -a /etc/hosts

Options Reference

Option	Long Version	Description
-a	--append	Append to the given files, do not overwrite.
-i	--ignore-interrupts	Ignore interrupt signals (like Ctrl+C).
-p		Diagnose errors writing to non-pipes.
--version		Output version information and exit.
--help		Display help and exit.

Advanced Patterns

Redirect to another command

Pipe the output to another process while saving the intermediate result.

cat data.txt | tee backup.txt | grep "Error"

Hide terminal output

If you want to write to a file and a pipe but don’t want to see it in the terminal, redirect stdout to /dev/null.

command | tee log.txt > /dev/null

Capture Stderr and Stdout

To capture everything (errors and regular output) into a file and the screen:

command 2>&1 | tee all_output.txt