Linux Tee Command with Examples

The tee command is used to read the standard input and write and writes to both standard output and one or more files at the same time. Generally, tee is used with combination of other commands through piping. In this tutorial, we’ll cover the basics of using the tee command.

tee Command Syntax

Below is the basic syntax of tee command:

tee [OPTIONS] [FILE]

Here, options are:
- -a (--append) – It will append to the given file instead of overwrite.
- -i (--ignore-interrupts) – Ignore interrupt signals.
- Use tee --help to view all available options.
FILE – One or more files. Each of which the output data is written to.

How to Use the tee Command

Usually, the tee command is used to display the standard output (stdout) of a program and write it in a file.

For example, we will get the disk space details using df command and store the output to the output.txt file by piping with tee command:

df -h | tee output.txt

Filesystem      Size  Used Avail Use% Mounted on
udev            984M     0  984M   0% /dev
tmpfs           200M  624K  199M   1% /run
/dev/vda1        25G  3.8G   21G  16% /
tmpfs           997M     0  997M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           997M     0  997M   0% /sys/fs/cgroup
/dev/vda15      105M  3.6M  101M   4% /boot/efi
tmpfs           200M     0  200M   0% /run/user/1000

You can view the content of the output.txt file using the cat command.

Write to Multiple File

You can also use tee command to write to multiple files. Pass the list of files separated by space as arguments:

command | tee file1.txt file2.txt file3.txt

Append to File

Use the -a (--append) option to append the output to the file. The tee command will overwrite the specified file.

command | tee -a file.txt

Ignore Interrupt

You can use -i (–ignore-interrupts) option to ignore interrupts. It’s useful when stopping the command during execution with Ctrl+C and want to exit gracefully.

command | tee -i file.txt

Hide the Output

To hide the standard output, redirect it to /dev/null:

command | tee file.txt >/dev/null

Using tee in Conjunction with sudo

When you try to write to a file owned by a root or sudo user, it will throw permission denied error. You should perform the redirection using sudo user.

sudo echo "newline" > /etc/nginx/file.conf

It will show something like this:

bash: /etc/nginx/file.conf: Permission denied

Simply prepend sudo before the tee command as shown below:

echo "newline" | sudo tee -a /etc/file.conf

The echo command will pass the output to the tee command and elevate to sudo permissions and write to the file.

Using tee in conjunction with sudo allows you to write to files owned by other users.

Conclusion

The tee command reads from standard input and writes it to standard output and one ore more files.

If you have any questions or feedback, feel free to leave a comment.

Tags: tee, terminal