Linux Tee Command with Examples

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The tee command reads from the standard input and writes to both standard output and one or more files at the same time. tee is mostly used in combination with other commands through piping.

In this tutorial, we’ll cover the basics of using the tee command.

tee Command Syntax

The syntax for the tee command is as follows:

tee [OPTIONS] [FILE]
  • OPTIONS:
    • -a (--append) - Do not overwrite the files instead append to the given files.
    • -i (--ignore-interrupts) - Ignore interrupt signals.
    • Use tee --help to view all available options.
  • FILE_NAMES - One or more files. Each of which the output data is written to.

How to Use the tee Command

The most basic usage of the tee command is to display the standard output (stdout) of a program and write it in a file.

In the following example, we are using the df command to get information about the amount of available disk space on the file system. The output is piped to the tee command, which displays the output to the terminal and writes the same information to the file disk_usage.txt.

df -h | tee disk_usage.txt
Filesystem      Size  Used Avail Use% Mounted on
dev             7.8G     0  7.8G   0% /dev
run             7.9G  1.8M  7.9G   1% /run
/dev/nvme0n1p3  212G  159G   43G  79% /
tmpfs           7.9G  357M  7.5G   5% /dev/shm
tmpfs           7.9G     0  7.9G   0% /sys/fs/cgroup
tmpfs           7.9G   15M  7.9G   1% /tmp
/dev/nvme0n1p1  511M  107M  405M  21% /boot
/dev/sda1       459G  165G  271G  38% /data
tmpfs           1.6G   16K  1.6G   1% /run/user/120

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

Write to Multiple File

The tee command can also write to multiple files. To do so, specify a list of files separated by space as arguments:

command | tee file1.out file2.out file3.out

Append to File

By default, the tee command will overwrite the specified file. Use the -a (--append) option to append the output to the file:

command | tee -a file.out

Ignore Interrupt

To ignore interrupts use the `-i (--ignore-interrupts) option. This is useful when stopping the command during execution with CTRL+C and want tee to exit gracefully.

command | tee -i file.out

Hide the Output

If you don’t want tee to write to the standard output, you can redirect it to /dev/null:

command | tee file.out >/dev/null

Using tee in Conjunction with sudo

Let’s say you want to write to a file that is owned by root as a sudo user. The following command will fail because the redirection of the output is not performed by sudo. The redirection is executed as the unprivileged user.

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

The output will look something like this:

bash: /etc/file.conf: Permission denied

Simply prepend sudo before the tee command as shown below:

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

tee will receive the output of the echo command, 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.