How to use the command 'tee' (with examples)

The tee command is a command-line utility that reads from standard input and writes to both standard output and files or commands. It is used to split the output of a command, allowing it to be displayed on the screen and redirected into one or more files simultaneously. This article will illustrate several use cases of the tee command.

Use case 1: Copying stdin to a file and stdout

Code:

echo "example" | tee path/to/file

Motivation: The motivation for using this example is to save the output of a command to a file while still being able to see it on the terminal. By using tee, we can achieve this without having to run the same command twice.

Explanation:

• echo "example": This command prints the string “example” to the standard output.
• tee path/to/file: The tee command reads the standard input from the pipe (|) and writes it to both the specified file and the standard output.

Example output:

example

Use case 2: Appending to a file without overwriting

Code:

echo "example" | tee -a path/to/file

Motivation: The motivation for using this example is to append the output of a command to a file without overwriting its contents. This is useful when you want to store the output of multiple commands in the same file.

Explanation:

• echo "example": This command prints the string “example” to the standard output.
• tee -a path/to/file: The -a option specifies that the output should be appended to the given file rather than overwriting it.

Example output:

example

Use case 3: Printing stdin to the terminal and piping it into another program

Code:

echo "example" | tee /dev/tty | xargs printf "[%s]"

Motivation: The motivation for using this example is to both display the output of a command on the terminal and process it further using another program. By using tee, we can redirect the output to /dev/tty to ensure it is displayed on the terminal before piping it into another program.

Explanation:

• echo "example": This command prints the string “example” to the standard output.
• tee /dev/tty: The /dev/tty file refers to the current terminal, so the output of tee will be displayed on the terminal before being further processed.
• xargs printf "[%s]": This command reads the output of the previous command from the pipe (|) and formats it using the printf command.

Example output:

example
[example]

Use case 4: Creating a directory, counting characters, and writing to the terminal

Code:

echo "example" | tee >(xargs mkdir) >(wc -c)

Motivation: The motivation for using this example is to perform multiple actions on the output of a command. By using tee with process substitution, we can create a directory using the output and count the number of characters in it simultaneously.

Explanation:

• echo "example": This command prints the string “example” to the standard output.
• tee >(xargs mkdir) >(wc -c): The >(command) syntax is used for process substitution. In this case, we are using it twice to create two separate processes that will receive the output of tee.
  • xargs mkdir: This command reads the output of tee from the pipe (|) and creates a directory with the name specified in the output.
  • wc -c: This command reads the output of tee from the pipe (|) and counts the number of characters in it.

Example output:

example
7

Conclusion:

The tee command is a versatile tool that allows you to split the output of a command, redirecting it to both files and standard output simultaneously. By understanding the different options and use cases of tee, you can effectively manage and process command output in various scenarios.