Overview
The tee command acts like a 'T' junction in a pipe, sending data from standard input to standard output while also recording it into specified files. This is very useful for monitoring intermediate results in a pipeline or saving the same data to multiple locations. By default, it overwrites the file if it exists, but the -a option allows appending to the existing content.
Key Features
- Simultaneously sends standard input to standard output and files
- Overwrites or appends to files
- Useful for checking intermediate results in pipelines
Key Options
The main options for the tee command control how data is written to files.
Writing Modes
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Description:
`tee` Executes the command.
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Usage Examples
Various examples of using the tee command.
Overwrite standard output to a file
echo "Hello World" | tee output.txtDefault behavior, overwrites the file if it exists.
Append standard output to a file
echo "Another line" | tee -a output.txtUse the -a option to append new content to the end of an existing file.
Write to multiple files simultaneously
ls -l | tee file1.txt file2.txtSpecify multiple file paths to write the same content to them concurrently.
Write to a file with sudo privileges
echo "Restricted content" | sudo tee -a /var/log/system.logUseful for writing to system files that regular users do not have write permissions for.
Check intermediate results in a pipeline
cat /etc/passwd | grep "root" | tee root_users.txt | wc -lUse tee in the middle of a pipeline to write data to a file while passing it to the next command.
Tips & Precautions
Useful tips and points to note when using the tee command.
Using with sudo
sudo teeis very useful for writing content to files that regular users do not have write permissions for. Whileecho "content" > /path/to/protected_filewill not havesudoapplied because redirection is handled by the shell,echo "content" | sudo tee /path/to/protected_fileallows theteecommand to run withsudoprivileges to write to the file.
Pipeline Utilization
teeacts as a data splitter when placed in the middle of a pipeline. This allows data to be recorded in a file while simultaneously being passed to the next command, making it effective for debugging or logging.
Importance of the -a Option
- If the
-aoption is not used,teewill overwrite the file by default. When adding data to important log files, always use the-aoption to preserve existing content.