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 tee` is very useful for writing content to files that regular users do not have write permissions for. While `echo "content" > /path/to/protected_file` will not have `sudo` applied because redirection is handled by the shell, `echo "content" | sudo tee /path/to/protected_file` allows the `tee` command to run with `sudo` privileges to write to the file.
Pipeline Utilization
- `tee` acts 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 `-a` option is not used, `tee` will overwrite the file by default. When adding data to important log files, always use the `-a` option to preserve existing content.