Explanation
The -a option to the tee command will cause the output to be appended to the end of the output file instead of overwriting the existing file contents. The tee command reads from standard input (STDIN) and writes to standard output (STDOUT) and one or more files simultaneously. For example, ls | tee file.txt will display the output of the ls command and also write it to file.txt. If file.txt already exists, it will be overwritten unless the
-a option is used. References: LPI Exam 101 Detailed Objectives, Topic 103: GNU and Unix Commands, Weight: 25, Objective 103.3: Perform basic file management, tee command