Explanation
The output of the given command line is foo bar. The command line consists of three commands that are connected by pipes (|). A pipe is a symbol that redirects the standard output of one command to the standard input of another command. The echo command prints its argument to the standard output, which is foo bar in this case. The tee command reads from the standard input and writes to both the standard output and a file. The file name is given as an argument, which is bar in this case. The cat command reads from the standard input and writes to the standard output. Therefore, the command line does the following:
* The echo command prints foo bar to the standard output, which is redirected to the standard input of the tee command by the first pipe.
* The tee command reads foo bar from the standard input and writes it to both the standard output and the file bar. The standard output of the tee command is redirected to the standard input of the cat command by the second pipe.
* The cat command reads foo bar from the standard input and writes it to the standard output, which is displayed on the terminal.
Hence, the output of the command line is foo bar. The other options are either incorrect or not applicable.
The cat, tee bar and bar are not printed by any of the commands. The foo is only part of the output, not the whole output. References:
* LPIC-1 Exam 101 Objectives, Topic 103: GNU and Unix Commands, 103.4 Use streams, pipes and redirects
* LPIC-1 Linux Administrator 101-500 Exam FAQ, LPIC-1 Exam 101 Objectives, GNU and Unix Commands (Total Weight: 25)