Which of the following commands redirects the output of cmd to the file foo.txt, in which an existing file is overwritten?

|| is the logical OR operator that runs the right-hand command only if the left-hand command fails; it does not redirect output to a file.

| is the pipe operator that connects the standard output of cmd to the standard input of another command; foo.txt is not a command and this would fail.

&& is the logical AND operator that runs the right-hand command only if the left-hand command succeeds; it does not redirect output to a file.

>> appends standard output to the file rather than overwriting it, so existing content is preserved.

The > operator in shell redirects standard output of cmd to foo.txt, truncating and overwriting the file if it exists, or creating it if it does not. This is the standard single-arrow output redirection in POSIX shells.