Linux does STDOUT | STDIN piping write data to disk?
Solution 1:
Pipes (or the temporary file system and named FIFO pipes) do seem to write to disk not directly, as commented by Glenn Jackman above, here and here, respectively.
But writing of sensitive data might occur indirectly with memory swapping (or hibernation), possibly even more unexpectedly than with the user knowing to check for undeleted unencrypted files - unless encrypted or disabled.