On Thu, Apr 11, 2019 at 06:02:41AM +0200, Jason A. Donenfeld wrote: > what about internally treating "x <<y" as "echo y | > x"? Are these somehow not quite equivalent because x is in a subshell > in one but not the other, or something like that?
cmd <<< string opens a temporary file for writing, dumps the string plus a newline to the temporary file, reopens the temporary file for reading as file descriptor 0 (stdin), and then runs cmd. If you want only string (no newline) to be written, you cannot use this approach. printf %s string | cmd forks two subshells (or one if lastpipe is enabled) with an anonymous pipe between them. The first subshell runs printf, and the second subshell runs cmd. If you want to add a newline, you may use '%s\n' instead of %s. The subshell(s) are run as a single "job" (process group) for job control purposes, unless monitor mode is disabled. cmd < <(printf %s string) runs printf in a background subshell, and cmd as a foreground command. Bash will use either a named pipe or a /dev/fd/ entry to connect them, depending on the platform. And, of course, you may always explicitly create your own temporary file and write whatever you like into it (newlines or not); or explicitly create your own named pipe and launch processes reading/writing from it however you wish. I do not believe it would be a wise decision to "internally treat <<< like a pipeline", because that removes one of the choices in the script writer's toolbox. If you don't like the semantics or the implementation of your chosen tool, choose a different one. Reducing the toolbox because 3 people out of the entire planet decided to pass passwords via <<< without knowing how <<< works seems like a really poor idea to me.
