It's actually process substitution: https://www.gnu.org/software/bash/manual/html_node/Process-Substitution.html https://www.gnu.org/software/bash/manual/html_n

It's actually process substitution: https://www.gnu.org/software/bash/manual/html_node/Process-Substitution.html https://www.gnu.org/software/bash/manual/html_node/Process-S... It's essentially running the process in another shell and sending its output to a tempfile. The name of that file is then substituted in the original command. So, in theory, equivalent to `inner > /tmp/file; outer /tmp/file`. This works with programs that don't read from stdin, or need two or more inputs, for example.