Process substitution can be used to create a file descriptor from the
evaluation of a shell command. The syntax for process substitution is
<(LIST) where LIST is one or more bash commands.
$ cat <(echo 'hello, world')
hello, world
This is particularly useful for commands that expect files, such as diff:
$ diff <(echo 'hello, world') <(echo 'hello, mars')
1c1
< hello, world
---
> hello, mars
Sources: Brian Dunn and Bash Guide for Beginners