Process #Substitution
▻http://tldp.org/LDP/abs/html/process-sub.html
Process Substitution
Piping the stdout of a command into the stdin of another is a powerful technique. But, what if you need to pipe the stdout of multiple commands? This is where process substitution comes in.
Process substitution feeds the output of a process (or processes) into the stdin of another process.
#bash
comm <(sort a.txt) <(sort b.txt)
diff <(ls $first_directory) <(ls $second_directory)