<( ) operator executes command inside the parenthesis and output the file descriptor
example
$ cat <(echo 'hello') <(echo 'world')helloworld​# is practically the same with​$ echo 'hello' > 1.txt$ echo 'world' > 2.txt$ cat 1.txt 2.txt​# replace cat with ls$ ls <(echo 'hello') <(echo 'world')/proc/self/fd/11 /proc/self/fd/12
you can use this command for example to compare 2 directory and find only uniq file
example:
$ comm -3 <(ls -1 dir1) <(ls -1 dir2)