> For the complete documentation index, see [llms.txt](https://til.yulrizka.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://til.yulrizka.com/unix/process-pipe-operator.md).

# process pipe operator

`<( )` operator executes command inside the parenthesis and output the file descriptor

example

```bash
$ cat <(echo 'hello') <(echo 'world')
hello
world

# 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:

```bash
$ comm -3 <(ls -1 dir1) <(ls -1 dir2)
```