# 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)
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://til.yulrizka.com/unix/process-pipe-operator.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.