# The Execution Process of 'ls > list' Command


## Question

![Question](https://vip2.loli.net/2023/01/13/lUe7vE2SH8GOdLy.webp)

```shell
root@VM-0-11-debian:~/linux/2023/01# ls
root@VM-0-11-debian:~/linux/2023/01# ls > list
root@VM-0-11-debian:~/linux/2023/01# ls
list
root@VM-0-11-debian:~/linux/2023/01# cat list
list
```

I know the `>` symbol redirects standard output to a file. If the file doesn't exist, it creates the file; otherwise, it replaces the file.

I want to ask whether the execution process of the shell command `ls > list` is as I describe below:

1) Because a file named "list" doesn't exist, it first creates a file named "list".

2) The `ls` command lists the contents of the directory (list), and the listed content is sent to standard output.

3) In a replacement mode, the content from standard output (list) is added to the file named "list".

My personal understanding of the execution process is as described above. I hope you can give me some guidance, thank you.

## Answer

![Answer](https://vip2.loli.net/2023/01/13/SDzKNMrwpI2bvCh.webp)

The file redirection operator `>` is handled by the shell and creates/truncates whatever file you write to before starting the binary (ls). That's why you can see the filename "list" in the file contents: the file was created before the ls process started.

Yes, your understanding is correct.

This is why it's not possible to do things like `sort txt > txt` — before sort reads the file, the file named txt will be truncated. You'll end up with an empty file. (Note: the sort command is used to sort all lines in a text file)

## Summary

The execution process of `ls > list`:

1) `> list` creates a file named "list"

2) `ls` command lists the directory contents (result is "list")

3) The result "list" is written to the file named "list" in replacement mode.

There's still a lot worth exploring in shell/Linux commands. Today I saw an article [What happens when you open a terminal and enter 'ls'](https://www.warp.dev/blog/what-happens-when-you-open-a-terminal-and-enter-ls). The article explains what happens when you open a terminal and enter the `ls` command. After browsing through it, I found many concepts and terms I didn't understand. Reading this article was somewhat painful for me, but it precisely points out the direction for my future efforts.

[Question Source](https://stackoverflow.com/questions/74993370/query-of-the-execution-step-of-shell-command-ls-list)