> For the complete documentation index, see [llms.txt](https://ret2basic.gitbook.io/ctfnote/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ret2basic.gitbook.io/ctfnote/web/os-command-injection/whitespace-bypass.md).

# Whitespace Bypass

## IFS

**Internal Field Separator (IFS)** refers to a variable which defines the character or characters used to separate a pattern into tokens for some operations. The value of IFS, typically includes the space, tab, and the newline by default. To keep it simple and stupid, just think **IFS = space**. 

## Shell Variables

Shell variables can be referenced using the `$` sign. For example, `$1` refers to the first shell variable and `$2` refers to the second shell variable. Similarly, `$9` refers to the `9th` shell varaible and it is an empty string in most cases.

## Bypassing Whitespace

If whitespaces are blocked by the application, we can try using the following payload to replace whitespace:

```bash
$IFS$9
```

Here `$IFS` acts as a whitespace and `$9` acts as a separator.