What is /dev/null in Unix / Linux ?

`/dev/null` is a special file in Unix-based operating systems that serves as a "bit bucket" or a sink for all data written to it. Any data written to `/dev/null` is discarded and not saved anywhere. 

Here's an example of how to use `/dev/null` to discard unwanted output from a command:

```

command > /dev/null

```

In this example, `command` is the command you want to run, and the `>` symbol redirects the output of the command to `/dev/null`. This means that any output that would normally be displayed on the screen is discarded and not saved.

For example, let's say you want to run a command that produces a lot of output, but you don't want to see the output on the screen. You can redirect the output to `/dev/null` like this:

```

ls -lR / > /dev/null

```

In this example, the `ls` command is used to list the contents of the root directory and all its subdirectories in a long format. The output of the command is redirected to `/dev/null`, so none of the output is displayed on the screen.

Overall, `/dev/null` is a useful device file in Unix-based operating systems for efficiently disposing of unwanted data.