I thought the convention was ending the command with `-`. Like the example

```
nc -l -p 12345 | tar xvzf -
```

And it also (to my knowledge) instructs the application to use stdin **and** stdout. This would allow for some nifty use-cases though, like

```
# take a file, read it, run it through traceur and gzip the result.
cat "$file" | traceur - | gzip --stdout > "$file.gz"
```