Short answer: You can't. rm removes files blindly, with no concept of 'trash'.
Some Unix and Linux systems try to limit its destructive ability by aliasing it to rm -i by default, but not all do.
Long answer: Depending on your filesystem, disk activity, and how long ago the deletion occured, you may be able to recover some or all of what you deleted. If you're using an EXT3 or EXT4 formatted drive, you can check out extundelete.
In the future, use rm with caution. Either create a del alias that provides interactivity, or use a file manager.