Using rm is relatively permanent
You can't easily 'un-rm' a file, unfortunately. The data are still there on disk, but all links to them in the file system table are removed. That's actually what rm does; it deletes the link to the file(s) in the file system table and frees the space so it can be used by other files in the future.
Using some (non-standard) software, it's possible to analyze the hard disk to find deleted files that haven't yet been overwritten. Using even more sophisticated hardware AND software, it's sometimes possible to recreate files that have only been overwritten once. Programs like shred overwrite the disk multiple times with random data specifically to thwart such methods.