What Type of File Is It?

I have a file that I don't know how to open. It's 2GB and from what I remember it was either a .zip or .dmg file. However some time ago when I made it I also removed the last 3 characters from the name and renamed it .mov. This changed the way that finder dealt with it. Now I would like to open it but when I change the suffix to either of the above they aren't recognised making me wonder if either the file is corrupt or maybe it's not a zip or dmg.

How can I tell what the file is? I've gone into terminal and queried it with the "file" command but it just tells me that it's data.

Any ideas?

What's in the file? That may help us understand what extension it has. Why did you change it to .mov?

Have you tried just double-clicking on it and seeing what the OS does with it? I would imagine the OS is using the magic number to determine the file type rather than the extension.

I don't remember what's in the file. I thought it was a .dmg or .sit image but these don't seem to work.

Double clicking just invokes the finder to try and open the application that is relevant to the suffix, ie. change it to .sit and it tries to unstuff it, change it to .mov and it treats it as a video file. I need to find the correct suffix first.

Try not putting an extension on it and double-clicking on it. Surely finder is smart enough to examine the magic number of the file (the first X number of bytes) before deciding it doesn't know what to do with it.

Just depending on the extension would be dumb.