A common mistake is to use the network file system to copy a program instead of FTP. For example, suppose you create a text file on a Macintosh which has an Appletalk link to the file server that also stores your Unix home directory. If you save the file in this disk directory (it will look like a folder on the Macintosh) the system will write the file OK, and you will be able to retrieve it later using the Macintosh again. However, if you now try to open the file with emacs on your Unix machine it will look like gibberish because the Macintosh application saved in Macintosh text format. If you want to open the file with a Unix application, copy it from the Mac to Unix with FTP and then open the copy.
It is often possible to recognize the type of a file (binary or text) by its name. This is especially true of files that have been placed in the public domain. The convention is to extend the name of a file with up to three letters. For example, documents that will be processed by the LaTeX text formatting program have file names that end in `` .tex''. Output files produced by LaTeX end in `` .aux'' (a text file with definitions of section numbers, etc. used in cross references) and `` .dvi'' (a binary file with the formatted document). Here are some common file extensions you will encounter: