What kind of "zip" file are you talking about?
A .tar.gz (or .tgz)? A .bz2? A .zip? A .Z file perhaps?
"unzip" is just one possibility. You can also use "tar" in some cases (GNU tar also has unzipping capabilities)
or "gunzip". Even "uncompress" or "zcat" may even work. Depends on the kind of zip file really.