ARCHIVED: In Unix, what are the two main classes of shells?

In Unix, there are two main classes of shells. The first class consists of the Bourne shell (sh) and its derivatives, which include ksh, bash, and zsh. The second class of shells consists of the C shell (csh) and its derivative tcsh. In addition, there is rc, which most people consider to be in a class by itself, although others argue that rc belongs in the Bourne shell class.

With the classification above, you can write scripts that will work for all the shells from the Bourne shell category, and write other scripts that will work for all of the shells from the C shell category.