sh or Bourne Shell – the original shell still used on UNIX systems and in UNIX related environments. This is the basic shell, a small program with few features. When in POSIX-compatible mode, bash will emulate this shell.
bash or Bourne Again SHell – the standard GNU shell, intuitive and flexible. Probably most advisable for beginning users while being at the same time a powerful tool for the advanced and professional user. On Linux, bash is the standard shell for common users. This shell is a so-called superset of the Bourne shell, a set of add-ons and plug-ins. This means that the Bourne Again SHell is compatible with the Bourne shell: commands that work in sh, also work in bash. However, the reverse is not always the case. All examples and exercises in this book use bash.
csh or C Shell – the syntax of this shell resembles that of the C programming language. Sometimes asked for by programmers.
tcsh or Turbo C Shell -a superset of the common C Shell, enhancing user-friendliness and speed.
ksh or the Korn shell – sometimes appreciated by people with a UNIX background. A superset of the Bourne shell; with standard configuration a nightmare for beginning users.
The /etc/shells file contains a list of login shells on the system: