The Unix Shell
Discussion
Other Shells
Before Bash became popular in the end of nineties, scientists widely used (and some still use) another shell, C-shell, or Csh. Bash and Csh have similar feature sets, but their syntax rules are different and this makes them incompatible with each other. A few other shells have appeared since, including ksh, zsh, and a number of others; they are mostly compatible with Bash, and Bash is the default shell on most modern implementations of Unix (including most packages that provide Unix-like tools for Windows) but if you get strange errors in shell scripts written by colleagues, check to see which shell they were written for.