What is 21sh

21sh is a bash-styled shell project completely written from scratch in C with very limited access to libraries and tools.

The learning goals of the project:

• Learn a lot more about the inner workings of the UNIX system.
• Learn about the different type of shell implementations.
• Learn what a lexer is and how to write it.
• Learn what a parser is and how to write it.
• Learn how to write nice and clean code.
• To create a stable and complete UNIX shell.

Functionality

1. Error monitoring without using errno.
2. Prompt display.
3. Complete management of input.
4. (Multiline) line edition.
5. Redirection with the following operators:
   • >
   • >>
   • <
   • <<
   • >&
   • <&
6. Control operators:
   • |
   • ||
   • &&
   • ;
7. Quoting managment ", ', and \.
8. Basic parameter expansion.
9. Command history
10. Autocomplete
11. Builtins:

• echo
• cd
• env
• setenv
• unsetenv
• exit
• type

Installing and running 21sh

Install:

make && make clean

Run:

./21sh

Authors

Volkov Ilya, Alex Buyanov