Seashell

Introduction

Seashell is a UNIX shell written in C.

Program description:

• Seashell can read and execute simple user commands:

Cli>/bin/ls

Cli>ls

• Also, it can interpret a command with arguments:

Cli>ls -l -a

• The commands can be combined in a pipe line (forward output to the next command):

Cli>ls -l -a | grep main

• And can handle pipe line, globing and separator:

Cli>ls -l -a | grep a | wc -l ; ls * ; echo 1

...

Setting up seashell

Clone the project to retrieve the sources:

$>git clone https://github.com/adugast/seashell.git

Go in the build directory of seashell:

$>cd seashell/build/

Build the project using CMake (from the build directory):

$>cmake ..

Finally, use make to compile the sources and so generate the binary (still from the build directory):

$>make

Usage:

Launch seashell:

$>./seashell

Output:

Cli>ls -l -a | grep a | wc -l
11
Cli>nproc
8
Cli>uname -r
3.10.0-327.10.1.el7.x86_64
Cli>ps
  PID TTY          TIME CMD
 8445 pts/56   00:00:00 bash
11615 pts/56   00:00:00 seashell
11616 pts/56   00:00:00 ps
Cli>
Cli>exit

Help:

Usage: ./seashell [params]
Available params:
 -h, --help     : Display this help and exit
 -v, --version  : Show version information
 -f, --features : Show seashell features

Supported features:

Done

Cursor motion:

• Left, Right Arrows : Move into command line
• Up, Down Arrows : Brows through commands history

Control keys:

• CTRL^L : Clear the screen
• CTRL^A : Move to the start of the line
• CTRL^E : Move to the end of the line

Command parsing:

• Separators: ;
• Globing: * ? [] {}
• Multipipes
• ...

Ongoing:

• Alias
• Redirections: < > >>
• Separators: && ||
• Autocompletion
• History whith file
• Builtins: cd, echo, exit, ...
• Job control

How seashell works:

+----------------------------+
|Processing of the user input|
+----------------------------+

+----------+
|user input|        -IN- user keyboard
+----+-----+
     |              A read function call is used to get input from STDIN
     |              and generates a buffer with RAW data.
     v              (contains printable and special characters)
 +---+--+
 |buffer|           (main interpret function)
 +---+--+
     |              Special characters are directly proceed to handle terminal
     |              management (i.e arrow keys, ctrl keys, delete, backspace, etc ...)
     |              and a new buffer line with only printable characters is reconstructed
     v    <-^
  +--+-+  | |
  |line|  | |       (main loop - read keyboard function)
  +--+-+  | |
     |    v->       After pressing "enter", the buffer line goes to the execution module
     |              and becomes the command line to execute.
     v              (i.e "ls -l -a | grep a | wc -l ; ls * ; echo 42")
 +---+----+
 |cmd line|         (execution module)
 +--------+
                    Then the command line is parsed by the parser module for each
                    ";", "|" and " " characters and executed.

";" commands separator
"|" split the commands to be executed in a pipeline (output of the executed command is transferred as input for the following command)
" " split the command with their own arguments

More info:

• Terminfo and Termcap - Introduction to terminal capabilities and database
• man (5) terminfo - Terminal capability database
• ANSI Escape Sequences - Keycode management
• ASCII Flow - Simple web based ascii flow diagram drawing tool

License

This project is licensed under the MIT License - see the LICENSE file for details