The Burning Bush

A simple UNIX command interpreter

Table of Contents

• About
• Installation
  • Requirements
  • How to install
• Run on Docker
• Usage
  • Supported Commands
  • Other features
• Examples
• Uninstallation
• Caveats
• Acknowledgement

Introduction

The Burning bush is a simple shell for UNIX-like operating systems. It is a bash (Bourne-Again Shell)-like, and is implemented in C.

Some string functions found in <string.h> header have been re-implemented in this project (for learning purposes).

This project is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Installation

Requirements

• UNIX-like environment, like macOS and Linux.
• GNU GCC, or LLVM Clang compiler.

How to install

Run the installation script with root privileges to install:

sudo ./install.sh

Additionally, you can compile The Burning Bush instead of installing it in your system using the compile.sh script.

Also, you can compile it on the command-line with -Wall -Werror -Wextra -pedantic flags to generate warnings for potential issues/bugs.

Use option -std=gnuXX where XX can be 99, 11, 17 or 2x, depending on the latest version of C supported by your compiler.

For example,

gcc -Wall -Werror -Wextra -pedantic -std=gnu2x *.c -o bush
# or
clang -Wall -Werror -Wextra -pedantic -std=gnu2x *.c -o bush

Alternatively, you can build using CMake and Ninja:

mkdir -p ./cmake-bush

"$(command -v cmake)" -DCMAKE_BUILD_TYPE=Release -DCMAKE_MAKE_PROGRAM="$(command -v ninja)" -G Ninja -S . -B ./cmake-bush

"$(command -v cmake)" --build ./cmake-bush --target bush -j 4

# You can now run
# cd cmake-bush/src && ./bush

Run on Docker

Pull the image from Docker Hub:

docker pull dr8co/bush

Run the image:

docker run -it dr8co/bush

Usage

Run the compiled executable to invoke the shell on the terminal, or invoke with bush command on the terminal to initiate a session if the program was successfully installed in your system.

Terminate with exit.

Supported Commands

The Burning Bush supports all the standard UNIX commands (every program in PATH) as well as a few builtin commands.

The builtins supported are:

• cd [directory]
  Changes the shell working directory. With no argument (or with ~ or ~/ arg), the working directory is changed to $HOME. cd - changes the working directory to the previous working directory.

• exit [status]
  Exits the shell with status (0 by default or if called with no argument).

• pwd
  Prints the shell working directory.

• export [name[=value]]
  Export attribute for shell variables.

• history
  Display history of commands.
  The ! operator is also supported for executing commands in the shell history. (eg !!, !23, !3).

• help [command]
  Displays help. help command displays help for command, where command can be cd, echo, and exit. help. Without any argument, (or with an invalid argument), the general shell help is printed.

Other Features

• Piped commands (eg ls | sort -r).
• Handle interrupt signal: Ctrl-C does not terminate the shell.
• I/O redirection (<, >).
• EOF (Ctrl-D) exits the shell.
• Bash-style multiline commands (commands ending with '\').
• Glob expansion (experimental).
• The primary and secondary prompts are similar to the defaults of bash:

# primary:
username@hostname:current_working_directory$
# secondary:
>

Examples

normal@prompt:bush$ gcc -Wall -Werror -Wextra -pedantic -std=gnu2x *.c -o bush

normal@prompt:bush$ ./bush

ian@github:bush$ help
The Burning Bush, version 1.0.0
These shell commands are defined internally.  Type 'help' to see this list.
Use 'man -k' or 'info' to find out more about commands not in this list.

cd [dir]
echo [arg ...]
exit [n]
export [name[=value] ...]
pwd
history

ian@github:bush$ ls -l src/ | grep "a" | sort -r
total 88
-rw-rw-r-- 1 ian ian  973 Dec 12 23:29 globs.c
-rw-rw-r-- 1 ian ian  801 Dec 11 16:02 prompt.c
-rw-rw-r-- 1 ian ian 6397 Dec 11 16:02 execution.c
-rw-rw-r-- 1 ian ian 4918 Dec 11 16:02 help_msgs.c
-rw-rw-r-- 1 ian ian  463 Dec 11 16:02 signal_handler.c
-rw-rw-r-- 1 ian ian 4608 Dec 11 16:02 strings_1.c
-rw-rw-r-- 1 ian ian 4032 Dec 11 16:02 strings_2.c
-rw-rw-r-- 1 ian ian 3976 Dec 11 16:02 history.c
-rw-rw-r-- 1 ian ian 3502 Dec 16 22:50 process_cmd.c
-rw-rw-r-- 1 ian ian 3460 Dec 11 16:02 main.c
-rw-rw-r-- 1 ian ian 3222 Dec 11 16:02 directories.c
-rw-rw-r-- 1 ian ian  294 Dec 12 16:48 CMakeLists.txt
-rw-rw-r-- 1 ian ian 2889 Dec 11 16:02 get_info.c
-rw-rw-r-- 1 ian ian 2603 Dec 11 16:02 fileops.c
-rw-rw-r-- 1 ian ian 2407 Dec 12 19:24 main.h
-rw-rw-r-- 1 ian ian 1807 Dec 11 16:02 environment.c
-rw-rw-r-- 1 ian ian 1454 Dec 11 16:02 memory.c
-rw-rw-r-- 1 ian ian 1378 Dec 17 23:49 numbers.c
-rw-rw-r-- 1 ian ian 1243 Dec 11 16:02 help.c

ian@github:bush$ echo $HOME
home/ian

ian@github:bush$ whoami > me.txt

ian@github:bush$ cat me.txt
ian

ian@github:bush$ echo "This is a \
> multi-line command."
This is a multi-line command.

ian@github:bush$ tail main.h
void print_prompt1();
void print_prompt2();

/* help.c */
void print_help(const char *str);

/* signal_handler.c */
void signalHandler(int sig_num);

#endif /* MAIN_H */

ian@github:bush$ ls *.sh
compile.sh  install.sh	uninstall.sh

ian@github:bush$ exit 98

normal@prompt:bush$ echo $?
98

Uninstallation

Run the uninstallation script with root privileges to uninstall The Burning Bush from your system:

sudo ./uninstall.sh

Caveats

• Command separators ;, ||, && are not supported.
• No support for background jobs.
• Wildcard expansion/ matching is not fully stable.

Acknowledgement

Project author: Ian Duncan

The "Mother Earth Burning Sticker" courtesy of Tenor and INTO ACTION. It can be found here.