The Burning Bush: A simple UNIX command interpreter

Table of Content

• About
• Installation
  • Requirements
  • How to install
• Usage
  • Supported Commands
  • Other features
• Uninstallation
• Examples
• Unsupported Functionalities
• 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 clang LLVM compiler.

How to install

Run the install.sh 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 (it is advisable to compile with the latest stable standards).

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

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

"$(which cmake)" --build cmake-bush --target bush -j 3

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

• echo [args]
  Writes arguments to the standard output.

• 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 '\').
• The primary and secondary prompts are similar to the defaults of bash:

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

Uninstallation

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

sudo ./uninstall.sh

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 | sort -r
total 104
-rw-rw-r-- 1 ian ian  834 Dec  5 18:44 help.c
-rw-rw-r-- 1 ian ian  801 Dec  2 21:51 prompt.c
-rw-rw-r-- 1 ian ian 6381 Dec  5 18:44 execution.c
-rw-rw-r-- 1 ian ian  463 Dec  5 18:44 signal_handler.c
-rw-rw-r-- 1 ian ian 4608 Dec  5 18:44 strings_1.c
-rw-rw-r-- 1 ian ian 4032 Dec  5 18:44 strings_2.c
-rw-rw-r-- 1 ian ian 3844 Dec  5 21:33 history.c
-rw-rw-r-- 1 ian ian 3502 Dec  5 18:44 process_cmd.c
-rw-rw-r-- 1 ian ian 3452 Dec  5 21:32 main.c
-rw-rw-r-- 1 ian ian 3323 Dec  5 18:44 help_msgs.c
-rw-rw-r-- 1 ian ian  328 Dec  5 18:44 CMakeLists.txt
-rw-rw-r-- 1 ian ian 3277 Dec  5 22:08 README.md
-rw-rw-r-- 1 ian ian 3222 Dec  5 18:44 directories.c
-rw-rw-r-- 1 ian ian 2657 Dec  5 21:11 get_info.c
-rw-rw-r-- 1 ian ian 2419 Dec  5 18:44 fileops.c
-rw-rw-r-- 1 ian ian 2386 Dec  5 21:23 main.h
-rw-rw-r-- 1 ian ian 1827 Dec  5 18:44 environment.c
-rw-rw-r-- 1 ian ian 1454 Dec  5 18:44 memory.c
-rw-rw-r-- 1 ian ian 1426 Dec  5 18:44 numbers.c
-rw-rw-r-- 1 ian ian  108 Nov 21 15:43 AUTHORS
-rw-rw-r-- 1 ian ian 1067 Nov 21 15:43 LICENSE
drwxrwxr-x 2 ian ian 4096 Nov 28 17:13 media

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 find_help(const char *str);

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

#endif /* MAIN_H */

ian@github:bush$ exit 98

normal@prompt:bush$ echo $?
98

Unsupported Functionalities (yet)

• Command separators ;, ||, &&.
• globs *, etc.
• Background jobs.

Acknowledgement

Repository author: Ian Duncan

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