MyMiniShell

MyMiniShell is a small Linux shell written in C as a learning project. Its goal is to build an understanding of input handling, parsing, built-in commands, processes, system calls, pipes, and redirection one stage at a time.

Learning roadmap

1. Build the REPL loop: prompt, read, repeat, and exit.
2. Parse input into a command and arguments.
3. Add built-in commands such as help, pwd, and cd.
4. Run external programs using Linux process APIs.
5. Add pipes.
6. Add input and output redirection.

Each stage should be understood and tested before moving to the next one.

Current stage: REPL loop

The first version can:

• display the minishell> prompt;
• read one line safely with fgets;
• remove the trailing newline;
• exit when the user enters exit;
• stop cleanly when it reaches end-of-file (Ctrl+D).

It does not execute external commands yet. That is intentional.

Current features

MyMiniShell currently supports:

• Interactive REPL prompt
• Command tokenization
• Built-in commands:
  • help
  • exit
  • pwd
  • cd
• External command execution using fork(), execvp(), and waitpid()
• Child-process exit status handling
• Output redirection:
  • > — create or truncate a file
  • >> — append to a file
• Input redirection with <
• Combined input and output redirection
• Pipelines containing multiple external commands
• Automated tests for tokenization, external commands, redirection, and pipelines

Examples

./minishell

minishell> pwd
/home/user/MyMiniShell

minishell> echo hello
hello

minishell> echo hello > output.txt
minishell> cat output.txt
hello

minishell> echo second >> output.txt

minishell> sort < unsorted.txt > sorted.txt

minishell> ls | grep test | wc -l

minishell> exit

Current limitations

MyMiniShell is a learning project and is not intended to replace a production shell.

The current parser:

• Requires spaces around operators such as |, <, >, and >>
• Does not yet understand single or double quotes
• Does not support escape sequences
• Does not support environment-variable expansion such as $HOME
• Does not support wildcard expansion such as *.c
• Does not yet combine redirection with pipelines
• Supports built-ins only outside pipelines
• Does not include job control or background execution with &

Tests

Build and run all tests with:

make clean test

The test suite currently covers:

• Tokenization
• External command execution and exit statuses
• Input, output, append, and combined redirection
• Single and multiple-command pipelines

Some negative tests intentionally print error messages while confirming that invalid commands return the expected status.

Project structure

MyMiniShell/
├── include/       # Header files when the project grows
├── src/
│   └── main.c
├── tests/         # Tests added with later stages
├── .gitignore
├── Makefile
└── README.md

Build and run

On Ubuntu, install the compiler tools once:

sudo apt update
sudo apt install build-essential git

Then build and run:

make
./minishell

Or use:

make run

Remove the compiled program with:

make clean

First manual checks

minishell> hello
minishell> exit

hello is only read at this stage; it is not executed. The second line exits the shell.