Ion

A simple shell built in C from scratch. It's a CLI interpreter that sits between you and the kernel — no extra layers, no magic.

Features

• Tab completion — completes command names from $PATH and filenames under the current directory
• Directory jumping — j <name> jumps to the most visited directory matching that name, no full path needed (fuzzy match using frecency)
• Built-in tree view — tree <depth> prints a directory tree without needing the tree package installed
• Pipes — cmd1 | cmd2 connects stdout of one process to stdin of another
• Redirections — > overwrite, >> append, < input redirection
• Signal handling — Ctrl+C kills the running command, not the shell. Ctrl+D exits cleanly
• Raw mode input — reads keypresses directly using termios, no line buffering. This is what makes tab completion and custom keybindings possible
• CWD in prompt — shows current directory with ~ shortening, updates on every command

Building

git clone https://github.com/Whitfrost21/Ion
cd ion
make
./ion

Usage

# pipes
ls | grep .c

# redirections
echo hello > out.txt
cat < out.txt
echo world >> out.txt

# directory jump (visits are tracked automatically on cd)
cd ~/workspace/syswork/shell
j shell        # jumps back to shell next time

# tree
tree 2         # print directory tree 2 levels deep

# tab completion
pw<tab>        # completes to pwd
cat io<tab>    # completes to ion.c

How it works

Every command goes through the same path: read → parse → execute.

Execution uses the Unix fork+execvp model. The shell forks a child process, the child calls execvp which replaces itself with the requested program, and the parent waits. Built-in commands like cd and exit skip this entirely and run directly in the shell process — a child process changing its directory would die immediately leaving the parent unchanged.

Pipes use pipe() + dup2() to connect the stdout of one child to the stdin of another. dup2 redirects file descriptors — the same trick powers redirections, just with files instead of pipe ends.

Directory jumping stores visited paths and their frequency in ~/.ion_history. j <partial> matches against the last component of each stored path using strstr(), picks the highest frequency match, and chdir()s there.

Tab completion scans every directory in $PATH for command matches, and the current directory for filename matches. All of this is possible because of raw mode — without termios the shell would never see the Tab keypress, the terminal would just insert a tab character.

Setting ion as your default shell(testing case)

# add ion to the list of valid shells
echo $(pwd)/ion | sudo tee -a /etc/shells

# set as default (replace /path/to/ion with the actual path)
chsh -s /path/to/ion

Roadmap

• Command history with arrow keys
• Left/right cursor navigation
• tree -a for hidden files
• Multiple pipes (cmd1 | cmd2 | cmd3)
• Prompt showing current git branch
• Config file (~/.config/ion/config)
• Flag completion per command

Contibutions

Contibutions are Welcome, feel free to start Discussions, Issues and send PRs.