OShell

A minimal Unix-like command shell implemented in C.

✅ Features

• Built-in commands: exit, cd, env, setenv, unsetenv, alias, path, man 🔧
• Alias support with expansion and automatic alias creation for successfully executed external commands ✨
• Command sequencing (;), conditionals (&&, ||), parallel execution (&) and output redirection (>) 🔗
• Interactive mode (prompt) and batch mode (run commands from a file, return last command's status) 📝
• Signal handling: interactive shell ignores Ctrl+C (SIGINT) while child processes get default behavior; Ctrl+D (EOF) exits the shell 📵
• Manual included (specialized man description) 📓
• Error handling 🪄 + White Space handling

Requirements

• POSIX-like environment (Linux, macOS) or compatible toolchain
• GCC or Clang
• make (optional)

Hawassa University

Operating System Project

Group Members

* Student Name-------------------------- Id
- Astawus Amsalu ------------------ NaScR/1352/16
- ABREHAM ENGIDA ------------------ NaScR/1142/16
- MESERET TAKELE ------------------ NaScR/2919/16
- HAWI KEBEDE --------------------- NaScR/2345/16
- BESUFIKAD TILAHUN --------------- NaScR/1499/16

Compilation instruction ( Build )

From the project root:

make
# or compile manually
gcc -std=c11 -Wall -Wextra -o oshell code/*.c 

#better to compile with make useing provided Makefile

Execution instructions ( Usage )

Interactive:

./oshell
$  # prompt appears

Batch (run commands from a file):

./oshell myscript.sh
# No prompt is printed; the program exits with the last command's exit status

Aliases

• Create or update an alias:

alias ll='ls -l'

• List aliases:

alias    # prints all
alias ll # prints the `ll` alias

• Alias expansion details:
  • Alias values may be quoted with single or double quotes.
  • Only the first token is expanded and any remaining arguments are appended to the expanded command.
  • Recursive expansions are limited to 10 levels to avoid infinite loops.
  • Automatic alias creation: when an external command is executed successfully, OShell creates an alias mapping the command name to the resolved full path (e.g., ls → /bin/ls) if not already present.

Note: There is no unalias builtin yet; you can overwrite an alias by re-defining it.

Signals / Keyboard behavior

• Ctrl+C (SIGINT): ignored by the interactive shell itself (so it won't exit the shell). Child processes restore default SIGINT and therefore can be interrupted.
• Ctrl+D (EOF): ends interactive session and exits the shell gracefully.

Quick manual tests

• Builtins affecting shell process:

  • cd /tmp then pwd should show /tmp.
  • setenv TEST yes then env | grep TEST should show TEST=yes.
  • exit 5 should exit the shell with code 5 (for batch files, check return value).

• Aliases:

  • alias ll='ls -l' → ll /tmp should list /tmp in long format.
  • Run ls and then alias ls should show a mapping to the resolved path.

• Redirection and builtin interaction:

  • echo hi > out.txt creates out.txt and the shell should continue to print normally after.

• Signals:

  • Start a long-running command: sleep 10 and press Ctrl+C to interrupt the child but remain in shell.
  • Press Ctrl+D at the prompt to exit.

File Structure

• Key sources:
  • code/main.c — entrypoint and interactive/batch handling
  • code/parser.c — tokenization, parsing, execution, redirection, and conditionals
  • code/builtin.c, code/builtin.h — builtins and alias storage
  • code/main.c - shell entry point
  • Makefile - easy compilation
• parser.h exports parse_line() which now returns an integer exit status for use in batch files.
• Aliases are stored in an in-memory table; persistence and unalias can be added later.

Quick tests

• Builtins affecting shell process:

  • cd /tmp then pwd shows /tmp.
  • setenv TEST yes then env | grep TEST shows TEST=yes.
  • exit 5 exits the shell with code 5 (for batch files, check return value).

• Aliases:

  • alias ll='ls -l' → ll /tmp lists /tmp in long format.
  • Run ls and then alias ls shows a mapping to the resolved path.

• Redirection and builtin interaction:

  • echo hi > out.txt creates out.txt and the shell continue to print normally after.

• Signals:

  • Start a long-running command: sleep 10 and press Ctrl+C to interrupt the child but remain in shell.
  • Press Ctrl+D at the prompt to exit.

Contributing

• Open an issue or create a pull request for features

  https://github.com/Zking4ever/Oshell