NovaShell-showcase1.webm

Example NovaShell session.

NovaShell

A custom shell implementation developed as part of the Operating Systems course at Theoretical Computer Science, Jagiellonian University, Cracow.

Implemented Features

NovaShell is implemented incrementally across five stages. The final version includes all functionality listed below.

1. Core command execution

• Interactive read-eval loop with configurable prompt (PROMPT_STR).
• Line-oriented input handling with length guard (MAX_LINE_LENGTH) and syntax error reporting.
• Process spawning with fork + execvp, including PATH lookup.
• Parent waits for foreground child completion and reports execution failures using assignment-defined messages.

2. Robust input stream handling

• Prompt is shown only for terminal input (interactive mode).
• Correct handling of partial reads and multiple lines delivered in a single read call.
• Supports script/file input where the last line may end at EOF without a trailing newline.

3. Built-in commands

• Built-in dispatch table in builtins.c checked before external execution.
• Implemented built-ins:
  • exit
  • lcd [path] (falls back to HOME)
  • lkill [ -signal ] pid (default: SIGTERM)
  • lls (lists non-hidden entries from current directory)
• Consistent built-in error path for invalid arguments and syscall failures.

4. Redirections and pipelines

• Input/output redirections per command (<, >, >>) with open/create/truncate/append semantics.
• Redirection setup via descriptor duplication (dup2) before program execution.
• Multi-process pipeline execution with pipe, one child per command, shell waits for pipeline completion in foreground mode.
• Support for multiple pipelines in one line, executed sequentially.
• Parser edge-case handling: invalid/empty commands inside multi-command pipelines are rejected as syntax errors.

5. Background jobs and signal handling

• Pipelines ending with & execute in background without blocking the shell.
• Foreground and background execution paths are separated so interactive shell remains responsive.
• Child-reaping logic prevents zombie accumulation.
• In interactive mode, deferred notifications are printed before the next prompt for terminated background processes:
  • normal exit status
  • termination by signal
• SIGINT behavior aligns with shell expectations: foreground jobs are interruptible by CTRL-C, background jobs are isolated from terminal interrupts.

Architecture notes

• Command parsing is provided by lexer/parser sources in shell/input_parse/.
• Execution logic is split into focused modules in shell/src/ (argument parsing, builtin handling, execution preparation, executor, subprocess management, input handling, and utility/debug helpers).

Getting Started

Prerequisites

gcc make byacc lex

Building NovaShell

cd shell
make bin/novash

Copyright (C) 2025, Kacper Orszulak

GNU General Public License v3.0+ (see LICENSE.txt or https://www.gnu.org/licenses/gpl-3.0.txt)