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Unix-Shell

A Unix-like shell built from scratch in C++ with pipelines, job control, I/O redirection, persistent history, and tab completion.

Features

  • Command execution — runs external commands via fork() + execvp()
  • Pipelines — two-command pipes using pipe(), fork(), and dup2()
  • Background jobs — run commands with &, track with a jobs builtin
  • Job control — job number recycling, async reaping via waitpid(WNOHANG)
  • I/O redirection — >, <, >> support
  • Shell history — persistent history with HISTFILE, history, history -r, history -w, history -a
  • Tab completion — custom TAB completion using complete -C external completer scripts with longest-common-prefix logic and bell-on-first / list-on-second behavior
  • Variable expansion — declare builtin and expandVars() for parameter expansion
  • GNU Readline — full readline integration for line editing

Builtins

Command Description
cd Change directory
pwd Print working directory
echo Print arguments
export Set environment variables
declare Declare shell variables
jobs List background jobs
history Show/manage command history
exit Exit the shell

Installation

Requirements: Linux, g++, GNU Readline

# Clone the repo
git clone https://github.com/vinaayy06/shell.git
cd shell

# Install readline (if not already installed)
sudo apt-get install libreadline-dev

# Build
g++ -std=c++17 src/*.cpp -lreadline -o shell

# Run
./shell

Usage

# Basic command
$ ls -la

# Pipeline
$ ls | grep .cpp

# Background job
$ sleep 10 &
[1] 12345

# Check jobs
$ jobs
[1]+ Running    sleep 10

# Redirect output
$ echo hello > out.txt

# Variable declaration
$ declare x=42
$ echo $x
42

# History
$ history
$ history -w   # write to HISTFILE
$ history -r   # read from HISTFILE

Technical Details

  • Process management: fork(), exec(), waitpid()
  • IPC: pipe(), dup2() for pipeline chaining
  • Signal handling: background job reaping with WNOHANG
  • Readline integration via GNU Readline library
  • Tab completion via external completer scripts (complete -C)

Languages

C++ 100%