Linux Shell in C++

A lightweight Unix-style shell implemented in C++ to explore process creation, command execution, pipes, I/O redirection, background processes, and Linux system calls.

Features

• External command execution – runs programs with their arguments in a child process.
• PATH lookup – resolves command names by searching the directories in PATH; commands containing a / (e.g. ./program, /bin/ls) are run directly.
• Pipelines – connects any number of commands with |.
• Input/output redirection – < reads stdin from a file, > writes stdout to a file (created or truncated).
• Background execution – a trailing & starts the command without waiting for it.
• Background job tracking – myjobs lists background processes with their PID, status (Running / Done) and command line.
• Command history – every executed command line is appended to history.txt in the current directory; myhistory prints it.

Built-in commands

Command	Description
myjobs	List background processes and their status
myhistory	Print the command history
exit	Exit the shell (Ctrl-D also exits)

Technical concepts

• fork() – each command in a pipeline runs in its own child process.
• execv() – replaces the child process image with the resolved program.
• waitpid() – the shell waits for all processes of a foreground pipeline, and polls finished background processes with WNOHANG so they are reaped and their status is updated.
• pipe() – creates the channel between consecutive pipeline stages.
• dup2() – rewires stdin/stdout onto pipe ends or redirection files before execv().
• File descriptors – unused pipe ends are closed in both parent and child so readers receive EOF correctly.
• Process management – foreground vs. background execution and tracking of background jobs.

Build and run

Requires Linux, a C++17 compiler (GCC or Clang) and CMake 3.10+.

cmake -S . -B build
cmake --build build
./build/shell

Or compile directly with g++:

g++ -std=c++17 -Wall -Wextra -o shell src/main.cpp
./shell

Example session

shell> ls -l
shell> ls | grep cpp
shell> cat < input.txt
shell> echo hello > output.txt
shell> sleep 10 &
Started process with PID: 4321
shell> myjobs
PID     Status          Command
4321    Running         sleep 10 &
shell> myhistory
ls -l
ls | grep cpp
cat < input.txt
echo hello > output.txt
sleep 10 &
shell> exit

Limitations

This is a learning project, not a full shell. Tokens are split on whitespace, so operators must be separated by spaces (ls | wc, not ls|wc). Quoting, escaping, environment variable expansion, globbing, cd and other shell built-ins, >> append and 2> redirection are not supported.

Project structure

.
├── CMakeLists.txt
├── README.md
└── src/
    └── main.cpp