Systems & CLI · Advanced
Build Your Own Shell
Write a Unix shell in C that runs external programs, pipes them together, redirects their I/O, and handles signals like a real terminal.
You build a working command-line shell in C that reads a line, tokenizes it, and either runs a builtin like cd or exit or launches an external program with fork and execvp. You then extend it to support pipelines (ls | grep | wc), input/output redirection with < and >, and correct signal handling so Ctrl-C interrupts the foreground job instead of killing your shell. It is worth building because it forces you to understand the process model that every operating system is built on, including file descriptors, the fork/exec/wait lifecycle, and how the kernel delivers signals. This is the kind of low-level systems fluency that separates engineers who can reason about production processes from those who only know one language's runtime.
What you build
- Reads and tokenizes a command line into arguments
- Implements builtins cd, exit, and pwd in-process
- Launches external programs with fork and execvp
- Connects commands with pipes using pipe() and dup2()
- Redirects stdin and stdout to files with < and >
- Handles SIGINT so Ctrl-C interrupts the foreground job
- Reports exit status and supports background jobs with &
What it teaches
- The fork/exec/wait process lifecycle
- File descriptors, pipe(), and dup2() plumbing
- POSIX signal handling and signal-safe code
- Parsing and tokenizing user input in C
- Manual memory management with malloc and free
- How a terminal coordinates foreground and background jobs
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Take it further
- Add command history and arrow-key line editing with readline.
- Support job control with fg, bg, and SIGTSTP.
- Add environment variable expansion and globbing of *.
