Why Write a Shell?
The shell is the interface between the user and the operating system. Understanding it at the implementation level reveals the elegant simplicity of Unix design.
Parsing Commands
The first challenge is parsing user input into a structured command representation. Handling quotes, escapes, pipes, redirects, and semicolons requires a proper tokenizer and parser.
Process Management
Each command spawns a child process via fork() and exec(). Pipes connect the stdout of one process to the stdin of the next. Job control adds background processes and signal handling.
The Surprising Complexity
A shell looks simple from the outside. But handling edge cases -- nested quotes, heredocs, subshells, command substitution -- reveals layers of complexity. POSIX compliance is deceptively hard.
What I Gained
After building a shell, I understand every tool I use daily at a deeper level. Pipes, redirects, environment variables, signals -- none of it is magic anymore.