simple_shell: UNIX Command Line Interpreter in C

A standards-compliant UNIX command language interpreter written in C, implementing interactive and non-interactive command execution, process lifecycle management, path resolution, and builtin commands.

graph TD
    Input[Standard Input / User Command] --> Reader["my_getline() Input Buffer"]
    Reader --> Tokenizer[Lexer & Command Tokenizer]
    Tokenizer --> Parser[Command Node & Argument Builder]
    Parser --> BuiltinCheck{Is Builtin?}
    BuiltinCheck -->|Yes: exit, env, cd| ExecBuiltin[Internal Command Dispatcher]
    BuiltinCheck -->|No| PathResolver["PATH Environment Search ('my_path')"]
    PathResolver --> Fork["fork() Child Process"]
    Fork --> Exec["execve() Binary Execution"]
    Exec --> Wait["waitpid() Parent Process Sync"]

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Core Subsystems

simple_shell mimics the core operational behavior of POSIX shells such as sh and dash:

Subsystem Breakdown

• Input Line Reader (my_getline.c): Custom zero-dependency line reader handling dynamic buffer allocations, newline trimming, and EOF detection without relying on GNU getline.
• Command Tokenizer & Chains (chain.c, my_string_fun.c): String lexer splitting input streams into executable tokens while managing command separator logic (;, &&, ||).
• Path Resolution (my_path.c): Searches system directories specified in the PATH environment variable, validating executable permissions using stat(2).
• Process Orchestration (my_hsh.c): Manages process execution via fork(2) and execve(2), tracking termination status codes and signal interrupts (SIGINT).
• Builtin Dispatcher (builtin_emlatours.c, env.c): Executes internal shell operations without process branching:
  • exit: Clean termination with exit status codes.
  • env: Prints active process environment variables.
  • cd: Modifies current working directory and updates PWD / OLDPWD.
  • alias: Shell alias storage and resolution.

Compilation & Usage

Interactive Mode

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh
./hsh
$ /bin/ls -la
$ exit

Non-Interactive Mode

echo "/bin/ls" | ./hsh