basic implementation

-added exit, echo, type commands
-added ability to execute programs in the $PATH variable

CMakeLists.txt

@@ -3,6 +3,9 @@ project(shell)
 
 set(CMAKE_CXX_STANDARD 23)
 
-add_executable(shell src/main.cpp)
+add_executable(shell src/main.cpp
+        src/shellUtils.cpp
+        include/shellUtils.h)
 
 target_link_libraries(shell PRIVATE readline)
+target_include_directories(shell PRIVATE include)

include/shellUtils.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <iostream>
+#include <string>
+#include <map>
+#include <cstdlib>
+#include <filesystem>
+
+namespace sh
+{
+    enum class Command
+    {
+        exit,
+        echo,
+        type,
+        unknown
+    };
+
+    inline const std::map<const std::string_view, const Command>commandMap
+    {
+                {"exit", Command::exit},
+                {"echo", Command::echo},
+                {"type", Command::type}
+    };
+
+    Command getCommand(std::string_view input);
+
+    std::optional<std::string> isExec(const std::string& input);
+
+    void printType(const std::string& input);
+}

src/main.cpp

@@ -1,7 +1,46 @@
 #include <iostream>
+#include <string>
+#include <map>
+#include <cstdlib>
+#include <filesystem>
+
+#include "shellUtils.h"
 
 int main()
 {
-    std::cout << "Hello, World!" << std::endl;
-    return 0;
+    std::cout << std::unitbuf;
+    std::cerr << std::unitbuf;
+
+    bool exit {false};
+    while (!exit)
+    {
+        std::string input;
+        std::cout << std::unitbuf;
+        std::cout << "$ ";
+        std::getline(std::cin, input);
+        std::optional<std::string> result;
+        switch (sh::Command command = sh::getCommand(input))
+        {
+            case sh::Command::exit:
+                exit = true;
+                break;
+            case sh::Command::echo:
+                std::cout << input.substr(5) << "\n";
+                break;
+            case sh::Command::unknown:
+                result = sh::isExec(input.substr(0, input.find(' ')));
+                if (result)
+                {
+                    std::system(input.c_str());
+                }
+                else
+                {
+                    std::cout << input << ": command not found\n";
+                }
+                break;
+            case sh::Command::type:
+                sh::printType(input.substr(5));
+                break;
+        }
+    }
 }

src/shellUtils.cpp

@@ -0,0 +1,78 @@
+#include "shellUtils.h"
+
+#include <iostream>
+#include <string>
+#include <map>
+#include <cstdlib>
+#include <filesystem>
+
+namespace sh
+{
+    Command getCommand(std::string_view input)
+    {
+        if (commandMap.contains(input.substr(0, input.find(' '))))
+        {
+            return commandMap.at(input.substr(0, input.find(' ')));
+        }
+        else
+        {
+            return Command::unknown;
+        }
+    }
+
+    std::optional<std::string> isExec(const std::string& input)
+    {
+
+        const std::string pathEnv {std::getenv("PATH")};
+#if _WIN32
+        constexpr char delimiter {';'};
+#else
+        constexpr char delimiter {':'};
+#endif
+        size_t startCharIndex{};
+        size_t nextDelimIndex{pathEnv.find(delimiter)};
+        while (nextDelimIndex != std::string::npos)
+        {
+            std::string currentPath {pathEnv.substr(startCharIndex, nextDelimIndex - startCharIndex)};
+            std::string fullPath {currentPath + "/" + input};
+            namespace fs = std::filesystem;
+
+            if (!fs::exists(fullPath))
+            {
+                startCharIndex = nextDelimIndex + 1;
+                nextDelimIndex = pathEnv.find(delimiter, startCharIndex);
+                continue;
+            }
+
+            if ((fs::status(fullPath).permissions() & fs::perms::owner_exec) != fs::perms::owner_exec)
+            {
+                startCharIndex = nextDelimIndex + 1;
+                nextDelimIndex = pathEnv.find(delimiter, startCharIndex);
+                continue;
+            }
+
+            return fullPath;
+        }
+        return std::nullopt;
+    }
+
+    void printType(const std::string& input)
+    {
+        const std::string command {input.substr(0, input.find(' '))};
+        if (commandMap.contains(command))
+        {
+            std::cout << command;
+            std::cout << " is a shell builtin\n";
+            return;
+        }
+
+        if (auto fullPath {isExec(input)})
+        {
+            std::cout << command << " is " << fullPath.value() << "\n";
+            return;
+        }
+
+        std::cout << command;
+        std::cout << ": not found\n";
+    }
+}