Util: Add convenience functions to save external process creation

src/util/system.cpp

@@ -4,6 +4,7 @@
 #include <cstdlib>    // exit, WEXITSTATUS
 #include <cstring>    // strcpy, strtok
 #include <functional> // function
+#include <sstream>    // istringstream
 #include <string>
 #include <string_view>
 #include <sys/wait.h> // waitpid
@@ -132,6 +133,81 @@ System System::operator||(System rhs)
 	return rhs;
 }
 
+// cut -f
+System& System::cut(uint32_t field)
+{
+	exec();
+
+	return apply([&field](std::vector<std::string>& lines) {
+		for (auto& line : lines) {
+			size_t count = 1;
+			size_t index = 0;
+			while (index != std::string::npos) {
+				if (count == field) {
+					line = line.substr(0, line.find_first_of(" "));
+					break;
+				}
+
+				index = line.find_first_of(" ");
+				line = line.substr(index + 1);
+				count++;
+			}
+		}
+	});
+}
+
+System& System::sort(bool unique)
+{
+	exec();
+
+	return apply([&unique](std::vector<std::string>& lines) {
+		std::sort(lines.begin(), lines.end());
+
+		if (unique) {
+			auto last = std::unique(lines.begin(), lines.end());
+			lines.erase(last, lines.end());
+		}
+	});
+}
+
+// tail -n
+System& System::tail(int32_t number, bool starting)
+{
+	exec();
+
+	return apply([&number, &starting](std::vector<std::string>& lines) {
+		number = abs(number);
+		if (!starting) {
+			lines.erase(lines.begin(), lines.end() - number);
+		}
+		else {
+			lines.erase(lines.begin(), lines.begin() + number - 1);
+		}
+	});
+}
+
+System& System::apply(LineCallback callback)
+{
+	exec();
+
+	std::vector<std::string> lines;
+
+	auto stream = std::istringstream(m_output);
+	std::string line;
+	while (std::getline(stream, line)) {
+		lines.push_back(line);
+	}
+
+	callback(lines);
+
+	m_output.clear();
+	for (size_t i = 0; i < lines.size(); ++i) {
+		m_output.append(lines.at(i) + '\n');
+	}
+
+	return *this;
+}
+
 void System::print(const std::vector<std::string>& arguments)
 {
 	if (!arguments.size()) {

src/util/system.h

@@ -1,7 +1,7 @@
 #ifndef SYSTEM_H
 #define SYSTEM_H
 
-#include <cstddef>    // size_t
+#include <cstdint>    // int32_t, uint32_t
 #include <functional> // function
 #include <string>
 #include <string_view>
@@ -9,7 +9,7 @@
 
 namespace Util {
 
-using SplitCallback = std::function<void(size_t, char*)>;
+using LineCallback = std::function<void(std::vector<std::string>&)>;
 
 class System {
 public:
@@ -36,6 +36,11 @@ public:
 	System operator&&(System rhs);
 	System operator||(System rhs);
 
+	System& cut(uint32_t field);
+	System& sort(bool unique = false);
+	System& tail(int32_t number, bool starting = false);
+	System& apply(LineCallback callback);
+
 	void print(const std::vector<std::string>& arguments);
 
 	const std::vector<std::string>& arguments() const { return m_arguments; }