diff --git a/source/matplot/backend/backend_interface.h b/source/matplot/backend/backend_interface.h
index f499310f..21185211 100644
--- a/source/matplot/backend/backend_interface.h
+++ b/source/matplot/backend/backend_interface.h
@@ -41,6 +41,7 @@ namespace matplot {
         class MATPLOT_EXPORTS backend_interface {
             /// Virtual functions you can override to create any backend
           public:
+            virtual ~backend_interface() noexcept = default;
             /// \brief True if backend is in interactive mode
             /// One backends might support both interactive and
             /// non-interactive mode.
@@ -213,7 +214,7 @@ namespace matplot {
             /// This is useful when tracing the gnuplot commands
             /// and when generating a gnuplot file.
             virtual void include_comment(const std::string &text);
-        };
+        }; // class backend_interface
     } // namespace backend
 
 } // namespace matplot
diff --git a/source/matplot/backend/gnuplot.cpp b/source/matplot/backend/gnuplot.cpp
index 674e1ff2..b0251b3c 100644
--- a/source/matplot/backend/gnuplot.cpp
+++ b/source/matplot/backend/gnuplot.cpp
@@ -7,7 +7,7 @@
 #include <matplot/util/common.h>
 #include <matplot/util/popen.h>
 #include <iostream>
-#include <regex>
+#include <charconv>
 #include <thread>
 #include <cstring>
 #include <cstdlib>
@@ -317,13 +317,28 @@ namespace matplot::backend {
         }
     }
 
+    /// returns the next word in text after prefix terminated with white space.
+    static std::string_view word_after(std::string_view text, std::string_view prefix)
+    {
+        auto res = text.substr(0,0);
+        if (auto b = text.find(prefix); b != std::string_view::npos) {
+            b += prefix.length();
+            while (b < text.length() && std::isspace(text[b]))
+                ++b; // skip white space before word
+            auto e = b;
+            while (e < text.length() && !std::isspace(text[e]))
+                ++e; // scan until white space or end
+            res = text.substr(b, e-b);
+        }
+        return res;
+    }
+
     std::string gnuplot::default_terminal_type() {
         static std::string terminal_type;
         const bool dont_know_term_type = terminal_type.empty();
         if (dont_know_term_type) {
             terminal_type = run_and_get_output("gnuplot -e \"show terminal\" 2>&1");
-            terminal_type = std::regex_replace(terminal_type,
-                    std::regex("[^]*terminal type is ([^ ]+)[^]*"), "$1");
+            terminal_type = word_after(terminal_type, "terminal type is ");
             const bool still_dont_know_term_type = terminal_type.empty();
             if (still_dont_know_term_type) {
                 terminal_type = "qt";
@@ -334,54 +349,45 @@ namespace matplot::backend {
 
     bool gnuplot::terminal_is_available(std::string_view term) {
         std::string msg = run_and_get_output("gnuplot -e \"set terminal " +
-                                     std::string(term.data()) + "\" 2>&1");
+                std::string{term} + "\" 2>&1");
         return msg.empty();
     }
 
+    template <typename T>
+    void convert_to(std::string_view text, T& value) {
+        std::from_chars(text.data(), text.data() + text.length(), value);
+    }
+
     std::tuple<int, int, int> gnuplot::gnuplot_version() {
-        static std::tuple<int, int, int> version{0, 0, 0};
-        const bool dont_know_gnuplot_version_yet =
-            version == std::tuple<int, int, int>({0, 0, 0});
-        if (dont_know_gnuplot_version_yet) {
-            std::string version_str =
-                run_and_get_output("gnuplot --version 2>&1");
-            std::string version_major = std::regex_replace(
-                version_str,
-                std::regex("[^]*gnuplot (\\d+)\\.\\d+ patchlevel \\d+ *"),
-                "$1");
-            std::string version_minor = std::regex_replace(
-                version_str,
-                std::regex("[^]*gnuplot \\d+\\.(\\d+) patchlevel \\d+ *"),
-                "$1");
-            std::string version_patch = std::regex_replace(
-                version_str,
-                std::regex("[^]*gnuplot \\d+\\.\\d+ patchlevel (\\d+) *"),
-                "$1");
-            try {
-                std::get<0>(version) = std::stoi(version_major);
-            } catch (...) {
-                std::get<0>(version) = 0;
-            }
-            try {
-                std::get<1>(version) = std::stoi(version_minor);
-            } catch (...) {
-                std::get<1>(version) = 0;
-            }
-            try {
-                std::get<2>(version) = std::stoi(version_patch);
-            } catch (...) {
-                std::get<2>(version) = 0;
-            }
-            const bool still_dont_know_gnuplot_version =
-                version == std::tuple<int, int, int>({0, 0, 0});
-            if (still_dont_know_gnuplot_version) {
-                // assume it's 5.2.6 by convention
-                version = std::tuple<int, int, int>({5, 2, 6});
+        constexpr auto version_zero = std::make_tuple(0, 0, 0);
+        static auto version = version_zero;
+        if (version == version_zero) { // unknown version
+            const auto version_str = run_and_get_output("gnuplot --version 2>&1");
+            // gnuplot version_str example: "5.2 patchlevel 6"
+            const auto major_minor = word_after(version_str, "gnuplot"); // "5.2"
+            const auto minor = word_after(major_minor, "."); // "2"
+            const auto patch = word_after(version_str, "patchlevel"); // "6"
+            if (!major_minor.empty() && !minor.empty() && !patch.empty()) {
+                convert_to(major_minor, std::get<0>(version));
+                convert_to(minor, std::get<1>(version));
+                convert_to(patch, std::get<2>(version));
             }
+            if (version == version_zero) // still unknown
+                version = {5, 2, 6}; // assume by convention
         }
         return version;
     }
 
+    bool gnuplot::gnuplot_includes_legends() {
+        return gnuplot_version() >= std::make_tuple(5, 2, 6);
+    }
+    bool gnuplot::gnuplot_has_wall_option() {
+        return gnuplot_version() >= std::make_tuple(5, 5, 0);
+    }
+    bool gnuplot::gnuplot_supports_keyentry() {
+        return gnuplot_version() >= std::make_tuple(5, 2, 6);
+    }
+
     bool gnuplot::terminal_has_title_option(const std::string &t) {
         SV_CONSTEXPR std::string_view whitelist[] = {
             "qt", "aqua", "caca", "canvas", "windows", "wxt", "x11"};
diff --git a/source/matplot/backend/gnuplot.h b/source/matplot/backend/gnuplot.h
index dc74abef..097e19a4 100644
--- a/source/matplot/backend/gnuplot.h
+++ b/source/matplot/backend/gnuplot.h
@@ -48,6 +48,9 @@ namespace matplot::backend {
         static std::string default_terminal_type();
         static bool terminal_is_available(std::string_view);
         static std::tuple<int, int, int> gnuplot_version();
+        static bool gnuplot_includes_legends();
+        static bool gnuplot_has_wall_option();
+        static bool gnuplot_supports_keyentry();
         static bool terminal_has_title_option(const std::string &t);
         static bool terminal_has_size_option(const std::string &t);
         static bool terminal_has_position_option(const std::string &t);
diff --git a/source/matplot/core/axes_type.cpp b/source/matplot/core/axes_type.cpp
index d7594a60..7c057502 100644
--- a/source/matplot/core/axes_type.cpp
+++ b/source/matplot/core/axes_type.cpp
@@ -426,7 +426,7 @@ namespace matplot {
             run_command("set polar");
         }
         auto set_or_unset_axis = [this](class axis_type &ax,
-                                        std::string axis_name,
+                                        const std::string &axis_name,
                                         bool minor_ticks = false) {
             // cb is the only axis we don't unset if tics are empty
             // r-axis labels should still be handled even if axis is invisible since we use the grid
@@ -694,10 +694,7 @@ namespace matplot {
         // Gnuplot version needs to be 5.2.6+ for keyentry
         bool ok = true;
         if (parent_->backend_->consumes_gnuplot_commands()) {
-            if (backend::gnuplot::gnuplot_version() <
-                std::tuple<int, int, int>{5, 2, 6}) {
-                ok = false;
-            }
+            ok = backend::gnuplot::gnuplot_supports_keyentry();
         }
         if (legend_ == nullptr || !legend_->visible() || !ok) {
             run_command("set key off");
@@ -916,9 +913,7 @@ namespace matplot {
             static bool msg_shown_once = false;
             // Gnuplot version needs to be 5.2.6+ for keyentry
             if (parent_->backend_->consumes_gnuplot_commands()) {
-                std::tuple<int, int, int> v =
-                    backend::gnuplot::gnuplot_version();
-                if (v < std::tuple<int, int, int>{5, 2, 6}) {
+                if (backend::gnuplot::gnuplot_includes_legends()) {
                     if (!msg_shown_once) {
                         std::cerr
                             << "You need gnuplot 5.2.6+ to include legends"
@@ -2745,9 +2740,9 @@ namespace matplot {
     }
 
     std::vector<function_line_handle>
-    axes_type::fplot(std::vector<function_line::function_type> equations,
-                     std::array<double, 2> x_range,
-                     std::vector<std::string> line_specs) {
+    axes_type::fplot(const std::vector<function_line::function_type> &equations,
+                     const std::array<double, 2> &x_range,
+                     const std::vector<std::string> &line_specs) {
         axes_silencer temp_silencer_{this};
         std::vector<function_line_handle> res;
         auto it_line_specs = line_specs.begin();
@@ -2764,9 +2759,9 @@ namespace matplot {
     }
 
     std::vector<function_line_handle>
-    axes_type::fplot(std::vector<function_line::function_type> equations,
-                     std::vector<double> x_range,
-                     std::vector<std::string> line_specs) {
+    axes_type::fplot(const std::vector<function_line::function_type>& equations,
+                     const std::vector<double>& x_range,
+                     const std::vector<std::string>& line_specs) {
         return this->fplot(equations, to_array<2>(x_range), line_specs);
     }
 
diff --git a/source/matplot/core/axes_type.h b/source/matplot/core/axes_type.h
index 227003f1..caedf10e 100644
--- a/source/matplot/core/axes_type.h
+++ b/source/matplot/core/axes_type.h
@@ -979,15 +979,15 @@ namespace matplot {
 
         /// Lambda function line plot - list of functions
         std::vector<function_line_handle>
-        fplot(std::vector<function_line::function_type> equations,
-              std::array<double, 2> x_range = {-5, 5},
-              std::vector<std::string> line_specs = {});
+        fplot(const std::vector<function_line::function_type> &equations,
+              const std::array<double, 2> &x_range = {-5, 5},
+              const std::vector<std::string> &line_specs = {});
 
         /// Lambda function line plot - list of functions and line specs
         std::vector<function_line_handle>
-        fplot(std::vector<function_line::function_type> equations,
-              std::vector<double> x_range,
-              std::vector<std::string> line_specs = {});
+        fplot(const std::vector<function_line::function_type> &equations,
+              const std::vector<double> &x_range,
+              const std::vector<std::string> &line_specs = {});
 
         using implicit_function_type = std::function<double(double, double)>;
 
diff --git a/source/matplot/core/figure_type.cpp b/source/matplot/core/figure_type.cpp
index a4ff0903..a895d6ea 100644
--- a/source/matplot/core/figure_type.cpp
+++ b/source/matplot/core/figure_type.cpp
@@ -633,9 +633,7 @@ namespace matplot {
     void figure_type::run_window_color_command() {
         // In gnuplot 5.5 we have the wall function to set the axes color
         // with a rectangle workaround, which does not work well for 3d.
-        static const auto v = backend::gnuplot::gnuplot_version();
-        const bool has_wall_option =
-            std::get<0>(v) > 5 || (std::get<0>(v) == 5 && std::get<1>(v) >= 5);
+        const bool has_wall_option = backend::gnuplot::gnuplot_has_wall_option();
         // So we only plot the default background if it's not 3d or version is
         // higher than 5.5. Otherwise, gnuplot won't be able to set the axes
         // colors.
@@ -895,4 +893,4 @@ namespace matplot {
 
     bool figure_type::should_close() { return backend_->should_close(); }
 
-} // namespace matplot
\ No newline at end of file
+} // namespace matplot