[FEATURE] Open man page

Author: eseiler

include/sharg/detail/format_man.hpp

@@ -13,6 +13,7 @@
 #pragma once
 
 #include <sharg/detail/format_base.hpp>
+#include <sharg/test/tmp_filename.hpp>
 
 namespace sharg::detail
 {
@@ -38,6 +39,9 @@ class format_man : public format_help_base<format_man>
     //!\brief Befriend the base class to give access to the private member functions.
     friend base_type;
 
+    //!\brief Whether to call man and open the man page.
+    bool open_man_page{false};
+
 public:
     /*!\name Constructors, destructor and assignment
      * \{
@@ -52,10 +56,35 @@ class format_man : public format_help_base<format_man>
     //!\copydoc sharg::detail::format_help_base::format_help_base
     format_man(std::vector<std::string> const & names,
                update_notifications const version_updates,
-               bool const advanced = false) :
-        base_type{names, version_updates, advanced} {};
+               bool const advanced = false,
+               bool const open_man_page = false) :
+        base_type{names, version_updates, advanced},
+        open_man_page{open_man_page} {};
     //!\}
 
+    void parse(parser_meta_data & parser_meta)
+    {
+        if (!open_man_page)
+            return base_type::parse(parser_meta);
+
+        sharg::test::tmp_filename tmp_file{parser_meta.app_name.c_str()};
+
+        {
+            std::ofstream out{tmp_file.get_path()};
+            std::streambuf * coutbuf = std::cout.rdbuf();
+            std::cout.rdbuf(out.rdbuf());
+
+            base_type::parse(parser_meta);
+
+            std::cout.rdbuf(coutbuf);
+        }
+
+        std::string command{"/usr/bin/man -l "};
+        command += tmp_file.get_path().c_str();
+        if (std::system(command.c_str()) != 0)
+            throw sharg::parser_error{"Unexpected failure."}; // LCOV_EXCL_LINE
+    }
+
 private:
     //!\brief Prints a help page header in man page format to std::cout.
     void print_header()

include/sharg/detail/terminal.hpp

@@ -46,6 +46,21 @@ inline bool input_is_terminal()
 #endif
 }
 
+/*!\brief Check whether the output is interactive.
+ * \ingroup parser
+ * \return True if code is run in a terminal, false otherwise.
+ * \details
+ * For example "./some_binary --help | less" will return false. "./some_binary --help" will return true.
+ */
+inline bool output_is_terminal()
+{
+#ifndef _WIN32
+    return isatty(STDOUT_FILENO);
+#else
+    return false;
+#endif
+}
+
 // ----------------------------------------------------------------------------
 // Function get_terminal_size()
 // ----------------------------------------------------------------------------

include/sharg/parser.hpp

@@ -758,6 +758,7 @@ class parser
         executable_name.emplace_back(argv[0]);
 
         bool special_format_was_set{false};
+        bool const use_man = detail::output_is_terminal() && !system("which /usr/bin/man > /dev/null 2>&1");
 
         for (int i = 1, argv_len = argc; i < argv_len; ++i) // start at 1 to skip binary name
         {
@@ -793,12 +794,18 @@ class parser
 
             if (arg == "-h" || arg == "--help")
             {
-                format = detail::format_help{subcommands, version_check_dev_decision, false};
+                if (use_man)
+                    format = detail::format_man{subcommands, version_check_dev_decision, false, true};
+                else
+                    format = detail::format_help{subcommands, version_check_dev_decision, false};
                 special_format_was_set = true;
             }
             else if (arg == "-hh" || arg == "--advanced-help")
             {
-                format = detail::format_help{subcommands, version_check_dev_decision, true};
+                if (use_man)
+                    format = detail::format_man{subcommands, version_check_dev_decision, true, true};
+                else
+                    format = detail::format_help{subcommands, version_check_dev_decision, true};
                 special_format_was_set = true;
             }
             else if (arg == "--version")