first version of system-cmd

ml.cpp

@@ -1213,6 +1213,47 @@ namespace builtin {
         return json.ivalualize();
     }
 
+    // Execute system command
+    MlValue system_cmd(std::vector<MlValue> args, MlEnvironment &env) {
+        eval_args(args, env);
+
+        // TODO add support for more params constructing options as one string
+        // TODO add support for stderr
+        if (args.size() != 1)
+            throw MlError(MlValue("system-cmd", system_cmd), env, args.size() > 1 ? TOO_MANY_ARGS : TOO_FEW_ARGS);
+
+        std::string cmd = args[0].as_string();
+
+        std::string cmd_output = "";
+        int stat;
+
+        // TODO better parameter here
+        // TODO handle reading of stderr
+        // https://stackoverflow.com/questions/478898/how-do-i-execute-a-command-and-get-the-output-of-the-command-within-c-using-po
+        // https://jineshkj.wordpress.com/2006/12/22/how-to-capture-stdin-stdout-and-stderr-of-child-program/
+        char buffer[128];
+        FILE *pipe = popen(cmd.c_str(), "r");
+        if (!pipe)
+            throw std::runtime_error("popen() failed!");
+        try {
+            while (!std::feof(pipe)) {
+                if (std::fgets(buffer, 128, pipe) != nullptr)
+                    cmd_output += buffer;
+            }
+        } catch (...) {
+            stat = pclose(pipe);
+            throw;
+        }
+        stat = pclose(pipe);
+        int cmd_retval = WEXITSTATUS(stat);
+
+        // TODO add helper function for this
+        std::vector<MlValue> lst;
+        lst.push_back(MlValue(cmd_retval));
+        lst.push_back(MlValue::string(cmd_output));
+        return lst;
+    }
+
 
     // Read a file and execute its code
     MlValue include(std::vector<MlValue> args, MlEnvironment &env) {
@@ -1738,6 +1779,7 @@ MlValue MlEnvironment::get(const std::string& name) const {
     if (name == "write-file") return MlValue("write-file", builtin::write_file);
     if (name == "read-url") return MlValue("read-url", builtin::read_url);
     if (name == "read-json") return MlValue("read-json", builtin::read_json);
+    if (name == "system-cmd") return MlValue("system-cmd", builtin::system_cmd);
 #endif
 
     // String operations