Add SET /ERASE as a way to clear the environment block

CHANGELOG

@@ -1,4 +1,7 @@
 NEXT
+  - SET command processing has been cleaned up and streamlined.
+    Added /ERASE command line switch to clear the environment
+    block (DOSBox-X extension). (joncampbell123).
   - VESA BIOS: Add new option to adjust reported linear framebuffer
     address by a specific number of pixels. This is needed by
     "Out of Control" by Contract which for whatever reason,

include/programs.h

@@ -102,6 +102,7 @@ class Program {
 	bool GetEnvNum(Bitu want_num,std::string & result);      //! Return an environment variable by index
 	Bitu GetEnvCount(void);                             //! Return the number of environmental variables
 	bool SetEnv(const char * entry,const char * new_string); //! Set environment variable
+	bool EraseEnv(void);
 	virtual void WriteOut(const char *format, const char * arguments);
 	void WriteOut(const char * format,...);				//! Write to standard output 
 	virtual int WriteOut_NoParsing(const char * format, bool dbcs = false); //! Write to standard output, no parsing

src/misc/programs.cpp

@@ -497,6 +497,26 @@ void Program::DebugDumpEnv() {
 	}
 }
 
+bool Program::EraseEnv(void) {
+	PhysPt env_base,env_fence;
+	size_t nsl = 0,el = 0,needs;
+
+	if (dos_kernel_disabled) {
+		LOG_MSG("BUG: Program::EraseEnv() called with DOS kernel disabled (such as OS boot).\n");
+		return false;
+	}
+
+	if (!LocateEnvironmentBlock(env_base,env_fence,psp->GetEnvironment())) {
+		LOG_MSG("Warning: SetEnv() was not able to locate the program's environment block\n");
+		return false;
+	}
+
+	for (PhysPt w=env_base;w < env_fence;w++)
+		mem_writeb(w,0);
+
+	return true;
+}
+
 /* NTS: "entry" string must have already been converted to uppercase */
 bool Program::SetEnv(const char * entry,const char * new_string) {
 	PhysPt env_base,env_fence,env_scan;

src/shell/shell_cmds.cpp

@@ -2732,7 +2732,8 @@ void DOS_Shell::CMD_SET(char * args) {
 	enum op_mode_t {
 		show_all_env,
 		set_env,
-		show_env
+		show_env,
+		erase_env
 	};
 
 	op_mode_t op_mode = show_all_env;
@@ -2753,6 +2754,9 @@ void DOS_Shell::CMD_SET(char * args) {
 				WriteOut("Set /P is not supported. Use Choice!"); /* TODO: What is SET /P supposed to do? */
 				return;
 			}
+			else if (sw == "ERASE") { /* DOSBox-X extension: Completely erase the environment block */
+				op_mode = erase_env;
+			}
 			else {
 				WriteOut("Unknown switch /");
 				WriteOut(sw.c_str());
@@ -2806,6 +2810,10 @@ void DOS_Shell::CMD_SET(char * args) {
 				WriteOut(MSG_Get("SHELL_CMD_SET_OUT_OF_SPACE"));
 
 			break;
+		case erase_env:
+			if (!EraseEnv())
+				WriteOut("Unable to erase environment block\n");
+			break;
 		default:
 			abort();
 			break;