SCP: Provide a way to gather input from a user into an environment variable

SET ENV -P "Prompt String" EnvVar=Default

README.md

@@ -261,7 +261,8 @@ The EXPECT command now exists to provide a means of reacting to simulator output
 #### New SCP Commands:
 
     SCREENSHOT filename.bmp          Save video window to the specified file
-    SET ENVIRONMENT Name=Value      Set Environment variable
+    SET ENV Name=Value               Set Environment variable
+    SET ENV -p "Prompt" Name=Default Gather User input into an Environment Variable
     SET ASYNCH                       Enable Asynchronous I/O
     SET NOASYNCH                     Disable Asynchronous I/O
     SET VERIFY                       Enable commang display while processing DO command files

scp.c

@@ -1161,10 +1161,19 @@ static const char simh_help[] =
       "3Asynch\n"
       "+set asynch                  enable asynchronous I/O\n"
       "+set noasynch                disable asynchronous I/O\n"
-#define HLP_SET_ENVIRON "*Commands SET Asynch"
+#define HLP_SET_ENVIRON "*Commands SET Environment"
       "3Environment\n"
+      "4Explicitily Changing A Variable\n"
       "+set environment name=val    set environment variable\n"
       "+set environment name        clear environment variable\n"
+      "4Gathering Input From A User\n"
+      " Input from a user can be obtained by:\n\n"
+      "+set environment -p \"Prompt String\" name=default\n\n"
+      " The -p switch indicates that the user should be prompted\n"
+      " with the indicated prompt string and the input provided\n"
+      " will be saved in the environment variable 'name'.  If no\n"
+      " input is provided, the value specified as 'default' will be\n"
+      " used.\n"
 #define HLP_SET_ON      "*Commands SET Command_Status_Trap_Dispatching"
       "3Command Status Trap Dispatching\n"
       "+set on                      enables error checking after command\n"
@@ -3996,10 +4005,42 @@ return SCPE_OK;
 
 t_stat sim_set_environment (int32 flag, CONST char *cptr)
 {
-char varname[CBUFSIZE];
+char varname[CBUFSIZE], prompt[CBUFSIZE];
 
 if ((!cptr) || (*cptr == 0))                            /* now eol? */
     return SCPE_2FARG;
+if (sim_switches & SWMASK ('P')) {
+    char cbuf[CBUFSIZE];
+    CONST char *deflt = NULL;
+
+    cptr = get_glyph_quoted (cptr, prompt, 0);          /* get prompt */
+    if (prompt[0] == '\0')
+        return sim_messagef (SCPE_2FARG, "Missing Prompt and Environment Variable Name\n");
+    if ((prompt[0] == '"') || (prompt[0] == '\'')) {
+        prompt[strlen (prompt) - 1] = '\0';
+        memmove (prompt, prompt + 1, strlen (prompt));
+        }
+    deflt = get_glyph (cptr, varname, '=');             /* get environment variable name */
+    if (deflt == NULL)
+        deflt = "";
+    if (*deflt) {
+        strlcat (prompt, " [", sizeof (prompt));
+        strlcat (prompt, deflt, sizeof (prompt));
+        strlcat (prompt, "] ", sizeof (prompt));
+        }
+    else
+        strlcat (prompt, " ", sizeof (prompt));
+    if (sim_rem_cmd_active_line == -1) {
+        cptr = read_line_p (prompt, cbuf, sizeof(cbuf), stdin);
+        if ((cptr == NULL) || (*cptr == 0))
+            cptr = deflt;
+        else
+            cptr = cbuf;
+        }
+    else
+        cptr = deflt;
+    }
+else
     cptr = get_glyph (cptr, varname, '=');              /* get environment variable name */
 setenv(varname, cptr, 1);
 return SCPE_OK;