Use standard markup '{}' like macros. Add coments.

dbms/src/Server/Client.cpp

@@ -381,7 +381,7 @@ private:
         Strings keys;
         config().keys("prompt_by_server_display_name", keys);
 
-        prompt_by_server_display_name = config().getString("prompt_by_server_display_name.default", "%display_name% :)");
+        prompt_by_server_display_name = config().getString("prompt_by_server_display_name.default", "{display_name} :) ");
 
         for (const String & key : keys)
         {
@@ -514,11 +514,8 @@ private:
     {
         String pattern = prompt_by_server_display_name;
 
-        for (const auto & [key, value]: colors)
+        for (const auto & [name, code]: colors)
         {
-            String name = static_cast<String>(key);
-            String code = static_cast<String>(value);
-
             boost::replace_all(pattern, "[" + name + "]",  "\33[1;" + code + "m");
             boost::replace_all(pattern, "[/" + name + "]", "\033[0m");
         }
@@ -533,7 +530,7 @@ private:
 
         for (const auto & [key, value]: environment)
         {
-            boost::replace_all(pattern, "%" + static_cast<String>(key) + "%",  static_cast<String>(value));
+            boost::replace_all(pattern, "{" + key + "}", value);
         }
 
         return pattern;

dbms/src/Server/HTTPHandler.cpp

@@ -198,7 +198,7 @@ HTTPHandler::HTTPHandler(IServer & server_)
     : server(server_)
     , log(&Logger::get("HTTPHandler"))
 {
-    display_name = server.config().getString("display_name", getFQDNOrHostName());
+    server_display_name = server.config().getString("display_name", getFQDNOrHostName());
 }
 
 
@@ -632,7 +632,7 @@ void HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Ne
     try
     {
         response.setContentType("text/plain; charset=UTF-8");
-        response.set("X-ClickHouse-Display-Name", display_name);
+        response.set("X-ClickHouse-Server-Display-Name", server_display_name);
         /// For keep-alive to work.
         if (request.getVersion() == Poco::Net::HTTPServerRequest::HTTP_1_1)
             response.setChunkedTransferEncoding(true);

dbms/src/Server/HTTPHandler.h

@@ -54,7 +54,9 @@ private:
 
     IServer & server;
     Poco::Logger * log;
-    String display_name;
+
+    /// It is the name of the server that will be sent in an http-header X-ClickHouse-Server-Display-Name. 
+    String server_display_name;
 
     CurrentMetrics::Increment metric_increment{CurrentMetrics::HTTPConnection};
 

dbms/src/Server/TCPHandler.cpp

@@ -31,7 +31,6 @@
 #include "TCPHandler.h"
 
 #include <Common/NetException.h>
-#include <Common/getFQDNOrHostName.h>
 
 
 namespace DB
@@ -511,7 +510,7 @@ void TCPHandler::sendHello()
     }
     if (client_revision >= DBMS_MIN_REVISION_WITH_SERVER_DISPLAY_NAME)
     {
-        writeStringBinary(server.config().getString("display_name", getFQDNOrHostName()), *out);
+        writeStringBinary(server_display_name, *out);
     }
     out->next();
 }

dbms/src/Server/TCPHandler.h

@@ -2,6 +2,7 @@
 
 #include <Poco/Net/TCPServerConnection.h>
 
+#include <Common/getFQDNOrHostName.h>
 #include <Common/CurrentMetrics.h>
 #include <Common/Stopwatch.h>
 #include <IO/Progress.h>
@@ -81,6 +82,7 @@ public:
         , connection_context(server.context())
         , query_context(server.context())
     {
+        server_display_name =  server.config().getString("display_name", getFQDNOrHostName());
     }
 
     void run();
@@ -111,7 +113,9 @@ private:
     QueryState state;
 
     CurrentMetrics::Increment metric_increment{CurrentMetrics::TCPConnection};
-
+    
+    /// It is the name of the server that will be sent to the client. 
+    String server_display_name;
 
     void runImpl();
 

dbms/src/Server/clickhouse-client.xml

@@ -13,9 +13,18 @@
             </invalidCertificateHandler>
         </client>
     </openSSL>
+    <!--
+        It's a custom prompt settings for the clickhouse-client
+        Possible macros: 
+            {host}
+            {port}
+            {user}
+            {database} 
+            {display_name}
+    -->
     <prompt_by_server_display_name>
-        <default>%display_name% :)</default>
-        <test>%display_name% [green]:)[/green]</test>
-        <production>%display_name% [red]:)[/red]</production> 
+        <default>{display_name} :) </default>
+        <test>{display_name} [green]:)[/green </test> <!-- if it matched to the substring "test" in the server display name - -->
+        <production>{display_name} [red]:)[/red] </production> <!-- if it matched to the substring "production" in the server display name -->
     </prompt_by_server_display_name>
 </config>