upd: ready to lex the command

backend/include/lexer.h

@@ -0,0 +1,10 @@
+#ifndef PROTECTOR_LEXER_H
+#define PROTECTOR_LEXER_H
+#include <regex>
+#include <sstream>
+#include <string>
+#include <vector>
+bool CommandShowLexer(const std::string &command, std::string &ISBN,
+                      std::string &name, std::string &author,
+                      std::string &keyword);
+#endif  // PROTECTOR_LEXER_H