Hello,
My PL/SQL Developer 11.0.6 assigns a value 'Developer\login.sql' to the substitution variable 1:
SQL> def
DEFINE _SQLPLUS_RELEASE = "000000000" (CHAR)
DEFINE _EDITOR = "PLSQLDev" (CHAR)
DEFINE _DATE = "01-11-2023" (CHAR)
DEFINE _PRIVILEGE = "" (CHAR)
DEFINE...