Per Bang

Per Bang (often written as !%) is a specific notation and concept primarily used in the context of mainframe systems, particularly within IBM's z/OS operating system environment, and programming languages like Assembler Language. It signifies a request or instruction to the assembler or preprocessor to perform a substitution or modification during the assembly or compilation process.

In essence, "Per Bang" is a form of meta-programming, allowing for dynamic generation of code based on predefined rules and symbols. It acts as a macro facility or preprocessor directive that enables conditional assembly, variable substitution, and other code manipulation techniques.

The exact syntax and functionality associated with "Per Bang" can vary depending on the specific assembler or preprocessor being used. However, the general principle remains consistent: it allows developers to alter the code before it's actually assembled or compiled, enabling greater flexibility and code reusability. It is used to manipulate the source code to provide features like macro processing, conditional compilation, and symbol definition. The features facilitate easier code maintenance and readability in large, complex systems.