In CEH v13 Module 05: System Hacking, and in lab-based exploitation exercises, this is a classic fuzzer for buffer overflow testing.
The script creates increasingly larger strings of "A" (50, 100, 150...).
These are passed as arguments to different vulnerable commands on the target service (127.0.0.1:9999).
The goal is to trigger a crash, typically when input exceeds buffer limits (i.e., buffer overflow).
This is part of exploit development to identify the offset and locate the instruction pointer overwrite (EIP overwrite).
Reference:
CEH v13 Module 05 - Buffer Overflow Concepts
CEH iLabs: Exploitation with Custom Fuzzers in Python
EC-Council Exploit Development Lab Manual