I use ns3.30 and I configured it to build and run within Eclipse. However, I continuously get this error "Error: Program "/waf" not found in PATH PATH=[/bin:/home/flower/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/usr/games:/usr/local/games:/snap/bin]" despite that everything working fine. Does that mean that am I may face a problem with my ns3 project later?, or, can I safely discard that error?
The path /waf refers to waf in the root directory. The problem is that you don't have a waf in the root directory. Change the path to ./waf to refer to waf the current working directory.
If you don't fix this, then any script you write will first have to be manually compiled by running ./waf from the terminal.