Typing in a delete command for a source file on the mainframe - someone interrupted me part way through. Finally looked back and hit return. Then realised I had only entered the directory name - and the delete command was the same format for file or directory.
Before my time someone had done a similar thing for an major application source that had no back up. They had to retype it from the latest listings. What was surprising was how many code bugs they found in the process.
Biting the hand that feeds IT
