The input file specification indicates the file to be formatted; TeX uses .tex as a default file extension. If you omit the input file entirely, TeX accepts input from the terminal. You specify command options by supplying a string as a parameter to the command; e.g.
latex '\nonstopmode\input foo.tex'
will process foo.tex without pausing after every error.
If LaTeX stops in the middle of the document and gives you a
‘*’ prompt, it is waiting for input. You can type \stop
(and return) and it will prematurely end the document.