Re: [TUHS] Systematic approach to command-line interfaces [ meta issues ]

I have considerable sympathy with the general idea of formally specifying and parsing inputs. Langsec people make a strong case for doing so. The white paper,"A systematic approach to modern Unix-like command interfaces", proposes to "simplify parsing by facilitating the creation of easy-to-use 'grammar-based' parsers". I'm not clear on what is meant by "parser". A plain parser is a beast that builds a parse tree according to a grammar. For most standard Unix programs, the parse tree has two kinds of leaves: non-options and options with k parameters. Getopt restricts k to {0,1}. Aside from fiddling with argc and argv, I see little difference in working with a parse tree for arguments that could be handled by getopt and working with using getopt directly. A more general parser could handle more elaborate grammatic constraints on options, for example, field specs in sort(1), requirements on presence of options in tar(1), or representation of multiple parameters in cut(1). In realizing the white paper's desire to "have the parser provide the results to the program", it's likely that the mechanism will, like Yacc, go beyond parsing and invoke semantic actions as it identifies tree nodes. Pioneer Yaccification of some commands might be a worthy demo. Doug