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

On 7/31/21 12:19 PM, Dan Cross wrote: This is essentially how the existing shells do it (bash, zsh, tcsh, etc.), but in an ad-hoc fashion. There is no standard way to obtain possible completions or list possible arguments, so the shells push that to external generators. Since you have to perform the completion in the shell, there has to be some way to tell the shell the possible completions for each command of interest, whether that's options or arguments. The different shells have solved that in essentially the same way, with a few syntactic variations. Bash provides a framework (complete/compgen/compctl) and pushes a lot of the command-specific work to external completers. It provides access to the shell internals (lists of builtins, functions, aliases, variables, and so on) and built-in ways to perform common completions (filenames, directory names, command names, etc.), and leaves the rest to external commands or shell functions. The real power and flexibility comes from being able to invoke these external commands or shell functions to generate lists of possible completions, and defining an API between the shell and those generators to specify enough of the command line to make it easy to find the word to be completed, the command for which completion is being attempted, and clarifying context around that word. In the same way, the shell provides an API for those generators to return possible completions. The knowledge about each command's options and arguments is embedded in these generators. A standard way to handle command line options and arguments would make generators easier to write, but doesn't address the other issues of what, exactly, the user wants to complete, so the existing mechanisms would likely not change very much. Something like `--shell-help', as long as it were context-sensitive, would help more. Chet -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRU chet(a)case.edu http://tiswww.cwru.edu/~chet/