When I use Linux, I almost always use it through a shell -- and I'm a HUGE fan of the [tab to auto-complete] feature (e.g. start typing a file name, press tab and voila, the shell figures it out or prompts for more detail if there is still ambiguity. The other day, I noticed for the first time that the shell has some way to determine what the valid parameters for a particular binary are.

Example: I was typing the command "unzip " and then I pressed [tab] expecting the sole archive in the current folder, archive.zip to appear. To my surprise, nothing appeared... well then I realized I forgot the 'x'tract parameter to unzip...so I retried "unzip x " [tab] and the shell auto-completed to "unzip x archive.zip" as expected.

I thought this behavior may have just been specially coded into the shell for common commands like unzip, so I downloaded a third party tool -- 7z (7zip). The shell was also able to discern when I neglected to specify a required command for 7z, before executing the command.

How is this done? I assume there is some convention that must be in place (man page? --help parameter? something else??) to make this work, but I'm not sure how to Google this for the answer.

Thanks for any answers/pointers on what to search for to find the answer.

I hope I'm right on this.

First off there isn't really a shell that is standard. There are many shells available, bash being maybe the most common. In bash there are different builds so that too is an issue.

Now back to your question. Example, I see no basis for your assumption that running a program would somehow decide to select options. Generally posix doesn't do that. Especially from any shell. So when you said that you completed the option portion of of the zip it now had something to do.

So, my wild guess is that your shell choice and version and build and maybe some other features allowed you to tab after this command. The tab feature was added quite later in the versions and is kind of new in way. What I am guessing is that the feature that uses the tab won't act on a blank space or maybe a single space bar because it has a form of test or other setting to tell user.

Try this. Do this same test but press the space bar after command only then tab and see what happens.

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A number of commands install extra data in /etc/bash_completions which is probably what yoy mean, not all programs do so but a number of the common ones do, when you press tab bash looks in the conpletions folder based on what has been typed before and trys to work out what uou zwant if npt it will check in the current folder for any thing that matches what you have typed and also what you want to do for instance if you start a line with ./ bash will assume you want to run a command so will match the commamd in the current folder that are executable to what you have alreafy typed.

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Thanks, Keith & Jefro! Sorry for my sketchy details around shell and distro -- but you still managed to nail it. I was indeed using Bash and the /etc/bash_completions was exactly what I was looking for.

Thanks again!
AF

Glad to help but please dont forget to mark your threads SOLVED when you are satisfied that your question has been answered

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