Re: standard for stdin / args handling?

[Pádraig Brady]

On 12/26/2012 09:18 PM, Aaron Davies wrote:
> afaict from my general *nx experience, the basic rule for text-handling utilities (filters, etc.) is as 
> follows: first, no argument(s) means stdin is used; second, argument(s) means stdin is ignored, unless 
> "-" is present as an argument, in which case stdin is used in the position in the sequence where 
> the first "-" occurs (later "-"s have no effect, presumably due to the way pipes behave); 
> finally, if no arguments and not receiving a pipe and in some sort of interactive context (stdin is a tty?), 
> stdin is accepted from the terminal (and handled line-by-line (rev(1)) or at end-of-file (tac(1)), as 
> appropriate).

That's the usual operation of a filter yes.
Though there are always exceptions like dd for example.
Note multiple '-' aren't usually ignored.

cat - - -
seq 10 | paste - - -
...

> cat(1) is the canonical example.
>
> my questions are: have i described the behavior correctly, and is there 
> anything (in any context--C, shell, etc.) to make creating new tools which 
> follow these rules easier?

I don't know of higher level abstractions for this behavior.

thanks,
Pádraig.