The "loop and a half"

[bartc]

On 06/10/2017 12:04, Rhodri James wrote:
> On 05/10/17 19:45, bartc wrote:
>> Yes, I tried typing 'sort' in Linux, where it apparently hangs (same 
>> on Windows actually). The reason: because it might have killed someone 
>> to have added a message saying what you are expected to type and how 
>> to end it. (Namely, press Ctrl-D start at the start of a line in 
>> Linux, and Ctrl-Z followed by Enter, I think also at the start, in 
>> Windows.)
> 
> Actually it might.  Linux tools are written not to assume that stdin and 
> stdout are the console, because they frequently aren't.  Extra puff 
> written to stdout at best makes it harder to use in a pipeline, and at 
> worst makes it useless; tools that do that tend not to get used.

A lot of people aren't getting it.

The internal utilities used within an operating system, primarily 
intended for file or redirected i/o with no live interaction, should be 
distinct from those designed to be used directly with a live user.

Or is it against the rules of Unix to have two different versions of a 
program?

Then you might have 'sort' for the non-interactive version, and 'isort' 
or whatever for the interactive.

Except you simply wouldn't use an interactive version of any program 
that reads an arbitrary long list of uninterrupted data, no matter how 
the ending is indicated. You'd use a text editor, enter the lines at 
your leisure, go back and forth to check and edit as needed, THEN you 
would submit that file to 'sort'. As an actual input file.

So I can't see the point of using that same pattern of input usage 
(reading from stream, file, pipe whatever until interrupted with an EOF 
signal) for a true interactive program that is used in a sensible manner.

(Say, an FTP program, which has a prompt, lots of commands, and usually 
instant feedback. An actual dialogue.

A program like 'python' might fit the bill too. Here, you can give it 
the name of a file, OR say nothing, and it will take input from stdin.

Funnily enough, you now get a message, and a prompt. And when entering 
multiple lines of code, you get a prompt before each line. You can also 
terminate the sequence by entering a blank line.

So it IS possible to do it properly after all!)

-- 
bartc