Command line activity output scroll direction

Question

When developing a command line applications, one could choose between two designs:

• put the command prompt at the bottom, and the output window above it, where responses and command history are appended at the end and which is autoscrolling down
• put the command prompt at the top, and the output window below it, new items appearing under the prompt and autoscrolling upwards

What are the trade-offs?

The first choice would be the traditional approach. It resembles a log file, which as a document is written from the top to the bottom, and is easier to implement (e.g. not requiring the itemisation even for multiline outputs - it just appends line after line). Often the prompt is integrated right into the same textfield that shows the output, it's not even a separate element. It's easy (mentally and implementationwise) to switch to document editing mode.

The second choice would have the most important elements - the input prompt and the most recent outputs - at the top, where they can be styled visually distinctive. This approach kinda resembles a news feed or activity stream. Each command-response pair would be an individual element appearing at the top, amidst other messages generated by the application. Twitter or Facebook - always longing for out input - work similar to this, even though they don't have commands but just can create feed items.

The only recommendation on the topic I found was to keep direction internally consistent. What else do I need to consider? Is the second approach a good idea? Has it ever been tried out for a command prompt interface?

Answer 1

If reading back and considering content in chronological order is important

Then put it at the bottom. Reading from bottom to top is awkward, at least for languages that are written from top to bottom.

If chronology is less important, like ‘recent’ or relevance-ordered content

Then put it at the top and don’t let it scroll with the content.

In my opinion.

Answer 2

All log files that I have ever come across have the most recent entry at the bottom, it's a simple case of text processing you almost always append to a file rather than preprend. So by default text files are always ordered in a specific direction, so to keep things familiar it would make sense to always have the most recent log at the bottom for a log viewing application.

Seeing as you're using stack, for things like GHCi, the output comes after the command, but the next command is always below the output:

Prelude> 1+2
3
Prelude> let x = 42 in x / 9
4.666666666666667
Prelude>

This is similar in most of the other console style applications I've seen, e.g. Python:

Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:54:40) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> list(map(lambda x: x*2, [1,2]))
[2, 4]
>>>

Other examples is the Firefox console:

Here's a image of an early Lisp Machine: