[Lazarus] How to clear screen in console app

[Michael Van Canneyt]

On Sat, 23 Apr 2016, Mark Morgan Lloyd wrote:

> Michael Van Canneyt wrote:
>> On Sat, 23 Apr 2016, Bo Berglund wrote:
>> 
>>> On Sat, 23 Apr 2016 07:32:55 +0200, Bo Berglund
>>> <bo.berglund at gmail.com> wrote:
>>> 
>>>> I need to make a console app that can run on Linux.
>>>> It would be a simple thing I believed, but no...
>>>> 
>>>> I cannot get the ClrScr command working, it just puts strange
>>>> characters on the screen instead of clearing it.
>>> ...
>>>> But the console debug window just shows a bunch of control characters
>>>> (square with 001B inside) plus [6n [H [m [H [2JEnter command:
>>>> And every command I enter results in a new line being displayed rather
>>>> than staying on the same line and erasing the previous output.
>>> 
>>> UPDATE:
>>> It seems to be caused by the Lazarus debug console window!
>>> If I go to the dir where the program resides in my terminal (both
>>> local and via SSH) and execute ~/tmp/project1 then it looks OK.
>>> 
>>> So my question now changes to:
>>> Why does the debug window show different output than the actual
>>> terminal console?
>>> 
>>> I am using Lazarus 1.6 release and fpc 3.0.0 both built from svn
>>> sources on a Raspberry Pi3 with Raspbian Jessie if that matters.
>> 
>> The console respects the special terminal control characters.
>> The debug window does not respect these characters, and just prints them 
>> out
>> to screen. I am not sure this can be properly handled. Maybe there is an
>> option that can be given to xterm to respect the characters.
>> 
>> If you are debugging using SSH, then you probably need to add the -t 
>> option.
>
> The console window in which the shell and app run might have different 
> commands, depending on what's actually being used (i.e. xterm, an SSH session 
> from a remote system and so on). The console window will have an associated 
> $TERM shell description, and strictly speaking the program that wants to 
> clear the screen should refer to this possibly using curses or libtinto.
>
> I don't know whether the ClrScr procedure refers to libtinfo,

No. It just uses ansi escape characters.

Michael.