Dynamically detect terminal size

[remkop]

The simplest solution is to rely on the LINES and COLUMNS environment variables. (Update: these are bash variables and may not be available as env variables unless explicitly exported...)

• In bash, these are set if shopt -s checkwinsize is set. Apparently this is enabled by default.
• In zsh, apparently these are set automatically

---

Alternatively (more advanced), the Lantern project (#633) shows how this can be done with ANSI escape sequences.

Example implementation to get the terminal size:

import java.io.IOException;

public class WinSize {
    /*
      /bin/stty -echo; /bin/stty -icanon; /bin/stty min 1; java WinSize; /bin/stty echo; /bin/stty icanon;
     */
    public static void main(String... args) throws IOException {
        String[] signals = new String[] {
                "\u001b[s",            // save cursor position
                "\u001b[5000;5000H",   // move to col 5000 row 5000
                "\u001b[6n",           // request cursor position
                "\u001b[u",            // restore cursor position
        };
        for (String s : signals) {
            System.out.print(s);
        }
        int read = -1;
        StringBuilder sb = new StringBuilder();
        byte[] buff = new byte[1];
        while ((read = System.in.read(buff, 0, 1)) != -1) {
            sb.append((char) buff[0]);
            //System.err.printf("Read %s chars, buf size=%s%n", read, sb.length());
            if ('R' == buff[0]) {
                break;
            }
        }
        String size = sb.toString();
        int rows = Integer.parseInt(size.substring(size.indexOf("\u001b[") + 2, size.indexOf(';')));
        int cols = Integer.parseInt(size.substring(size.indexOf(';') + 1, size.indexOf('R')));
        System.err.printf("rows = %s, cols = %s%n", rows, cols);
    }
}

[remkop]

API to enable this:

• Command: usageHelpAutoWidth: boolean
• UsageMessageSpec: autoWidth: boolean
• If system property "picocli.usage.width" has value AUTO or TERM or TERMINAL, then autoWidth becomes true
• CommandLine: get/setUsageHelpAutoWidth : boolean

[yschimke]

FWIW I've done this with https://github.com/yschimke/oksocial-output/blob/master/src/main/kotlin/com/baulsupp/oksocial/output/ConsoleHandler.kt#L179

I'd love to switch to whatever you come up with particularly if it doesn't require launching commands etc.

[remkop]

Thanks for the link, just saw that. (Wasn't aware of the -f vs -F difference for MacOS, that's a good catch!)
I am working on this right now, once I get it to work I'm planning to release 4.0.0-beta-2.

My current approach is similar to what you did in ConsoleHandler, but still experimenting with various approaches to find something that also works in Cygwin. What the Lantern project is doing with the ANSI escape sequences may work, but also depends on executing (a number of) commands: bin/stty -echo; /bin/stty -icanon; /bin/stty min 1; for setup, then /bin/stty echo; /bin/stty icanon; for teardown...

[charphi]

FYI, here are two other ways to get the console width:

• Powershell: powershell -command (Get-Host).ui.rawui.windowsize.width
• MingwXterm: tput cols

[remkop]

@charphi picocli 4.0.0-beta-2 should work (be able to detect the terminal width) with Powershell and MINGW. Is this not working correctly?

[charphi]

I've not tested it yet.
My comment was just alternatives in case of problem.

[remkop]

I see! That’s good. :-)
I tested MINGW so that should be fine.
I think that the command for Windows will work from Powershell too but I didn’t test.

[garretwilson]

What a coincidence that I found this after I was looking for a way to detect the console width. Can I find the console width with Java? mentions some of the same techniques mentioned here. fusesource/jansi#24 says to use jline, although I didn't understand why if jline3 used Jansi then why I couldn't use Jansi myself to find the console width. (I'm using Jansi already.)

But it sounds like you've implemented something in this ticket to detect the console width. So how can I access the value picocli detected so that I can use it in my application?

[garretwilson]

Oh, I see. 😭 You hid all that useful code deep in some private method. I'll open a ticket.