Eiffel: is there a way to print colorized characters into a terminal (console)

Question

Trying to write some logger enhancements I'd like to deal with ANSI codes interpretation, and it seems that it's not working with the standard io.putstring method neither with print I wonder there is a way to do something such as

echo -e "\u001B[31mSome_red_txt" in bash

Seems other languages can do it but I can't in Eiffel.

score 3 · Answer 1 · answered Oct 17 '18 at 16:51

3

Using ANSI codes interpretation, you can do

print ("%/27/[31mSome_red_txt%N")
print ("%/27/[1;31mbold red text%/27/[0m%N")

You may check for existing C libraries like ncurses. Note it will not work on Windows console, as now it does not support ANSI code anymore, so you need to use the Windows API.

answered Oct 17 '18 at 16:51

Jocelyn

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May I suggest you to add some comment about escaping characters with Eiffel which was my error trying to get it working with `\001B` – Pipo Oct 18 '18 at 16:52

Alexander Kogtenkov · Answer 2 · 2018-10-18T08:33:09.193

3

To complement Jocelyn's answer, the same ANSI code sequences can be used on Windows with recent update by making sure the console is initialized to handle the sequences:

    -- Make sure the console is allocated in a non-console application.
io.output.end_of_file.do_nothing
    -- Set console to terminal mode.
initialize_terminal
    -- Use ANSI codes to color text.
print ("%/27/[31mSome_red_txt")

where

initialize_terminal
    external "C inline"
    alias "[
        #ifdef EIF_WINDOWS
            {
                HANDLE hOut = GetStdHandle(STD_OUTPUT_HANDLE);
                if (hOut == INVALID_HANDLE_VALUE) return;
                DWORD dwMode = 0;
                if (!GetConsoleMode(hOut, &dwMode)) return;
                dwMode |= ENABLE_VIRTUAL_TERMINAL_PROCESSING;
                SetConsoleMode(hOut, dwMode);
            }
        #endif
    ]"
    end

After such initialization, print statements work the same on Windows and Linux.

If output can go not only to the console, but also to a file, a pipe, etc., error status of setting the terminal mode on Windows console can be recorded in the external feature and used later to avoid outputting ANSI sequences in such cases.

edited Oct 18 '18 at 08:33

answered Oct 17 '18 at 17:40

Alexander Kogtenkov

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Based on Alexander's answer. I built quickly a quick and dirty example. See https://gist.github.com/jocelyn/c2a211315898639fc65c3108343a950b (tested on Windows and Debian) – Jocelyn Oct 18 '18 at 12:58
What about the case of ssh from MS's windows to Unix or form Unix to MS`s Windows (is that possible)? – ctrl-alt-delor Nov 22 '18 at 20:42
@ctrl-alt-delor `ssh` uses standard input and output, so there should be no specific issues. – Alexander Kogtenkov Nov 22 '18 at 21:48
Expect the program will see that it is running on Unix, and not set up the colour on the MS-Windows terminal. (Does the MS-Windows support any standards, to allow this to happen.) – ctrl-alt-delor Nov 23 '18 at 07:49
@ctrl-alt-delor A program that wants to use escape sequences also checks what kind of standard output it is attached to, whether it is a terminal or something else, and uses the escape sequences only when they are supported. For example, the environment variable `TERM` can be used to pass the information about capabilities of the terminal, shells have their own mechanisms to enable colored output, etc. – Alexander Kogtenkov Nov 23 '18 at 11:29
@AlexanderKogtenkov Yes you see, my point, and how it needs to be done. However, this is not what your program does. (or am I wrong?) – ctrl-alt-delor Nov 23 '18 at 11:38
@ctrl-alt-delor The question is about a possibility to do colored output, when the output is known to go to a terminal. How to detect whether the output indeed goes to a terminal is a different question. – Alexander Kogtenkov Nov 23 '18 at 11:55
@ctrl-alt-delor OK, I missed your point. Indeed, the result of functions `GetConsoleMode` and `SetConsoleMode` can be used to see whether terminal facilities (such as colored output) are supported by the associated output stream on Windows. Similar functionality [exists](https://stackoverflow.com/questions/1061575/detect-in-c-if-outputting-to-a-terminal) on Linux. Some other means should be used to do it when output generated on one machine is to be displayed on another. – Alexander Kogtenkov Nov 23 '18 at 12:18
You will never know what machine it is displayed on until run time. So you need to write code to do that. I know it can be done, on Unixes. But don't know about MS, or the cmd terminal. – ctrl-alt-delor Nov 23 '18 at 12:20

Eiffel: is there a way to print colorized characters into a terminal (console)

2 Answers2