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TTY Problem

The Gnu Emacs and Cygwin tty problem has been haunting me since I have started using them the first day. I did not understand the cause of the problem at that time. After sufficient researches, I think I have now understood the cause of it, but I have no solution to it. Hopefully someone brilliant can solve the problem for me.

TTY Problem on Gnu Emacs

For Gnu Emacs running in Windows, if a shell is invoked (regardless of cmd.exe shell, emacs eshell or cygwin bash shell), the shell is not run under a tty terminal. This can be verified by invoking the tty.exe command distributed with cygwin. The output from the tty.exe command simply says "not a tty". (For Gnu Emacs running in Unix environment, tty command says "/dev/ttyN".)

If an application is not invoked within a tty terminal, usually the application assumes that its output is redirected to a file. The application will buffer the output. This means the output will not be flushed until a sufficient amount of output has accumulated.

TTY Problem on Cygwin rxvt

Considered the following simple buffer.c program.

#include <stdio.h>

int main(int argc, char** argv)
    char buf[1000];

    if( _isatty( _fileno( stdout ) ) )
        printf( "stdout has not been redirected to a file\n" );
        printf( "stdout has been redirected to a file\n");

    printf("Hello World\n");

Running Cygwin Bash shell under Cygwin rxvt terminal, the TTY problem appears when running the .exe of buffer.c generated by Microsoft Visual C compiler or using Cygwin gcc with -mno-cygwin option.

Under the same settings, running the .exe of buffer.c generated by Cygwin gcc does not exhibit any problem.

The "tty" command executed in a rxvt Bash Shell says that it is "/dev/ttyN". This is to say that .exe generated by Microsoft Visual C compiler or using Cygwin gcc with -mno-cygwin option does not respect the tty settings.

In short, all Cygwin applications work well in a rxvt terminal. All Windows applications that do not involve user inputs work in a rxvt terminal as well. The problem is with all Windows applications that require user inputs.

(assuming xxxx is your input)

More information about this problem


I do not know the solution. The workaround is to run Windows applications that require user inputs in a Cygwin Bash shell in a Windows DOS Prompt console. Let me know if you have found a solution.

Langkawi Sunset