vim, vimdiff, ex, view, rvim and rview: How do they start in a different way when they are symlinks to the same binary?

Question

I just installed version 8 of Vim and notice in the bin directory of the install location that all the above mentioned programs point to the same binary – vim. Then, how does it know when I invoke ex to open in the ex mode and so on?

Answer 1

Inside vim's source code, there is a main function roughly like

int main(int argc, char **argv) {
    if (!strcmp(argv[0], "ex"))
        do_ex_setup();

    main_loop();

    return 0;
}

This function is where the operating system starts the execution of the vim executable. The naming and arguments differ between operating systems, but we'll assume -nix style. By convention, the shell passes words from the command line you typed as strings in the argv array when starting the program. E.g.,

ex filename

becomes char *argv[] = {"ex", "filename"};

Similarly for view, vimdiff, etc.