Does bash makes the terminal translates a newline (\n) to a carriage return (\r)?

Question

I opened two terminals, and from the below terminal I executed cat to read from the above terminal:

In the above terminal I type "Hello World<Enter>Bye", but looks like the above terminal sent the Enter key as a carriage return (\r).

So does bash changes the settings of the terminal to make it translates a newline (\n) to a carriage return (\r)?

Answer 1

Bash has changed the terminal to "raw" mode, which means typer characters are not processed in any way. The enter key produces a Carriage Return character (\r), not a Line Feed (\n), so no translation takes place.

Answer 2

raw and cooked modes are descriptive terms. stty raw uses different settings than bash.

Bash does terminal initialization in prepare_terminal_settings (an internal function of the readline library), setting the terminal mode to allow reading a single character at a time without echoing:

  tiop->c_lflag &= ~(ICANON | ECHO);

however, the carriage-return translation is reset in a different part of the function:

  /* Make sure we differentiate between CR and NL on input. */
  tiop->c_iflag &= ~(ICRNL | INLCR);

If you compare prepare_terminal_settings to the coreutils stty, the latter does less (several points, but bash resets INLCR as well):

      else if (STREQ (info->name, "raw") || STREQ (info->name, "cooked"))
        {
          if ((info->name[0] == 'r' && reversed)
              || (info->name[0] == 'c' && !reversed))
            {
              /* Cooked mode. */
              mode->c_iflag |= BRKINT | IGNPAR | ISTRIP | ICRNL | IXON;
              mode->c_oflag |= OPOST;
              mode->c_lflag |= ISIG | ICANON;
#if VMIN == VEOF
              mode->c_cc[VEOF] = CEOF;
#endif
#if VTIME == VEOL
              mode->c_cc[VEOL] = CEOL;
#endif
            }
          else
            {
              /* Raw mode. */
              mode->c_iflag = 0;
              mode->c_oflag &= ~OPOST;
              mode->c_lflag &= ~(ISIG | ICANON
#ifdef XCASE
                                 | XCASE
#endif
                );
              mode->c_cc[VMIN] = 1;
              mode->c_cc[VTIME] = 0;
            }
        }

POSIX says of stty raw:

Enable (disable) raw input and output. Raw mode shall be equivalent to setting:

stty cs8 erase ^- kill ^- intr ^- \
    quit ^- eof ^- eol ^- -post -inpck

which interestingly enough (following the descriptions of -post and -inpck) does not address carriage return translation on input.

Since the terms raw and cooked (either POSIX or coreutils stty) do not correspond to what bash does, mentioning the POSIX termios features that correspond to what it actually does are the way to go: icrnl (input carriage-return to newline translation).