Cygwin's default person interface is definitely the bash shell running in the mintty terminal emulator.[25] The DLL also implements pseudo terminal (pty) devices, and Cygwin ships with numerous terminal emulators which are according to them, which includes rxvt/urxvt and xterm. The Edition of GCC that includes Cygwin has different extensions https://dantesutts.shoutmyblog.com/36145904/acgwin-no-further-a-mystery