tcgetpgrp —
get foreground process group ID
Standard C Library (libc, -lc)
#include <unistd.h>
pid_t
  
  tcgetpgrp(int
    fd);
The tcgetpgrp function returns the value of the process
  group ID of the foreground process group associated with the terminal device.
  If there is no foreground process group, tcgetpgrp
  returns an invalid process ID.
If an error occurs, tcgetpgrp returns -1 and the global
  variable errno is set to indicate the error, as follows:
  - [EBADF]
- The fd argument is not a valid file descriptor.
- [ENOTTY]
- The calling process does not have a controlling terminal or the underlying
      terminal device represented by fd is not the
      controlling terminal.
Thetcgetpgrp function conforms to IEEE
  Std 1003.1-1990 (“POSIX.1”).