|| FreeBSD Library Functions Manual
get foreground process group ID
Standard C Library (libc, -lc)
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,
() returns -1 and the global variable
is set to indicate the error, as follows:
fd argument is not a valid file descriptor.
The calling process does not have a controlling terminal or the underlying terminal device represented by
fd is not the controlling terminal.
tcgetpgrp() function is expected to be compliant with the IEEE Std 1003.1-1988 (“POSIX.1”) specification.