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TCGETPGRP(3) Library Functions Manual TCGETPGRP(3)

get foreground process group ID

#include <unistd.h>
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:
The 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.

setpgid(2), setsid(2), tcsetpgrp(3)

The tcgetpgrp() function is expected to be compliant with the IEEE Std 1003.1-1988 (“POSIX.1”) specification.
December 12, 2013 OpenBSD-current