In OpenBSD, with the fcntl system call https://github.com/openbsd/src/blob/master/lib/libc/gen/isatty.c https://github.com/openbsd/src/blob/master/lib/libc/gen

In OpenBSD, with the fcntl system call https://github.com/openbsd/src/blob/master/lib/libc/gen/isatty.c https://github.com/openbsd/src/blob/master/lib/libc/gen/isat... https://man.openbsd.org/fcntl https://man.openbsd.org/fcntl https://github.com/openbsd/src/blob/master/sys/sys/fcntl.h https://github.com/openbsd/src/blob/master/sys/sys/fcntl.h https://github.com/openbsd/src/blob/ba496e5267528b649ec87212f12281fc753215ab/sys/kern/kern_descrip.c#L479 https://github.com/openbsd/src/blob/ba496e5267528b649ec87212... https://github.com/openbsd/src/blob/ba496e5267528b649ec87212f12281fc753215ab/sys/sys/vnode.h#L143 https://github.com/openbsd/src/blob/ba496e5267528b649ec87212...