11-13-2005
Quote:
Originally Posted by fdarkangel
i too have a question on the topic.
how do i read from keyboard if stdin is actually stdout of another program. an example is less/more: keyboard input still works when they're piped.
This is more of a separate question. You probably should have started a new thread.
If you type "tty", you will see the name of your controlling terminal. If it is, say, /dev/pty/j2, then you could simply open that file to gain access to the keyboard. But it is a lot of work to get the name of your particular terminal, so there is a second way. In the unix environment, a process with a controlling terminal can open the special file /dev/tty and get their own controlling terminal. This won't work if there is no crontrolling terminal such as with a cron job. Even though there is only one file on the system called /dev/tty, each user that opens it will get his or her own keyboard.
However, this may not be a great move to make. Suppose that I have a complicated pipeline of 4 processes. If they all do this at the same time it will be pretty hopeless to get it all straight. And look at all the threads we get where folks need to script the su command and must "expect" to do it. Users tend to dislike programs that do this.
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LEARN ABOUT OSX
mount_fdesc
MOUNT_FDESC(8) BSD System Manager's Manual MOUNT_FDESC(8)
NAME
mount_fdesc -- mount the file-descriptor file system
SYNOPSIS
mount_fdesc [-o options] fdesc mount_point
DESCRIPTION
The mount_fdesc command attaches an instance of the per-process file descriptor namespace to the global filesystem namespace. The conven-
tional mount point is /dev and the filesystem should be union mounted in order to augment, rather than replace, the existing entries in /dev.
This command is normally executed by mount(8) at boot time.
The options are as follows:
-o Options are specified with a -o flag followed by a comma separated string of options. See the mount(8) man page for possible options
and their meanings.
The contents of the mount point are fd, stderr, stdin, stdout and tty.
fd is a directory whose contents appear as a list of numbered files which correspond to the open files of the process reading the directory.
The files /dev/fd/0 through /dev/fd/# refer to file descriptors which can be accessed through the file system. If the file descriptor is
open and the mode the file is being opened with is a subset of the mode of the existing descriptor, the call:
fd = open("/dev/fd/0", mode);
and the call:
fd = fcntl(0, F_DUPFD, 0);
are equivalent.
The files /dev/stdin, /dev/stdout and /dev/stderr appear as symlinks to the relevant entry in the /dev/fd sub-directory. Opening them is
equivalent to the following calls:
fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
fd = fcntl(STDERR_FILENO, F_DUPFD, 0);
Flags to the open(2) call other than O_RDONLY, O_WRONLY and O_RDWR are ignored.
The /dev/tty entry is an indirect reference to the current process's controlling terminal. It appears as a named pipe (FIFO) but behaves in
exactly the same way as the real controlling terminal device.
FILES
/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr
/dev/tty
SEE ALSO
mount(2), unmount(2), tty(4), fstab(5), mount(8)
CAVEATS
No ~. and .. entries appear when listing the contents of the /dev/fd directory. This makes sense in the context of this filesystem, but is
inconsistent with usual filesystem conventions. However, it is still possible to refer to both ~. and .. in a pathname.
This filesystem may not be NFS-exported.
HISTORY
The mount_fdesc utility first appeared in 4.4BSD.
4.4BSD March 27, 1994 4.4BSD