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How to write to stdin of another program (program A -> [stdin]program B)

 
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Old 04-30-2008
How to write to stdin of another program (program A -> [stdin]program B)
Hi,
Program A: uses pipe()

I am able to read the stdout of PROGAM B (stdout got through system() command) into PROGRAM A using:

* child
-> dup2(fd[1], STDOUT_FILENO);
-> execl("/path/PROGRAM B", "PROGRAM B", NULL);

* parent
-> char line[100];
-> read(fd[0], line, 100);


Question:
---------
How to write to stdin of PROGRAM B from PROGRAM A?
* should I use a different pipe?
* how to I read stdin in PROGRAM B? using cin?

Thanks in advance,
Vivek
 
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LEARN ABOUT FREEBSD

stdin

FD(4)							   BSD Kernel Interfaces Manual 						     FD(4)

NAME

     fd, stdin, stdout, stderr -- file descriptor files

DESCRIPTION

     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.

     Opening the files /dev/stdin, /dev/stdout and /dev/stderr 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.

IMPLEMENTATION NOTES

     By default, /dev/fd is provided by devfs(5), which provides nodes for the first three file descriptors.  Some sites may require nodes for
     additional file descriptors; these can be made available by mounting fdescfs(5) on /dev/fd.

FILES

     /dev/fd/#
     /dev/stdin
     /dev/stdout
     /dev/stderr

SEE ALSO

     tty(4), devfs(5), fdescfs(5)

BSD
								   June 9, 1993 							       BSD