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Top Forums UNIX for Dummies Questions & Answers How to write to stdin of another program (program A -> [stdin]program B) Post 302190772 by vvaidyan on Wednesday 30th of April 2008 12:36:39 PM
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
 
Test Your Knowledge in Computers #625
Difficulty: Medium
Functions are defined using the defineFunction reserved keyword in Python.
True or False?

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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

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