pipe — create pipe
#include <unistd.h>
int
pipe( |
int | filedes[2]) ; |
pipe
() creates a pair of
file descriptors, pointing to a pipe inode, and places them
in the array pointed to by filedes
. filedes[0]
is for reading,
filedes[1]
is for
writing.
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
filedes
is
not valid.
Too many file descriptors are in use by the process.
The system limit on the total number of open files has been reached.
The following program creates a pipe, and then fork(2)s to create a child process. After the fork(2), each process closes the descriptors that it doesn't need for the pipe (see pipe(7)). The parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a time from the pipe and echoes it on standard output.
#include <sys/wait.h> #include <assert.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> int main(int argc, char *argv[]) { int pfd[2]; pid_t cpid; char buf; assert(argc == 2); if (pipe(pfd) == −1) { perror("pipe"); exit(EXIT_FAILURE); } cpid = fork(); if (cpid == −1) { perror("fork"); exit(EXIT_FAILURE); } if (cpid == 0) { /* Child reads from pipe */ close(pfd[1]); /* Close unused write end */ while (read(pfd[0], &buf, 1) > 0) write(STDOUT_FILENO, &buf, 1); write(STDOUT_FILENO, "\n", 1); close(pfd[0]); _exit(EXIT_SUCCESS); } else { /* Parent writes argv[1] to pipe */ close(pfd[0]); /* Close unused read end */ write(pfd[1], argv[1], strlen(argv[1])); close(pfd[1]); /* Reader will see EOF */ wait(NULL); /* Wait for child */ exit(EXIT_SUCCESS); } }
fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)
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