pipes/simple_pipe.c

+/* simple_pipe.c
+
+   Simple demonstration of the use of a pipe to communicate
+   between a parent and a child process.
+
+   Usage: simple_pipe "string"
+
+   The program creates a pipe, and then calls fork() to create a child process.
+   After the fork(), the parent writes the string given on the command line
+   to the pipe, and the child uses a loop to read data from the pipe and
+   print it on standard output.
+*/
 #include <sys/wait.h>
 #include "tlpi_hdr.h"
 
 #define BUF_SIZE 10
 
 int
 main(int argc, char *argv[])
 {
     int pfd[2];                             /* Pipe file descriptors */
     char buf[BUF_SIZE];
     ssize_t numRead;
 
     if (argc != 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s string\n", argv[0]);
 
     if (pipe(pfd) == -1)                    /* Create the pipe */
         errExit("pipe");
 
     switch (fork()) {
     case -1:
         errExit("fork");
 
     case 0:             /* Child  - reads from pipe */
         if (close(pfd[1]) == -1)            /* Write end is unused */
             errExit("close - child");
 
         for (;;) {              /* Read data from pipe, echo on stdout */
             numRead = read(pfd[0], buf, BUF_SIZE);
             if (numRead == -1)
                 errExit("read");
             if (numRead == 0)
                 break;                      /* End-of-file */
             if (write(STDOUT_FILENO, buf, numRead) != numRead)
                 fatal("child - partial/failed write");
         }
 
         write(STDOUT_FILENO, "\n", 1);
         if (close(pfd[0]) == -1)
             errExit("close");
         exit(EXIT_SUCCESS);
 
     default:            /* Parent - writes to pipe */
         if (close(pfd[0]) == -1)            /* Read end is unused */
             errExit("close - parent");
 
         if (write(pfd[1], argv[1], strlen(argv[1])) != strlen(argv[1]))
             fatal("parent - partial/failed write");
 
         if (close(pfd[1]) == -1)            /* Child will see EOF */
             errExit("close");
         wait(NULL);                         /* Wait for child to finish */
         exit(EXIT_SUCCESS);
     }
 }