How to Run a Linux Command and Redirect its output to a socket in C Post: 302258408

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Top Forums Programming How to Run a Linux Command and Redirect its output to a socket in C Post 302258408 by Corona688 on Friday 14th of November 2008 01:03:22 PM

11-14-2008

Registered User

I think you can redirect the output to a stream socket if you fork and exec rather than using popen. This is because the redirection has to happen before you run the program, not after.

Code:

{
  pid_t pid=fork();
  int st;

  if(pid < 0)
  {
    perror("Couldn't fork");
  }
  else if(pid == 0) /* child code, run in a seperate process */
  {
    dup2(sock, 1); /* Duplicate socket's FD over FD #1, aka stdout */
    dup2(sock, 0); /* Duplicate socket's FD over FD #0, aka stdin */
    close(sock); /* Only closes the child's copy.  And the stdin/stdout copies remain. */
    execlp("/bin/echo", "HEY GUYS ALJ AF MY FACE IS A ROTTORN BANANA");
    /* Code below will never happen unless exec fails */
    perror("Couldn't exec");
    exit(1);
  }
  else
  {
    close(sock); /* Parent doesn't need socket anymore */
    waitpid(pid, &st, 0); /* Wait for child to finish */
  }
}

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LEARN ABOUT BSD

fork

FORK(3F)																  FORK(3F)

NAME

       fork - create a copy of this process

SYNOPSIS

       integer function fork()

DESCRIPTION

       Fork  creates  a  copy  of  the	calling  process.   The only distinction between the 2 processes is that the value returned to one of them
       (referred to as the `parent' process) will be the process id of the copy.  The copy is usually referred to as  the  `child'  process.   The
       value returned to the `child' process will be zero.

       All logical units open for writing are flushed before the fork to avoid duplication of the contents of I/O buffers in the external file(s).

       If the returned value is negative, it indicates an error and will be the negation of the system error code.  See perror(3F).

       A corresponding exec routine has not been provided because there is no satisfactory way to retain open logical units across the exec.  How-
       ever, the usual function of fork/exec can be performed using system(3F).

FILES

       /usr/lib/libU77.a

SEE ALSO

       fork(2), wait(3F), kill(3F), system(3F), perror(3F)

4.2 Berkeley Distribution					   May 27, 1986 							  FORK(3F)