vpopen(3)                           CLIX                           vpopen(3)



  NAME

    vpopen - Initiates a pipe to/from a process

  LIBRARY

    Standard C Library (libc.a)

  SYNOPSIS

    #include <stdio.h>

    FILE *vpopen(
      char *command ,
      char *type );

  PARAMETERS

    command   A shell command line.

    type      A character flag representing a read or write mode.

  DESCRIPTION

    The vpopen() function creates a pipe between the calling program and the
    command to be executed.

    The arguments to vpopen() are pointers to null-terminated strings.  The
    command parameter consists of a shell command line.  The parameter type is
    an I/O mode, either r for reading or w for writing.  The value returned is
    a stream pointer such that one can write to stdin of the command by
    writing to the file stream, if the I/O mode is w.  Also, if the I/O mode
    is r, one can read from stdout of the command by reading from the file
    stream.

    Since open files are shared, a type r command may be used as an input
    filter, and a type w may be used as an output filter.

  EXAMPLE

    A typical call may be as follows:

    char *cmd = "ls *.c";
    FILE *ptr;

    if ((ptr = vpopen(cmd, "r")) != NULL)
         while (fgets(buf, n, ptr) != NULL)
              (void) printf("%s",buf);

    This example displays, in stdout (see stdio(4)), all the filenames in the
    current directory having a .c suffix.



  2/94 - Intergraph Corporation                                              1

  vpopen(3)                           CLIX                           vpopen(3)



  NOTES

    The vpopen() function is equivalent to the popen() function, except that
    vpopen() uses vfork() instead of fork() for more efficient memory usage.

  CAUTIONS

    If the original and the vpopen()ed processes read or write a common file
    concurrently, neither should use buffered I/O.  This causes a buffering
    mix-up.  Prevent output filter problems by using careful buffer flushing;
    for example, using fflush().  Also, refer to fclose(3).

  RETURN VALUES

    If files or processes cannot be created, vpopen() returns a NULL pointer.

  RELATED INFORMATION

    Functions:  popen(3), fork(2), vfork(2), pipe(2), wait(2), fclose(3),
    fopen(3), system(3)

    Files:  stdio(4)
































  2                                              Intergraph Corporation - 2/94