popen(3)                            CLIX                            popen(3)



  NAME

    popen, pclose - Initiates a pipe to/from a process

  LIBRARY

    Standard C Library (libc.a)

  SYNOPSIS

    #include <stdio.h>

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

    int pclose(
      FILE *stream );

  PARAMETERS

    command   A shell command line

    type      A character flag representing a read or write mode

    stream    A stream pointer

  DESCRIPTION

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

    A stream opened by popen() should be closed by pclose(), which waits for
    the associated process to terminate and returns the exit status of the
    command.

    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:

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



  2/94 - Intergraph Corporation                                              1

  popen(3)                            CLIX                            popen(3)



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

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

  CAUTIONS

    If the original and the popen()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() .

  RETURN VALUES

    If files or processes cannot be created, the popen() returns a NULL
    pointer.  If stream is not associated with a popen()ed command, the
    pclose() returns -1.

  RELATED INFORMATION

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

    Files:  stdio(4)





























  2                                              Intergraph Corporation - 2/94