popen(3)                                                       popen(3)

  popen()

  NAME

    popen(), pclose() - process I/O with pipes

  SYNOPSIS

    #include 

    FILE * popen (const char *command, const char *type)
    int pclose (FILE *stream)

  DESCRIPTION

    The popen(3) function opens a process by creating a pipe, forking, and
    invoking the shell. Since a pipe is by definition unidirectional, the type
    argument may specify only reading or writing, not both; the resulting
    stream is correspondingly read-only or write-only.

    The command argument is a pointer to a null-terminated string containing a
    shell command line. This command is passed to /bin/sh using the -c flag;
    interpretation, if any, is performed by the shell. The type argument is a
    pointer to a null-terminated string which must be either r for reading or
    w for writing.

    The return value from popen(3) is a normal standard I/O stream in all
    respects save that it must be closed with pclose(3) rather than fclose(3).
    Writing to such a stream writes to the standard input of the command; the
    command's standard output is the same as that of the process that called
    popen(3) unless this is altered by the command itself. Conversely, reading
    from a popened stream reads the command's standard output, and the
    command's standard input is the same as that of the process that called
    popen(3).

    Note that output popen(3) streams are fully buffered by default.

    The pclose(3) function waits for the associated process to terminate and
    returns the exit status of the command.

  RETURN VALUE

    The popen(3) function returns NULL if the fork(2) or pipe(2) calls fail,
    or if it cannot allocate memory.

    On success, the pclose(3) function the exit status of the terminating
    command. On failure, pclose(3) returns -1 if stream is not associated with
    a popen(3)'ed command, or if stream already pclose(3)'d

  ERRORS

    The popen(3) function does not reliably set errno

  SEE ALSO

    sh(1)

    fork(2)

    pipe(2)

    fflush(3)

    fclose(3)

    fopen(3)

    system(3)

  USAGE NOTES

    All of these functions are thread safe.

    None of these functions are async-signal safe.