我正在开发一个简单的shell,但现在我只是尝试理解重定向。我只是在硬编码ls命令并尝试将其写入文件。目前,ls运行,输出文件被创建,但输出仍然会到stdout,并且文件为空。我对此感到困惑。谢谢提前。
以下是我的代码:
以下是我的代码:
int main()
{
int ls_pid; /* The new process id for ls*/
char *const ls_params[] = {"/bin/ls", NULL}; /* for ls */
int file; /* file for writing */
/* Open file check user permissions */
if (file = open("outfile", O_WRONLY|O_CREAT) == -1) /* , S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP */
{
perror("Failed to open file");
_exit(EXIT_FAILURE);
}
ls_pid = fork(); /* Create new process for ls */
if (ls_pid == -1) /* error check */
{
perror("Error forking ls (pid == -1)");
_exit(EXIT_FAILURE);
}
else if (ls_pid == 0) /* Child of ls */
{
/* Redirect output to file */
if (dup2(file, STDOUT_FILENO) == -1) /* STDOUT_FILENO = 1 */
{
perror("Error duping to file");
_exit(EXIT_FAILURE);
}
close(file);
execvp("ls", ls_params); /* create the sort process */
/* execlp("ls", "ls", NULL); */
/* if this does not end the program, something is wrong */
perror("Exec failed at sort");
_exit(EXIT_FAILURE);
}
else /* ls parent (1) */
{
/* wait for child */
if (wait(NULL) == -1)
{
perror("fork failed on parent");
_exit(EXIT_FAILURE);
}
}
}