C dup2错误的文件描述符
我正在尝试将管道实现到我的shell。现在它可以处理ls、who、date等常规命令 通过阅读大量内容,并进入其他堆栈溢出帖子,检查管道应该如何工作,我已经提出了这段代码,我将为大家演示。该函数基本上接受一个应该处理的命令C dup2错误的文件描述符,c,shell,pipe,C,Shell,Pipe,我正在尝试将管道实现到我的shell。现在它可以处理ls、who、date等常规命令 通过阅读大量内容,并进入其他堆栈溢出帖子,检查管道应该如何工作,我已经提出了这段代码,我将为大家演示。该函数基本上接受一个应该处理的命令 void runCommand(Command *cmd){ char **pl = cmd->pgm->pgmlist; int status; Pgm *p = cmd->pgm; //Count the number
void
runCommand(Command *cmd){
char **pl = cmd->pgm->pgmlist;
int status;
Pgm *p = cmd->pgm;
//Count the number of pipes and create the right number of filedescriptors
int numPipes = countPipes(cmd->pgm);
int pipefds[2*numPipes];
//Pipe the file descriptors here and check if there was an error.
for(int i = 0; i < (numPipes); i++){
if(pipe(pipefds + i*2) < 0) {
perror("couldn't pipe");
exit(EXIT_FAILURE);
}
}
pid_t pid, wpid;
int fdr;
int fd;
int j = 0;
while(p != NULL) {
pid = fork();
if (pid == 0) {
// Child process
if (cmd->bakground == 1) // Check if it should be running in the background, if so, assign a new PID
{
setpgid(pid, 0);
}
// Check if RSTDOUT is on or not
if(cmd->rstdout != NULL){
fd = open(cmd->rstdout, O_WRONLY | O_CREAT | O_TRUNC , S_IRUSR | S_IRGRP | S_IWGRP | S_IWUSR);
//fclose(fopen(cmd->rstdout, "w"));
printf("in first\n");
dup2(fd,1);
close(fd);
}
// Check if RSTIN is on or not
if(cmd->rstdin != NULL) {
fdr = open(cmd->rstdin, O_RDONLY);
printf("in second\n");
dup2(fdr, 0);
close(fdr);
}
//if not last command
if(p->next){
printf("in third\n");
if(dup2(pipefds[j + 1], 1) < 0){
perror("dup2");
exit(EXIT_FAILURE);
}
}
//if not first command&& j!= 2*numPipes
if(j != 0 ){
printf("in fourth: %d\n", j);
if(dup2(pipefds[j-2], 0) < 0){
perror(" dup2");///j-2 0 j+1 1
exit(EXIT_FAILURE);
}
}
for(int i = 0; i < 2*numPipes; i++){
printf("in fifth\n");
close(pipefds[i]);
}
j += 2;
printf("%s\n",pl[0] );
if (execvp(pl[0], pl) == -1) {
perror("lsh");
}
exit(EXIT_FAILURE);
}
else if (pid < 0) {
// Error forking
perror("lsh");
}
else if(cmd->bakground != 1){ // check in the parent process if it was running in background, if so dont call for wait()
// Parent process
j+=2;
pl = p->pgmlist;
p = p->next;
for(int i = 0; i < 2 * numPipes; i++){
printf("in sixth\n");
close(pipefds[i]);
}
int returnStatus;
waitpid(pid, &returnStatus, 0); // Parent process waits here for child to terminate.
if (returnStatus == 0) // Verify child process terminated without error.
{
printf("The child process terminated normally.");
}
if (returnStatus == 1)
{
printf("The child process terminated with an error!.");
}
}
else
printf("Child process with ID %d is running in background\n",pid );
}
}
当我读到这篇文章时,我认为这意味着我很快就要早起了,或者我对文件描述符的处理很糟糕。我试着修复它,但没有成功,我转向你们,他们可能会看到一些我看不到的东西。如果您需要任何进一步的信息,请发表意见,我将尽我所能提供帮助
******编辑1******
我将printf添加到我使用的每个dup2或close中,将它们命名为第一个、第二个、第三个等等,只是为了确切地知道我在哪个dup或close中得到了错误。这是我运行命令时的结果:
> ls | wc
in sixth
in sixth
in third
in sixth
in sixth
in fourth: 2
dup2: Bad file descriptor
所以我们至少知道它在哪里失败
******编辑2******
我还添加了我们正在写入、读取或关闭的文件描述符:
In parent closing fd: 0
In parent closing fd: 1
in child third writing to fd: 1
In parent closing fd: 0
In parent closing fd: 1
in child fourth reading from fd: 0
dup2: Bad file descriptor
我认为dup2的问题在于:
if(cmd->rstdin != NULL) {
fdr = open(cmd->rstdin, O_RDONLY);
dup2(fd, 0);
close(fdr);
}
您正在打开“fdr”,但在dup2中使用了“fd”。“fd”未打开或已在前一个if{}中关闭。此外,在这两个条件中,您不检查dup2的返回值。只是在dup2中将其更改为fdr,但仍然不起作用。而且那部分和管道无关。如果我正在使用这些命令ls
gcc-Wall-Werror-g-o myprog&&gdb--args myprog
您忘了添加gcc myprog,您希望我添加输出中给出的错误吗@JonathonReinhartI忘了myprog.c
,对不起。但是不,我希望您修复编译中的所有错误。我怀疑你的程序可能会在你这样做的时候起作用。这就是为什么我们要编译语言——在运行前检测编程问题“fork等人的隐式声明。在我看来,我没有实现fork或所有其他函数是错误的吗@JonathonReinhart假设使用Linux,您可以在strace-f-o/path/to/output/file…
下运行,查看系统调用级别的情况。
if(cmd->rstdin != NULL) {
fdr = open(cmd->rstdin, O_RDONLY);
dup2(fd, 0);
close(fdr);
}