[英]Unix C Shell - Job Control Issue!
I've been working on creating my own Unix Shell in C to get practice with its interworkings...I'm having some issues getting my process to run in the background while allowing my shell to continue taking user input . 我一直在努力用C创建自己的Unix Shell,以实现其互操作性…… 在让我的Shell继续接受用户输入的同时,我的程序在后台运行时遇到了一些问题 。 If you could take the time to dissect what I've got below it would be much appreciated! 如果您能花时间剖析一下我的不足,将不胜感激!
My variables are below, just incase that helps understand things more... 我的变量在下面,以防万一,有助于您进一步了解...
#define TRUE 1
static char user_input = '\0';
static char *cmd_argv[5]; // array of strings of command
static int cmd_argc = 0; // # words of command
static char buffer[50]; // input line buffer
static int buffer_characters = 0;
int jobs_list_size = 0;
/* int pid; */
int status;
int jobs_list[50];
Here is my main function. 这是我的主要功能。
int main(int argc, char **argv)
{
printf("[MYSHELL] $ ");
while (TRUE) {
user_input = getchar();
switch (user_input) {
case EOF:
exit(-1);
case '\n':
printf("[MYSHELL] $ ");
break;
default:
// parse input into cmd_argv - store # commands in cmd_argc
parse_input();
//check for zombie processes
check_zombies();
if(handle_commands() == 0)
create_process();
printf("\n[MYSHELL] $ ");
}
}
printf("\n[MYSHELL] $ ");
return 0;
}
Parse Input...I know, I can't get readline to work on this box :( If provided the & operator, create the job in the background... (see below) 解析输入...我知道,我无法在此框上使用readline :(如果提供了&运算符,请在后台创建作业...(请参阅下文)
void parse_input()
{
// clears command line
while (cmd_argc != 0) {
cmd_argv[cmd_argc] = NULL;
cmd_argc--;
}
buffer_characters = 0;
// get command line input
while ((user_input != '\n') && (buffer_characters < 50)) {
buffer[buffer_characters++] = user_input;
user_input = getchar();
}
// clear buffer
buffer[buffer_characters] = 0x00;
// populate cmd_argv - array of commands
char *buffer_pointer;
buffer_pointer = strtok(buffer, " ");
while (buffer_pointer != NULL) {
cmd_argv[cmd_argc] = buffer_pointer;
buffer_pointer = strtok(NULL, " ");
//check for background process execution
if(strcmp(cmd_argv[cmd_argc], "&")==0){
printf("Started job %d\n", getpid());
make_background_job();
}
cmd_argc++;
}
}
Make background job. 进行后台工作。 Closes child process STDIN, opens new STDIN, and executes. 关闭子进程STDIN,打开新的STDIN,然后执行。
void make_background_job()
{
int pid;
pid = fork();
fclose(stdin); // close child's stdin
fopen("/dev/null", "r"); // open a new stdin that is always empty
fprintf(stderr, "Child pid = %d\n", getpid());
//add pid to jobs list
jobs_list[jobs_list_size] = getpid();
/* printf("jobs list %d", *jobs_list[jobs_list_size]); */
jobs_list_size++;
execvp(*cmd_argv,cmd_argv);
// this should never be reached, unless there is an error
fprintf (stderr, "unknown command: %s\n", cmd_argv[0]);
}
The meat of my job control. 我的工作控制的肉。 Fork spawns child, returns 0 for child and PID for parent. Fork产生子代,子代返回0,父代返回PID。
void create_process()
{
pid_t pid;
pid = fork();
status = 0;
switch(pid){
case -1:
perror("[MYSHELL ] $ (fork)");
exit(EXIT_FAILURE);
case 0:
make_background_job();
printf("\n\n----Just made background job in case 0 of create_process----\n\n");
break;
default:
printf("\n\n----Default case of create_process----\n\n");
// parent process, waiting on child...
waitpid(pid, &status, 0);
if (status != 0)
fprintf (stderr, "error: %s exited with status code %d\n", cmd_argv[0], status);
else
break;
}
}
My problem is when I execute a job in the background, its executing the command twice, and exiting out of the shell. 我的问题是,当我在后台执行作业时,它执行两次命令,然后退出外壳。 (It functions correctly otherwise if no background process is enabled). (否则,如果未启用任何后台进程,它将正常运行)。 Where am I getting confused? 我在哪里感到困惑? I think it may have to do with issues regarding my PID's, as I'm not populating the list correctly either in 'make_background_job' 我认为这可能与我的PID有关,因为我没有在'make_background_job'中正确填充列表
Here is my output, the example.sh just throws out helloWorld: 这是我的输出,example.sh只是抛出helloWorld:
[MYSHELL] $ ./example.sh &
Started job 15479
Child pid = 15479
Child pid = 15481
Hello World
Hello World
What seems to happen is 似乎发生的是
main()
the prompt is displayed, expecting a command 在main()
中显示提示,要求输入命令 parse_input()
is called 输入命令时,将调用parse_input()
&
where it calls make_background_jobs()
它会构建命令数组,直到找到&
并调用make_background_jobs()
execvp()
该函数快速分叉,并在两个进程execvp()
中并行执行 execvp()
replaces each of the two processes to execute the command execvp()
替换两个进程中的每个进程以执行命令 The problem is in make_background_jobs()
where, I think, the expected behavior was that only one of the two processes should execute the command, and the other one (father) returns, to keep the program active. 问题出在make_background_jobs()
中,我认为预期的行为是两个进程中只有一个应该执行该命令,而另一个(父亲)返回,以保持程序处于活动状态。
This can be solved by modifying that function, making the father process return: 这可以通过修改该函数来解决,使父进程返回:
void make_background_job()
{
int pid;
pid = fork();
if (pid) return; // The father process returns to keep program active
...
edit 编辑
I gave it a try, removing the unnecessary 我尝试了一下,删除了不必要的
void make_background_job()
{
int pid;
pid = fork();
if ( ! pid)
{
fclose(stdin); // close child's stdin
fopen("/dev/null", "r"); // open a new stdin that is always empty
fprintf(stderr, "Child Job pid = %d\n", getpid());
//add pid to jobs list
jobs_list[jobs_list_size] = getpid();
/* printf("jobs list %d", *jobs_list[jobs_list_size]); */
jobs_list_size++;
execvp(*cmd_argv,cmd_argv);
// this should never be reached, unless there is an error
fprintf (stderr, "unknown command: %s\n", cmd_argv[0]);
exit(1);
}
waitpid(pid, &status, 0);
}
The background job is created in another process. 后台作业是在另一个过程中创建的。 The father waits for the job to complete. 父亲等待工作完成。
void parse_input()
{
// clears command line
while (cmd_argc != 0) {
cmd_argv[cmd_argc] = NULL;
cmd_argc--;
}
buffer_characters = 0;
// get command line input
while ((user_input != '\n') && (buffer_characters < 50)) {
buffer[buffer_characters++] = user_input;
user_input = getchar();
}
// clear buffer
buffer[buffer_characters] = 0x00;
// populate cmd_argv - array of commands
char *buffer_pointer;
buffer_pointer = strtok(buffer, " ");
int ok = 0;
while (buffer_pointer != NULL) {
cmd_argv[cmd_argc] = buffer_pointer;
buffer_pointer = strtok(NULL, " ");
//check for background process execution
if(strcmp(cmd_argv[cmd_argc], "&")==0){
ok = 1;
break;
}
cmd_argc++;
}
if (!ok) cmd_argv[cmd_argc = 0] = NULL; // If no & found, reset commands
}
Only parses input. 仅解析输入。
Below a new handle_commands()
that return 0
if there is a command to play, and the main
follows. 在新的handle_commands()
下方,如果有要播放的命令,则返回0
,随后是main
。
int handle_commands() { return cmd_argc > 0 ? 0:1; }
int main(int argc, char **argv)
{
printf("[MYSHELL] $ ");
while (TRUE) {
user_input = getchar();
switch (user_input) {
case EOF:
exit(-1);
case '\n':
printf("[MYSHELL] $ ");
break;
default:
// parse input into cmd_argv - store # commands in cmd_argc
parse_input();
//check for zombie processes
check_zombies();
if(handle_commands() == 0)
make_background_job(); // Call directly the bg job
printf("\n[MYSHELL] $ ");
}
}
printf("\n[MYSHELL] $ ");
return 0;
}
The main()
calls directly make_background_job()
. main()
直接调用make_background_job()
。
There is only one fork()
in make_background_job. make_background_job中只有一个fork()
。 create_process()
has been removed. create_process()
已被删除。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.