【发布时间】：2014-05-08 15:02:17
【问题描述】：
我有一个任务是用 C 代码制作一个 shell，并且我有一个大多数时间都可以使用的解决方案。如果程序存在，我的解决方案就可以工作，我可以使用 Control-D 或键入 exit 退出我的 shell。但是当我尝试一个我知道不存在的命令时，我的 shell 将打印一条错误消息，指出找不到命令，但我必须键入 exit 或按 Control-D 相同的次数由于输入了无效命令，即如果我输入了 3 次错误命令，则必须按 Control-D 3 次。我真的不知道这里发生了什么。我检查了所有变量，当我按下 Control-D 时读取为 -1，但似乎跳过了 if 语句。
这是我认为问题所在的源代码部分：
comp20200Shell.c
#include "comp20200Shell_header.h"
#include <signal.h>
/*
* Name: ****
* Student Number: ****
* Email: ****
*
* This is the main function of my shell implementation.
*
*/
int main(void)
{
bool end_program = false;
size_t length = 0;
ssize_t read;
char* current_directory = NULL;
char* current_time = NULL;
/* Sets up signal handler to catch SIGINT*/
if(signal(SIGINT, sigintHandler) == SIG_ERR)
{
error("An error occured while setting a signal handler\n");
}
/* Infinitive loop, so after command or invalid comman will prompt again*/
while(end_program != true)
{
char* input = NULL;
/* Gets current working directory */
current_directory = return_current_directory();
/* Gets current date and time */
current_time = return_time();
/* Prints Prompt */
printf("%s\x5b%s\x5d %s%s %s%s%s", MAGENTA_TEXT, current_time, GREEN_TEXT, current_directory, BLUE_TEXT, PROMPT, RESET_COLOUR);
/* Frees the pointers returned by return_time() and return_current_directory() */
free(current_time);
free(current_directory);
/* Reads one line from standard input */
read = getline(&input, &length, stdin);
/* Checks if ctrl d, i.e. end of file is found or exit is typed */
if(strcmp(input, "exit\n") == 0 || read == -1)
{
if(read == -1)
{
putchar('\n');
}
/* Frees input */
free(input);
return(0);
}
/* Removes newline character that will be at the end */
remove_trailing_newline(input);
/* Passes input to process input, and the return value is passed in to process errors */
process_errors(process_input(&input));
/* Frees input */
free(input);
}
return(0);
}
process_input.c
#include "comp20200Shell_header.h"
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
/*
* Name: ****
* Student Number: ****
* Email: ****
*
* This function is used to process the command entered by the user
*
* return: the error value or 0 when everything whent ok
* arguments: the command entered by the user
*
*/
int process_input(char** input)
{
bool redirect_stdout = false;
bool redirect_stderr = false;
pid_t child_pid;
int child_status;
char** argument = malloc(sizeof(char*));
int count = 0;
char* temp = strtok(*input, " ");
while(temp != NULL)
{
argument[count] = temp;
count ++;
argument = realloc(argument, (count+2) * sizeof(char *));
temp = strtok(NULL, " ");
}
argument[count] = NULL;
if(argument[0] == NULL)
{
return(0);
}
else if(strcmp(argument[0], "cd") == 0)
{
return(change_directory(argument[1]));
}
int index;
for(index = 1; argument[index] != NULL; index++)
{
if(strcmp(argument[index], ">0") == 0)
{
if(argument[index + 1] == NULL)
{
return(EINVAL);
}
redirect_stdout = true;
break;
}
else if(strcmp(argument[index], ">2") == 0)
{
if(argument[index + 1] == NULL)
{
return(EINVAL);
}
redirect_stderr = true;
break;
}
}
child_pid = fork();
if(child_pid == 0)
{
int file;
if(redirect_stdout == true)
{
file = open(argument[index + 1], O_WRONLY|O_CREAT|O_TRUNC, 0666);
dup2(file, 1);
edit_arguments(argument, index);
execvp(argument[0], argument);
return(-1);
}
else if(redirect_stderr == true)
{
file = open(argument[index + 1], O_WRONLY|O_CREAT|O_TRUNC, 0666);
dup2(file, 2);
edit_arguments(argument, index);
execvp(argument[0], argument);
return(-1);
}
execvp(argument[0], argument);
return(-1);
}
else
{
wait(&child_status);
}
return(child_status);
}
comp20200Shell_header.h
/*
* Name: ****
* Student Number: ****
* Email: ****
*
* This is my header file, It includes all common used headerfiles on the top.
* Any specific header file that is only used once will be included with the .c file that needs it.
*
*/
/* included headerfiles begin */
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <stdbool.h>
/* included headerfiles end */
/* defenitions begin */
#define PROMPT "# "
#define BUFFER_SIZE 1024
#define BLUE_TEXT "\x1B[34m"
#define MAGENTA_TEXT "\x1B[35m"
#define GREEN_TEXT "\x1B[32m"
#define RESET_COLOUR "\x1B[0m"
/* defenitions end */
/* Function prototypes begin */
void remove_trailing_newline(char *input);
void sigintHandler(int sig_num);
int process_input(char** input);
char* return_time(void);
void error(const char *fmt, ...);
int change_directory(char* path);
char* return_current_directory(void);
void process_errors(int return_value);
void edit_arguments(char** argument, int index);
/* Function prototypes end */
我省略了其余的源代码，因为我认为问题不存在。
【问题讨论】：