minishell.c

unix shell的简单实现

 	#include <sys/types.h>
 	#include <unistd.h>
 	#include <sys/wait.h>
 	#include <string.h>
 	#include <errno.h>
 	#include <stdio.h>

 	void do_cd(char *argv[]);
 	void execute_new(char *argv[]);

	main()
	{
		char *cmd=(void *)malloc(256*sizeof(char));
		char *cmd_arg[10];
		int cmdlen,i,j,tag;

		do{
			/* 初始化cmd */
			for(i=0;i<255;i++) cmd[i]='\0';

			printf("My Shell| ");
			fgets(cmd,256,stdin);

			cmdlen=strlen(cmd);
			cmdlen--;
			cmd[cmdlen]='\0';

			/* 把命令行分解为指针数组cmd_arg */
			for(i=0;i<10;i++) cmd_arg[i]=NULL;
			i=0; j=0; tag=0;
			while(i<cmdlen && j<10){
				if(cmd[i]==' '){
					cmd[i]='\0';
					tag=0;
				}else{
					if(tag==0)
						cmd_arg[j++]=cmd+i;
					tag=1;
				}
				i++;
			}

			/* 如果参数超过10个，就打印错误，并忽略当前输入 */
			if(j>=10 && i<cmdlen){
				printf("TOO MANY ARGUMENTS\n");
				continue;
			}

			/* 命令quit：退出Mini Shell */
			if(strcmp(cmd_arg[0],"quit")==0)
				break;

			/* 命令cd */
			if(strcmp(cmd_arg[0],"cd")==0){
				do_cd(cmd_arg);
				continue;
			}

			/* 外部命令或应用程序 */
			execute_new(cmd_arg);
		}while(1);
	}

	/* 实现cd的功能 */
	void do_cd(char *argv[])
	{
		if(argv[1]!=NULL){
			if(chdir(argv[1])<0)
				switch(errno){
				case ENOENT:
					printf("DIRECTORY NOT FOUND\n");
					break;
				case ENOTDIR:
					printf("NOT A DIRECTORY NAME\n");
					break;
				case EACCES:
					printf("YOU DO NOT HAVE RIGHT TO ACCESS\n");
					break;
				default:
					printf("SOME ERROR HAPPENED IN CHDIR\n");
				}
		}

	}

	/* 执行外部命令或应用程序 */
	void execute_new(char *argv[])
	{
		pid_t pid;

		pid=fork();
		if(pid<0){
			printf("SOME ERROR HAPPENED IN FORK\n");
			exit(2);
		}else if(pid==0){
			if(execvp(argv[0],argv)<0)
				switch(errno){
				case ENOENT:
					printf("COMMAND OR FILENAME NOT FOUND\n");
					break;
				case EACCES:
					printf("YOU DO NOT HAVE RIGHT TO ACCESS\n");
					break;
	                        default:
	                                printf("SOME ERROR HAPPENED IN EXEC\n");
				}
			exit(3);
		}else
			wait(NULL);
	}