main.c

自编的linux shell的程序可以模拟实现linux 中SHELL功能

#include"stdio.h"
#include"string.h"
#include"malloc.h"
#include"unistd.h"
#include"stdlib.h"
#include"sys/types.h"
#include"sys/wait.h"

#define BUFFERSIZE 255

char buffer[BUFFERSIZE+1];
int is_fileexist(char *comm);

int main()
{
	char *path;
	while(1)
	{
		path = get_current_dir_name();
		printf("%s>$",path);
		char lc_char;
		int li_inputlen = 0;
		char *input;
		
		lc_char = getchar();
		while(lc_char != '\n' && li_inputlen < BUFFERSIZE){
			buffer[li_inputlen++] = lc_char;
			lc_char = getchar();
		}
		if(li_inputlen >= BUFFERSIZE){
			printf("Your command is too long!Please re-enter your command!<=%d\n",BUFFERSIZE);
			li_inputlen = 0;
			continue ;
		}
		if(li_inputlen == 0)
			continue ;
		else
			buffer[li_inputlen] = '\0';
		input = (char*) malloc(sizeof(char) * (li_inputlen+1));
		strcpy(input,buffer);
		
		int i;
		int j;
		int k;
		int is_bj = 0;
		int is_back = 0;
		int pid;
		int status;
		char *arg[20];
		for(i = 0,j =0, k = 0;i <= li_inputlen;i++){
			if(input[i] =='<' || input[i] =='>' || input[i] == '|'){
				if(input[i] == '|')
					printf("command is not supported!");

				else
					printf("command is not supported!");
				is_bj = 1;
				break ;
			}
			if(input[i] ==' ' || input[i] =='\t' || input[i] =='\0'){
				if(j == 0)
					continue;
				else{
					buffer[j++]='\0';
					arg[k] = (char *)malloc(sizeof(char)*j);
					strcpy(arg[k],buffer);
					j = 0;
					k++;
				}
			}
			else{
				if(input[i] == '&' && input[i+1] == '\0'){
					is_back = 1;
					continue ;
				}
				buffer[j++] = input[i];
			}
		}
		free(input);
		if(strcmp(arg[0],"leave") ==0){
			printf("bye-bye\n");
			break ;
		}
		if(strcmp(arg[0],"cd") ==0)
		{
			if(k ==1)
			continue ;
			if(k >2)
			printf("parameter error!\n");
			else if(chdir(arg[1]) ==-1)
			printf("path error!\n");
			continue ;
		}
		if(is_bj ==0){
			arg[k] = (char *) 0;
			if(is_fileexist(arg[0]) == -1){
				printf("This command is not found?!\n");
				for(i = 0;i < k; i++)
					free(arg[i]);
				continue ;
			}
			else{
				if((pid = fork()) ==0)
				execv(buffer,arg);
				else if(is_back == 0)
				    waitpid(pid,&status,0);
				for(i = 0;i <k; i++)
				   free(arg[i]);    
				
			}
		}
	}
		return 0;
}

int is_fileexist(char *comm)
{
	char *path,*p;
	int i;
	
	i=0;
	path = getenv("PATH");
	p = path;
	while(*p != '\0'){
		if(*p != ':')
            buffer[i++] = *p;
		else{
			buffer[i++] = '/';
			buffer[i] = '\0';
			strcat(buffer,comm);
			
			if(access(buffer,F_OK) ==0)
				return 0;
			else
				i = 0;
		}
		p++;
	}
	return -1;
}