bzshell.c

shell 实现 操作系统课程设计 实现一个shell程序

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <string.h>


char *parse_cmd(char *cmd, char **argarr, int *narg, int *s) {
        enum states { S_START, S_IN_TOKEN, S_IN_QUOTES, S_SEMI };
        int argc=0;
        int loop=1;
        enum states state = S_START;
        int lastch;

        while (loop) {
                switch (state) {
                case S_START:
                        if (*cmd == '"') {
                                *argarr++ = cmd + 1;
                                ++argc;
                                state = S_IN_QUOTES;
                        }
                        else if (*cmd == 0 || *cmd == ';' || *cmd == '|' || *cmd == '>' || *cmd == '<')
                                loop = 0;
                        else if (*cmd <= ' ')
                                *cmd = 0;
                        else {
                                *argarr++ = cmd;
                                ++argc;
                                state = S_IN_TOKEN;
                        }
                        break;
                case S_IN_TOKEN:
                        if (*cmd == 0 || *cmd == ';' || *cmd == '|' || *cmd == '>' || *cmd == '<')
                                loop = 0;
                        else if (*cmd <= ' ') {
                                *cmd=0;
                                state=S_START;
                        }
                        break;
                case S_IN_QUOTES:
                        if (*cmd == 0)
                                loop = 0;
                        else if (*cmd == '"') {
                                *cmd = 0;
                                state = S_START;
                        }
                }
                cmd++;
        }
        *argarr = NULL;

        if(narg != NULL) *narg = argc;

        lastch = cmd[-1];
        cmd[-1] = 0;
        if( lastch == '|')
            *s = 1;
        else if( lastch == '>')
            *s = 2;
        else if( lastch == '<')
            *s = 3;
        else *s = 0;
        return (lastch == ';' || lastch == '|' || lastch == '>'|| lastch == '<') ? cmd : NULL;
}

int main(int argc, char **argv) {
        char cmd[80];
        char *source = NULL;
        char *arg[21];
        int statval;
        char *prompt="bzsh";
        char *test_env;
        int numargs;
        int state;
        int fd;
        char *file;
	char path[100];
	FILE *fp;
	int pipepre=0;
	int prepipe[2];
	int postpipe[2];
  
        if (test_env=getenv("BSPROMPT"))
                prompt=test_env;
        while (1) {
                if(source == NULL) {
			getcwd(path, sizeof(path));
                        printf("%s[%s]#", prompt, path);
                        source = gets(cmd);
                        if(source == NULL) exit(0);
                }

                source = parse_cmd(source, arg, &numargs, &state);
                if (numargs == 0) continue;

                if (!strcmp(arg[0],"exit"))
                                exit(0);
		while(*source == ' ')
			source ++;
                if( state == 2 || state == 3 )
               	{
                    file = source;
                    while( *source != ' ' && *source != 0 )
                        source ++;
		    *source = 0;
		    source++;
		    while(*source == ' ')
			    source ++;
                    if(*source == 0) source = NULL;
	       	}
		if(!strcmp(arg[0], "cd"))
		{
			chdir(arg[1]);
			continue;
		}
		prepipe[0]=postpipe[0];
		prepipe[1]=postpipe[1];
		pipe(postpipe);
                if (fork()==0) {
                    if(state == 2 )
                    {
                        fd = creat( file, 0644 );
                        dup2( fd, 1 );
                        close( fd );
                    }
                    if(state == 3 )
                    {
                        fd = open( file, O_RDONLY );
                        dup2( fd, 0 );
                        close( fd );
                    }
		    if(pipepre == 1)
		    {
			    close(prepipe[1]);
			    dup2(prepipe[0], 0);
			    close(prepipe[0]);
		    }
		    if(state == 1)
		    {
			    close(postpipe[0]);
			    dup2(postpipe[1], 1);
			    close(postpipe[1]);
		    }
		    execvp(arg[0],arg);
                    printf("failed\n");
                    exit(1);
                }
		else{
			if(pipepre == 1)
			{
				close(prepipe[0]);
				close(prepipe[1]);
			}
			wait(&statval);
			if(state == 1)
				pipepre = 1;
			else pipepre = 0;
		}
        }
}