c – 程序奇怪地返回到循环的顶部

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main()
{

    int MAX_INPUT_SIZE = 200;
    volatile int running = 1;
    while (running)
    {

        char input[MAX_INPUT_SIZE];
        char *tokens[100];
        const char *cmds[] = { "wait","pwd","cd","exit" };
        char *cmdargs[100];

        printf("shell> ");
        fgets(input,MAX_INPUT_SIZE,stdin);

        // remove newline character at end
        int nl = strlen(input) - 1;
        if (input[nl] == 'n')
        {
            input[nl] = '';
        }

        // tokenize input string,put each token into an array
        char *space;
        space = strtok(input," ");
        tokens[0] = space;

        int i = 1;
        while (space != NULL)
        {
            space = strtok(NULL," ");
            tokens[i] = space;
            ++i;
        }

        // copy tokens after first one into string
        int noargscheck;
        if (tokens[1] != NULL)
        {
            noargscheck = 0;
            strcpy((char *)cmdargs,tokens[1]);
            for (i = 2; tokens[i] != NULL; i++)
            {
                strcat((char *)cmdargs," ");
                strcat((char *)cmdargs,tokens[i]);
            }
        }
        else
        {
            noargscheck = 1;
        }

        // compare tokens[0] to list of internal commands
        int isInternal = -1;
        for (i = 0; i < 4; i++)
        {
            if (strcmp(tokens[0],cmds[i]) == 0)
            {
                isInternal = i;
            }
        }


        // internal commands
        char wd[200];
        if (isInternal != -1)
        {
            switch (isInternal)
            {
            case 0:
                // wait
                break;
            case 1:
                // pwd
                if (getcwd(wd,sizeof(wd)) == NULL)
                {
                    perror("getcwd() error!");
                }
                else
                {
                    printf("%sn",wd);
                }
                break;
            case 2:
                // cd
                if (noargscheck)
                {
                    chdir("/home");
                }
                else if (chdir((const char *)cmdargs) != 0)
                {
                    perror("cd failed");
                }
                break;
            case 3:
                // exit
                exit(1);
                break;
            }
        }

        else
        {
            // external commands

            pid_t child_pid;
            switch (child_pid = fork())
            {
            case -1:
                perror("Fork failed");
                return 1;
            case 0:
                // child
                printf("nHEREn"); // for debugging
                execvp(tokens[0],cmdargs);
                break;
            }
        }
    }
}

当我使用输入echo hello world运行此代码时,程序在第二个switch语句中以switch(child_pid = fork())成功输入case 0 case,但输出是意外的,如下所示：

输出:(包括在提示符下显示我的输入的一行)

外壳> echo hello world(我的输入)

外壳> (这是我不明白的部分)

这里

外壳> (程序现在等待下一个用户输入的提示)

我无法弄清楚为什么额外的外壳>提示正在打印.任何人都能看到问题吗？

编辑：修复了execvp的第一个参数.从“回声”(这是因为我很傻)改为令牌[0].