编写my_shell
基本需求：
实现 管道（也就是 | ）
实现 输入输出重定向(<> >>)
实现 后台运行（ &）(ps:linuxc上的&实现其实并不是真正的后台运行，可以考虑一下为什么)
实现 内建命令（cd ）
屏蔽一些信号（如ctrl + c 不能终止）
通过设置环境变量 可以直接使用 (在任意地方都可以运行你的shell)
界面美观
进阶需求：
实现 tab补全 （提示:使用readline库）
实现内置命令history
实现光标的移动
在编写my_shell中需要准备的：
1.实现tab补全，内置命令history，光标的移动都需要使用到动态库
这个readline动态库的使用总结的不错，点一点进去看看
使用动态库后跑代码时要加在后面加 -lreadline
2 屏蔽Ctrl+C杀死程序只需要一行代码即可
signal(SIGINT, SIG_IGN);
代码如下，还有一些功能不太完善，日后会继续完善
# include <stdio.h>
# include <stdlib.h>
# include <unistd.h>
# include <string.h>
# include <sys/types.h>
# include <sys/wait.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <dirent.h>
# include <readline/readline.h>
# include <readline/history.h>
# define normal 0 //一般的命令
# define out_readirect 1 //输出重定向>
# define in_readdirect 2 //输入重定向<
# define have_pipe 3 //命令中有管道|
# define outt_readirect 4 //>>
void print_prompt(); //打印提示符
void get_input(char **buf); //得到输入的命令
void explain_input(char *, int *, char (*)[256]); //对输入的命令进行解析
void do_cmd(int, char (*)[256]); //执行命令
int find_command(char *); //查找命令中的可执行程序
char *myshell; //myshell提示信息的输出
void ShowHistory()
{
int i = 0;
HIST_ENTRY ** ren;
ren = history_list();
while(ren[i] != NULL)
printf("%s\n", ren[i++]->line);
}
int main(int argc, char **argv)
{
signal(SIGINT, SIG_IGN); //ctrl + c 不能终止程序
system("clear");
setbuf(stdout,NULL); //序在接受到SIGINT信号时转入的处理函数不处理缓冲区会转入下一行
read_history(NULL);
int i;
int argcount = 0;
char arglist[100][256];
char **arg = NULL;
char *buf = NULL;
buf = (char *)malloc(256);
if (buf == NULL) {
perror("malloc failed");
exit(-1);
}
while(1) {
char *buf = (char*)malloc(256);
//将buf所指的空间清零
memset(buf, 0, 256);
print_prompt();
get_input(&buf);
if ( strcmp(buf, "exit\n") == 0 || strcmp(buf, "logout\n") == 0)
break;
for (i = 0; i < 100; i++) {
arglist[i][0] = '\0';
}
argcount = 0;
explain_input(buf, &argcount, arglist);
if (!strcmp(buf,"history")) {
ShowHistory();
continue;
}
do_cmd(argcount, arglist);
}
if (buf != NULL) {
free(buf);
buf = NULL;
}
exit(0);
}
void print_prompt()
{
setbuf(stdout,NULL);
myshell = (char *)malloc(100);
getcwd(myshell, 100); //getcwd()会将当前工作目录的绝对路径复制到参数buffer所指的内存空间中,参数size为buf的空间大小
printf("\033[47;31m myshell@ytt:%s$ \033[0m", myshell);
printf("\001\033[0m\002");
free(myshell);
}
//获取用户输入
void get_input(char **buf)
{
int len = 0;
int ch = '\0';
// ch = getchar();
// while (len < 256 && ch != '\n') {
// buf[len++] = ch;
// ch = getchar();
// }
// if (len == 256) {
// printf("\033[47;31m command is too long\033[47;31m myshell@ytt:%s$ \033[0m\n");
// exit(-1);
// }
// buf[len] = '\n';
// len++;
// buf[len] = '\0';
*buf = readline("my_shell@"); //不在这里加字符串可能会出现缓冲区问题 导致光标移动异常
add_history( *buf );
write_history(NULL);
if (len == 256) {
printf("\033[47;31m command is too long\033[47;31m myshell@ytt:%s$ \033[0m\n");
return;
}
}
//解析buf中的命令，将结果存入arglist中，命令以回车符号\n结束
void explain_input(char *buf, int *argcount, char (*arglist)[256])
{
char *p = buf;
char *q = buf;
int number = 0;
int i;
while(1) {
if (p[0] == '\n')
break;
if (p[0] == ' ')
p++;
else {
q = p;
number = 0;
while( (q[0] != ' ') && (q[0] != '\n') ) {
if ( q[0] == 92 ) {
//如果第一个字符为‘\’
q[0] = ' ';
q[1] = q[2];
for(i = 2; ; i++) {
q[i] = q[i+1];
if((q[i] == ' ') || (q[i] == '\n'))
break;
}
}
number++;
q++;
}
strncpy(arglist[*argcount], p, number + 1);
arglist[*argcount][number] = '\0';
*argcount = *argcount + 1;
p = q;
}
}
}
void do_cmd(int argcount, char (*arglist)[256])
{
int flag = 0;
int how = 0; //用于指示命令中是否含有> 、 < 、 |
int background = 0; //标识命令中是否有后台运行的标识符＆
int status;
int i;
int fd;
char *arg[argcount + 1];
char *argnext[argcount + 1];
char *file;
pid_t pid;
//将命令取出
for (i = 0; i < argcount; i++) {
arg[i] = (char *)arglist[i];
}
arg[argcount] = NULL;
//查看命令行是否有后台运行符
for (i = 0; i < argcount; i++) {
if (strncmp(arg[i], "&", 1) == 0) {
if (i == argcount - 1) {
background = 1;
arg[argcount - 1] = NULL;
break;
} else {
printf("wrong command\n");
return;
}
}
}
for (i = 0; arg[i] != NULL; i++) {
if (strcmp(arg[i], ">") == 0) {
flag++;
how = out_readirect;
if (arg[i + 1] == NULL)
flag++;
}
if (strcmp(arg[i], "<") == 0) {
flag++;
how = in_readdirect;
if (i == 0)
flag++;
}
if (strcmp(arg[i], "|") == 0) {
flag++;
how = have_pipe;
if (arg[i+1] == NULL)
flag++;
if (i == 0)
flag++;
}
if (strcmp(arg[i], ">>") == 0) {
flag++;
how = outt_readirect;
if (arg[i+1] == NULL)
flag++;
}
}
//flag大于1,说明命令中含有多个> < |符号，本程序是不支持这样的命令的，或命令格式不对
if (flag > 1) {
printf("wrong command\n");
return;
}
if (strcmp(arg[0],"ls") == 0) {
strcpy(arglist[argcount],"--color");
arg[argcount] = (char *)arglist[argcount];
argcount = argcount + 1;
arg[argcount] = NULL;
} else {
arg[argcount] = NULL;
}
if (how == outt_readirect) {
for (i = 0; arg[i] != NULL; i++) {
if (strcmp(arg[i],">>") == 0) {
file = arg[i+1];
arg[i] = NULL;
}
}
}
if (how == out_readirect) {
//命令只含有一个输出重定向符号>
for (i = 0; arg[i] != NULL; i++) {
if(strcmp(arg[i], ">") == 0) {
file = arg[i+1];
arg[i] = NULL;
}
}
}
if (how == in_readdirect) {
//命令只含有一个输入重定向
for (i = 0; arg[i] != NULL; i++) {
if (strcmp(arg[i], "<") == 0) {
file = arg[i + 1];
arg[i] == NULL;
}
}
}
if (how == have_pipe) {
//命令只有一个管道符号，把管道符后面的部分存入argnext中，管道后面的部分是一个可执行的shell命令
for (i = 0; arg[i] != NULL; i++) {
if (strcmp(arg[i], "|") == 0) {
arg[i] = NULL;
int j;
for (j = i + 1; arg[j] != NULL; j++) {
argnext[j-i-1] = arg[j];
}
argnext[j-i-1] = arg[j];
break;
}
}
}
if ( (arg[0] != NULL) && (strcmp(arg[0], "cd") == 0) ) {
//內建cd
if (arg[1] == NULL)
return;
if (strcmp(arg[1], "~") == 0)
strcpy(arg[1], "/home/ytt/");
if ( chdir(arg[1]) == -1 )
perror("cd");
return ;
}
if ( (pid = fork()) < 0 ) {
printf("fork error\n");
return;
}
switch(how)
{
case 0:
//pid为0说明是子进程，在子进程中执行输入的命令
//输入的命令中不含> < |
if (pid == 0) {
if ( !(find_command(arg[0])) ) {
printf("%s : command not found\n", arg[0]);
exit(0);
}
execvp(arg[0], arg);
exit(0);
}
break;
case 1:
//输入的命令中含有输出重定向符>
if (pid == 0) {
if ( !(find_command(arg[0])) ) {
printf("%s : command not found\n", arg[0]);
exit(0);
}
// 打开或新建输出重定向的文件
fd = open(file, O_RDWR|O_CREAT|O_TRUNC, 0644);
// 将标准输出复制到打开的文件描述符，即用文件描述符替换标准输出
dup2(fd, 1); // dup2(int oldfd, int newfd)
execvp(arg[0], arg);
exit(0);
}
break;
case 2:
//输入的命令中含有输入重定向<
if (pid == 0) {
if( !(find_command (arg[0])) ) {
printf("%s : command not found\n", arg[0]);
exit(0);
}
fd = open(file, O_RDONLY);
dup2(fd, 0);
execvp(arg[0], arg);
exit(0);
}
break;
case 3:
//输入的命令中含有管道符|
if (pid == 0) {
int pid2;
int status2;
int fd2;
if ( (pid2 = fork()) < 0 ) {
printf("fork2 error\n");
return;
} else if ( pid2 == 0 ) {
if ( !(find_command(arg[0])) ) {
printf("%s : command not found\n", arg[0]);
exit(0);
}
fd2 = open("/tmp/youdonotknowfile", O_WRONLY|O_CREAT|O_TRUNC, 0644);
dup2(fd2, 1);
execvp(arg[0], arg);
exit(0);
}
if ( waitpid(pid2, &status2, 0) == -1 )
printf("wait for child process error\n");
if ( !(find_command(argnext[0])) ) {
printf("%s : command not found\n", argnext[0]);
exit(0);
}
fd2 = open("/tmp/youdonotknowfile", O_RDONLY);
dup2(fd2, 0);
execvp (argnext[0], argnext);
if ( remove("/tmp/youdonotknowfile") ) //remove()成功时返回0,如果发生错误返回非零.
printf("remove error\n");
exit(0);
}
break;
case 4:
if (pid == 0) {
if ( !(find_command(arg[0])) ) {
printf("%s : command not found\n", arg[0]);
exit(0);
}
int fd = open(file, O_RDWR|O_APPEND|O_CREAT, 0644);
dup2(fd, 1);
execvp(arg[0],arg);
exit(0);
}
break;
default:
break;
}
//若命令中有&，表示后台执行，父进程直接返回，不等待子进程结束
if ( background == 1 ) {
printf("[process id %d]\n", pid);
return;
}
//父进程等待子进程结束
if ( waitpid(pid, &status, 0) == -1 )
printf("wait for child process error\n");
}
//查找命令中的可执行程序
int find_command(char *command)
{
DIR *dp;
struct dirent *dirp;
char *path[] = {
"./", "/bin", "/usr/bin", NULL};
//使当前目录下的程序可以运行，如命令“./fork”可以被正确解释和执行
if( strncmp(command, "./", 2) == 0 )
command = command + 2;
//分别在当前目录，/bin和/usr/bin目录查找要执行的程序
int i = 0;
while ( path[i] != NULL ) {
if ( ( dp= opendir(path[i]) ) == NULL )
printf("can not open /bin \n");
while ( ( dirp = readdir(dp) ) != NULL ) {
if ( strcmp(dirp->d_name, command) == 0 ) {
closedir(dp);
return 1;
}
}
closedir(dp);
i++;
}
return 0;
}