简易shell

done，故意写成=，表示先赋值，再判断，分割之后，strtok会返回NULL，刚好让gArgv最后一个元素是NULL，并且while判断结束

Makefile

  1 myshell:myshell.c                                                                                                                                                      
  2   gcc -o $@ $^
  3 .PHONY:clean
  4 clean:
  5   rm -f myshell

myshell.c

  1 #include<stdio.h>
  2 #include<unistd.h>
  3 #include<sys/types.h>
  4 #include<sys/wait.h>
  5 #include<stdlib.h>
  6 #include<string.h>
  7 #include<errno.h>
  8 
  9 #define SIZE 512
 10 #define ZERO '\0'
 11 #define SEP " "
 12 #define NUM 32
 13 #define SkipPath(p) do{p += (strlen(p) - 1);while(*p != '/') p--;}while(0)
 14 
 15 char cwd[SIZE*2];
 16 char *gArgv[NUM];
 17 int lastcode = 0;
 18 void Die()
 19 {
 20     exit(1);
 21 }
 22 
 23 const char *GetHome()
 24 {
 25     const char *home = getenv("HOME");                                                                                                                                 
 26     if(home == NULL) return "/";
 27     return home;
 28 }
 29 const char *Getusername()
 30 {
 31     const char *name = getenv("USER");
 32     if(name == NULL) return "None";
 33     return name;
 34 }
 35 const char *Gethostname()
 36 {                                                                                                                                                                      
 37     const char *hostname = getenv("HOSTNAME");
 38     if(hostname == NULL) return "None";
 39     return hostname;
 40 }
 41 const char *Getcwd()
 42 {
 43     const char *cwd = getenv("PWD");
 44     if(cwd == NULL) return "None";
 45     return cwd;
 46 }
 47 
 48 void makecommandline()
 49 {
 50     char line[SIZE];
 51     const char *username = Getusername();
 52     const char *hostname = Gethostname();
 53     const char *cwd = Getcwd();
 54                                                                                                                                                                        
 55     SkipPath(cwd);
 56     snprintf(line, sizeof(line), "[%s@%s %s] love:", username, hostname, strlen(cwd) == 1 ? "/" : cwd + 1);
 57     printf("%s", line);
 58     fflush(stdout);
 59 }
 60 
 61 int Getusercommand(char command[], size_t n)
 62 {
 63     char *s = fgets(command, n, stdin);
 64     if(s == NULL) return -1;
 65 
 66     command[strlen(command) - 1] = ZERO;
 67     return strlen(command);
 68 }
 69 
 70 void SplitCommand(char command[], size_t n)
 71 {
 72     (void)n;
 73     gArgv[0] = strtok(command, SEP);
 74     int index = 1;
 75     while((gArgv[index++] = strtok(NULL, SEP)));                                                                                                                       
 76 }
 77 void ExecuteCommand()
 78 {
 79     pid_t id = fork();
 80     if(id < 0) Die();
 81     else if(id == 0)
 82     {
 83         //child
 84         execvp(gArgv[0], gArgv);
 85         exit(errno);
 86     }
 87     else 
 88     {
 89         //father
 90         int status = 0;
 91         pid_t rid = waitpid(id, &status, 0);
 92         if(rid > 0)
 93         {
 94             lastcode = WEXITSTATUS(status);
 95             if(lastcode != 0) printf("%s:%s:%d\n", gArgv[0], strerror(lastcode), lastcode);
 96         }
 97     }
 98 }
 99 
100 void Cd()
101 {
102     const char *path = gArgv[1];
103     if(path == NULL) path =GetHome();
104 
105     chdir(path);                                                                                                                                                       
106     //刷新环境变量
107     char temp[SIZE*2];
108     getcwd(temp, sizeof(temp));
109     snprintf(cwd, sizeof(cwd), "PWD=%s", temp);
110     putenv(cwd);
111 }
112 int CheckBuildin()
113 {
114     int yes = 0;
115     const char *enter_cmd = gArgv[0];
116     if(strcmp(enter_cmd, "cd") == 0)
117     {
118         yes = 1;
119         Cd();
120     }
121     else if(strcmp(enter_cmd, "echo") == 0 && strcmp(gArgv[1], "$?") == 0)
122     {
123         yes = 1;
124         printf("%d\n", lastcode);
125         lastcode = 0;
126     }
127 
128     return yes;
129 }
130 int main()
131 {
132     int quit = 0;                                                                                                                                                      
133     while(!quit)
134     {
135         makecommandline();
136 
137         char usercommand[SIZE];
138         int n = Getusercommand(usercommand, sizeof(usercommand));
139         if(n <= 0) return 1;
140 
141         SplitCommand(usercommand, sizeof(usercommand));
142         
143         n = CheckBuildin();
144         if(n) continue;
145         ExecuteCommand();
146     }
147     
148     return 0;
149 }