C语言实现一个迷你Shell

简介

俄勒冈州立大学（Oregon State University) CS 344作业,使用C语言实现一个Shell.

要求

• 内置 cd,status和exit 命令
• 支持输入和输出的重定向
• 支持后台运行(&)
• Ctrl-Z 与 Ctrl-C
• 调用系统其他命令
• 替换命令中的$$为Shell的PID

参考资料

作业pdf

测试脚本

p3testscript view raw

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#!/bin/bash echo "PRE-SCRIPT INFO" echo " Grading Script PID: $$" echo ' Note: your smallsh will report a different PID when evaluating $$' ./smallsh <<'___EOF___' echo BEGINNING TEST SCRIPT echo echo -------------------- echo Using comment (5 points if only next prompt is displayed next) #THIS COMMENT SHOULD DO NOTHING echo echo echo -------------------- echo ls (10 points for returning dir contents) ls echo echo echo -------------------- echo ls out junk ls > junk echo echo echo -------------------- echo cat junk (15 points for correctly returning contents of junk) cat junk echo echo echo -------------------- echo wc in junk (15 points for returning correct numbers from wc) wc < junk echo echo echo -------------------- echo wc in junk out junk2; cat junk2 (10 points for returning correct numbers from wc) wc < junk > junk2 cat junk2 echo echo echo -------------------- echo test -f badfile (10 points for returning error value of 1, note extraneous &) test -f badfile status & echo echo echo -------------------- echo wc in badfile (10 points for returning text error) wc < badfile echo echo echo -------------------- echo badfile (10 points for returning text error) badfile echo echo echo -------------------- echo sleep 100 background (10 points for returning process ID of sleeper) sleep 100 & echo echo echo -------------------- echo pkill -signal SIGTERM sleep (10 points for pid of killed process, 10 points for signal) echo (Ignore message about Operation Not Permitted) pkill sleep echo echo echo -------------------- echo sleep 1 background (10 pts for pid of bg ps when done, 10 for exit value) sleep 1 & sleep 1 echo echo echo -------------------- echo pwd pwd echo echo echo -------------------- echo cd cd echo echo echo -------------------- echo pwd (10 points for being in the HOME dir) pwd echo echo echo -------------------- echo mkdir testdir$$ mkdir testdir$$ echo echo echo -------------------- echo cd testdir$$ cd testdir$$ echo echo echo -------------------- echo pwd (5 points for being in the newly created dir) pwd echo -------------------- echo Testing foreground-only mode (20 points for entry & exit text AND ~5 seconds between times) kill -SIGTSTP $$ date sleep 5 & date kill -SIGTSTP $$ exit ___EOF___

源码

smallsh.c view raw

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#include #include #include #include #include #include #include #include #define MAX_INPUT_LENGTH 2048 #define MAX_ARG_NUMBER 512 #define SPLIT_CHAR " \t\r\n" int allowBg = 1; char *readLine() { size_t maxLength = MAX_INPUT_LENGTH; char *line = (char *)malloc(sizeof(char) * maxLength); fgets(line, maxLength, stdin); int i = 0; for (i = 0; i < maxLength; i++) { if (line[i] == '\n') { line[i] = '\0'; } } return line; } char **parse(char *line, int *num, int *back) { size_t maxNumber = MAX_ARG_NUMBER; int i = 0; char **arr = (char **)malloc(sizeof(char *) * maxNumber); char *token; token = strtok(line, SPLIT_CHAR); while (token != NULL) { arr[i] = token; // replace $$ int j = 0; for (j = 0; j < strlen(arr[i])-1; j++) { if (arr[i][j] == '$' && arr[i][j + 1] == '$') { arr[i][j] = '\0'; arr[i][j+1] = '\0'; char t[10]; char newArg[50]; memset(t, '\0', 10); memset(newArg, '\0', 50); strncpy(newArg, arr[i], j); sprintf(t, "%d", getpid()); strcat(newArg, t); // sprintf(arr[i], newArg); arr[i] = newArg; } } i++; token = strtok(NULL, SPLIT_CHAR); } if (i >= 2 && strcmp(arr[i - 1], "&") == 0) { arr[i - 1] = NULL; i--; if(allowBg == 1){ *back = 1; } } *num = i; arr[i] = NULL; return arr; } void printStatus(int status) { if (status == 0 || status == 1) printf("exit value %d\n", status); else printf("terminated by signal %d\n", status); } void catchSIGTSTP(int sig) { if (allowBg == 1) { char *message = "Entering foreground-only mode(& is now ignored)\n"; write(STDOUT_FILENO, message, 49); fflush(stdout); allowBg = 0; } else { char *message = "Exiting foreground-only mode\n"; write(STDOUT_FILENO, message, 30); fflush(stdout); allowBg = 1; } } void catchSIGINT(int signo) { char message[] = "terminated by signal "; char t[10]; memset(t, '\0', 10); sprintf(t, "%d", signo); strcat(message, t); strcat(message, "\n"); printf("%s", message); fflush(stdout); fflush(stdin); } int newProcess(char **arr, int num, int back) { pid_t pid = fork(); int status, fd; int input_flag = -1; int output_flag = -1; int i = 0; for (i = 0; i < num; i++) { if (strcmp(arr[i], "<") == 0) input_flag = i; else if (strcmp(arr[i], ">") == 0) output_flag = i; } if (pid == 0) { struct sigaction sigint = {0}; sigint.sa_handler = catchSIGINT; sigemptyset(&sigint.sa_mask); sigint.sa_flags = 0; sigaction(SIGINT, &sigint, NULL); // input redirect if (input_flag > -1) { fd = open(arr[input_flag + 1], O_RDONLY, 0644); if (fd == -1) { printf("cannot open %s for input\n", arr[input_flag + 1]); exit(1); } else { if (dup2(fd, 0) == -1) { printf(": Could not redirect stdin for input file %s\n", arr[input_flag + 1]); exit(1); } arr[input_flag] = NULL; close(fd); } } //output redirect if (output_flag > -1) { fd = open(arr[output_flag + 1], O_WRONLY | O_CREAT | O_TRUNC, 0644); if (fd == -1) { printf("cannot not open %s for output\n", arr[output_flag + 1]); exit(1); } else { if (dup2(fd, 1) == -1) { printf("Could not redirect stdout for output file %s\n", arr[output_flag + 1]); exit(1); } arr[output_flag] = NULL; close(fd); } } if (back == 1 && input_flag < 0) { fd = open("/dev/null", O_RDONLY, 0644); if (fd == -1) { printf("Could not open \"/dev/null\"\n"); exit(1); } else { if (dup2(fd, 0) == -1) { printf("Could not redirect stdin to \"/dev/null\"\n"); exit(1); } close(fd); } } // printf("%c\n", arr[0][0]); if (execvp(arr[0], arr) == -1 && arr[0][0] >= 'a' && arr[0][0] <= 'z') { printf("%s: no such file or directory\n", arr[0]); fflush(stdout); exit(1); } } else if (pid < 0) { printf("Smallsh !\n"); return 1; } else { // parent if (back == 1) { printf("Background pid is %d.\n", pid); fflush(stdout); } else { waitpid(pid, &status, WUNTRACED); if (WIFEXITED(status)) return (WEXITSTATUS(status)); else if (WIFSIGNALED(status)) return (WTERMSIG(status)); } } return status; } int executeCommand(char **arr, int status, int num, int back) { if (arr[0] == NULL || strcmp("#", arr[0]) == 0) return status; else if (strcmp(arr[0], "exit") == 0) exit(0); else if (strcmp(arr[0], "status") == 0) printStatus(status); else if (strcmp(arr[0], "cd") == 0) { char *directory; if (arr[1] == NULL) directory = getenv("HOME"); else directory = arr[1]; if (chdir(directory) == -1) { printf("cd: No such file or directory\n"); fflush(stdout); } return status; } else { int t = newProcess(arr, num, back); // printf("------------%d---\n",t); // fflush(stdout); return t; } } int main() { char *input; char **arr; int status = 0; struct sigaction sigint = {0}; sigint.sa_handler = SIG_IGN; sigemptyset(&sigint.sa_mask); sigint.sa_flags = 0; sigaction(SIGINT, &sigint, NULL); struct sigaction sigtstp = {0}; sigtstp.sa_handler = catchSIGTSTP; sigfillset(&sigtstp.sa_mask); sigtstp.sa_flags = 0; sigaction(SIGTSTP, &sigtstp, NULL); while (1) { int num = 0; int back = 0; printf(": "); fflush(stdout); input = readLine(); arr = parse(input, &num, &back); status = executeCommand(arr, status, num, back); //background pid_t childPid = waitpid(-1, &status, WNOHANG); if (childPid > 0) { printf("background pid %d is done: ", childPid); if (WIFEXITED(status)) printf("exit value %d\n", WEXITSTATUS(status)); else printf("terminated by signal %d\n", status); fflush(stdout); } fflush(stdin); free(input); free(arr); } return 0; }

总结

wait()函数

1 2	pid_t wait(int* status); pid_t waitpid(pid_t pid, int* status, int options);

• WNOHANG 如果该子进程没有结束，则以非阻塞方式等待子进程，并且返回0;如果该子进程已经结束，返回其pid.如果没有子进程退出，则立刻返回-1
• WUNTRACED 若子进程进入暂停状态，则马上返回

WIFEXTED与WEXITSTATUS

• WIFEXTED(status) 这个宏用来获取是否正常退出，正常退出获得true
• WEXITSTATUS(status) 只可在WIFEXITED为true时使用，获取正常退出的状态码

WIFSIGNALED与WTERMSIG

• WIFSIGNALED(status) 这个宏用来获取是否异常退出，异常退出获得true
• WTERMSIG(status) 只可在WIFSIGNALED为true时使用，获取异常退出的状态码 smallsh.c view raw

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  waitpid(pid, &status, WUNTRACED); if (WIFEXITED(status)) return (WEXITSTATUS(status)); else if (WIFSIGNALED(status)) return (WTERMSIG(status));