1 files changed, 195 insertions, 0 deletions

diff --git a/cmd.c b/cmd.c
new file mode 100644
index 0000000..e38da41
--- /dev/null
+++ b/cmd.c
@@ -0,0 +1,195 @@
+#include "cmd.h"
+
+Command *newCmd() {
+    Command *cmd = (Command *)malloc(sizeof(Command));
+    cmd->argc = 0;
+    cmd->args = NULL;
+    cmd->type = CMD_NORMAL;
+    cmd->left = NULL;
+    cmd->right = NULL;
+    for (int i = 0; i < 3; i++) {
+        cmd->redirectFile[i] = NULL;
+        cmd->redirectFD[i] = i;
+    }
+    cmd->background = false;
+    return cmd;
+}
+
+void freeCmd(Command *cmd) {
+    if (cmd == NULL) {
+        return;
+    }
+    if (cmd->left != NULL) {
+        freeCmd(cmd->left);
+    }
+    if (cmd->right != NULL) {
+        freeCmd(cmd->right);
+    }
+    int i;
+    for (i = 0; i < cmd->argc; i++) {
+        free(cmd->args[i]);
+    }
+    free(cmd->args);
+    for (i = 0; i < 3; i++) {
+        if (cmd->redirectFile[i] != NULL) {
+            free(cmd->redirectFile[i]);
+        }
+    }
+    free(cmd);
+}
+
+int runCmd(Command *cmd) {
+    int status;
+    if (cmd == NULL) {
+        fprintf(stderr, "cmd is NULL\n");
+        return -1;
+    }
+    switch (cmd->type) {
+    case CMD_NORMAL:
+        status = runNormalCmd(cmd);
+        break;
+    case CMD_PIPE:
+        status = runPipeCmd(cmd);
+        break;
+    case CMD_AND:
+    case CMD_OR:
+        status = runAndOrCmd(cmd);
+        break;
+    }
+
+    freeCmd(cmd);
+    return status;
+}
+
+int runNormalCmd(Command *cmd) {
+    pid_t pid;
+    int status;
+    if (!strcmp(cmd->args[0], "exit")) {
+        printf("Good Bye, %s!\n", username);
+        exit(0);
+    } else if (!strcmp(cmd->args[0], "cd")) {
+        if (cmd->argc == 1) {
+            chdir(getenv("HOME"));
+        } else {
+            chdir(cmd->args[1]);
+        }
+        printf("\r");
+        getcwd(pwd, sizeof(pwd));
+    } else {
+        if ((pid = fork()) == 0) {
+            // consider the redirection now
+            // it's just a part of normal command
+            // but not in other commands
+            redirect(cmd);
+            exit(execvp(cmd->args[0], cmd->args));
+        } else {
+            if (!cmd->background) {
+                waitpid(pid, &status, 0);
+                if (!WIFEXITED(status)) {
+                    if (WIFSIGNALED(status)) {
+                        fprintf(stderr, "Process %d was killed by signal %d\n",
+                                pid, WTERMSIG(status));
+                    } else {
+                        fprintf(stderr, "Process %d exited with status %d\n",
+                                pid, WEXITSTATUS(status));
+                    }
+                }
+            }
+        }
+        // return the exit status of the child process
+        return WEXITSTATUS(status);
+    }
+}
+
+int runPipeCmd(Command *cmd) {
+    int status;
+    // create a pipe file and gets two file descriptors
+    // fd[0] is the read end, while fd[1] the write end
+    int fd[2];
+    pid_t left, right;
+    pipe(fd);
+    if ((left = fork()) == 0) {
+        /*
+         * close the read end of the pipe, so that the child process
+         * can only write to it; then redirect the standard output
+         * to the write end of the pipe, and close the write end
+         * itself as a file descriptor.
+         */
+        close(fd[0]);
+        dup2(fd[1], 1);
+        close(fd[1]);
+        exit(runCmd(cmd->left));
+    }
+    if ((right = fork()) == 0) {
+        close(fd[1]);
+        dup2(fd[0], 0);
+        close(fd[0]);
+        exit(runCmd(cmd->right));
+    }
+    // close the pipe, because the parent process doesn't need it
+    // and wait for the two child processes to exit
+    close(fd[0]);
+    close(fd[1]);
+    waitpid(left, NULL, 0);
+    waitpid(right, NULL, 0);
+}
+
+int runAndOrCmd(Command *cmd) {
+    int status;
+    if (cmd->type == CMD_AND) {
+        if (fork() == 0) {
+            exit(runCmd(cmd->left));
+        } else {
+            waitpid(-1, &status, 0);
+            if (WIFEXITED(status) && WEXITSTATUS(status) == 0 && fork() == 0) {
+                status = runCmd(cmd->right);
+            }
+            wait(NULL);
+        }
+    } else if (cmd->type == CMD_OR) {
+        if (fork() == 0) {
+            exit(runCmd(cmd->left));
+        } else {
+            waitpid(-1, &status, 0);
+            if (WIFEXITED(status) && WEXITSTATUS(status) != 0 && fork() == 0) {
+                status = runCmd(cmd->right);
+            }
+            wait(NULL);
+        }
+    }
+}
+
+void redirect(Command *cur) {
+    int fd;
+    char *rfile;
+    for (int i = 0; i < 3; i++) {
+        fd = cur->redirectFD[i];
+        rfile = cur->redirectFile[i];
+        if (fd < -1 || fd > 2) {
+            fprintf(stderr, "file descriptor %d is invalid\n", fd);
+            exit(1);
+        }
+        if (fd == i && rfile == NULL) {
+            continue;
+        }
+        if (fd == -1) {
+            // append
+            fd = open(rfile, O_WRONLY | O_CREAT | O_APPEND, 0666);
+        } else if (rfile != NULL) {
+            // normal redirection
+            fd = open(rfile, O_WRONLY | O_CREAT | O_TRUNC, 0666);
+        } else {
+            // file descriptor redirection
+            // when here, fd is surely in 0, 1, 2
+            ;
+        }
+
+        if (fd < 0) {
+            fprintf(stderr, "open file %s failed\n", rfile);
+            exit(1);
+        }
+        close(i);
+        dup2(fd, i);
+        close(fd);
+    }
+}
\ No newline at end of file