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WEEK-7/dshlib.c

+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/wait.h>
+
+#include "dshlib.h"
+
+int exec_local_cmd_loop() {
+    char cmd_buff[SH_CMD_MAX];
+    command_list_t clist;
+    
+    while (1) {
+        // Suppress prompt during testing
+        if (isatty(STDIN_FILENO)) {
+            printf("%s", SH_PROMPT);
+        }
+
+        // Read user input
+        if (fgets(cmd_buff, SH_CMD_MAX, stdin) == NULL) {
+            printf("\n");
+            break;  // Exit if EOF is reached
+        }
+
+        // Remove trailing newline character
+        cmd_buff[strcspn(cmd_buff, "\n")] = '\0';
+
+        // Ignore empty input
+        if (strlen(cmd_buff) == 0) {
+            continue;
+        }
+
+        // Exit command
+        if (strcmp(cmd_buff, EXIT_CMD) == 0) {
+            printf("exiting...\n");
+            return OK_EXIT;
+        }
+
+        // Parse the command into a list
+        int parse_status = build_cmd_list(cmd_buff, &clist);
+
+        // Error handling for parsing
+        if (parse_status < 0) {
+            continue;
+        }
+
+        // Execute the parsed commands
+        execute_pipeline(&clist);
+
+        // Free allocated memory
+        free_cmd_list(&clist);
+    }
+
+    return OK;
+}
+
+/**
+ * Parses the command buffer into a list of commands for execution, handling redirection.
+ */
+int build_cmd_list(char *cmd_line, command_list_t *clist) {
+    char *token;
+    int i = 0;
+
+    // Initialize command list
+    clist->num = 0;
+
+    // Tokenize input based on pipes (|)
+    token = strtok(cmd_line, "|");
+    while (token != NULL) {
+        // Trim leading spaces
+        while (*token == ' ') token++;
+
+        char *cmd_part = strtok(token, " ");
+        int j = 0;
+        clist->commands[i].infile = NULL;
+        clist->commands[i].outfile = NULL;
+        clist->commands[i].append = false;
+
+        while (cmd_part != NULL) {
+            if (strcmp(cmd_part, "<") == 0) {  
+                cmd_part = strtok(NULL, " ");
+                if (cmd_part) {
+                    clist->commands[i].infile = strdup(cmd_part);
+                }
+            } else if (strcmp(cmd_part, ">") == 0) {
+                cmd_part = strtok(NULL, " ");
+                if (cmd_part) {
+                    clist->commands[i].outfile = strdup(cmd_part);
+                    clist->commands[i].append = false;
+                }
+            } else if (strcmp(cmd_part, ">>") == 0) {
+                cmd_part = strtok(NULL, " ");
+                if (cmd_part) {
+                    clist->commands[i].outfile = strdup(cmd_part);
+                    clist->commands[i].append = true;
+                }
+            } else {
+                clist->commands[i].argv[j++] = cmd_part;
+            }
+            cmd_part = strtok(NULL, " ");
+        }
+        clist->commands[i].argv[j] = NULL; // Null-terminate argument list
+        clist->num++; // Increment command count
+        token = strtok(NULL, "|"); // Get next command
+        i++;
+
+        if (i >= CMD_MAX) {
+            fprintf(stderr, CMD_ERR_PIPE_LIMIT, CMD_MAX);
+            return ERR_TOO_MANY_COMMANDS;
+        }
+    }
+
+    return OK;
+}
+
+/**
+ * Executes commands using pipes and handles input/output redirection.
+ */
+int execute_pipeline(command_list_t *clist) {
+    int num_cmds = clist->num;
+    int pipes[num_cmds - 1][2]; // Pipes for communication between commands
+    pid_t pids[num_cmds]; // Array to store process IDs
+
+    for (int i = 0; i < num_cmds; i++) {
+        // Create pipes except for the last command
+        if (i < num_cmds - 1) {
+            if (pipe(pipes[i]) == -1) {
+                perror("pipe");
+                return ERR_MEMORY;
+            }
+        }
+
+        // Fork a child process
+        pids[i] = fork();
+        if (pids[i] < 0) {
+            perror("fork");
+            return ERR_MEMORY;
+        }
+
+        if (pids[i] == 0) {  // Child process
+            // Handle input redirection
+            if (clist->commands[i].infile) {
+                int fd = open(clist->commands[i].infile, O_RDONLY);
+                if (fd < 0) {
+                    perror("open infile");
+                    exit(ERR_EXEC_CMD);
+                }
+                dup2(fd, STDIN_FILENO);
+                close(fd);
+            }
+
+            // Handle output redirection ONLY for the last command
+            if (i == num_cmds - 1 && clist->commands[i].outfile) {
+                int fd;
+                if (clist->commands[i].append) {
+                    fd = open(clist->commands[i].outfile, O_WRONLY | O_CREAT | O_APPEND, 0644);
+                } else {
+                    fd = open(clist->commands[i].outfile, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+                }
+                if (fd < 0) {
+                    perror("open outfile");
+                    exit(ERR_EXEC_CMD);
+                }
+                dup2(fd, STDOUT_FILENO);
+                close(fd);
+            }
+
+            // Redirect input/output for pipes
+            if (i > 0) {
+                dup2(pipes[i - 1][0], STDIN_FILENO);
+            }
+            if (i < num_cmds - 1) {
+                dup2(pipes[i][1], STDOUT_FILENO);
+            }
+
+            // Close all pipes
+            for (int j = 0; j < num_cmds - 1; j++) {
+                close(pipes[j][0]);
+                close(pipes[j][1]);
+            }
+
+            // **Fix: Ensure echo does not add extra quotes**
+            if (strcmp(clist->commands[i].argv[0], "echo") == 0) {
+                for (int j = 1; clist->commands[i].argv[j] != NULL; j++) {
+                    printf("%s", clist->commands[i].argv[j]);
+                    if (clist->commands[i].argv[j + 1] != NULL) {
+                        printf(" "); // Ensure words are properly spaced
+                    }
+                }
+                printf("\n"); // Print newline at the end
+                fflush(stdout);
+                exit(0);
+            }
+
+            execvp(clist->commands[i].argv[0], clist->commands[i].argv);
+
+            // Print error message before exiting
+            fprintf(stderr, "error: command not found: %s\n", clist->commands[i].argv[0]);
+            fflush(stderr);
+            exit(ERR_EXEC_CMD);
+        }
+    }
+
+    // Close all pipes in parent process
+    for (int i = 0; i < num_cmds - 1; i++) {
+        close(pipes[i][0]);
+        close(pipes[i][1]);
+    }
+
+    // Wait for all child processes to finish
+    for (int i = 0; i < num_cmds; i++) {
+        waitpid(pids[i], NULL, 0);
+    }
+
+    return OK;
+}
+
+/**
+ * Frees allocated memory for command list.
+ */
+int free_cmd_list(command_list_t *cmd_lst) {
+    for (int i = 0; i < cmd_lst->num; i++) {
+        if (cmd_lst->commands[i].infile) {
+            free(cmd_lst->commands[i].infile);
+            cmd_lst->commands[i].infile = NULL;
+        }
+        if (cmd_lst->commands[i].outfile) {
+            free(cmd_lst->commands[i].outfile);
+            cmd_lst->commands[i].outfile = NULL;
+        }
+    }
+
+    // Reset the command list
+    cmd_lst->num = 0;
+    
+    return OK;
+}