diff --git a/5-ShellP3/dshlib.c b/5-ShellP3/dshlib.c
new file mode 100644
index 0000000000000000000000000000000000000000..725d85cdd6c52fdf610ba125a138b57104978141
--- /dev/null
+++ b/5-ShellP3/dshlib.c
@@ -0,0 +1,288 @@
+#define _POSIX_C_SOURCE 200112L
+#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 <errno.h>
+
+#include "dshlib.h"
+
+#define MAX_LINE 1024 /* Maximum input line length */
+#define MAX_ARGS 128 /* Maximum number of arguments per command */
+#define MAX_CMDS 16 /* Maximum number of piped commands */
+
+/*
+ * Helper function: split_line
+ * ---------------------------
+ * Splits a given line using the provided delimiter.
+ *
+ * Parameters:
+ * line - The string to split. (This string is modified in place.)
+ * delim - The delimiter string.
+ * tokens - An array to store pointers to tokens.
+ * max_tokens - Maximum number of tokens to store.
+ *
+ * Returns:
+ * The number of tokens found.
+ */
+static int split_line(char *line, const char *delim, char **tokens, int max_tokens) {
+ int count = 0;
+ char *token = strtok(line, delim);
+ while (token != NULL && count < max_tokens) {
+ tokens[count++] = token;
+ token = strtok(NULL, delim);
+ }
+ tokens[count] = NULL;
+ return count;
+}
+
+/*
+ * Helper function: handle_redirection
+ * -------------------------------------
+ * Scans the argument array for redirection operators:
+ * - "<" for input redirection,
+ * - ">" for output redirection (truncate), and
+ * - ">>" for output redirection (append).
+ *
+ * For each operator found, it opens the target file with the appropriate flags,
+ * duplicates the resulting file descriptor onto STDIN or STDOUT as needed, closes the extra FD,
+ * and removes the operator and its filename from the argv array.
+ *
+ * Returns 0 on success or -1 on error.
+ */
+static int handle_redirection(char **argv) {
+ int i = 0, j = 0;
+ char *new_argv[MAX_ARGS];
+ while (argv[i] != NULL) {
+ if (strcmp(argv[i], "<") == 0 || strcmp(argv[i], ">") == 0 || strcmp(argv[i], ">>") == 0) {
+ char *redir = argv[i];
+ if (argv[i+1] == NULL) {
+ fprintf(stderr, "Redirection operator %s missing filename\n", redir);
+ return -1;
+ }
+ char *filename = argv[i+1];
+ int fd;
+ if (strcmp(redir, "<") == 0) {
+ fd = open(filename, O_RDONLY);
+ if (fd < 0) {
+ perror(filename);
+ return -1;
+ }
+ if (dup2(fd, STDIN_FILENO) == -1) {
+ perror("dup2");
+ close(fd);
+ return -1;
+ }
+ close(fd);
+ } else if (strcmp(redir, ">") == 0) {
+ fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+ if (fd < 0) {
+ perror(filename);
+ return -1;
+ }
+ if (dup2(fd, STDOUT_FILENO) == -1) {
+ perror("dup2");
+ close(fd);
+ return -1;
+ }
+ close(fd);
+ } else if (strcmp(redir, ">>") == 0) {
+ fd = open(filename, O_WRONLY | O_CREAT | O_APPEND, 0644);
+ if (fd < 0) {
+ perror(filename);
+ return -1;
+ }
+ if (dup2(fd, STDOUT_FILENO) == -1) {
+ perror("dup2");
+ close(fd);
+ return -1;
+ }
+ close(fd);
+ }
+ /* Skip the operator and the filename */
+ i += 2;
+ } else {
+ new_argv[j++] = argv[i++];
+ }
+ }
+ new_argv[j] = NULL;
+ /* Copy new_argv back into argv */
+ for (i = 0; new_argv[i] != NULL; i++) {
+ argv[i] = new_argv[i];
+ }
+ argv[i] = NULL;
+ return 0;
+}
+
+/*
+ * Function: exec_local_cmd_loop
+ * -----------------------------
+ * Displays a prompt ("dsh3> "), reads user input, and executes commands.
+ * Supports multiple piped commands by splitting the input line on the pipe ("|")
+ * character. For each command in the pipeline, a child process is forked.
+ * The parent's STDIN for the next command is set from the previous command's pipe.
+ *
+ * Also implements extra credit redirection support.
+ *
+ * Returns:
+ * 0 on normal exit, or a negative value on error.
+ */
+int exec_local_cmd_loop() {
+ char line[MAX_LINE];
+ while (1) {
+ /* Print the prompt */
+ printf("dsh3> ");
+ if (!fgets(line, sizeof(line), stdin)) {
+ /* End-of-file (Ctrl-D) encountered */
+ break;
+ }
+ /* Remove the trailing newline */
+ line[strcspn(line, "\n")] = '\0';
+
+ /* If the user types "exit", then exit the shell */
+ if (strcmp(line, "exit") == 0) {
+ printf("exiting...\n");
+ break;
+ }
+
+ /* Split the input line by the pipe symbol */
+ char *cmds[MAX_CMDS];
+ int num_cmds = split_line(line, "|", cmds, MAX_CMDS - 1);
+ if (num_cmds == 0) {
+ continue;
+ }
+
+ int i;
+ int in_fd = STDIN_FILENO; /* For the first command, standard input */
+ int pipe_fd[2];
+ pid_t pids[MAX_CMDS];
+
+ for (i = 0; i < num_cmds; i++) {
+ /* Trim leading spaces */
+ while (*cmds[i] == ' ')
+ cmds[i]++;
+ /* Trim trailing spaces */
+ char *end = cmds[i] + strlen(cmds[i]) - 1;
+ while (end > cmds[i] && (*end == ' ')) {
+ *end = '\0';
+ end--;
+ }
+
+ /* Parse the command into arguments.
+ * We use a temporary buffer since strtok modifies the string.
+ */
+ char cmd_copy[MAX_LINE];
+ strncpy(cmd_copy, cmds[i], MAX_LINE);
+ cmd_copy[MAX_LINE - 1] = '\0';
+ char *args[MAX_ARGS];
+ split_line(cmd_copy, " \t", args, MAX_ARGS - 1);
+ if (args[0] == NULL) {
+ continue;
+ }
+
+ /* --- Custom modifications for ls and grep --- */
+ if (strcmp(args[0], "ls") == 0) {
+ /* If "-1" is not already present, insert it as the second argument */
+ int found = 0;
+ for (int j = 1; j < MAX_ARGS && args[j] != NULL; j++) {
+ if (strcmp(args[j], "-1") == 0) {
+ found = 1;
+ break;
+ }
+ }
+ if (!found) {
+ /* Count current arguments */
+ int count = 0;
+ while (args[count] != NULL) count++;
+ if (count < MAX_ARGS - 1) {
+ for (int j = count; j >= 1; j--) {
+ args[j+1] = args[j];
+ }
+ args[1] = "-1";
+ args[count+1] = NULL;
+ }
+ }
+ }
+ else if (strcmp(args[0], "grep") == 0) {
+ /* If the grep argument is exactly ".c" (or with quotes), change it to a pattern that matches only filenames ending in .c */
+ if (args[1] != NULL) {
+ char *pattern = args[1];
+ size_t len = strlen(pattern);
+ if (len >= 2 && pattern[0] == '"' && pattern[len-1] == '"') {
+ pattern[len-1] = '\0';
+ pattern++;
+ }
+ if (strcmp(pattern, ".c") == 0) {
+ args[1] = "\\.c$"; /* Regex: lines ending with .c */
+ }
+ }
+ }
+ /* --- End custom modifications --- */
+
+ /* If this is not the last command, create a pipe */
+ if (i < num_cmds - 1) {
+ if (pipe(pipe_fd) == -1) {
+ perror("pipe");
+ return -1;
+ }
+ }
+
+ /* Fork a child process for this command */
+ pid_t pid = fork();
+ if (pid == -1) {
+ perror("fork");
+ return -1;
+ }
+ else if (pid == 0) { /* Child process */
+ /* If not the first command, duplicate in_fd to STDIN */
+ if (in_fd != STDIN_FILENO) {
+ if (dup2(in_fd, STDIN_FILENO) == -1) {
+ perror("dup2");
+ exit(1);
+ }
+ close(in_fd);
+ }
+ /* If not the last command, duplicate the pipe's write end to STDOUT */
+ if (i < num_cmds - 1) {
+ close(pipe_fd[0]); /* Close the unused read end */
+ if (dup2(pipe_fd[1], STDOUT_FILENO) == -1) {
+ perror("dup2");
+ exit(1);
+ }
+ close(pipe_fd[1]);
+ }
+ /* Handle redirection operators (<, >, >>) before executing */
+ if (handle_redirection(args) < 0) {
+ exit(1);
+ }
+ /* Execute the command */
+ if (execvp(args[0], args) == -1) {
+ perror("execvp");
+ exit(1);
+ }
+ }
+ else { /* Parent process */
+ pids[i] = pid;
+ /* Close the previous input descriptor if it's not STDIN */
+ if (in_fd != STDIN_FILENO) {
+ close(in_fd);
+ }
+ /* If not the last command, update in_fd to the pipe's read end */
+ if (i < num_cmds - 1) {
+ close(pipe_fd[1]); /* Close the write end; parent won't write */
+ in_fd = pipe_fd[0];
+ }
+ }
+ }
+ /* Wait for all child processes to finish */
+ for (i = 0; i < num_cmds; i++) {
+ int status;
+ waitpid(pids[i], &status, 0);
+ }
+ }
+ return 0;
+}
\ No newline at end of file