finished full_path

shell.c

@@ -88,9 +88,62 @@ void parse(char* line, command_t* p_cmd) {
     }
 }
 
+/**
+ * Determines if the executable in p_cmd (i.e., p_cmd->argv[0]) can be found
+ * in one of the directories in $PATH. Returns true if so, else false.
+ * If the executable is found in $PATH, then p_cmd->argv[0] is mutated to be
+ * the absolute path of the executable.
+ *
+ * To see the format of $PATH, run `echo $PATH` in your terminal, which should
+ * output something like
+ * /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/mnt/learncli/bin
+ *
+ * For example, suppose the executable is "ls". This function needs to find its
+ * absolute path in the file system. For the $PATH above,
+ * it appends "/ls" to the first directory, resulting in
+ * /usr/local/sbin/ls. However, this file does not exist, and same for the next
+ * two directories. However, /usr/bin/ls exists, so p_cmd->argv[0] is set to
+ * "/usr/bin/ls", and the function returns true.
+ *
+ * If the executable is "doesnotexist", then this function would not find that
+ * file after checking all directories in $PATH, so it would return false.
+ *
+ * Note: This behaves similarly to the `which` command, e.g., `which ls`.
+ *
+ * To access $PATH within C, use getenv.
+ * For example, char* path = getenv("PATH");
+ *
+ * To parse PATH, we recommend strtok, as described in the docstring for the
+ * parse function.
+ *
+ * To check if a file exists, use access with amode F_OK
+ * (https://pubs.opengroup.org/onlinepubs/009695299/functions/access.html).
+ *
+ * @param p_cmd
+ * @return true (if command in PATH) | false (if command not in PATH). Remember
+ * to mutate p_cmd->argv[0] to be the full path of the executable if it is in
+ * PATH
+ */
 bool find_full_path(command_t* p_cmd) {
-    // TODO:
-    return true;
+    char* path_tokens = strtok(getenv("PATH"), ":");
+
+    while (path_tokens != NULL) {
+        char* full_path = (char*)malloc(MAX_ARG_LEN * sizeof(char));
+        strcpy(full_path, path_tokens);
+        strcat(full_path, "/");
+        strcat(full_path, p_cmd->argv[0]);
+
+        if (access(full_path, F_OK) == 0) {
+            strcpy(p_cmd->argv[0], full_path);
+            free(full_path);
+            return true;
+        }
+
+        free(full_path);
+        path_tokens = strtok(NULL, ":");
+    }
+
+    return false;
 }
 
 int execute(command_t* p_cmd) {