diff --git a/hw/hwsh.c b/hw/hwsh.c
new file mode 100644
index 0000000..6a46a08
--- /dev/null
+++ b/hw/hwsh.c
@@ -0,0 +1,303 @@
+#include <assert.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+// Simplifed xv6 shell.
+
+#define MAXARGS 10
+
+// All commands have at least a type. Have looked at the type, the code
+// typically casts the *cmd to some specific cmd type.
+struct cmd {
+  int type; //  ' ' (exec), | (pipe), '<' or '>' for redirection
+};
+
+struct execcmd {
+  int type;            // ' '
+  char *argv[MAXARGS]; // arguments to the command to be exec-ed
+};
+
+struct redircmd {
+  int type;        // < or >
+  struct cmd *cmd; // the command to be run (e.g., an execcmd)
+  char *file;      // the input/output file
+  int mode;        // the mode to open the file with
+  int fd;          // the file descriptor number to use for the file
+};
+
+struct pipecmd {
+  int type;          // |
+  struct cmd *left;  // left side of pipe
+  struct cmd *right; // right side of pipe
+};
+
+int fork1(void); // Fork but exits on failure.
+struct cmd *parsecmd(char *);
+
+// Execute cmd.  Never returns.
+void runcmd(struct cmd *cmd) {
+  int p[2], r;
+  struct execcmd *ecmd;
+  struct pipecmd *pcmd;
+  struct redircmd *rcmd;
+
+  if (cmd == 0)
+    exit(0);
+
+  switch (cmd->type) {
+  default:
+    fprintf(stderr, "unknown runcmd\n");
+    exit(-1);
+
+  case ' ':
+    ecmd = (struct execcmd *)cmd;
+    if (ecmd->argv[0] == 0)
+      exit(0);
+    execv(ecmd->argv[0], ecmd->argv);
+    break;
+
+  case '>':
+  case '<':
+    rcmd = (struct redircmd *)cmd;
+    fprintf(stderr, "redir not implemented\n");
+    // Your code here ...
+    runcmd(rcmd->cmd);
+    break;
+
+  case '|':
+    pcmd = (struct pipecmd *)cmd;
+    fprintf(stderr, "pipe not implemented\n");
+    // Your code here ...
+    break;
+  }
+  exit(0);
+}
+
+int getcmd(char *buf, int nbuf) {
+
+  if (isatty(fileno(stdin)))
+    fprintf(stdout, "6.828$ ");
+  memset(buf, 0, nbuf);
+  fgets(buf, nbuf, stdin);
+  if (buf[0] == 0) // EOF
+    return -1;
+  return 0;
+}
+
+int main(void) {
+  static char buf[100];
+  int fd, r;
+
+  // Read and run input commands.
+  while (getcmd(buf, sizeof(buf)) >= 0) {
+    if (buf[0] == 'c' && buf[1] == 'd' && buf[2] == ' ') {
+      // Clumsy but will have to do for now.
+      // Chdir has no effect on the parent if run in the child.
+      buf[strlen(buf) - 1] = 0; // chop \n
+      if (chdir(buf + 3) < 0)
+        fprintf(stderr, "cannot cd %s\n", buf + 3);
+      continue;
+    }
+    if (fork1() == 0)
+      runcmd(parsecmd(buf));
+    wait(&r);
+  }
+  exit(0);
+}
+
+int fork1(void) {
+  int pid;
+
+  pid = fork();
+  if (pid == -1)
+    perror("fork");
+  return pid;
+}
+
+struct cmd *execcmd(void) {
+  struct execcmd *cmd;
+
+  cmd = malloc(sizeof(*cmd));
+  memset(cmd, 0, sizeof(*cmd));
+  cmd->type = ' ';
+  return (struct cmd *)cmd;
+}
+
+struct cmd *redircmd(struct cmd *subcmd, char *file, int type) {
+  struct redircmd *cmd;
+
+  cmd = malloc(sizeof(*cmd));
+  memset(cmd, 0, sizeof(*cmd));
+  cmd->type = type;
+  cmd->cmd = subcmd;
+  cmd->file = file;
+  cmd->mode = (type == '<') ? O_RDONLY : O_WRONLY | O_CREAT | O_TRUNC;
+  cmd->fd = (type == '<') ? 0 : 1;
+  return (struct cmd *)cmd;
+}
+
+struct cmd *pipecmd(struct cmd *left, struct cmd *right) {
+  struct pipecmd *cmd;
+
+  cmd = malloc(sizeof(*cmd));
+  memset(cmd, 0, sizeof(*cmd));
+  cmd->type = '|';
+  cmd->left = left;
+  cmd->right = right;
+  return (struct cmd *)cmd;
+}
+
+// Parsing
+
+char whitespace[] = " \t\r\n\v";
+char symbols[] = "<|>";
+
+int gettoken(char **ps, char *es, char **q, char **eq) {
+  char *s;
+  int ret;
+
+  s = *ps;
+  while (s < es && strchr(whitespace, *s))
+    s++;
+  if (q)
+    *q = s;
+  ret = *s;
+  switch (*s) {
+  case 0:
+    break;
+  case '|':
+  case '<':
+    s++;
+    break;
+  case '>':
+    s++;
+    break;
+  default:
+    ret = 'a';
+    while (s < es && !strchr(whitespace, *s) && !strchr(symbols, *s))
+      s++;
+    break;
+  }
+  if (eq)
+    *eq = s;
+
+  while (s < es && strchr(whitespace, *s))
+    s++;
+  *ps = s;
+  return ret;
+}
+
+int peek(char **ps, char *es, char *toks) {
+  char *s;
+
+  s = *ps;
+  while (s < es && strchr(whitespace, *s))
+    s++;
+  *ps = s;
+  return *s && strchr(toks, *s);
+}
+
+struct cmd *parseline(char **, char *);
+struct cmd *parsepipe(char **, char *);
+struct cmd *parseexec(char **, char *);
+
+// make a copy of the characters in the input buffer, starting from s through
+// es.
+// null-terminate the copy to make it a string.
+char *mkcopy(char *s, char *es) {
+  int n = es - s;
+  char *c = malloc(n + 1);
+  assert(c);
+  strncpy(c, s, n);
+  c[n] = 0;
+  return c;
+}
+
+struct cmd *parsecmd(char *s) {
+  char *es;
+  struct cmd *cmd;
+
+  es = s + strlen(s);
+  cmd = parseline(&s, es);
+  peek(&s, es, "");
+  if (s != es) {
+    fprintf(stderr, "leftovers: %s\n", s);
+    exit(-1);
+  }
+  return cmd;
+}
+
+struct cmd *parseline(char **ps, char *es) {
+  struct cmd *cmd;
+  cmd = parsepipe(ps, es);
+  return cmd;
+}
+
+struct cmd *parsepipe(char **ps, char *es) {
+  struct cmd *cmd;
+
+  cmd = parseexec(ps, es);
+  if (peek(ps, es, "|")) {
+    gettoken(ps, es, 0, 0);
+    cmd = pipecmd(cmd, parsepipe(ps, es));
+  }
+  return cmd;
+}
+
+struct cmd *parseredirs(struct cmd *cmd, char **ps, char *es) {
+  int tok;
+  char *q, *eq;
+
+  while (peek(ps, es, "<>")) {
+    tok = gettoken(ps, es, 0, 0);
+    if (gettoken(ps, es, &q, &eq) != 'a') {
+      fprintf(stderr, "missing file for redirection\n");
+      exit(-1);
+    }
+    switch (tok) {
+    case '<':
+      cmd = redircmd(cmd, mkcopy(q, eq), '<');
+      break;
+    case '>':
+      cmd = redircmd(cmd, mkcopy(q, eq), '>');
+      break;
+    }
+  }
+  return cmd;
+}
+
+struct cmd *parseexec(char **ps, char *es) {
+  char *q, *eq;
+  int tok, argc;
+  struct execcmd *cmd;
+  struct cmd *ret;
+
+  ret = execcmd();
+  cmd = (struct execcmd *)ret;
+
+  argc = 0;
+  ret = parseredirs(ret, ps, es);
+  while (!peek(ps, es, "|")) {
+    if ((tok = gettoken(ps, es, &q, &eq)) == 0)
+      break;
+    if (tok != 'a') {
+      fprintf(stderr, "syntax error\n");
+      exit(-1);
+    }
+    cmd->argv[argc] = mkcopy(q, eq);
+    argc++;
+    if (argc >= MAXARGS) {
+      fprintf(stderr, "too many args\n");
+      exit(-1);
+    }
+    ret = parseredirs(ret, ps, es);
+  }
+  cmd->argv[argc] = 0; // Add final NULL arg. See `man 2 exec`
+  return ret;
+}
diff --git a/hw/test.sh b/hw/test.sh
new file mode 100644
index 0000000..cc348f9
--- /dev/null
+++ b/hw/test.sh
@@ -0,0 +1,6 @@
+ls > y
+cat < y | sort | uniq | wc > y1
+cat y1
+rm y1
+ls |  sort | uniq | wc
+rm y