From b19d0ea31817928655f84addb933cf4ba3187cb8 Mon Sep 17 00:00:00 2001
From: Jonas Maier <jonas@x77.dev>
Date: Fri, 6 Mar 2026 13:03:26 +0100
Subject: support `cd -`

---
 src/main.rs        |  2 ++
 src/run/builtin.rs | 28 +++++++++++++++++++++-------
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 19e7743..c4113f9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -55,6 +55,7 @@ pub struct Session {
     line: LineBuf,
     history: Vec<BString>,
     dispatch: CommandDispatch,
+    prev_path: BString,
 }
 
 /// relative path -- in case it is a proper subpath the result starts with a slash `/`
@@ -138,6 +139,7 @@ fn event_loop() {
         line: LineBuf::new(),
         history: Vec::new(),
         dispatch: CommandDispatch::new(),
+        prev_path: vec![b'.'],
     };
 
     print!("{}", se.prompt());
diff --git a/src/run/builtin.rs b/src/run/builtin.rs
index b342dd0..e715bd7 100644
--- a/src/run/builtin.rs
+++ b/src/run/builtin.rs
@@ -1,6 +1,6 @@
 #![allow(non_camel_case_types)]
 
-use std::{fs::OpenOptions, path::PathBuf};
+use std::{env::*, fs::OpenOptions, path::PathBuf};
 
 use super::Builtin;
 use crate::*;
@@ -10,15 +10,29 @@ impl Builtin for cd {
     fn name(&self) -> &str {
         "cd"
     }
-    fn mod_session(&self, _: &mut Session, args: &[BString]) {
-        let target: &Path = match args.get(0).map(|v| &v[..]) {
-            Some(b"-") => todo!("prev"),
-            Some(path) => OsStr::from_bytes(path).as_ref(),
-            None => todo!("homedir"),
+    fn mod_session(&self, se: &mut Session, args: &[BString]) {
+        let mut dir = match current_dir() {
+            Ok(path) => path.as_os_str().as_bytes().to_vec(),
+            Err(_) => vec![b'.'],
         };
 
+        std::mem::swap(&mut dir, &mut se.prev_path);
+
+        match args.get(0).map(|v| &v[..]) {
+            Some(b"-") => {
+                let _ = set_current_dir(OsStr::from_bytes(&dir));
+            }
+            Some(path) => {
+                let _ = set_current_dir(OsStr::from_bytes(path));
+            }
+            None => {
+                if let Some(home) = std::env::var_os("HOME") {
+                    let _ = set_current_dir(home);
+                }
+            }
+        }
+
         // TODO: let mod_session builtins return nonzero exit code
-        let _ = std::env::set_current_dir(target);
     }
 }
 
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