Tags:

- [Terminal](/content/p/explore.html?t=Terminal/index.html)
- [POSIX](/content/p/explore.html?t=POSIX/index.html)
- [Shell](/content/p/explore.html?t=Shell/index.html)

I’m currently going through the POSIX specification and wanted to document some of the lesser known things you can do.

The `cd` command is a shell “builtin”, meaning it isn’t a program on disk but something built into the shell itself.

## Go to the home directory  
Simply running `cd` without any arguments is equivalent to `cd ~` which goes to the `$HOME` directory.

```
~/foo$ cd
~$ _
```

## Go to the previous directory  
`cd -` will go to the previous directory, specifically `$OLDPWD` which gets updated on a successful `cd`. It will also print the directory when this happens.

```
~$ cd foo
~/foo$ cd -
/home/daniel/foo
~$ _
```

## Make directories more accessible via $CDPATH  
The `$CDPATH` environment variable allows specifying paths to check if the directory exists within, before checking the current directory. It will also print the directory when this happens.

```
~$ mkdir -p foo/bar
~$ cd bar
cd: bar: No such file or directory
~$ export CDPATH=~/foo
~$ cd bar
/home/daniel/foo/bar
~/foo/bar$ _
```

As you might have guessed, just like `$PATH` you can use multiple paths separated by `:` that will be checked in order:

```
~$ mkdir -p foo/bar b
~$ export CDPATH=.:~/foo # check the current directory first
~$ cd bar
/home/daniel/bar
~/bar$ _
```

## Resolving symlinks  
Normally when navigating to a symlink directory the path will remain as the symlink name:

```
~$ mkdir real
~$ ln -s real fake
~$ cd fake
~/fake$ _
```

You can force symlinks to be resolved via the `-P` option:

```
~$ cd -P fake
~/real$ _
```

The opposite of this option is `-L` which is the default. Since it is the default, the only reason I can think of why you would want to use it is if you have an alias to change the default to `-P`:

```
~$ alias cd='cd -P'
~$ cd fake
~/real$ cd -L ../fake
~/fake$ _
```

## References  
- [IEEE Std 1003.1-2017](https://pubs.opengroup.org/onlinepubs/9699919799/)