# Debian Shell and environment

**Bash is the default shell** on Debian. When you log in, bash reads `/etc/profile` (system-wide) and `~/.bashrc` (user-specific) to set up your environment. Add commands and variables to `~/.bashrc` to customize your shell.

```bash
$ echo $SHELL                   # current shell
$ chsh -s /bin/bash             # change default shell (on next login)
$ cat ~/.bashrc                 # view bash configuration
$ source ~/.bashrc              # reload configuration
```

Environment variables are inherited by child processes. Set them in `~/.bashrc` or `~/.bash_profile`:

```bash
export PATH=$PATH:~/.local/bin  # add directory to PATH
export EDITOR=vim               # set default editor
export PS1='\u@\h:\w$ '         # customize prompt
```

Common variables:

- `$PATH` — directories searched for executables (colon-separated)
- `$HOME` — user's home directory
- `$USER` — current username
- `$SHELL` — current shell
- `$EDITOR` — default text editor
- `$LANG`, `$LC_*` — language and locale settings

Tip: If you add to `$PATH`, put user directories (`~/.local/bin`) before system directories to override installed programs locally.