tags: linux gnu bash

See [the docs](https://tldp.org/LDP/abs/html/internalvariables.html)

## Shorthands
```csv sep=- vert cols=2
$$   - current bash PID of the current script
$?   - exist status of last command
$_   - final arg of last command
$!   - PID of last background job
$-   - flags passed to script
```

## Long names
Some are:
```csv sep=- vert cols=2
$BASH           - path to bash itself
$BASH_ENV       - startup file when bash was invoked
$BASH_SUBSHELL  - subshell level
$BASHPID        - current bash PID, not the same as $$
$DIRSTACK[@]    - dir stack as an array, $DIRSTACK or $DIRSTACK[0] are top of the stack
$FUNCNAME       - current function name
$PIPESTATUS[@]  - return codes from elements of last pipe
```