Fix for dash compatible

# Fix for dash compatible

If you like `/bin/sh` better than `/bin/bash`, you would love this patch :grin:

If not, you probably should change the shebang to `/bin/bash` :tongue: 


----

There are original erros as follows:

```
$ sudo host/install_host.sh
host/install_host.sh: 9: [: Linux: unexpected operator
host/install_host.sh: 25: host/install_host.sh: Bad substitution
```