chsh -s /usr/bin/r2

Radare2’s prompt is quite powerful and handy to use, but sometimes you need to interact with the filesystem or spawn system programs.. and spawning new shells or quitting r2 is not an option. For those cases, the simplest solution would be to just type ! and then type the shell command you like. This prefix command will just escape to the shell and run the text you type as in the system shell.