Shell execute - run shell command and capture output (!! is short-hand).

%system has two aliases: %sx and !!.

To run a system command in IPython, like ls, you can put a single leading ! in front of it, e.g.

In [1]: !ls
LICENSE   book        book.toml   src

Two leading !! is the short-hand for %system or %sx. The difference between using single or double exclamation points is that !! returns the results in a list that is split on \n, and since it is returned, it will be stored in the output history.

In [2]: !!ls
Out[2]: ['LICENSE', '', 'book', 'book.toml', '', 'src']