How to get the base directory in visual studio code snippet?

This supports Windows & Unix:

${TM_DIRECTORY/^.+[\\/\\\\]+(.*)$/$1/}

I wanted to add that in Windows the code above will print the entire directory.

You need to add a quadruple backslash vs the forward-slash:

${TM_DIRECTORY/^.+\\\\(.*)$/$1/}

Ok, finally found it.

${TM_DIRECTORY/^.+\\/(.*)$/$1/} gives the base directory.

The part I didn't get was the "double escape" of the directory separator / -> \\/.