Why does colon in shell command read the wrong file?

Question

I write ruby test files in vim, and regularly run tests from the file I'm editing by running

:!rspec %:N

or something similar (to execute the test at line N). The problem is that when the first digit of N is an 8, like:

:!rspec %:89

I get an error:

cannot load such file -- /.../foo_spec.rb9

So it looks like the sequence %:8 means something inside of a colon command. Additionally, if I escape the colon: rspec %\:89 works fine.

But why is this happening?

Answer 1

As you already know % in the vim command line is resolved to the path name of the file in the current buffer. But % can be modified by adding a modifier. A modifier starts with a : and :8 is a valid modifier.

See :help filename-modifiers for the full list of modifiers. For :8 it says:

  :8  Converts the path to 8.3 short format (currently only on
      MS-Windows).  Will act on as much of a path that is an
      existing path.

On Linux a %:8 is just like %, so %:89 results in %9.