rspec - Why does vim "cancel out" the last two characters when running `%:8` in an external command? -

a simple work flow use when running rspec test have been working on, in vim, follows:

15:   "my example test" 16:     expect(1 == 1).to true 17:   end 

and run test, can do:

!rspec %:15 

this runs rspec external command. % expands current filename, , :15 tells rspec run test line 15, rather tests in file.

this technique works fine under normal circumstances. however, if try run test on lines 80-89 strange happens:

84:   "my other test" 85:     expect(4 > 3).to false 86:   end  !rspec %:84 

this runs command rspec [filename]4 - i.e. :8 characters disappear! (and "file not found" error.)

a workaround avoid problem press tab after entering %, expands % full path name.

however, what's reason behind strange vim behaviour? bug, or feature?

a different, related question led me finding answer this.

you can find answer, along more detail, running :help filename-modifiers in vim. here summary of key point:

the file name modifiers can used after "%", "#", "#n", "<cfile>", "<sfile>", "<afile>" or "<abuf>".

:8 converts path 8.3 short format (currently on ms-windows). act on of path existing path.

8 numerical filename-modifier. if wish disable feature entirely, can compile vim without +modify_fname feature.