From Generalized Columns.
Ends slide apart (to allow for two dancer-sized positions of space between
  them) as Centers do two Phantom Column Circulates; all adjust to end such that
  the resulting Lines are close together.
Notes:
- 
Some callers say File To A Wave when the call ends in
    Parallel Waves, and File To A Line otherwise.  Other callers
    always say File To A Line, no matter what the ending
    formation will be.
Variation: From a Butterfly, the caller can say Centers (Start) File
  To A Line in
  which case the Centers do two Phantom Column Circulates and all
  adjust to end in adjacent Lines.
Magic File To A Line [C2V]:
 Ends Spread apart as Centers do two Phantom Column 
  Magic Column 
  Circulates; all adjust to end in adjacent Lines.
For those of you who are checker-pushers, File To A Line is
  choreographically equivalent to Centers Box Circulate as Ends 
  Stable 
  Divide.