How can I do a column select across the entire file?

This should do it:

1. Ctrl+A - select all.
2. Ctrl+Shift+L - split selection into lines.
3. Then move all cursors with left/right, select with Shift+left/right. Move all cursors to start of line with Home.

OS X

You can click the following and drag to create a selection of one or more columns of characters:

• Left mouse button + option
• Middle mouse button

To add to an existing selection, hold command while doing the above.

To subtract from an existing selection, hold command + shift while doing the above

Windows

You can click the following and drag to create a selection of one or more columns of characters:

• Right Mouse Button + shift
• Middle Mouse Button

To add to an existing selection, hold Ctrl while doing the above.

To subtract from an existing selection, hold Alt while doing the above.

In Mac OS X, replace Ctrl with CMD key. So it'll be,

CMD+A - select all. CMD+Shift+L - split selection into lines. Then move all cursors with left/right, select with Shift+left/right. Move all cursors to start of line with Home.