vi Line Commands Versus Character Commands (Unix Power Tools, 3rd Edition)

17.26. vi Line Commands Versus Character Commands

[Quite a few vi users understand how to build vi commands with the (number)(command)(text object) model. But not too many people understand the difference between line commands and character commands. This article explains that and gives some examples. -- JP]

The _ (underscore) command is very similar to the ^ (caret) command in that it moves to the first nonblank character of the current line. The key difference is that _ is a line command while ^ is a character command. This is important for all functions that read an "address" -- for example, d, y, and c.

In fact, delete, yank, and so on all call a common internal routine in vi to get an "address." If the address is of a particular character, vi does a character-mode delete or yank or whatever. If it is a line address, vi does a line-mode operation. The "address" command may be any of the regular positioning commands (e.g., W, b, $, or /pattern/) or the original character repeated (as in dd or yy).

Some examples are found in Table 17-1.

Table 17-1. Examples of vi character and line commands

Keystrokes	Results
`dd`	Deletes the current line.
`d'a`	Deletes all lines between the current line and the line containing mark `a`, inclusive.
`d'a`	Deletes all characters between the current character and the character at mark `a`. This works much like an Emacs `W` in that the two endpoints are considered to be between two characters. Note that a character-oriented delete may delete newlines.
`c/accord/`	Changes all characters (not lines!) between the current character up to but not including the `a` in `accord`. (However, see the following Note.)
`c?accord?`	Changes all characters between the current character and the `accord`, including the word `accord`.
`yj`	Yanks two lines: the current line and the one below.
`yH`	Yanks all the lines from the top of the screen to the current line, inclusive.
`<G`	Unindents or "dedents" the lines between the current line and the last line, inclusive. (The variable shiftwidth determines the amount of dedenting.) Note that this command turns character addresses into line addresses (so does `>`).
`!}fmt`	Runs the lines between the current line and the end of the paragraph through the program fmt (Section 17.28).

NOTE: If you have wrapscan set, a search like c?accord? may wrap from the beginning of the file to the end. This can cause unexpected results and is one reason why I have set nows in my .exrc. Unfortunately, turning off wrapscan breaks tags in many versions of vi.

vi combines the repeat count on the command character with the repeat count on the motion command, so that 2y2j yanks five lines. Interestingly, 2y2_ yanks 4 lines (so does 2y2y) since the _ command moves down (repeat count minus 1) lines. Beware, however, of using repeat counts on all of the motion commands; they're not all implemented in the same way. 4$ moves to the end of the third line below the current; 4 merely moves to the first nonblank character of the current line. | (vertical bar) is a synonym for 0 (zero); given a repeat count, it goes that many characters to the right of the beginning of the line (as if you had typed | (rept-1) l). (Exercise for the reader: why can't you give a repeat count to 0?)

Uppercase letters do different things depending on the command. The exact actions may not always seem sensible, but typically they affect the "current line": D acts like d$; C acts like c$; Y acts like yy. The list must merely be memorized, or you can use a good vi reference guide.

-- CT