Moving Around in the History List

The next group of vi control mode commands we cover allows you to move around in and search your command history. This is the all-important functionality that lets you go back and fix an erroneous command without retyping the entire line. These commands are summarized in Table 2-12.

Table 2-12. vi control mode commands for searching the command history

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Command

Description

k or -

Move backward one line

j or +

Move forward one line

G

Move to line given by repeat count

/string

Search backward for string

?string

Search forward for string

n

Repeat search in same direction as previous

N

Repeat search in opposite direction of previous

The first two can also be accomplished with the up and down cursor movement keys if your keyboard has them. The first three can be preceded by repeat counts (e.g., 3k or 3- moves back three lines in the command history).

If you aren't familiar with vi and its cultural history, you may be wondering at the wisdom of choosing such seemingly poor mnemonics as h, j, k, and l for backward character, forward line, backward line, and forward character, respectively. Well, there actually is a rationale for the choices—other than that they are all together on the standard keyboard. Bill Joy originally developed vi to run on Lear-Siegler ADM-3a terminals, which were the first popular models with addressable cursors (meaning that a program could send an ADM-3a command to move the cursor to a specified location on the screen). The ADM-3a's h, j, k, and l keys had little arrows on them, so Joy decided to use those keys for appropriate commands in vi. Another (partial) rationale for the command choices is that CTRL-H is the traditional backspace key, and CTRL-J denotes linefeed.

Perhaps + and - are better mnemonics than j and k, but the latter have the advantage of being more easily accessible to touch typists. In either case, these are the most basic commands for moving around the history list. To see how they work, let's use the same examples from the emacs-mode section earlier.

You enter the example command (RETURN works in both input and control modes, as does LINEFEED or CTRL-J):

$ fgrep -l Duchess < ~cam/book/alice_in_wonderland

but you get an error message saying that your option letter was wrong. You want to change it to -s without having to retype the entire command. Assuming you are in control mode (you may have to type ESC to put yourself in control mode), you type k or - to get the command back. Your cursor will be at the beginning of the line:

$ [f]grep -l Duchess < ~cam/book/alice_in_wonderland

Type w to get to the -, then l to get to the l. Now you can replace it by typing rs; press RETURN to run the command.

Now let's say you get another error message, and you finally decide to look at the manual page for the fgrep command. You remember having done this a while ago today, so rather than typing in the entire man command, you search for the last one you used. To do this, type ESC to enter control mode (if you are already in control mode, this will have no effect), then type / followed by man or ma. To be on the safe side, you can also type ^ma; the ^ means match only lines that begin with ma.[7]

But typing /^ma doesn't give you what you want: instead, the shell gives you:

$ make myprogram

To search for "man" again, you can type n, which does another backward search using the last search string. Typing / again without an argument and hitting RETURN will accomplish the same thing.

The G command retrieves the command whose number is the same as the numeric prefix argument you supply. G depends on the command numbering scheme described in Chapter 3 Section 3.4.2.3. Without a prefix argument, it goes to command number 1. This may be useful to former C shell users who still want to use command numbers.