I like using a macro recording for this kind of task, since that allows me to use the Vim commands I know already to move and edit, rather than having to write (and debug!) regexps to accomplish the task.
Using a macro recording, you can use the exact commands you'd use for this sequence:
\item (and space after it), add
& (and space after it) after 3 words, and add
\\ at the end of the line.
Start in the first line of the block you want to change, with command
qa to initiate recording into a macro stored in register
@a (you can use any named register for recording.)
^ to ensure you're in the first non-blank character in the line, in your case, the start of
\item. Then use
dW to delete that word, including the space after it. At this point, you can either use
3W to jump 3 words, or use
f( to skip to the
( character, either way, the cursor will be under the
( character (but using
f( might be more reliable getting there if different lines have different number of words before it.) Then you can use
i to start Insert mode, type
& (including the space after it), then press Esc to leave Insert mode. At this point, you can use
A to append to the end of the line, followed by
\\ (including the space before it), then Esc again to leave Insert mode.
You can then use
q to stop recording the macro.
At this point, you can use the
@a Normal-mode command on any line and it will repeat those editing steps.
But there's a more convenient way:
Then, repeat that over the next 4 lines as well (5 lines in total).
You can use the
:normal command with a range to repeat a Normal-mode command on each line of the range.
Use a Visual selection for the range, start on the second line of the block (the first line will already be fixed, during the recording of the macro) and extend it until the last line of the block (for example, using
3j for a 4-line block.)
: to go into Command-line mode. Vim will automatically populate the range from the Visual and it will show you
:'<,'>, which indicates that specific range. Keep that range on, and issue the rest of the command:
This will execute the Normal-mode command
@a, which is the execution of macro
@a (that you just recorded) in each line of the block. There you are!
If you happen to have many such blocks around your file and you'd like to process them all, you can also use a
:g command (assuming you have a search pattern that will match all relevant lines.) For example, to execute the macro on all lines matching
item some text (where the
item is matching the last part of
\item), you could use:
:g/item some text/norm @a
Recording macros can be pretty neat, since you can use the Vim editing commands you already know how to use, rather than writing regexps. Furthermore, using
:normal (possibly together with
:g) to replay your macros on large blocks or sets of lines makes them extremely productive.