An easy way to center text between first and last non-white word in vim? - vim

Question

Is there an easy way using a macro or ~10 line function (no plugin!) to center some text between the first and last word (=sequence of non-blank characters) on a line? E.g. to turn
>>> No user serviceable parts below. <<<
into
>>> No user serviceable parts below. <<<
by balancing the spaces +/-1? You can assume no tabs and the result should not contain tabs, but note that the first word may not start in column 1. (EDIT: ... in fact, both delimiter words as well as the start and end of the text to center may be on arbitrary columns.)

Answer 1

source this function:
fun! CenterInSpaces()
let l = getline('.')
let lre = '\v^\s*\S+\zs\s*\ze'
let rre = '\v\zs\s*\ze\S+\s*$'
let sp = matchstr(l,lre)
let sp = sp.matchstr(l,rre)
let ln = len(sp)
let l = substitute(l,lre,sp[:ln/2-1],'')
let l = substitute(l,rre,sp[ln/2:],'')
call setline('.',l)
endf
note
this function might NOT work in all cases. I just wrote it quick for usual case. this is not a plugin after all
the codes lines could be reduced by combining function calls. but i think it is clear in this way, so I just leave it like this.
if it worked for you, you could create a map
it works like this: (last two lines I typed #: to repeat cmd call)

Answer 2

You can use the :s command with the \= aka sub-replace-expression.
:s#\v^\s*\S+\zs(\s+)(.{-})(\s+)\ze\S+\s*$#\=substitute(submatch(1).submatch(3),'\v^(\s*)(\1\s=)$','\1'.escape(submatch(2),'~&\').'\2','')#
Overview
Capture the text (including white-space) between the >>> and <<< marks. Divide up the white-space on both sides of the text in half and substitute in the non-white-space text in between. This white-space balancing act is done via the regex engine's backtracking because math is hard. Lets go shopping!
Notes:
using \v or very magic mode to reduce escaping as this command is long enough
already
use # as an alternative separator instead of the usual / for :s/pat/sub/ in hopes to make it slightly more readable
Matching Pattern
:s#\v^\s*\S+\zs(\s+)(.{-})(\s+)\ze\S+\s*$#...
:s with no range supplied only do the substitution on the current line.
^\s*\S+ match the starting white-space followed by non-white-space. >>> in this case.
(\s+)(.{-})(\s+) match white-space followed by the "text" followed by white-space
3 capture groups: 1) leading white-space, 2) the "text", and 3) trailing white-space. These will be later referenced by submatch(1), submatch(2), and submatch(3) respectively
.{-} is vim-speak for non-greedy matching or .*? in perl-speak
without the non-greedy matching the second capture group would include too much white-space at its end
\S+\s*$ match the non-white-space (i.e. <<<) and any trailing white-space
Use \zs and ze to designate the start and end of the match to be replaced
Replacement
\=substitute(submatch(1).submatch(3),'\v^(\s*)(\1\s=)$','\1'.escape(submatch(2),'~&\').'\2','')
\= tells vim that replacement will be a vim expression. Also allows the use of submatch() functions
substitute({str}, {pat}, {sub}, {flags}) Our expression will be a nested substitution
substitute(submatch(1).submatch(3), ...) do a substitute over the concatenation of leading and trailing white-spacing captured in submatch(1) and submatch(3)
The {pat} is ^(\s*)(\1\s=)$. Match some white-space followed by white-space of the same length as the first or 1 character longer. Capture both halves.
escape(submatch(2),'~&\') escape submatch(2) for any special characters. e.g. ~,&,\1, ...
The {sub} is '\1'.escape(submatch(2),'~&\').'\2'. Replace with the the escaped submatch(2) (i.e. the "text" we want to center) in between the halves of white-space, \1 and \2 from the {pat}
No {flag}'s are needed so ''
Usage
If you use this often I would suggest creating a command and putting it in ~/.vimrc.
command! -range -bar -nargs=0 CenterBetween <line1>,<line2>s#\v^\s*\S+\zs(\s+)(.{-})(\s+)\ze\S+\s*$#\=substitute(submatch(1).submatch(3),'\v^(\s*)(\1\s=)$','\1'.submatch(2).'\2','')#`
Otherwise use this once and then repeat the last substitution via & on each needed line.
For more help see
:h :s/
:h :s/\=
:h sub-replace-\=
:h submatch(
:h substitute(
:h escape(
:h /\v
:h /\S
:h /\{-
:h /\zs
:h &
EDIT by Kent
Don't be jealous, your answer has it too. ^_^
I didn't change the command, just cp/paste to my vim. only add |noh at the end to disable highlighting.
If execute this command, it looks like:

Answer 3

I don't know of any good way. I usually do it in a semi-automatic way, by using :center on a line of text that only contains the parts that are to be centered and then move the result into the line containing the surrounding parts.
If nobody else has a better answer, perhaps boxes can help if you need to do this kind of thing a lot.