substitution - How do I substitute from a list of strings in VIM?

Question

I am a vim user, and I want to be able to loop over a range of substrings when I am substituting. How can I use some vim magic to go from a set of lines like this:

Afoo
Bfoo
Cfoo
Dfoo

to

Abar
Bbar
Cbaz
Dbaz

?

I want to search my file from the start for the next occurance of foo, and replace the first two instances with bar, and the second two with baz. Is using a for loop the best option? If so, then how do I use the loop variable in the substitution command?

Answer 1

I would use a function that has a state, and call this function from %s. Something like:

" untested code
function! InitRotateSubst()
    let s:rs_idx = 0
endfunction

function! RotateSubst(list)
    let res = a:list[s:rs_idx]
    let s:rs_idx += 1
    if s:rs_idx == len(a:list)
        let s:rs_idx = 0
    endif
    return res
endfunction

And use them with:

:call InitRotateSubst()
:%s/foo/=RotateSubst(['bar', 'bar', 'baz', 'baz'])/

The call to the two commands could be encapsulated into a single command if you wish.

---

EDIT: Here is a version integrated as a command that:

• accepts as many replacements as we wish, all the replacements needs to be separated with the separator-character ;
• supports back-references ;
• can replace only the N first occurrences, N == the number of replacements specified if the command call is banged (with a !)
• does not support usual flags like g, i (:h :s_flags) -- for that, we would have for instance to impose the command call to always ends up with a / (or whatever separator-character), if not the last text is interpreted as flags.

Here is the command definition:

:command! -bang -nargs=1 -range RotateSubstitute <line1>,<line2>call s:RotateSubstitute("<bang>", <f-args>)

function! s:RotateSubstitute(bang, repl_arg) range
  let do_loop = a:bang != "!"
  " echom "do_loop=".do_loop." -> ".a:bang
  " reset internal state
  let s:rs_idx = 0
  " obtain the separator character
  let sep = a:repl_arg[0]
  " obtain all fields in the initial command
  let fields = split(a:repl_arg, sep)

  " prepare all the backreferences
  let replacements = fields[1:]
  let max_back_ref = 0
  for r in replacements
    let s = substitute(r, '.{-}(\d+)', '1', 'g')
    " echo "s->".s
    let ls = split(s, '\')
    for d in ls
      let br = matchstr(d, 'd+')
      " echo '##'.(br+0).'##'.type(0) ." ~~ " . type(br+0)
      if !empty(br) && (0+br) > max_back_ref
    let max_back_ref = br
      endif
    endfor
  endfor
  " echo "max back-ref=".max_back_ref
  let sm = ''
  for i in range(0, max_back_ref)
    let sm .= ','. 'submatch('.i.')' 
    " call add(sm,)
  endfor

  " build the action to execute
  let action = '=s:DoRotateSubst('.do_loop.',' . string(replacements) . sm .')'
  " prepare the :substitute command
  let args = [fields[0], action ]
  let cmd = a:firstline . ',' . a:lastline . 's' . sep . join(args, sep)
  " echom cmd
  " and run it
  exe cmd
endfunction

function! s:DoRotateSubst(do_loop, list, replaced, ...)
  " echom string(a:000)
  if ! a:do_loop && s:rs_idx == len(a:list)
    return a:replaced
  else
    let res0 = a:list[s:rs_idx]
    let s:rs_idx += 1
    if a:do_loop && s:rs_idx == len(a:list)
        let s:rs_idx = 0
    endif

    let res = ''
    while strlen(res0)
      let ml = matchlist(res0, '(.{-})(\d+)(.*)')
      let res .= ml[1]
      let ref = eval(substitute(ml[2], '\(d+)', 'a:1', ''))
      let res .= ref
      let res0 = ml[3]
    endwhile

    return res
  endif
endfunction

which could be used this way:

:%RotateSubstitute#foo#bar#bar#baz#baz#

or even, considering the initial text:

AfooZ
BfooE
CfooR
DfooT

the command

%RotateSubstitute/(.)foo(.)/2bar1/1bar2/

would produce:

ZbarA
BbarE
RbarC
DbarT