Vim substitute a Regex with randomly generated numbers

Question

Is it possible to substitute a regular expression with a randomly generated number in Vim ? The (random) number to be replaced should be different for each pattern that matches the regular expression. Here's an example of what I need.

Input File:

<a>XYZ</a>
<a>XYZ</a>
<a>XYZ</a>
<a>XYZ</a>

After substituting XYZ with random numbers, the output could be:

<a>599</a>  
<a>14253</a>    
<a>1718</a>
<a>3064</a>

Answer 1

If you don't mind a little perl in your vim, you can use

:%! perl -pne 's/XYZ/int(rand 1000)/ge'

Edit: updated to allow unlimited substitutions on a given line, per suggestion by @hobbes3, so

XYZ XYZ
XYZ XYZ XYZ 
XYZ XYZ XYZ XYZ XYZ XYZ
XYZ XYZ

Becomes something like

86 988
677 477 394 
199 821 193 649 502 471
732 208

Answer 2

Try this: put the below code to a buffer then source it (:source %).

let rnd = localtime() % 0x10000 

function! Random() 
  let g:rnd = (g:rnd * 31421 + 6927) % 0x10000 
  return g:rnd 
endfun 

function! Choose(n) " 0 n within 
  return (Random() * a:n) / 0x10000 
endfun 

Then you can do:

:s_\(<a>\).*\(</a>\)_\1\=Choose(line('.')*100).\2_