Mine

#!/usr/bin/perl

use warnings;
use strict;
my @t;
my $i;

while (<>) {
  @t = split /([<>])/, $_; 
  for ($i = 0; $i <= $#t; $i++) { 
    next if $i % 4 != 0; $t[$i] =~ s/_/ /g; 
  }
  print join "", @t;
}