Not quite. The first method does not assign to the same $_ that the while loop uses. If it did, you couldn't use $_ in that for loop at all.

while (<FH>) {
  # localized $_
  for (split ' ') {
    # localized $_
  }
  # previous $_
}
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It's when you start doing silly and dangerous things like:

sub foo {
  $_ = shift;  # TSK!  local $_
  tr/aeiou/AEIOU/;
  return $_;
}
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that problems occur. It is a bad idea to assign to a global $_ -- where "global" means "not localized".

japhy -- Perl and Regex Hacker