$myfile =~ s!([A-Z]+)!$1!g; ##

##

  $ perl -lwe '$_="hi MOM and DAD"; print;
               s!([A-Z]+)!$1!g; print'
  hi MOM and DAD
  hi MOM and DAD

##

##

  $myfile =~ s!\b([A-Z]+)\b!$1!g;

##

##

  perl -i~ -plwe 's/mom/dad/g' *.txt

##

##

  open my $fh, "source-data.txt"
    or die "opening source-data.txt: $!";
  print "\n";
  while ( my $line = <$fh> )
  {
      # protect against most egregious HTML violations
      $line =~ s/&/&/g;
      $line =~ s//>/g;

      # mark upper-case words as italic.  not locale-safe.
      $line =~ s!\b([A-Z])+\b!$1!g;

      # output the result
      print $fh $line;
  }
  print $fh "\n";
  close $fh
    or die "closing source-data.txt: $!";

##

##

  while ( <$fh> )
  {
      # protect against most egregious HTML violations
      s/&/&/g; s//>/g;

      # mark upper-case words as italic.  not locale-safe.
      s!\b([A-Z])+\b!$1!g;

      # output the result
      print $fh $_;
  }