Fish.

use HTML::TokeParser ();
my %verb = ( S => 4, E => 2, T => 1, C => 1, D => 1, PI => 2 );
my $p = HTML::TokeParser->new( "foo.html" )
  or die "can't open foo.html: $!\n";
while( my $t = $p->get_token ) {
  if( $t->[0] eq 'S' and $t->[1] eq 'font' ) {
    my $attr = $t->[2];
    delete $attr->{face};
    print "<font ", 
      join( " ", map { qq{$_="$attr->{$_}"} } keys %{$attr} ), ">";
  } else {
    ## print verbatim . . .
    print $t->[ $verb{ $t->[0] } ]
  }
}
exit 0;
__END__
[download]

Nice code. It's even easier with HTML::TokeParser::Simple, though.

use HTML::TokeParser::Simple;

my $p = HTML::TokeParser::Simple->new( "foo.html" )
   or die "can't open foo.html: $!\n";
while( my $t = $p->get_token ) {
   if( $t->is_start_tag('font') ) {
       my $attr = $t->return_attr;
       delete $attr->{face};
       my $attributes =  join( " ", map { qq{$_="$attr->{$_}"} } keys 
+%$attr );
       print "<font $attributes>";
   } else {
       print $t->as_is;
   }
}
[download]

Cheers,
Ovid

New address of my CGI Course.
Silence is Evil (feel free to copy and distribute widely - note copyright text)

It can act in a more or less fine-grained way - you can specify permitted tags, permitted attributes of each tag, and permitted values for each attribute in as much detail as you like.

hope this helps,

This probably doesn't work ... somewhere? But on the all the most pathological pages I could find (sample of 5 in the DATA section), it seems to do fine.

#! perl -slw
use strict;
use LWP::Simple;

while( <DATA> ) {
    chomp;
    my $html = get $_;

    $html =~ s[( <FONT \s+ (?: (?:"[^"]+") | (?:'[^']+') | [^>]* ) > )
+]  #"
    {
        my $tag = $1;
        $tag =~ s[ face \s* = \s* (?: (?:"[^"]+") | (?:'[^']+') | [^\s
+]+ ) ][]ixm; #"
        $tag
    }eximg;

    my $out = $ENV{TMP} . '\\' .time() . '.htm';
    open OUT, '>', $out or warn $!;
    print OUT $html;
    close OUT;
    system( $out );
}

__DATA__
http://www.webdiner.com/annexe/font/font.htm
http://www.electricearl.com/fonttest.html
http://www.ilovethisplace.com/webdesign/fonts.html
http://www.york.ac.uk/depts/maths/symbchrc.htm
http://www.tedmontgomery.com/tutorial/style.html#face
[download]

Note: system probably won't load the modifed sample directly into the browser on systems who's commands line don't know what do with .htm files.