Recipe 20.15. Program: hrefsub

20.15. Program: hrefsub

hrefsub makes substitutions in HTML files, so that the changes only apply to the text in HREF fields of <A HREF="..."> tags. For instance, if you had the scooby.html file from the previous example, and you've moved shergold.html to be cards.html, you need simply say:

% hrefsub shergold.html cards.html scooby.html
<HTML><HEAD><TITLE>Hi!</TITLE></HEAD><BODY>
<H1>Welcome to Scooby World!</H1>
I have <A HREF="pictures.html">pictures</A> of the crazy dog
himself.  Here's one!<P>
<IMG SRC="scooby.jpg" ALT="Good doggy!"><P>
<BLINK>He's my hero!</BLINK>  I would like to meet him some day,
and get my picture taken with him.<P>
P.S. I am deathly ill.  <a href="cards.html">Please send
cards</A>.
</BODY></HTML>

The HTML::Filter manual page has a BUGS section that says:

Comments in declarations are removed from the declarations and then inserted as separate comments after the declaration. If you turn on strict_comment(), then comments with embedded "-\|-" are split into multiple comments.

This version of hrefsub will always lowercase the <a> and the attribute names within this tag when substitution occurs. If $foo is a multiword string, then the text given to MyFilter->text may be broken such that these words do not come together; i.e., the substitution does not work. There should probably be a new option to HTML::Parser to make it not return text until the whole segment has been seen. Also, some people may not be happy with having their 8-bit Latin-1 characters replaced by ugly entities, so htmlsub does that, too.

Example 20.12: hrefsub

#!/usr/bin/perl -w
# hrefsub - make substitutions in <A HREF="..."> fields of HTML files
# from Gisle Aas <gisle@aas.no>

sub usage { die "Usage: $0 <from> <to> <file>...\n" }

my $from = shift or usage;
my $to   = shift or usage;
usage unless @ARGV;

# The HTML::Filter subclass to do the substitution.

package MyFilter;
require HTML::Filter;
@ISA=qw(HTML::Filter);
use HTML::Entities qw(encode_entities);

sub start {
   my($self, $tag, $attr, $attrseq, $orig) = @_;
   if ($tag eq 'a' && exists $attr->{href}) {
           if ($attr->{href} =~ s/\Q$from/$to/g) {
               # must reconstruct the start tag based on $tag and $attr.
               # wish we instead were told the extent of the 'href' value
               # in $orig.
               my $tmp = "<$tag";
               for (@$attrseq) {
                   my $encoded = encode_entities($attr->{$_});
                   $tmp .= qq( $_="$encoded ");
               }
               $tmp .= ">";
               $self->output($tmp);
               return;
           }
   }
   $self->output($orig);
}

# Now use the class.

package main;
foreach (@ARGV) {
        MyFilter->new->parse_file($_);
}