Recipe 20.21 Program: hrefsub
hrefsub makes substitutions in HTML files, so changes apply only to text in <A HREF="..." > tags. For instance, if you had the scooby.html file from the previous recipe, and you've moved shergold.html to be cards.html, you need but 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 (shown in Example 20-13) always lowercases 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 20-13. 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 $to = shift or usage;
usage unless @ARGV;
# The HTML::Filter subclass to do the substitution.
package MyFilter;
use HTML::Filter;
@ISA=qw(HTML::Filter);
use HTML::Entities qw(encode_entities);
sub start {
my($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($_);
}
