Replacing text between two html comments

redbeard has asked for the wisdom of the Perl Monks concerning the following question:

I have an html file stored as a variable $template with the following in it

<!-- MEMBERSHIPS -->
.
a bunch of stuff
.
<!-- BANQUET -->
[download]

I would like to replace all of this with something else under certain conditions. Seems simple. However, the following

$template=~s/<!-- MEMBERSHIPS -->(.*?)<!-- BANQUET -->/$paidstring/i;
[download]

where $paidstring is what I want to replace it with, seems not to work. Furthermore, I did some playing around, and found that both

/<!-- MEMBERSHIPS -->(.*?)/
and
/(.*?)<!-- BANQUET -->/
[download]

will match just fine, but putting everything together shows no match. What is going on here? Is there something I am missing in attempting to search and replace text between two html comments?

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Re: Replacing text between two html comments by mojotoad (Monsignor) on Jul 28, 2010 at 01:59 UTC
You want to add /s as an option on your regular expression, thereby treating the whole string as a single line. Furthermore, as you have it currently, you're also zapping your delineators without replacing them. Maybe capture them as well and include their buck-whaps ($1, $3) in the replacement expression. You're probably okay with this as long as you can reasonably guarantee that your comment tokens are unique within any given document. Otherwise use a real parser, such as HTML::Parser. Or use a template system like Text::Template. Cheers, Matt	[reply]
Re: Replacing text between two html comments by wfsp (Abbot) on Jul 28, 2010 at 07:08 UTC
Another approach to this type of task is to not use comments in your HTML but to use div tags, each one having an id attribute. Using a parser you can find that div and replace it with the new content. This example uses HTML::TreeBuilder. #! /usr/bin/perl use strict; use warnings; use HTML::TreeBuilder; my $new_div = HTML::Element->new_from_lol( [ q{div}, {id => q{memberships}}, [q{p}, q{new stuff}] ], ); my $p = HTML::TreeBuilder->new_from_file(*DATA) or die qq{H::TB new failed\n}; my $memberships_div = $p->look_down( _tag => q{div}, id => q{memberships}, ) or die qq{memberships div not found\n}; $memberships_div->replace_with($new_div); print $p->as_HTML(undef, q{ }, {}); __DATA__ <html><head><title>replace test</title></head> <body> <p>keep</p> <p>keep</p> <div id="memberships"> <p>stuff to replace</p> </div> <div id="banquet"> <p>all about the banquet</p> </div> <p>keep</p> <p>keep</p> </body> </html> [download] `<html> <head> <title>replace test</title> </head> <body> <p>keep</p> <p>keep</p> <div id="memberships"> <p>new stuff</p> </div> <div id="banquet"> <p>all about the banquet</p> </div> <p>keep</p> <p>keep</p> </body> </html>` [download] If you haven't come across it before there is a bit of a learning curve but if you need to work with HTML it is well worth it. I avoid using regexes on HTML at all costs. Here there be dragons. :-)	[reply] [d/l] [select]
Re^2: Replacing text between two html comments by metaperl (Curate) on Jul 29, 2010 at 15:20 UTC
HTML::Seamstress is what I'd use if I were going to use TreeBuilder for this sort of thing `;)` The mantra of every experienced web application developer is the same: thou shalt separate business logic from display. Ironically, almost all template engines allow violation of this separation principle, which is the very impetus for HTML template engine development. -- Terence Parr, "Enforcing Strict Model View Separation in Template Engines"	[reply] [d/l]
Re: Replacing text between two html comments by StommePoes (Scribe) on Jul 29, 2010 at 07:03 UTC
Well, as Andrew Clover states, HTML is not a regular language, so parsing with regular expressions is not recommended beyond simple cases, ahem, but in slightly more colourful language. : ) I like wfsp's idea, and ideally in a semantic page you'd likely have a header tag (h2 or something) stating "Memberships" and "Banquets" anyway... I'd rather use those for searches than comments. Plus IE has a duplicate content bug if you float stuff between comments, so fewer comments in live code are better anyway.	[reply]


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