hosts .htaccess tricks and tips part one and part two

Here are two links to some of the best information on htaccess and mod-rewrite by cor:

http://corz.org/serv/tricks/htaccess.php

http://corz.org/serv/tricks/htaccess2.php

Here is the data from that site, in case it goes down before this one does:

.htaccess tips and tricks

Introduction to .htaccess..

This work in constant progress is some collected wisdom, stuff I've learned on the topic of .htaccess hacking, commands I've used successfully in the past, on a variety of server setups, and in most cases still do. You may have to tweak the examples some to get the desired result, though, and a reliable test server is a powerful ally, preferably one with a very similar setup to your "live" server. Okay, to begin..

.htaccess files are invisible

There's a good reason why you won't see .htaccess files on the web; almost every web server in the world is configured to ignore them, by default. Same goes for most operating systems. Mainly it's the dot "." at the start, you see?

If you don't  see, you'll need to disable your operating system's invisible file functions, or use a text editor that allows you to open hidden files, something like bbedit on the Mac platform. On windows, showing invisibles in explorer should allow any text editor to open them, and most decent editors to save them too**. Linux dudes know how to find them without any help from me.

In both images, the operating system has been instructed to display invisible files. ugly, but necessary sometimes. You will also need to instruct your ftp client to do the same.

By the way; the windows screencap is more recent than the mac one, moved files are likely being handled by my clever 404 script.

** even notepad can save files beginning with a dot, if you put double-quotes around the name when you save it; i.e.. ".htaccess". You can also use your ftp client to rename files beginning with a dot, even on your local filesystem; works great in FileZilla.

What are .htaccess files anyway?

Simply put, they are invisible plain text files where one can store server directives. Server directives are anything you might put in an Apache config file (httpd.conf) or even a php.ini**, but unlike those "master" directive files, these .htaccess directives apply only to the folder in which the .htaccess file resides, and all the folders inside.

This ability to plant .htaccess files in any directory of our site allows us to set up a finely-grained tree of server directives, each subfolder inheriting properties from its parent, whilst at the same time adding to, or over-riding certain directives with its own .htaccess file. For instance, you could use .htacces to enable indexes all over your site, and then deny indexing in only certain subdirectories, or deny index listings site-wide, and allow indexing in certain subdirectories. One line in the .htaccess file in your root and your whole site is altered. From here on, I'll probably refer to the main .htaccess in the root of your website as "the master .htaccess file", or "main" .htaccess file.

There's a small performance penalty for all this .htaccess file checking, but not noticeable, and you'll find most of the time it's just on and there's nothing you can do about it anyway, so let's make the most of it..

** Your main php.ini, that is, unless you are running under phpsuexec, in which case the directives would go inside individual  php.ini files
 

Is .htaccess enabled?

It's unusual, but possible that .htaccess is not enabled on your site. If you are hosting it yourself, it's easy enough to fix; open your httpd.conf in a text editor, and locate this section..

Your DocumentRoot may be different, of course..
# This should be changed to whatever you set DocumentRoot to.
#
<Directory "/var/www/htdocs">
#


..locate the line that reads..

AllowOverride None


..and change it to..

AllowOverride All


Restart Apache. Now .htaccess will work. You can also make this change inside a virtual host, which would normally be preferable.

If your site is hosted with someone else, check your control panel (Plesk. CPanel, etc.) to see if you can enable it there, and if not, contact your hosting admins. Perhaps they don't allow this. In which case, switch to a better web host.

 

What can I do with .htaccess files?

Almost any directive that you can put inside an httpd.conf file will also function perfectly inside an .htaccess file. Unsurprisingly, the most common use of .htaccess is to..

 

Control access..

.htaccess is most often used to restrict or deny access to individual files and folders. A typical example would be an "includes" folder. Your site's pages can call these included scripts all they like, but you don't want users accessing these files directly, over the web. In that case you would drop an .htaccess file in the includes folder with content something like this..

NO ENTRY!
# no one gets in here!
deny from all


which would deny ALL direct access to ANY files in that folder. You can be more specific with your conditions, for instance limiting access to a particular IP range, here's a handy top-level rule for a local test server..

NO ENTRY outside of the LAN!
# no nasty crackers in here!
order deny,allow
deny from all
allow from 192.168.0.0/24
# this would do the same thing..
#allow from 192.168.0


Generally these sorts of requests would bounce off your firewall anyway, but on a live server (like my dev mirror sometimes is) they become useful for filtering out undesirable IP blocks, known risks, lots of things. By the way, in case you hadn't spotted; lines beginning with "#" are ignored by Apache; handy for comments.

Sometimes, you will only want to ban one IP, perhaps some persistent robot that doesn't play by the rules..

post user agent every fifth request only. hmmm. ban IP..
# someone else giving the ruskies a bad name..
order allow,deny
deny from 83.222.23.219
allow from all


The usual rules for IP addresses apply, so you can use partial matches, ranges, and so on. Whatever, the user gets a 403 "access denied" error page in their client software (browser, usually), which certainly gets the message across. This is probably fine for most situations, but in part two I'll demonstrate some cooler ways to deny access, as well as how to deny those nasty web suckers, bad referrers, script kiddies and more.

 

Custom error documents..

I guess I should briefly mention that .htaccess is where most folk configure their error documents. Usually with sommething like this..

the usual method. the "err" folder (with the custom pages) is in the root
# custom error documents
ErrorDocument 401 /err/401.php
ErrorDocument 403 /err/403.php
ErrorDocument 404 /err/404.php
ErrorDocument 500 /err/500.php


You can also specify external URLs, though this can be problematic, and is best avoided. One quick and simple method is to specify the text in the directive itself, you can even use HTML (though there is probably a limit to how much HTML you can squeeze onto one line). Remember, for Apache 1; begin with a ", but DO NOT end with one. For Apache 2, you can put a second quote at the end, as normal.

measure twice, quote once..
# quick custom error "document"..
ErrorDocument 404 "NO!

There is nothing here.. go away quickly!


Using a custom error document is a Very Good Idea, and will give you a second chance at your almost-lost visitors. I recommend you download mine. But then, I would.

 

Password protected directories..

The next most obvious use for our .htaccess files is to allow access to only specific users, or user groups, in other words; password protected folders. a simple authorisation mechanism might look something like this..

a simple sample .htaccess file for password protection:
AuthType Basic
AuthName "restricted area"
AuthUserFile /usr/local/var/www/html/.htpasses
require valid-user


You can use this same mechanism to limit only certain kinds of requests, too..

only valid users can POST in here, anyone can GET, PUT, etc:
AuthType Basic
AuthName "restricted area"
AuthUserFile /usr/local/var/www/html/.htpasses

 require valid-user


You can find loads of online examples of how to setup authorization using .htaccess, and so long as you have a real  user (or create one, in this case, 'jimmy') with a real  password (you will be prompted for this, twice) in a real  password file (the -c switch will create it)..

htpasswd -c /usr/local/var/www/html/.htpasses jimmy

..the above will work just fine. htpasswd is a tool that comes free with Apache, specifically for making and updating password files, check it out. The windows version is the same; only the file path needs to be changed; to wherever you want to put the password file.

Note: if the Apache bin/ folder isn't in your PATH, you will need to cd into that directory before performing the command. Also note: You can use forward and back-slashes interchangeably with Apache/php on Windows, so this would work just fine..

htpasswd -c c:/unix/usr/local/Apache2/conf/.htpasses jimmy

Relative paths are fine too; assuming you were inside the bin/ directory of our fictional Apache install, the following would do exactly the same as the above..

htpasswd -c ../conf/.htpasses jimmy

Naming the password file .htpasses is a habit from when I had to keep that file inside the web site itself, and as web servers are configured to ignore files beginning with .ht, they too, remain hidden. If you keep your password file outside the web root (a better idea), then you can call it whatever you like, but the .ht_something habit is a good one to keep, even inside the web tree, it is secure enough for our basic  purpose..

Once they are logged in, you can access the remote_user environmental variable, and do stuff with it..

the remote_user variable is now available..
RewriteEngine on
RewriteCond %{remote_user} !^$ [nc]
RewriteRule ^(.*)$ /users/%{remote_user}/$1


Which is a handy directive, utilizing mod_rewrite; a subject I delve into far more deeply, in part two.

 

Get better protection..

The authentication examples above assume that your web server supports "Basic" http authorisation, as far as I know they all do (it's in the Apache core). Trouble is, some browsers aren't sending password this way any more, personally I'm looking to php to cover my authorization needs. Basic auth works okay though, even if it isn't actually very secure - your password travels in plain text over the wire, not clever.

If you have php, and are looking for a more secure login facility, check out pajamas. It's free. If you are looking for a password-protected download facility (and much more, besides), check out my distro machine, also free.

 

500 error..

If you add something that the server doesn't understand or support, you will get a 500 error page, aka.. "the server did a boo-boo". Even directives that work perfectly on your test server at home may fail dramatically at your real site. In fact this is a great way to find out if .htaccess files are enabled on your site; create one, put some gibberish in it, and load a page in that folder, wait for the 500 error. if there isn't one, probably they are not enabled.

If they are, we need a way to safely do live-testing without bringing the whole site to a 500 standstill.

Fortunately, in much the same way as we used the tag above, we can create conditional directives, things which will only come into effect if certain conditions are true. The most useful of these is the "ifModule" condition, which goes something like this..

only if PHP is loaded, will this directive have any effect (switch the 4 for a 5 if using php5)

 php_value default_charset utf-8


..which placed in your master .htaccess file, that would set the default character encoding of your entire site to utf-8 (a good idea!), at least, anything output by PHP. If the PHP4** module isn't running on the server, the above .htaccess directive will do exactly nothing; Apache just ignores it. As well as proofing us against knocking the server into 500 mode, this also makes our .htaccess directives that wee bit more portable. Of course, if your syntax is messed-up, no amount of if-module-ing is going to prevent a error of some kind, all the more reason to practice this stuff on a local test server.

** note: if you are using php5, you would obviously instead use .

 

 

Groovy things to do with .htaccess..

So far we've only scratched the surface. Aside from authorisation, the humble .htaccess file can be put to all kinds of uses. If you've ever had a look in my public archives you will have noticed that that the directories are fully browsable, just like in the old days before adult web hosts realized how to turn that feature off! A line like this..

bring back the directories!
Options +Indexes +MultiViews +FollowSymlinks


..will almost certainly turn it back on again. And if you have mod_autoindex.c installed on your server (probably, yes), you can get nice fancy indexing, too..

show me those files!

 IndexOptions FancyIndexing


..which, as well as being neater, allows users to click the titles and, for instance, order the listing by date, or file size, or whatever. It's all for free too, built-in to the server, we're just switching it on. You can control certain parameters too..

let's go all the way!

 IndexOptions FancyIndexing IconHeight=16 IconWidth=16


Other parameters you could add include..

NameWidth=30
DescriptionWidth=30
IconsAreLinks SuppressHTMLPreamble (handy!)


I'm not mentioning the "XHTML" parameter in Apache2, because it still isn't! Anyways, I've chucked one of my old fancy indexing .htaccess file onsite for you to have some fun with. Just add readme.html and away you go! note: these days I use a single header files for all  the indexes..

HeaderName /inc/header.html


.. and only drop in local "readme" files. Check out the example, and my public archives for more details.

 

custom directory index files

While I'm here, it's worth mentioning that .htaccess is where you can specify which files you want to use as your indexes, that is, if a user requests /foo/, Apache will serve up /foo/index.html, or whatever file you specify.

You can also specify multiple files, and Apache will look for each in order, and present the first one it finds. It's generally setup something like..

DirectoryIndex index.html index.php index.htm



It really is worth scouting around the Apache documentation, often you will find controls for things you imagined were uncontrollable, thereby creating new possibilities, better options for your website. My experience of the magic "LAMP" (Linux-Apache-MySQL-PHP) has been.. "If you can imagine that it can be done, it can be done". Swap "Linux" for any decent operating system, the "AMP" part runs on most of them.

Okay, so now we have nice fancy directories, and some of them password protected, if you don't watch out, you're site will get popular, and that means bandwidth..

 

Save bandwidth with .htaccess!

If you pay for your bandwidth, this wee line could save you hard cash..

save me hard cash! and help the internet!

 php_value zlib.output_compression 16386


All it does is enables PHP's built-in transparent zlib compression. This will half your bandwidth usage in one stroke, more than that, in fact. Of course it only works with data being output by the PHP module, but if you design your pages with this in mind, you can use php echo statements, or better yet, php "includes" for your plain html output and just compress everything! Remember, if you run phpsuexec, you'll need to put php directives in a local php.ini file, not .htaccess. See here for more details.

 

Hide and deny files..

Do you remember I mentioned that any file beginning with .ht is invisible? .."almost every web server in the world is configured to ignore them, by default" and that is, of course, because .ht_anything files generally have server directives and passwords and stuff in them, most  servers will have something like this in their main configuration..

Standard setting..

 Order allow,deny
 Deny from all
 Satisfy All


which instructs the server to deny access to any file beginning with .ht, effectively protecting our .htaccess and other files. The "." at the start prevents them being displayed in an index, and the .ht prevents them being accessed. This version..

ignore what you want

 Order allow,deny
 Deny from all
 Satisfy All


tells the server to deny access to *.log files. You can insert multiple file types into each rule, separating them with a pipe "|", and you can insert multiple blocks into your .htaccess file, too. I find it convenient to put all the files starting with a dot into one, and the files with denied extensions into another, something like this..

the whole lot
# deny all .htaccess, .DS_Store $hî†é and ._* (resource fork) files

 Order allow,deny
 Deny from all
 Satisfy All


# deny access to all .log and .comment files

 Order allow,deny
 Deny from all
 Satisfy All


would cover all ._* resource fork files, .DS_Store files (which the Mac Finder creates all over the place) *.log files, *.comment files and of course, our .ht* files. You can add whatever file types you need to protect from direct access. I think it's clear now why the file is called ".htaccess".

 

 

These days, using is preferred over , mainly because you can use regular expression in the conditions (very handy), produce clean, more readable code. Here's an example. which I use for my php-generated style sheets..

parse file.css and file.style with the php machine..
# handler for phpsuexec..
<FilesMatch ".(css|style)$">
 SetHandler application/x-httpd-php


Any files with a *.css or *.style extension will now be handled by php, rather than simply served up by Apache. And because you can use regexp, you could do stuff like <FilesMatch ".s?html$">, which is handy. Any statements you come across can be advantageously replaced by statements. Good to know.

 

More stuff..

At the end of my .htaccess files, there always seems to be a section of "stuff"; miscellaneous commands, mainly php flags and switches; so it seems logical to finish up the page with a wee selection of those..

php flags, switches and other stuff..
# let's enable php (non-cgi, aka. 'module') for EVERYTHING..'
AddType application/x-httpd-php5 .htm .html .php .blog .comment .inc

# better yet..
AddHandler php5-script .php

# legacy php4 version..'
AddType application/x-httpd-php .htm .html .php .blog .comment .inc

# don't even think about setting this to 'on'
php_value register_globals off

# no session id's in the URL PULEEZE!
php_value session.use_trans_sid 0
# should be the same as..
php_flag session.use_trans_sid off
# using both should also work fine!

# php error logs..
php_flag display_errors off
php_flag log_errors on
php_value track_errors on
php_value error_log /home/cor/errors/phperr.log

# if you like to collect interesting php system shell access and web hack scripts
# get yourself a SECURE upload facility, and just let the script-kiddies come …
# in no time you will have a huge selection of fascinating code. If you want folk to
# also upload zips and stuff, you might want to increase the upload capacities..
php_value upload_max_filesize 12M
php_value post_max_size 12M

# php 5 only, afaik. handy when your server isn't where YOU are.
php_value date.timezone Europe/Aberdeen
# actually, Europe/Aberdeen isn't a valid php timezone, so that won't work.
# I recommend you check the php manual for this function, because many crazy places ARE!


Note: For most of the flags I've tested, you can use on/off and true/false interchangeably, as well as 0/1, also php_value and php_flag can be switched around while things continue to work as expected! I guess, logically, booleans should always be php_flag, and values, php_value; but suffice to say, if some php erm, directive  isn't working, these would all be good things to fiddle with!

Of course, the php manual explains all. The bottom line is; both will work fine, but if you use the wrong type in .htaccess, say, set a php_flag using php_value, a php ini_get() command, for instance, would return true, even though you had set the value to off, because it reads off value as a string, which of course evaluates to not-zero, i.e. 1, or "true". If you don't rely on get_ini(), or similar, it's not a problem, though clearly it's better to get it right from the start. By the way; one of the values above is incorrectly set. Did you spot it?

Most php settings, you can override inside your actual scripts, but I do find it handy to be able to set defaults for a folder, or an entire site, using .htaccess.

 

over to you..

That should get you started with .htaccess, quite easy when you know how. If you really want to bend your brain out of shape, follow the link below for part two of the series, where I delve into the arcane mysteries of URL rewriting.

more .htaccess tips and tricks..


more clever stuff here
 

redirecting and rewriting

"The great thing about mod_rewrite is it gives you all the configurability and flexibility of Sendmail. The downside to mod_rewrite is that it gives you all the configurability and flexibility of Sendmail."

- Brian Behlendorf, Apache Group
 

 

One of the more powerful tricks of the .htaccess hacker is the ability to rewrite URLs. This enables us to do some mighty manipulations on our links; useful stuff like transforming very long URL's into short, cute URLs, transforming dynamic ?generated=page&URL's into /friendly/flat/links, redirect missing pages, preventing hot-linking, performing automatic language translation, and much, much more.

Make no mistake, mod_rewrite is complex. This isn't the subject for a quick bite-size tech-snack, probably not even a week-end crash-course, I've seen guys pull off some real cute stuff with mod_rewrite, but with kudos-hat tipped firmly towards that bastard operator from hell, Ralf S. Engelschall, author of the magic module itself, I have to admit that a great deal of it still seems so much voodoo to me.

The way that rules can work one minute and then seem not to the next, how browser and other in-between network caches interact with rules and testing rules is often baffling, maddening. When I feel the need to bend my mind completely out of shape, I mess around with mod_rewrite!

After all this, it does work, and while I'm not planning on taking that week-end crash-course any time soon, I have picked up a few wee tricks myself, messing around with web servers and web sites, this place..

The plan here is to just drop some neat stuff, examples, things that have proven useful, and work on a variety of server setups; there are Apache's all over my LAN, I keep coming across old .htaccess files stuffed with past rewriting experiments that either worked; and I add them to my list, or failed dismally; and I'm surprised that more often these days, I can see exactly why!

Very little here is my own invention. Even the bits I figured out myself were already well documented, I just hadn't understood the documents, or couldn't find them. Sometimes, just looking at the same thing from a different angle can make all the difference, so perhaps this humble stab at URL Rewriting might be of some use. I'm writing it for me, of course. but I do get some credit for this..

# time to get dynamic, see..
RewriteRule (.*).htm $1.php
 

 

beginning rewriting..

Whenever you use mod_rewrite (the part of Apache that does all this magic), you need to do..


..before any ReWrite rules. note: +FollowSymLinks must be enabled for any rules to work, this is a security requirement of the rewrite engine. Normally it's enabled in the root and you shouldn't have to add it, but it doesn't hurt to do so, and I'll insert it into all the examples on this page, just in case*.

The next line simply switches on the rewrite engine for that folder. if this directive is in you main .htaccess file, then the ReWrite engine is theoretically enabled for your entire site, but it's wise to always add that line before you write any redirections, anywhere.

* Although highly unlikely, your host may have +FollowSymLinks enabled at the root level, yet disallow its addition in .htaccess; in which case, adding +FollowSymLinks will break your setup (probably a 500 error), so just remove it, and your rules should work fine.

Important: While some of the directives on this page may appear split onto two lines in your browser, in your .htaccess file they must exist completely on one line. If you drag-select and copy the directives on this page, they should paste just fine into any text editor.
 

 

simple rewriting

Simply put, Apache scans all incoming URL requests, checks for matches in our .htaccess file and rewrites those matching URLs to whatever we specify. something like this..

all requests to whatever.htm will be sent to whatever.php:
Options +FollowSymlinks
RewriteEngine on
RewriteRule ^(.*).htm$ $1.php [NC]

Handy for anyone updating a site from static htm (you could use .html, or .htm(.*), .htm?, etc) to dynamic php pages; requests to the old pages are automatically rewritten to our new urls. no one notices a thing, visitors and search engines can access your content either way. leave the rule in; as an added bonus, this enables us to easily split php code and its included html structures into two separate files, a nice idea; makes editing and updating a breeze. The [NC] part at the end means "No Case", or "case-insensitive"; more on the switches, later.

Folks can link to whatever.htm or whatever.php, but they always get whatever.php in their browser, and this works even if whatever.htm doesn't exist! But I'm straying..

As it stands, it's a bit tricky; folks will still have whatever.htm in their browser address bar, and will still keep bookmarking your old .htm URL's. Search engines, too, will keep on indexing your links as .htm, some have even argued that serving up the same content from two different places could have you penalized by the search engines. This may or not bother you, but if it does, mod_rewrite can do some more magic..

this will do a "real" external redirection:
Options +FollowSymlinks
RewriteEngine on
RewriteRule ^(.+).htm$ http://corz.org/$1.php [R,NC]

This time we instruct mod_rewrite to do a proper external rewrite, aka, "redirection". Now, instead of just background rewriting on-the-fly, the user's browser is physically redirected to a new URI, and whatever.php appears in their browser's address bar - search engines and other spidering entities will automatically update their links to the .php versions; everyone wins. You can take your time with the updating, too.

Note: if you use [R] alone, it defaults to sending an HTTP "MOVED TEMPORARILY" redirection, aka, "302". But you can send other codes, like so..

this performs the exact same as the previous example RewriteRule.
RewriteRule ^(.+).htm$ http://corz.org/$1.php [R=302,NC]

Okay, I sent the exact same code, but I didn't have to. For details of the many 30* response codes you can send, see here. Most people seem to want to send 301, aka, "MOVED PERMENENTLY".

Note: if you add an "L" flag to the mix; meaning "Last Rule", e.g. [R=302,NC,L]; Apache will stop processing rules for this request at that point, which may or may not be what you want. Either way, it's useful to know.
 

 

not-so-simple rewriting ... flat links and more

You may have noticed, the above examples use regular expression to match variables. What that simply means is.. match the part inside (.+) and use it to construct "$1" in the new URL. In other words, (.+) = $1 you could have multiple (.+) parts and for each, mod_rewrite automatically creates a matching $1, $2, $3, etc, in your target (aka. 'substitution') URL. This facility enables us to do all sorts of tricks, and the most common of those, is the creation of "flat links"..

Even a cute short link like http://mysite/grab?file=my.zip is too ugly for some people, and nothing less than a true old-school solid domain/path/flat/link will do. Fortunately, mod_rewrite makes it easy to convert URLs with query strings and multiple variables into exactly this, something like..

a more complex rewrite rule:
Options +FollowSymlinks
RewriteEngine on
RewriteRule ^files/([^/]+)/([^/]+).zip /download.php?section=$1&file=$2 [NC]

would allow you to present this link as..

  http://mysite/files/games/hoopy.zip

and in the background have that transparently translated, server-side, to..

  http://mysite/download.php?section=games&file=hoopy

which some script could process. You see, many search engines simply don't follow our ?generated=links, so if you create generating pages, this is useful. However, it's only the dumb search engines that can't handle these kinds of links; we have to ask ourselves.. do we really want to be listed by the dumb search engines? Google will handle a good few parameters in your URL without any problems, and the (hungry hungry) msn-bot stops at nothing to get that page, sometimes again and again and again…

I personally feel it's the search engines that should strive to keep up with modern web technologies, in other words; we shouldn't have to dumb-down for them. But that's just my opinion. Many users will prefer /files/games/hoopy.zip to /download.php?section=games&file=hoopy but I don't mind either way. As someone pointed out to me recently, presenting links as standard/flat/paths means you're less likely to get folks doing typos in typed URL's, so something like..

an even more complex rewrite rule:
Options +FollowSymlinks
RewriteEngine on
RewriteRule ^blog/([0-9]+)-([a-z]+) http://corz.org/blog/index.php?archive=$1-$2 [NC]

would be a neat trick, enabling anyone to access my blog archives by doing..

 http://corz.org/blog/2003-nov

in their browser, and have it automagically transformed server-side into..

 http://corz.org/blog/index.php?archive=2003-nov

which corzblog would understand. It's easy to see that with a little imagination, and a basic understanding of posix regular expression, you can perform some highly cool URL manipulations.

Here's the very basics of regexp (expanded from the Apache mod_rewritedocumentation)..
 

Escaping:

	char escape that particular char

		For instance to specify special characters.. [].() etc.

	Text:

	.             Any single character  (on its own = the entire URI)
	[chars]       Character class: One of following chars
	[^chars]      Character class: None of following chars
	text1|text2   Alternative: text1 or text2 (i.e. "or")

		e.g. [^/] matches any character except /
			 (foo|bar).html matches foo.html and bar.html

	Quantifiers:

	? 0 or 1 of the preceding text
	* 0 or N of the preceding text  (hungry)
	+ 1 or N of the preceding text

		e.g. (.+).html? matches foo.htm and foo.html
			 (foo)?bar.html matches bar.html and foobar.html

	Grouping:

	(text)  Grouping of text

		Either to set the borders of an alternative or
		for making backreferences where the nthe group can 
		be used on the target of a RewriteRule with $n

		e.g.  ^(.*).html foo.php?bar=$1

	Anchors:

	^    Start of line anchor
	$    End   of line anchor

		An anchor explicitly states that the character right next to it MUST 
		be either the very first character ("^"), or the very last character ("$")
		of the URI string to match against the pattern, e.g.. 
		
		^foo(.*) matches foo and foobar but not eggfoo
		(.*)l$ matches fool and cool, but not foo

shortening URLs

One common use of mod_rewrite is to shorten URL's. Shorter URL's are easier to remember and, of course, easier to type. An example..

beware the regular expression:
Options +FollowSymlinks
RewriteEngine On
RewriteRule ^grab /public/files/download/download.php

this rule would transform this user's URL..

  http://mysite/grab?file=my.zip

server-side, into..

  http://mysite/public/files/download/download.php?file=my.zip

which is a wee trick I use for my distro machine, among other things. everyone likes short URL's, and so will you; using this technique, you can move /public/files/download/ to anywhere else in your site, and all the old links still work fine; simply alter your .htaccess file to reflect the new location. edit one line, done - nice - means even when stuff is way deep in your site you can have cool links like this.. /trueview/sample.php and this; links which are not only short, but flat..
 

capturing variables

Slapping (.*) onto the end of the request part of a ReWriteRule is just fine when using a simple $_GET variable, but sometimes you want to do trickier things, like capturing particular variables and converting them into other variables in the target URL. Or something else..

When capturing variables, the first thing you need to know about, is the [QSA] flag, which simply tags all the original variables back onto the end of the target url. This may be all you need, and will happen automatically for simple rewrites. The second thing, is %{QUERY_STRING}, an Apache server string we can capture variables from, using simple RewriteCond (aka. conditional ) statements.

RewriteCond is very like doing if...then...do in many programming languages. If a certain condition is true, then do the rewrite that follows..

In the following example, the RewriteCond statement checks that the query string has the foo variable set, and captures its value while it's there. In other words, only requests for /grab that have the variable foo set, will be rewritten, and while we're at it, we'll also switch foo, for bar, just because we can..

capturing a $_GET variable:
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{QUERY_STRING} foo=(.*)
RewriteRule ^grab(.*) /page.php?bar=%1

would translate a link/user's request for..

http://domain.com/grab?foo=bar

server-side, into..

http://domain.com/page.php?bar=bar

Which is to say, the user's browser would be fed page.php (without an [R] flag in the RewriteRule, their address bar would still read /grab?foo=bar). The variable bar would be available to your script, with its value set to bar. This variable has been magically created, by simply using a regular ? in the target of the RewriteRule, and tagging on the first captured backreference, %1.. ?bar=%1

Note how we use the % character, to specify variables captured in RewriteCond statements, aka "Backreferences". This is exactly like using $1 to specify numbered backreferences captured in RewriteRule patterns, except for strings captured inside a RewriteCond statement, we use % instead of $. Simple.

You can use the [QSA] flag in addition to these query string manipulations, merge them. In the next example, the value of foo becomes the directory in the target URL, and the variable file is magically created. The original query string is then tagged back onto the end of the whole thing..
QSA Overkill!
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{QUERY_STRING} foo=(.+)
RewriteRule ^grab/(.*) /%1/index.php?file=$1 [QSA]

So a request for..

http://domain.com/grab/foobar.zip?level=5&foo=bar

is translated, server-side, into..

http://domain.com/bar/index.php?file=foobar.zip&level=5&foo=bar

Depending on your needs, you could even use flat links and dynamic variables together, something like this could be useful..


By the way, you can easily do the opposite, strip a query string from a URL, by simply putting a ? right at the end of the target part. This example does exactly that, whilst leaving the actual URI intact..

just a demo!
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{QUERY_STRING} .
RewriteRule foo.php(.*) /foo.php? [L]
The RewriteCond statement only allows requests that have something in their query string, to be processed by the RewriteRule, or else we'd end up in that hellish place, dread to all mod_rewriters.. the endless loop. RewriteCond is often used like this; as a safety-net.

If all you are after is a /simple/flat/link/ to server-side.php?query=variable translation, use something like this..

cooler access denied

In part one I demonstrated a drop-dead simple mechanism for denying access to particular files and folders. The trouble with this is the way our user gets a 403 "Access Denied" error, which is a bit like having a door slammed in your face. Fortunately, mod_rewrite comes to the rescue again and enables us to do less painful things. One method I often employ is to redirect the user to the parent folder..

they go "huh?.. ahhh!"
# send them up!
Options +FollowSymlinks
RewriteEngine on
RewriteRule ^(.*)$ ../ [NC]

It works great, though it can be a wee bit tricky with the URLs, and you may prefer to use a harder location, which avoids potential issues in indexed directories, where folks can get in a loop..

they go damn! Oh!
# send them exactly there!
Options +FollowSymlinks
RewriteEngine on
RewriteRule ^(.*)$ /comms/hardware/router/ [NC]

Sometimes you'll only want to deny access to most of the files in the directory, but allow access to maybe one or two files, or file types, easy..
deny with style!
# users can load only "special.zip", and the css and js files.
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !^(.+).css$
RewriteCond %{REQUEST_FILENAME} !^(.+).js$
RewriteCond %{REQUEST_FILENAME} !special.zip$
RewriteRule ^(.+)$ /chat/ [NC]

Here we take the whole thing a stage further. Users can access .css (stylesheet) and Javascript files without problem, and also the file called "special.zip", but requests for any other file types are immediately redirected back up to the main "/chat/" directory. You can add as many types as you need. You could also bundle the filetypes into one line using | (or) syntax, though individual lines are perhaps clearer.

Here's what's currently cooking inside my /inc/ directory..

all-in-one control..
RewriteEngine on
Options +FollowSymlinks
# allow access with no restrictions to local machine at 192.168.1.3
RewriteCond %{REMOTE_ADDR} !192.168.1.3
# allow access to all .css and .js in sub-directories..
RewriteCond %{REQUEST_URI} !.css$
RewriteCond %{REQUEST_URI} !.js$
# allow access to the files inside img/, but not a directory listing..
RewriteCond %{REQUEST_URI} !img/(.*).
# allow access to these particular files...
RewriteCond %{REQUEST_URI} !comments.php$
RewriteCond %{REQUEST_URI} !corzmail.php$
RewriteCond %{REQUEST_URI} !digitrack.php$
RewriteCond %{REQUEST_URI} !gd-verify.php$
RewriteCond %{REQUEST_URI} !post-dumper.php$
RewriteCond %{REQUEST_URI} !print.php$
RewriteCond %{REQUEST_URI} !source-dump.php$
RewriteCond %{REQUEST_URI} !textview.php$
RewriteRule ^(.*)$ / [R,NC,L]
 

Ban User Agents, referrers, script-kiddies and more..

There are many valid reasons to ban a particular request from sucking up your site's resources; resources that could be better served to valid, interested users. It might be some cross-site attack script, or inward link from a place you don't want to be associated with, or perhaps a web sucker or download manager, whatever; .htaccess + mod_rewrite provides ways to protect your content from unwanted "guests".

The basic formula is standard if-then logic: if the request meets a particular CONDITION, then REWRITE the request. The "conditions" can be many things; perhaps the referrer header sent by their browser (the site they came from), or the page they asked for, or a particular query parameter, or the type of client (browser, etc.) they are using, or any other piece of information Apache has attached to the request. Here's an example which will deny access to "Teleport Pro", a download manager which is known to suck, hard..

Who need's a local copy, when I'm right here?..
RewriteCond %{HTTP_USER_AGENT} ^Teleport Pro [NC]
RewriteRule . abuse.txt [L]

It's your site, and just like your home, you have every right to exert some control over who gets in. You may have a huge list of user agents you'd rather not have eating your bandwidth; so use the [OR] flag, and line 'em up..

A little garlic for the net vampires..
RewriteCond %{HTTP_USER_AGENT} ^BackWeb [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^Bandit [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^BatchFTP [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^BecomeBot [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^BlackWidow [NC,OR]
# etc..
RewriteCond %{HTTP_USER_AGENT} ^Net Vampire [NC]
RewriteRule . abuse.txt [L]

This forms the basis of what often becomes a HUGE list of ban-lines. Remember, we aren't limited to user agent strings..

Suckers, h4x0rz, kiddies, cross-site scripters and more.. Bye now!
# why not come visit me directly?
RewriteCond %{HTTP_REFERER} .opendirviewer. [NC,OR]
# this prevents stoopid cross-site discovery attacks..
RewriteCond %{THE_REQUEST} ? HTTP/ [NC,OR]
# please stop pretending to be the Googlebot..
RewriteCond %{HTTP_REFERER} users.skynet.be.* [NC,OR]
# really, we need a special page for these twats..
RewriteCond %{QUERY_STRING} =|w| [NC,OR]
RewriteCond %{THE_REQUEST} etc/passwd [NC,OR]
RewriteCond %{REQUEST_URI} owssvr.dll [NC,OR]
# you can probably work these out..
RewriteCond %{QUERY_STRING} =|w| [NC,OR]
RewriteCond %{THE_REQUEST} /* HTTP/ [NC,OR]
# etc..
RewriteCond %{HTTP_USER_AGENT} Sucker [NC]
RewriteRule . abuse.txt [L]

Fortunately, mod_rewrite can parse enormous lists of ban-lines in milliseconds, so feel free to be as specific and comprehensive as required.

As ever, thorough testing is strongly recommended. Simply send requests matching your conditions and see what happens. And importantly; normal requests, too. Firefox, Opera, Konqueror, and most other decent browsers, allow you to alter the user agent string; though you would quickly find the process tedious in a testing situation. Far better to use some tool better designed to send fake HTTP requests..

It's not too difficult to mock up a web request on the command-line with any-old user agent using a scripting language like php or Perl, if you have these things available (read: most Linux/UNIX/BSD/etc. as well as many other OS). Many examples exist online. In fact, you could quickly create a suite of tests, designed to interrogate all your rewrite rules, with results logging and much more, if required. cURL is always useful for jobs like this, so long as you don't add a cURL ban-line!

On a Windows desktop, Sam Spade can send a single spoofed request with a couple of clicks, along with a stack of similarly handy tricks, and regularly proves itself invaluable.
 

Don't let just anyone  hammer your site!

While I'm on the subject of abusive web clients, you will probably have noticed that many clients (bots, spiders, automated suckers and such) like to disguise their user agent information, in fact any information, in an attempt to bring your site to its knees, hammering your pages umpteen times per second in the process. Not good.

If you are interested in a way to defeat hammering web clients regardless of who they pretend to be or whether or not they accept cookies or any such malarkey, protecting your valuable server resources for genuine clients, check out: Anti-Hammer. It's free.
 
 

prevent hot-linking

Believe it or not, there are some webmasters who, rather than coming up with their own content will steal yours. Really! Even worse, they won't even bother to copy to their own server to serve it up, they'll just link to your content!  no, it's true, in fact, it used to be incredibly common. These days most people like to prevent this sort of thing, and .htaccess is one of the best ways to do it.

This is one of those directives where the mileage variables are at their limits, but something like this works fine for me..

how DARE they!
Options +FollowSymlinks
# no hot-linking
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www.)?corz.org/ [NC]
RewriteCond %{REQUEST_URI} !hotlink.(gif|png) [NC]
RewriteRule .*.(gif|jpg|png)$ http://corz.org/img/hotlink.png [NC]

 

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