Apache HTTP Server Version 2.2
Apache Module mod_alias
| Description: | Provides for mapping different parts of the host filesystem in the document tree and for URL redirection |
|---|---|
| Status: | Base |
| Module Identifier: | alias_module |
| Source File: | mod_alias.c |
Summary
The directives contained in this module allow for manipulation
and control of URLs as requests arrive at the server. The
Alias and ScriptAlias directives are used to
map between URLs and filesystem paths. This allows for content
which is not directly under the DocumentRoot served as part of the web
document tree. The ScriptAlias directive has the
additional effect of marking the target directory as containing
only CGI scripts.
The Redirect
directives are used to instruct clients to make a new request with
a different URL. They are often used when a resource has moved to
a new location.
mod_alias is designed to handle simple URL
manipulation tasks. For more complicated tasks such as
manipulating the query string, use the tools provided by
mod_rewrite.
Order of Processing
Aliases and Redirects occurring in different contexts are processed
like other directives according to standard merging rules. But when multiple
Aliases or Redirects occur in the same context (for example, in the
same <VirtualHost>
section) they are processed in a particular order.
First, all Redirects are processed before Aliases are processed,
and therefore a request that matches a Redirect or RedirectMatch will never have Aliases
applied. Second, the Aliases and Redirects are processed in the order
they appear in the configuration files, with the first match taking
precedence.
For this reason, when two or more of these directives apply to the same sub-path, you must list the most specific path first in order for all the directives to have an effect. For example, the following configuration will work as expected:
Alias /foo/bar /baz
Alias /foo /gaq
But if the above two directives were reversed in order, the
/foo Alias
would always match before the /foo/bar Alias, so the latter directive would be
ignored.
Alias Directive
| Description: | Maps URLs to filesystem locations |
|---|---|
| Syntax: | Alias URL-path
file-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
The Alias directive allows documents to
be stored in the local filesystem other than under the
DocumentRoot. URLs with a
(%-decoded) path beginning with URL-path will be mapped
to local files beginning with directory-path. The
URL-path is case-sensitive, even on case-insensitive
file systems.
Example:
Alias /image /ftp/pub/image
A request for http://example.com/image/foo.gif would cause
the server to return the file /ftp/pub/image/foo.gif. Only
complete path segments are matched, so the above alias would not match a
request for http://example.com/imagefoo.gif. For more complex
matching using regular expressions, see the AliasMatch directive.
Note that if you include a trailing / on the URL-path then the server will require a trailing / in order to expand the alias. That is, if you use
Alias /icons/ /usr/local/apache/icons/
then the URL /icons will not be aliased, as it lacks
that trailing /. Likewise, if you omit the slash on the
URL-path then you must also omit it from the
file-path.
Note that you may need to specify additional <Directory> sections which
cover the destination of aliases. Aliasing occurs before
<Directory> sections
are checked, so only the destination of aliases are affected.
(Note however <Location>
sections are run through once before aliases are performed, so
they will apply.)
In particular, if you are creating an Alias to a
directory outside of your DocumentRoot, you may need to explicitly
permit access to the target directory.
Example:
Alias /image /ftp/pub/image
<Directory /ftp/pub/image>
Order allow,deny
Allow from all
</Directory>
Any number of slashes in the URL-path parameter matches any number of slashes in the requested URL-path.
AliasMatch Directive
| Description: | Maps URLs to filesystem locations using regular expressions |
|---|---|
| Syntax: | AliasMatch regex
file-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
This directive is equivalent to Alias, but makes use of
regular expressions,
instead of simple prefix matching. The
supplied regular expression is matched against the URL-path, and
if it matches, the server will substitute any parenthesized
matches into the given string and use it as a filename. For
example, to activate the /icons directory, one might
use:
AliasMatch ^/icons(.*) /usr/local/apache/icons$1
The full range of regular expression power is available. For example, it is possible to construct an alias with case-insensitive matching of the URL-path:
AliasMatch (?i)^/image(.*) /ftp/pub/image$1
One subtle difference
between Alias
and AliasMatch is
that Alias will
automatically copy any additional part of the URI, past the part
that matched, onto the end of the file path on the right side,
while AliasMatch will
not. This means that in almost all cases, you will want the
regular expression to match the entire request URI from beginning
to end, and to use substitution on the right side.
In other words, just changing
Alias to
AliasMatch will not
have the same effect. At a minimum, you need to
add ^ to the beginning of the regular expression
and add (.*)$ to the end, and add $1 to
the end of the replacement.
For example, suppose you want to replace this with AliasMatch:
Alias /image/ /ftp/pub/image/
This is NOT equivalent - don't do this! This will send all requests that have /image/ anywhere in them to /ftp/pub/image/:
AliasMatch /image/ /ftp/pub/image/
This is what you need to get the same effect:
AliasMatch ^/image/(.*)$ /ftp/pub/image/$1
Of course, there's no point in
using AliasMatch
where Alias would
work. AliasMatch lets
you do more complicated things. For example, you could
serve different kinds of files from different directories:
AliasMatch ^/image/(.*)\.jpg$ /files/jpg.images/$1.jpg
AliasMatch ^/image/(.*)\.gif$ /files/gif.images/$1.gif
Multiple leading slashes in the requested URL are discarded by the server before directives from this module compares against the requested URL-path.
Redirect Directive
| Description: | Sends an external redirect asking the client to fetch a different URL |
|---|---|
| Syntax: | Redirect [status] URL-path
URL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
| Compatibility: | Support for specifying a URL-path as the final argument was added in Apache HTTP Server 2.2.6 |
The Redirect directive maps an old URL into a new one by asking the client to refetch the resource at the new location.
The old URL-path is a case-sensitive (%-decoded) path beginning with a slash. A relative path is not allowed. The new URL should be an absolute URL beginning with a scheme and hostname. In Apache HTTP Server 2.2.6 and later, a URL-path beginning with a slash may also be used, in which case the scheme and hostname of the current server will be added.
Then any request beginning with URL-path will return a redirect request to the client at the location of the target URL. Additional path information beyond the matched URL-path will be appended to the target URL.
Example:
Redirect /service http://foo2.example.com/service
If the client requests http://example.com/service/foo.txt,
it will be told to access
http://foo2.example.com/service/foo.txt
instead. Only complete path segments are matched, so the above
example would not match a request for
http://example.com/servicefoo.txt. For more complex matching
using regular expressions, see the RedirectMatch directive.
Note
Redirect directives take precedence over Alias and ScriptAlias directives, irrespective of their ordering in the configuration file.
If no status argument is given, the redirect will be "temporary" (HTTP status 302). This indicates to the client that the resource has moved temporarily. The status argument can be used to return other HTTP status codes:
- permanent
- Returns a permanent redirect status (301) indicating that the resource has moved permanently.
- temp
- Returns a temporary redirect status (302). This is the default.
- seeother
- Returns a "See Other" status (303) indicating that the resource has been replaced.
- gone
- Returns a "Gone" status (410) indicating that the resource has been permanently removed. When this status is used the URL argument should be omitted.
Other status codes can be returned by giving the numeric
status code as the value of status. If the status is
between 300 and 399, the URL argument must be present,
otherwise it must be omitted. Note that the status must be
known to the Apache code (see the function
send_error_response in http_protocol.c).
Example:
Redirect permanent /one http://example.com/two
Redirect 303 /three http://example.com/other
RedirectMatch Directive
| Description: | Sends an external redirect based on a regular expression match of the current URL |
|---|---|
| Syntax: | RedirectMatch [status] regex
URL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
This directive is equivalent to Redirect, but makes use of
regular expressions,
instead of simple prefix matching. The
supplied regular expression is matched against the URL-path, and
if it matches, the server will substitute any parenthesized
matches into the given string and use it as a filename. For
example, to redirect all GIF files to like-named JPEG files on
another server, one might use:
RedirectMatch (.*)\.gif$ http://www.anotherserver.com$1.jpg
RedirectPermanent Directive
| Description: | Sends an external permanent redirect asking the client to fetch a different URL |
|---|---|
| Syntax: | RedirectPermanent URL-path URL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
This directive makes the client know that the Redirect is
permanent (status 301). Exactly equivalent to Redirect
permanent.
RedirectTemp Directive
| Description: | Sends an external temporary redirect asking the client to fetch a different URL |
|---|---|
| Syntax: | RedirectTemp URL-path URL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
This directive makes the client know that the Redirect is
only temporary (status 302). Exactly equivalent to
Redirect temp.
ScriptAlias Directive
| Description: | Maps a URL to a filesystem location and designates the target as a CGI script |
|---|---|
| Syntax: | ScriptAlias URL-path
file-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
The ScriptAlias directive has the same
behavior as the Alias
directive, except that in addition it marks the target directory
as containing CGI scripts that will be processed by mod_cgi's cgi-script handler. URLs with a case-sensitive
(%-decoded) path beginning with URL-path will be mapped
to scripts beginning with the second argument, which is a full
pathname in the local filesystem.
Example:
ScriptAlias /cgi-bin/ /web/cgi-bin/
A request for http://example.com/cgi-bin/foo would cause the
server to run the script /web/cgi-bin/foo. This configuration
is essentially equivalent to:
Alias /cgi-bin/ /web/cgi-bin/
<Location /cgi-bin >
SetHandler cgi-script
Options +ExecCGI
</Location>
DocumentRoot in order to
avoid accidentally revealing their source code if the
configuration is ever changed. The
ScriptAlias makes this easy by mapping a
URL and designating CGI scripts at the same time. If you do
choose to place your CGI scripts in a directory already
accessible from the web, do not use
ScriptAlias. Instead, use <Directory>, SetHandler, and Options as in:
<Directory /usr/local/apache2/htdocs/cgi-bin >
SetHandler cgi-script
Options ExecCGI
</Directory>
ScriptAlias and revealing the source code
of the CGI scripts if they are not restricted by a
Directory section.See also
ScriptAliasMatch Directive
| Description: | Maps a URL to a filesystem location using a regular expression and designates the target as a CGI script |
|---|---|
| Syntax: | ScriptAliasMatch regex
file-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
This directive is equivalent to ScriptAlias, but makes use of
regular expressions,
instead of simple prefix matching. The
supplied regular expression is matched against the URL-path,
and if it matches, the server will substitute any parenthesized
matches into the given string and use it as a filename. For
example, to activate the standard /cgi-bin, one
might use:
ScriptAliasMatch ^/cgi-bin(.*) /usr/local/apache/cgi-bin$1
As for AliasMatch, the full range of regular expression power is available. For example, it is possible to construct an alias with case-insensitive matching of the URL-path:
ScriptAliasMatch (?i)^/cgi-bin(.*) /usr/local/apache/cgi-bin$1
The considerations related to the difference between
Alias and
AliasMatch
also apply to the difference between
ScriptAlias and
ScriptAliasMatch.
See AliasMatch for
details.