Apache HTTP Server Version 2.4
Description: | Provides for mapping different parts of the host filesystem in the document tree and for URL redirection |
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Status: | Base |
Module Identifier: | alias_module |
Source File: | mod_alias.c |
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.
When the Alias
,
ScriptAlias
and
Redirect
directives are used
within a <Location>
or <LocationMatch>
section, expression syntax can be used
to manipulate the destination path or URL.
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
.
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.
When the Alias
,
ScriptAlias
and
Redirect
directives are used
within a <Location>
or <LocationMatch>
section, these directives will take precedence over any globally
defined Alias
,
ScriptAlias
and
Redirect
directives.
Description: | Maps URLs to filesystem locations |
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Syntax: | Alias [URL-path]
file-path|directory-path |
Context: | server config, virtual host, directory |
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.
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.
Alias "/image" "/ftp/pub/image" <Directory "/ftp/pub/image"> Require all granted </Directory>
Any number slashes in the URL-path parameter matches any number of slashes in the requested URL-path.
If the Alias
directive is used within a
<Location>
or <LocationMatch>
section the URL-path is omitted, and the file-path is interpreted
using expression syntax.
This syntax is available in Apache 2.4.19 and later.
<Location "/image"> Alias "/ftp/pub/image" </Location> <LocationMatch "/error/(?<NUMBER>[0-9]+)"> Alias "/usr/local/apache/errors/%{env:MATCH_NUMBER}.html" </LocationMatch>
Note that when the AliasPreservePath
directive is on, the full path is mapped to the destination. When
the directive is off, all URLs are mapped to the single target
URL.
# /files/foo and /files/bar mapped to /ftp/pub/files/foo and /ftp/pub/files/bar <Location "/files"> AliasPreservePath on Alias "/ftp/pub/files" </Location> # /errors/foo and /errors/bar mapped to /var/www/errors.html <Location "/errors"> AliasPreservePath off Alias "/var/www/errors.html" </Location>
Description: | Maps URLs to filesystem locations using regular expressions |
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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$2"
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.
Description: | Map the full path after the alias in a location. |
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Syntax: | AliasPreservePath OFF|ON |
Default: | AliasPreservePath OFF |
Context: | server config, virtual host, directory |
Status: | Base |
Module: | mod_alias |
Compatibility: | 2.4.58 and later |
When using the two parameter version of the
Alias
directive, the full path after the alias
is preserved. When using the one parameter version of the
Alias
directive inside a
Location
directive, the full path is dropped,
and all URLs are mapped to the target expression.
To make the one parameter version of the
Alias
directive preserve paths in the same way
that the two parameter version of the Alias
directive, enable this setting.
Description: | Sends an external redirect asking the client to fetch a different URL |
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Syntax: | Redirect [status] [URL-path]
URL |
Context: | server config, virtual host, directory, .htaccess |
Override: | FileInfo |
Status: | Base |
Module: | mod_alias |
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 may be either an absolute URL beginning with a scheme and hostname, or a URL-path beginning with a slash. In this latter 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.
# Redirect to a URL on a different host Redirect "/service" "http://foo2.example.com/service" # Redirect to a URL on the same host Redirect "/one" "/two"
If the client requests http://example.com/service/foo.txt
,
it will be told to access
http://foo2.example.com/service/foo.txt
instead. This includes requests with GET
parameters, such as
http://example.com/service/foo.pl?q=23&a=42
,
it will be redirected to
http://foo2.example.com/service/foo.pl?q=23&a=42
.
Note that POST
s will be discarded.
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 the expression syntax, omit the URL-path
argument as described below. Alternatively, for matching using regular
expressions, see the RedirectMatch
directive.
Redirect
directives take precedence over Alias
and ScriptAlias
directives, irrespective of their ordering in the configuration
file. Redirect
directives inside a Location take
precedence over Redirect
and Alias
directives with an URL-path.
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:
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.
If the status is not between 300 and 399, the
URL argument must be omitted. The status must be a valid
HTTP status code, known to the Apache HTTP Server (see the function
send_error_response
in http_protocol.c).
Redirect permanent "/one" "http://example.com/two" Redirect 303 "/three" "http://example.com/other"
If the Redirect
directive is used within a
<Location>
or <LocationMatch>
section with the URL-path omitted, then the URL parameter
will be interpreted using expression syntax.
This syntax is available in Apache 2.4.19 and later.
<Location "/one"> Redirect permanent "http://example.com/two" </Location> <Location "/three"> Redirect 303 "http://example.com/other" </Location> <LocationMatch "/error/(?<NUMBER>[0-9]+)"> Redirect permanent "http://example.com/errors/%{env:MATCH_NUMBER}.html" </LocationMatch>
Description: | Sends an external redirect based on a regular expression match of the current URL |
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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://other.example.com$1.jpg"
The considerations related to the difference between
Alias
and
AliasMatch
also apply to the difference between
Redirect
and
RedirectMatch
.
See AliasMatch
for
details.
Description: | Sends an external permanent redirect asking the client to fetch a different URL |
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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
.
Description: | Allows relative redirect targets. |
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Syntax: | RedirectRelative On|Off |
Default: | RedirectRelative Off |
Context: | server config, virtual host, directory |
Status: | Base |
Module: | mod_alias |
Compatibility: | 2.4.58 and later |
By default, if the target URL of a Redirect
directive is a relative URL beginning with a '/' character, the server
converts it to an absolute URL before responding to the client. By
setting RedirectRelative
to the value "On",
the relative URL is presented to the client directly.
Description: | Sends an external temporary redirect asking the client to fetch a different URL |
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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
.
Description: | Maps a URL to a filesystem location and designates the target as a CGI script |
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Syntax: | ScriptAlias [URL-path]
file-path|directory-path |
Context: | server config, virtual host, directory |
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.
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>
ScriptAlias
can also be used in conjunction with
a script or handler you have. For example:
ScriptAlias "/cgi-bin/" "/web/cgi-handler.pl"
In this scenario all files requested in /cgi-bin/
will be
handled by the file you have configured, this allows you to use your own custom
handler. You may want to use this as a wrapper for CGI so that you can add
content, or some other bespoke action.
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>This is necessary since multiple URL-paths can map to the same filesystem location, potentially bypassing the
ScriptAlias
and revealing the source code
of the CGI scripts if they are not restricted by a
Directory
section.If the ScriptAlias
directive is used within
a <Location>
or <LocationMatch>
section with the URL-path omitted, then the URL parameter will be
interpreted using expression syntax.
This syntax is available in Apache 2.4.19 and later.
<Location "/cgi-bin"> ScriptAlias "/web/cgi-bin/" </Location> <LocationMatch "/cgi-bin/errors/(?<NUMBER>[0-9]+)"> ScriptAlias "/web/cgi-bin/errors/%{env:MATCH_NUMBER}.cgi" </LocationMatch>
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.