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Apache > HTTP Server > Documentation > Version 2.5 > Modules

Apache Module mod_substitute

Available Languages:  en 

Description:Perform search and replace operations on response bodies
Status:Extension
Module Identifier:substitute_module
Source File:mod_substitute.c

Summary

mod_substitute provides a mechanism to perform both regular expression and fixed string substitutions on response bodies.

Directives

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Substitute Directive

Description:Pattern to filter the response content
Syntax:Substitute s/pattern/substitution/[infq]
Context:directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_substitute

The Substitute directive specifies a search and replace pattern to apply to the response body.

The meaning of the pattern can be modified by using any combination of these flags:

i
Perform a case-insensitive match.
n
By default the pattern is treated as a regular expression. Using the n flag forces the pattern to be treated as a fixed string.
f
The f flag causes mod_substitute to flatten the result of a substitution allowing for later substitutions to take place on the boundary of this one. This is the default.
q
The q flag causes mod_substitute to not flatten the buckets after each substitution. This can result in much faster response and a decrease in memory utilization, but should only be used if there is no possibility that the result of one substitution will ever match a pattern or regex of a subsequent one.

Example

<Location />
    AddOutputFilterByType SUBSTITUTE text/html
    Substitute s/foo/bar/ni
</Location>

If either the pattern or the substitution contain a slash character then an alternative delimiter should be used:

Example of using an alternate delimiter

<Location />
    AddOutputFilterByType SUBSTITUTE text/html
    Substitute "s|<BR */?>|<br />|i"
</Location>

Backreferences can be used in the comparison and in the substitution, when regular expressions are used, as illustrated in the following example:

Example of using backreferences and captures

<Location />
    AddOutputFilterByType SUBSTITUTE text/html
    # "foo=k,bar=k" -> "foo/bar=k" 
    Substitute "s|foo=(\w+),bar=\1|foo/bar=$1"
</Location>

A common use scenario for mod_substitute is the situation in which a front-end server proxies requests to a back-end server which returns HTML with hard-coded embedded URLs that refer to the back-end server. These URLs don't work for the end-user, since the back-end server is unreachable.

In this case, mod_substutite can be used to rewrite those URLs into something that will work from the front end:

Rewriting URLs embedded in proxied content

ProxyPass /blog/ http://internal.blog.example.com
ProxyPassReverse /blog/ http://internal.blog.example.com/

Substitute "s|http://internal.blog.example.com/|http://www.example.com/blog/|i"

ProxyPassReverse modifies any Location (redirect) headers that are sent by the back-end server, and, in this example, Substitute takes care of the rest of the problem by fixing up the HTML response as well.

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SubstituteMaxLineLength Directive

Description:Set the maximum line size
Syntax:SubstituteMaxLineLength bytes(b|B|k|K|m|M|g|G)
Default:SubstituteMaxLineLength 1m
Context:directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_substitute
Compatibility:Available in httpd 2.4.11 and later

The maximum line size handled by mod_substitute is limited to restrict memory use. The limit can be configured using SubstituteMaxLineLength. The value can be given as the number of bytes and can be suffixed with a single letter b, B, k, K, m, M, g, G to provide the size in bytes, kilobytes, megabytes or gigabytes respectively.

Example

<Location />
    AddOutputFilterByType SUBSTITUTE text/html
    SubstituteMaxLineLength 10m
    Substitute s/foo/bar/ni
</Location>

Available Languages:  en 

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Comments

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