Apache HTTP Server Version 2.3

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# 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
Compatibility: | Available in Apache HTTP Server 2.2.7 and later

### Summary

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

### Directives

## 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.

Available Languages: en