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<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX This file is generated from xml source: DO NOT EDIT XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX --><title>Environment Variables in Apache - Apache HTTP Server</title><link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /><link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link href="./images/favicon.ico" rel="shortcut icon" /></head><body id="manual-page"><div id="page-header"><p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p><p class="apache">Apache HTTP Server Version 2.0</p><img alt="" src="./images/feather.gif" /></div><div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div><div id="path"><a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>Environment Variables in Apache</h1><div class="toplang"><p><span>Available Languages: </span><a href="./en/env.html" title="English"> en </a> |<a href="./es/env.html" hreflang="es" rel="alternate" title="Espa駉l"> es </a> |<a href="./fr/env.html" hreflang="fr" rel="alternate" title="Fran鏰is"> fr </a> |<a href="./ja/env.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |<a href="./ko/env.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p></div> <p>The Apache HTTP Server provides a mechanism for storing information in named variables that are called <em>environment variables</em>. This information can be used to control various operations such as logging or access control. The variables are also used as a mechanism to communicate with external programs such as CGI scripts. This document discusses different ways to manipulate and use these variables.</p> <p>Although these variables are referred to as <em>environment variables</em>, they are not the same as the environment variables controlled by the underlying operating system. Instead, these variables are stored and manipulated in an internal Apache structure. They only become actual operating system environment variables when they are provided to CGI scripts and Server Side Include scripts. If you wish to manipulate the operating system environment under which the server itself runs, you must use the standard environment manipulation mechanisms provided by your operating system shell.</p> </div><div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#setting">Setting Environment Variables</a></li><li><img alt="" src="./images/down.gif" /> <a href="#using">Using Environment Variables</a></li><li><img alt="" src="./images/down.gif" /> <a href="#special">Special Purpose Environment Variables</a></li><li><img alt="" src="./images/down.gif" /> <a href="#examples">Examples</a></li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div><div class="section"><h2><a name="setting" id="setting">Setting Environment Variables</a></h2> <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_env.html">mod_env</a></code></li><li><code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code></li><li><code class="module"><a href="./mod/mod_setenvif.html">mod_setenvif</a></code></li><li><code class="module"><a href="./mod/mod_unique_id.html">mod_unique_id</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_setenvif.html#browsermatch">BrowserMatch</a></code></li><li><code class="directive"><a href="./mod/mod_setenvif.html#browsermatchnocase">BrowserMatchNoCase</a></code></li><li><code class="directive"><a href="./mod/mod_env.html#passenv">PassEnv</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewriterule">RewriteRule</a></code></li><li><code class="directive"><a href="./mod/mod_env.html#setenv">SetEnv</a></code></li><li><code class="directive"><a href="./mod/mod_setenvif.html#setenvif">SetEnvIf</a></code></li><li><code class="directive"><a href="./mod/mod_setenvif.html#setenvifnocase">SetEnvIfNoCase</a></code></li><li><code class="directive"><a href="./mod/mod_env.html#unsetenv">UnsetEnv</a></code></li></ul></td></tr></table> <h3><a name="basic-manipulation" id="basic-manipulation">Basic Environment Manipulation</a></h3> <p>The most basic way to set an environment variable in Apache is using the unconditional <code class="directive"><a href="./mod/mod_env.html#setenv">SetEnv</a></code> directive. Variables may also be passed from the environment of the shell which started the server using the <code class="directive"><a href="./mod/mod_env.html#passenv">PassEnv</a></code> directive.</p> <h3><a name="conditional" id="conditional">Conditional Per-Request Settings</a></h3> <p>For additional flexibility, the directives provided by mod_setenvif allow environment variables to be set on a per-request basis, conditional on characteristics of particular requests. For example, a variable could be set only when a specific browser (User-Agent) is making a request, or only when a specific Referer [sic] header is found. Even more flexibility is available through the mod_rewrite's <code class="directive"><a href="./mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> which uses the <code>[E=...]</code> option to set environment variables.</p> <h3><a name="unique-identifiers" id="unique-identifiers">Unique Identifiers</a></h3> <p>Finally, mod_unique_id sets the environment variable <code>UNIQUE_ID</code> for each request to a value which is guaranteed to be unique across "all" requests under very specific conditions.</p> <h3><a name="standard-cgi" id="standard-cgi">Standard CGI Variables</a></h3> <p>In addition to all environment variables set within the Apache configuration and passed from the shell, CGI scripts and SSI pages are provided with a set of environment variables containing meta-information about the request as required by the <a href="http://cgi-spec.golux.com/">CGI specification</a>.</p> <h3><a name="caveats" id="caveats">Some Caveats</a></h3> <ul> <li>It is not possible to override or change the standard CGI variables using the environment manipulation directives.</li> <li>When <code class="program"><a href="./programs/suexec.html">suexec</a></code> is used to launch CGI scripts, the environment will be cleaned down to a set of <em>safe</em> variables before CGI scripts are launched. The list of <em>safe</em> variables is defined at compile-time in <code>suexec.c</code>.</li> <li>For portability reasons, the names of environment variables may contain only letters, numbers, and the underscore character. In addition, the first character may not be a number. Characters which do not match this restriction will be replaced by an underscore when passed to CGI scripts and SSI pages.</li> </ul> </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div><div class="section"><h2><a name="using" id="using">Using Environment Variables</a></h2> <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_access.html">mod_access</a></code></li><li><code class="module"><a href="./mod/mod_cgi.html">mod_cgi</a></code></li><li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code></li><li><code class="module"><a href="./mod/mod_headers.html">mod_headers</a></code></li><li><code class="module"><a href="./mod/mod_include.html">mod_include</a></code></li><li><code class="module"><a href="./mod/mod_log_config.html">mod_log_config</a></code></li><li><code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_access.html#allow">Allow</a></code></li><li><code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code></li><li><code class="directive"><a href="./mod/mod_access.html#deny">Deny</a></code></li><li><code class="directive"><a href="./mod/mod_ext_filter.html#extfilterdefine">ExtFilterDefine</a></code></li><li><code class="directive"><a href="./mod/mod_headers.html#header">Header</a></code></li><li><code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewritecond">RewriteCond</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewriterule">RewriteRule</a></code></li></ul></td></tr></table> <h3><a name="cgi-scripts" id="cgi-scripts">CGI Scripts</a></h3> <p>One of the primary uses of environment variables is to communicate information to CGI scripts. As discussed above, the environment passed to CGI scripts includes standard meta-information about the request in addition to any variables set within the Apache configuration. For more details, see the <a href="howto/cgi.html">CGI tutorial</a>.</p> <h3><a name="ssi-pages" id="ssi-pages">SSI Pages</a></h3> <p>Server-parsed (SSI) documents processed by mod_include's <code>INCLUDES</code> filter can print environment variables using the <code>echo</code> element, and can use environment variables in flow control elements to makes parts of a page conditional on characteristics of a request. Apache also provides SSI pages with the standard CGI environment variables as discussed above. For more details, see the <a href="howto/ssi.html">SSI tutorial</a>.</p> <h3><a name="access-control" id="access-control">Access Control</a></h3> <p>Access to the server can be controlled based on the value of environment variables using the <code>allow from env=</code> and <code>deny from env=</code> directives. In combination with <code class="directive"><a href="./mod/mod_setenvif.html#setenvif">SetEnvIf</a></code>, this allows for flexible control of access to the server based on characteristics of the client. For example, you can use these directives to deny access to a particular browser (User-Agent). </p> <h3><a name="logging" id="logging">Conditional Logging</a></h3> <p>Environment variables can be logged in the access log using the <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code> option <code>%e</code>. In addition, the decision on whether or not to log requests can be made based on the status of environment variables using the conditional form of the <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> directive. In combination with <code class="directive"><a href="./mod/mod_setenvif.html#setenvif">SetEnvIf</a></code> this allows for flexible control of which requests are logged. For example, you can choose not to log requests for filenames ending in <code>gif</code>, or you can choose to only log requests from clients which are outside your subnet.</p> <h3><a name="response-headers" id="response-headers">Conditional Response Headers</a></h3> <p>The <code class="directive"><a href="./mod/mod_headers.html#header">Header</a></code> directive can use the presence or absence of an environment variable to determine whether or not a certain HTTP header will be placed in the response to the client. This allows, for example, a certain response header to be sent only if a corresponding header is received in the request from the client.</p> <h3><a name="external-filter" id="external-filter">External Filter Activation</a></h3> <p>External filters configured by <code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code> using the <code class="directive"><a href="./mod/mod_ext_filter.html#extfilterdefine">ExtFilterDefine</a></code> directive can by activated conditional on an environment variable using the <code>disableenv=</code> and <code>enableenv=</code> options.</p> ⌨️ 快捷键说明
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