1 <?xml version="1.0" encoding="ISO-8859-1"?>
2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
3 <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
5 This file is generated from xml source: DO NOT EDIT
6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
8 <title>Apache Tutorial: Dynamic Content with CGI - Apache HTTP Server</title>
9 <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
10 <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
11 <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
12 <link href="../images/favicon.ico" rel="shortcut icon" /></head>
13 <body id="manual-page"><div id="page-header">
14 <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>
15 <p class="apache">Apache HTTP Server Version 2.0</p>
16 <img alt="" src="../images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
19 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">How-To / Tutorials</a></div><div id="page-content"><div id="preamble"><h1>Apache Tutorial: Dynamic Content with CGI</h1>
21 <p><span>Available Languages: </span><a href="../en/howto/cgi.html" title="English"> en </a> |
22 <a href="../ja/howto/cgi.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
23 <a href="../ko/howto/cgi.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
26 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#intro">Introduction</a></li>
27 <li><img alt="" src="../images/down.gif" /> <a href="#configuring">Configuring Apache to permit CGI</a></li>
28 <li><img alt="" src="../images/down.gif" /> <a href="#writing">Writing a CGI program</a></li>
29 <li><img alt="" src="../images/down.gif" /> <a href="#troubleshoot">But it's still not working!</a></li>
30 <li><img alt="" src="../images/down.gif" /> <a href="#behindscenes">What's going on behind the scenes?</a></li>
31 <li><img alt="" src="../images/down.gif" /> <a href="#libraries">CGI modules/libraries</a></li>
32 <li><img alt="" src="../images/down.gif" /> <a href="#moreinfo">For more information</a></li>
34 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
36 <h2><a name="intro" id="intro">Introduction</a></h2>
39 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code></li><li><code class="module"><a href="../mod/mod_cgi.html">mod_cgi</a></code></li></ul></td><td><ul><li><code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code></li><li><code class="directive"><a href="../mod/core.html#options">Options</a></code></li><li><code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code></li></ul></td></tr></table>
41 <p>The CGI (Common Gateway Interface) defines a way for a web
42 server to interact with external content-generating programs,
43 which are often referred to as CGI programs or CGI scripts. It
44 is the simplest, and most common, way to put dynamic content on
45 your web site. This document will be an introduction to setting
46 up CGI on your Apache web server, and getting started writing
48 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
50 <h2><a name="configuring" id="configuring">Configuring Apache to permit CGI</a></h2>
53 <p>In order to get your CGI programs to work properly, you'll
54 need to have Apache configured to permit CGI execution. There
55 are several ways to do this.</p>
57 <h3><a name="scriptalias" id="scriptalias">ScriptAlias</a></h3>
61 <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>
63 directive tells Apache that a particular directory is set
64 aside for CGI programs. Apache will assume that every file in
65 this directory is a CGI program, and will attempt to execute
66 it, when that particular resource is requested by a
69 <p>The <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>
70 directive looks like:</p>
72 <div class="example"><p><code>
73 ScriptAlias /cgi-bin/ /usr/local/apache2/cgi-bin/
76 <p>The example shown is from your default <code>httpd.conf</code>
77 configuration file, if you installed Apache in the default
78 location. The <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>
79 directive is much like the <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code> directive, which defines a URL prefix that
80 is to mapped to a particular directory. <code class="directive">Alias</code>
81 and <code class="directive">ScriptAlias</code> are usually used for
82 directories that are outside of the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> directory. The difference between
83 <code class="directive">Alias</code> and <code class="directive">ScriptAlias</code>
84 is that <code class="directive">ScriptAlias</code> has the added meaning
85 that everything under that URL prefix will be considered a CGI
86 program. So, the example above tells Apache that any request for a
87 resource beginning with <code>/cgi-bin/</code> should be served from
88 the directory <code>/usr/local/apache2/cgi-bin/</code>, and should be
89 treated as a CGI program.</p>
91 <p>For example, if the URL
92 <code>http://www.example.com/cgi-bin/test.pl</code>
93 is requested, Apache will attempt to execute the file
94 <code>/usr/local/apache2/cgi-bin/test.pl</code>
95 and return the output. Of course, the file will have to
96 exist, and be executable, and return output in a particular
97 way, or Apache will return an error message.</p>
100 <h3><a name="nonscriptalias" id="nonscriptalias">CGI outside of ScriptAlias directories</a></h3>
103 <p>CGI programs are often restricted to <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>'ed directories for security reasons.
104 In this way, administrators can tightly control who is allowed to
105 use CGI programs. However, if the proper security precautions are
106 taken, there is no reason why CGI programs cannot be run from
107 arbitrary directories. For example, you may wish to let users
108 have web content in their home directories with the
109 <code class="directive"><a href="../mod/mod_userdir.html#userdir">UserDir</a></code> directive.
110 If they want to have their own CGI programs, but don't have access to
111 the main <code>cgi-bin</code> directory, they will need to be able to
112 run CGI programs elsewhere.</p>
114 <p>There are two steps to allowing CGI execution in an arbitrary
115 directory. First, the <code>cgi-script</code> handler must be
116 activated using the <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code> or <code class="directive"><a href="../mod/core.html#sethandler">SetHandler</a></code> directive. Second,
117 <code>ExecCGI</code> must be specified in the <code class="directive"><a href="../mod/core.html#options">Options</a></code> directive.</p>
120 <h3><a name="options" id="options">Explicitly using Options to permit CGI execution</a></h3>
123 <p>You could explicitly use the <code class="directive"><a href="../mod/core.html#options">Options</a></code> directive, inside your main server configuration
124 file, to specify that CGI execution was permitted in a particular
127 <div class="example"><p><code>
128 <Directory /usr/local/apache2/htdocs/somedir><br />
129 <span class="indent">
130 Options +ExecCGI<br />
135 <p>The above directive tells Apache to permit the execution
136 of CGI files. You will also need to tell the server what
137 files are CGI files. The following <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code> directive tells the server to treat all
138 files with the <code>cgi</code> or <code>pl</code> extension as CGI
141 <div class="example"><p><code>
142 AddHandler cgi-script .cgi .pl
146 <h3><a name="htaccess" id="htaccess">.htaccess files</a></h3>
149 <p>The <a href="htaccess.html"><code>.htaccess</code> tutorial</a>
150 shows how to activate CGI programs if you do not have
151 access to <code>httpd.conf</code>.</p>
154 <h3><a name="userdir" id="userdir">User Directories</a></h3>
157 <p>To allow CGI program execution for any file ending in
158 <code>.cgi</code> in users' directories, you can use the
159 following configuration.</p>
161 <div class="example"><p><code>
162 <Directory /home/*/public_html><br />
163 <span class="indent">
164 Options +ExecCGI<br />
165 AddHandler cgi-script .cgi<br />
170 <p>If you wish designate a <code>cgi-bin</code> subdirectory of
171 a user's directory where everything will be treated as a CGI
172 program, you can use the following.</p>
174 <div class="example"><p><code>
175 <Directory /home/*/public_html/cgi-bin><br />
176 <span class="indent">
177 Options ExecCGI<br />
178 SetHandler cgi-script<br />
185 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
186 <div class="section">
187 <h2><a name="writing" id="writing">Writing a CGI program</a></h2>
190 <p>There are two main differences between ``regular''
191 programming, and CGI programming.</p>
193 <p>First, all output from your CGI program must be preceded by
194 a MIME-type header. This is HTTP header that tells the client
195 what sort of content it is receiving. Most of the time, this
198 <div class="example"><p><code>
199 Content-type: text/html
202 <p>Secondly, your output needs to be in HTML, or some other
203 format that a browser will be able to display. Most of the
204 time, this will be HTML, but occasionally you might write a CGI
205 program that outputs a gif image, or other non-HTML
208 <p>Apart from those two things, writing a CGI program will look
209 a lot like any other program that you might write.</p>
211 <h3><a name="firstcgi" id="firstcgi">Your first CGI program</a></h3>
214 <p>The following is an example CGI program that prints one
215 line to your browser. Type in the following, save it to a
216 file called <code>first.pl</code>, and put it in your
217 <code>cgi-bin</code> directory.</p>
219 <div class="example"><p><code>
220 #!/usr/bin/perl<br />
221 print "Content-type: text/html\n\n";<br />
222 print "Hello, World.";
225 <p>Even if you are not familiar with Perl, you should be able
226 to see what is happening here. The first line tells Apache
227 (or whatever shell you happen to be running under) that this
228 program can be executed by feeding the file to the
229 interpreter found at the location <code>/usr/bin/perl</code>.
230 The second line prints the content-type declaration we
231 talked about, followed by two carriage-return newline pairs.
232 This puts a blank line after the header, to indicate the end
233 of the HTTP headers, and the beginning of the body. The third
234 line prints the string "Hello, World.". And that's the end
237 <p>If you open your favorite browser and tell it to get the
240 <div class="example"><p><code>
241 http://www.example.com/cgi-bin/first.pl
244 <p>or wherever you put your file, you will see the one line
245 <code>Hello, World.</code> appear in your browser window.
246 It's not very exciting, but once you get that working, you'll
247 have a good chance of getting just about anything working.</p>
249 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
250 <div class="section">
251 <h2><a name="troubleshoot" id="troubleshoot">But it's still not working!</a></h2>
254 <p>There are four basic things that you may see in your browser
255 when you try to access your CGI program from the web:</p>
258 <dt>The output of your CGI program</dt>
259 <dd>Great! That means everything worked fine. If the output is correct,
260 but the browser is not processing it correctly, make sure you have the
261 correct <code>Content-Type</code> set in your CGI program.</dd>
263 <dt>The source code of your CGI program or a "POST Method Not
264 Allowed" message</dt>
265 <dd>That means that you have not properly configured Apache
266 to process your CGI program. Reread the section on
267 <a href="#configuring">configuring
268 Apache</a> and try to find what you missed.</dd>
270 <dt>A message starting with "Forbidden"</dt>
271 <dd>That means that there is a permissions problem. Check the
272 <a href="#errorlogs">Apache error log</a> and the section below on
273 <a href="#permissions">file permissions</a>.</dd>
275 <dt>A message saying "Internal Server Error"</dt>
277 <a href="#errorlogs">Apache error log</a>, you will probably
278 find that it says "Premature end of
279 script headers", possibly along with an error message
280 generated by your CGI program. In this case, you will want to
281 check each of the below sections to see what might be
282 preventing your CGI program from emitting the proper HTTP
286 <h3><a name="permissions" id="permissions">File permissions</a></h3>
289 <p>Remember that the server does not run as you. That is,
290 when the server starts up, it is running with the permissions
291 of an unprivileged user - usually <code>nobody</code>, or
292 <code>www</code> - and so it will need extra permissions to
293 execute files that are owned by you. Usually, the way to give
294 a file sufficient permissions to be executed by <code>nobody</code>
295 is to give everyone execute permission on the file:</p>
297 <div class="example"><p><code>
301 <p>Also, if your program reads from, or writes to, any other
302 files, those files will need to have the correct permissions
307 <h3><a name="pathinformation" id="pathinformation">Path information and environment</a></h3>
310 <p>When you run a program from your command line, you have
311 certain information that is passed to the shell without you
312 thinking about it. For example, you have a <code>PATH</code>,
313 which tells the shell where it can look for files that you
316 <p>When a program runs through the web server as a CGI program,
317 it may not have the same <code>PATH</code>. Any programs that you
318 invoke in your CGI program (like <code>sendmail</code>, for
319 example) will need to be specified by a full path, so that the
320 shell can find them when it attempts to execute your CGI
323 <p>A common manifestation of this is the path to the script
324 interpreter (often <code>perl</code>) indicated in the first
325 line of your CGI program, which will look something like:</p>
327 <div class="example"><p><code>
331 <p>Make sure that this is in fact the path to the
334 <p>In addition, if your CGI program depends on other <a href="#env">environment variables</a>, you will need to
335 assure that those variables are passed by Apache.</p>
339 <h3><a name="syntaxerrors" id="syntaxerrors">Program errors</a></h3>
342 <p>Most of the time when a CGI program fails, it's because of
343 a problem with the program itself. This is particularly true
344 once you get the hang of this CGI stuff, and no longer make
345 the above two mistakes. The first thing to do is to make
346 sure that your program runs from the command line before
347 testing it via the web server. For example, try:</p>
349 <div class="example"><p><code>
350 cd /usr/local/apache2/cgi-bin<br />
354 <p>(Do not call the <code>perl</code> interpreter. The shell
355 and Apache should find the interpreter using the <a href="#pathinformation">path information</a> on the first line of
358 <p>The first thing you see written by your program should be
359 a set of HTTP headers, including the <code>Content-Type</code>,
360 followed by a blank line. If you see anything else, Apache will
361 return the <code>Premature end of script headers</code> error if
362 you try to run it through the server. See <a href="#writing">Writing a CGI program</a> above for more
366 <h3><a name="errorlogs" id="errorlogs">Error logs</a></h3>
369 <p>The error logs are your friend. Anything that goes wrong
370 generates message in the error log. You should always look
371 there first. If the place where you are hosting your web site
372 does not permit you access to the error log, you should
373 probably host your site somewhere else. Learn to read the
374 error logs, and you'll find that almost all of your problems
375 are quickly identified, and quickly solved.</p>
378 <h3><a name="suexec" id="suexec">Suexec</a></h3>
381 <p>The <a href="../suexec.html">suexec</a> support program
382 allows CGI programs to be run under different user permissions,
383 depending on which virtual host or user home directory they are
384 located in. Suexec has very strict permission checking, and any
385 failure in that checking will result in your CGI programs
386 failing with <code>Premature end of script headers</code>.</p>
388 <p>To check if you are using suexec, run <code>apachectl
389 -V</code> and check for the location of <code>SUEXEC_BIN</code>.
390 If Apache finds an <code class="program"><a href="../programs/suexec.html">suexec</a></code> binary there on startup,
391 suexec will be activated.</p>
393 <p>Unless you fully understand suexec, you should not be using it.
394 To disable suexec, simply remove (or rename) the <code class="program"><a href="../programs/suexec.html">suexec</a></code>
395 binary pointed to by <code>SUEXEC_BIN</code> and then restart the
396 server. If, after reading about <a href="../suexec.html">suexec</a>,
397 you still wish to use it, then run <code>suexec -V</code> to find
398 the location of the suexec log file, and use that log file to
399 find what policy you are violating.</p>
401 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
402 <div class="section">
403 <h2><a name="behindscenes" id="behindscenes">What's going on behind the scenes?</a></h2>
406 <p>As you become more advanced in CGI programming, it will
407 become useful to understand more about what's happening behind
408 the scenes. Specifically, how the browser and server
409 communicate with one another. Because although it's all very
410 well to write a program that prints "Hello, World.", it's not
411 particularly useful.</p>
413 <h3><a name="env" id="env">Environment variables</a></h3>
416 <p>Environment variables are values that float around you as
417 you use your computer. They are useful things like your path
418 (where the computer searches for the actual file
419 implementing a command when you type it), your username, your
420 terminal type, and so on. For a full list of your normal,
421 every day environment variables, type
422 <code>env</code> at a command prompt.</p>
424 <p>During the CGI transaction, the server and the browser
425 also set environment variables, so that they can communicate
426 with one another. These are things like the browser type
427 (Netscape, IE, Lynx), the server type (Apache, IIS, WebSite),
428 the name of the CGI program that is being run, and so on.</p>
430 <p>These variables are available to the CGI programmer, and
431 are half of the story of the client-server communication. The
432 complete list of required variables is at
433 <a href="http://hoohoo.ncsa.uiuc.edu/cgi/env.html">http://hoohoo.ncsa.uiuc.edu/cgi/env.html</a>.</p>
435 <p>This simple Perl CGI program will display all of the
436 environment variables that are being passed around. Two
437 similar programs are included in the
440 directory of the Apache distribution. Note that some
441 variables are required, while others are optional, so you may
442 see some variables listed that were not in the official list.
443 In addition, Apache provides many different ways for you to
444 <a href="../env.html">add your own environment variables</a>
445 to the basic ones provided by default.</p>
447 <div class="example"><p><code>
448 #!/usr/bin/perl<br />
449 print "Content-type: text/html\n\n";<br />
450 foreach $key (keys %ENV) {<br />
451 <span class="indent">
452 print "$key --> $ENV{$key}<br>";<br />
458 <h3><a name="stdin" id="stdin">STDIN and STDOUT</a></h3>
461 <p>Other communication between the server and the client
462 happens over standard input (<code>STDIN</code>) and standard
463 output (<code>STDOUT</code>). In normal everyday context,
464 <code>STDIN</code> means the keyboard, or a file that a
465 program is given to act on, and <code>STDOUT</code>
466 usually means the console or screen.</p>
468 <p>When you <code>POST</code> a web form to a CGI program,
469 the data in that form is bundled up into a special format
470 and gets delivered to your CGI program over <code>STDIN</code>.
471 The program then can process that data as though it was
472 coming in from the keyboard, or from a file</p>
474 <p>The "special format" is very simple. A field name and
475 its value are joined together with an equals (=) sign, and
476 pairs of values are joined together with an ampersand
477 (&). Inconvenient characters like spaces, ampersands, and
478 equals signs, are converted into their hex equivalent so that
479 they don't gum up the works. The whole data string might look
482 <div class="example"><p><code>
483 name=Rich%20Bowen&city=Lexington&state=KY&sidekick=Squirrel%20Monkey
486 <p>You'll sometimes also see this type of string appended to
487 a URL. When that is done, the server puts that string
488 into the environment variable called
489 <code>QUERY_STRING</code>. That's called a <code>GET</code>
490 request. Your HTML form specifies whether a <code>GET</code>
491 or a <code>POST</code> is used to deliver the data, by setting the
492 <code>METHOD</code> attribute in the <code>FORM</code> tag.</p>
494 <p>Your program is then responsible for splitting that string
495 up into useful information. Fortunately, there are libraries
496 and modules available to help you process this data, as well
497 as handle other of the aspects of your CGI program.</p>
499 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
500 <div class="section">
501 <h2><a name="libraries" id="libraries">CGI modules/libraries</a></h2>
504 <p>When you write CGI programs, you should consider using a
505 code library, or module, to do most of the grunt work for you.
506 This leads to fewer errors, and faster development.</p>
508 <p>If you're writing CGI programs in Perl, modules are
509 available on <a href="http://www.cpan.org/">CPAN</a>. The most
510 popular module for this purpose is <code>CGI.pm</code>. You might
511 also consider <code>CGI::Lite</code>, which implements a minimal
512 set of functionality, which is all you need in most programs.</p>
514 <p>If you're writing CGI programs in C, there are a variety of
515 options. One of these is the <code>CGIC</code> library, from
516 <a href="http://www.boutell.com/cgic/">http://www.boutell.com/cgic/</a>.</p>
517 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
518 <div class="section">
519 <h2><a name="moreinfo" id="moreinfo">For more information</a></h2>
522 <p>There are a large number of CGI resources on the web. You
523 can discuss CGI problems with other users on the Usenet group
524 <a href="news:comp.infosystems.www.authoring.cgi">comp.infosystems.www.authoring.cgi</a>. And the -servers mailing
525 list from the HTML Writers Guild is a great source of answers
526 to your questions. You can find out more at
527 <a href="http://www.hwg.org/lists/hwg-servers/">http://www.hwg.org/lists/hwg-servers/</a>.</p>
529 <p>And, of course, you should probably read the CGI
530 specification, which has all the details on the operation of
531 CGI programs. You can find the original version at the
532 <a href="http://hoohoo.ncsa.uiuc.edu/cgi/interface.html">NCSA</a> and there is an updated draft at the
533 <a href="http://web.golux.com/coar/cgi/">Common Gateway
534 Interface RFC project</a>.</p>
536 <p>When you post a question about a CGI problem that you're
537 having, whether to a mailing list, or to a newsgroup, make sure
538 you provide enough information about what happened, what you
539 expected to happen, and how what actually happened was
540 different, what server you're running, what language your CGI
541 program was in, and, if possible, the offending code. This will
542 make finding your problem much simpler.</p>
544 <p>Note that questions about CGI problems should <strong>never</strong>
545 be posted to the Apache bug database unless you are sure you
546 have found a problem in the Apache source code.</p>
548 <div class="bottomlang">
549 <p><span>Available Languages: </span><a href="../en/howto/cgi.html" title="English"> en </a> |
550 <a href="../ja/howto/cgi.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
551 <a href="../ko/howto/cgi.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
552 </div><div id="footer">
553 <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
554 <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></div>