| 1 | <html><head><title>CGI Script output</title></head><body><h1><img alt="" src="out_files/CGIlogo.gif"> CGI Script Output</h1>
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| 2 | <hr>
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| 3 |
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| 4 | <h2>Script output</h2>
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| 5 |
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| 6 | The script sends its output to stdout. This output can either be a
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| 7 | document generated by the script, or instructions to the server for
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| 8 | retrieving the desired output. <p>
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| 9 | </p><hr>
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| 10 |
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| 11 | <h2>Script naming conventions</h2>
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| 12 |
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| 13 | Normally, scripts produce output which is interpreted and sent back to
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| 14 | the client. An advantage of this is that the scripts do not need to
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| 15 | send a full HTTP/1.0 header for every request. <p>
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| 16 | <a name="nph">
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| 17 | Some scripts may want to avoid the extra overhead of the server
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| 18 | parsing their output, and talk directly to the client. In order to
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| 19 | distinguish these scripts from the other scripts, CGI requires that
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| 20 | the script name begins with nph- if a script does not want the server
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| 21 | to parse its header. In this case, it is the script's responsibility
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| 22 | to return a valid HTTP/1.0 (or HTTP/0.9) response to the client. </a></p><p>
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| 23 |
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| 24 | </p><hr>
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| 25 | <h2><a name="nph">Parsed headers</a></h2>
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| 26 |
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| 27 | <a name="nph">The output of scripts begins with a small header. This header consists
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| 28 | of text lines, in the same format as an </a><a href="http://www.w3.org/hypertext/WWW/Protocols/HTTP/Object_Headers.html">
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| 29 | HTTP header</a>, terminated by a blank line (a line with only a
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| 30 | linefeed or CR/LF). <p>
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| 31 |
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| 32 | Any headers which are not server directives are sent directly back to
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| 33 | the client. Currently, this specification defines three server
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| 34 | directives:</p><p>
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| 35 |
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| 36 | </p><ul>
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| 37 | <li> <code>Content-type</code> <p>
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| 38 |
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| 39 | This is the MIME type of the document you are returning. </p><p>
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| 40 |
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| 41 | </p></li><li> <code>Location</code> <p>
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| 42 |
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| 43 | This is used to specify to the server that you are returning a
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| 44 | reference to a document rather than an actual document. </p><p>
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| 45 |
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| 46 | If the argument to this is a URL, the server will issue a redirect
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| 47 | to the client. </p><p>
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| 48 |
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| 49 | If the argument to this is a virtual path, the server will
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| 50 | retrieve the document specified as if the client had requested
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| 51 | that document originally. ? directives will work in here, but #
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| 52 | directives must be redirected back to the client.</p><p>
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| 53 |
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| 54 |
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| 55 | </p></li><li> <a name="status"><code>Status</code></a><p>
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| 56 |
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| 57 | This is used to give the server an HTTP/1.0 <a href="http://www.w3.org/hypertext/WWW/Protocols/HTTP/HTRESP.html">status
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| 58 | line</a> to send to the client. The format is <code>nnn xxxxx</code>,
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| 59 | where <code>nnn</code> is the 3-digit status code, and
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| 60 | <code>xxxxx</code> is the reason string, such as "Forbidden".</p><p>
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| 61 |
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| 62 | </p></li></ul>
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| 63 |
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| 64 | <hr>
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| 65 | <h2>Examples</h2>
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| 66 |
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| 67 | Let's say I have a fromgratz to HTML converter. When my converter is
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| 68 | finished with its work, it will output the following on stdout (note
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| 69 | that the lines beginning and ending with --- are just for illustration
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| 70 | and would not be output): <p>
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| 71 |
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| 72 | </p><pre>--- start of output ---
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| 73 | Content-type: text/html
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| 74 |
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| 75 | --- end of output ---
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| 76 | </pre>
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| 77 |
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| 78 | Note the blank line after Content-type. <p>
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| 79 |
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| 80 | Now, let's say I have a script which, in certain instances, wants to
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| 81 | return the document <code>/path/doc.txt</code> from this server just
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| 82 | as if the user had actually requested
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| 83 | <code>http://server:port/path/doc.txt</code> to begin with. In this
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| 84 | case, the script would output: </p><p>
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| 85 | </p><pre>--- start of output ---
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| 86 | Location: /path/doc.txt
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| 87 |
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| 88 | --- end of output ---
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| 89 | </pre>
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| 90 |
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| 91 | The server would then perform the request and send it to the client.
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| 92 | <p>
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| 93 |
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| 94 | Let's say that I have a script which wants to reference our gopher
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| 95 | server. In this case, if the script wanted to refer the user to
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| 96 | <code>gopher://gopher.ncsa.uiuc.edu/</code>, it would output: </p><p>
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| 97 |
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| 98 | </p><pre>--- start of output ---
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| 99 | Location: gopher://gopher.ncsa.uiuc.edu/
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| 100 |
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| 101 | --- end of output ---
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| 102 | </pre>
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| 103 |
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| 104 | Finally, I have a script which wants to talk to the client directly.
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| 105 | In this case, if the script is referenced with <a href="http://hoohoo.ncsa.uiuc.edu/cgi/env.html#protocol"><code>SERVER_PROTOCOL</code></a> of HTTP/1.0,
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| 106 | the script would output the following HTTP/1.0 response: <p>
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| 107 |
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| 108 | </p><pre>--- start of output ---
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| 109 | HTTP/1.0 200 OK
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| 110 | Server: NCSA/1.0a6
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| 111 | Content-type: text/plain
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| 112 |
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| 113 | This is a plaintext document generated on the fly just for you.
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| 114 |
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| 115 | --- end of output ---
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| 116 | </pre>
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| 117 |
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| 118 |
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| 119 | <hr>
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| 120 |
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| 121 | <a href="http://hoohoo.ncsa.uiuc.edu/cgi/interface.html"><img alt="[Back]" src="out_files/back.gif">Return to the
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| 122 | interface specification</a> <p>
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| 123 |
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| 124 | CGI - Common Gateway Interface
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| 125 | </p><address><a href="http://hoohoo.ncsa.uiuc.edu/cgi/mailtocgi.html">cgi@ncsa.uiuc.edu</a></address>
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| 126 | </body></html>
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