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Chip Salzenberg > perl5.004 > CGI



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Module Version: 2.36   Source   Latest Release: perl-5.6.2


CGI - Simple Common Gateway Interface Class


  use CGI;
  # the rest is too complicated for a synopsis; keep reading


This perl library uses perl5 objects to make it easy to create Web fill-out forms and parse their contents. This package defines CGI objects, entities that contain the values of the current query string and other state variables. Using a CGI object's methods, you can examine keywords and parameters passed to your script, and create forms whose initial values are taken from the current query (thereby preserving state information).

The current version of is available at


CGI is a part of the base Perl installation. However, you may need to install a newer version someday. Therefore:

To install this package, just change to the directory in which this file is found and type the following:

        perl Makefile.PL
        make install

This will copy to your perl library directory for use by all perl scripts. You probably must be root to do this. Now you can load the CGI routines in your Perl scripts with the line:

        use CGI;

If you don't have sufficient privileges to install in the Perl library directory, you can put into some convenient spot, such as your home directory, or in cgi-bin itself and prefix all Perl scripts that call it with something along the lines of the following preamble:

        use lib '/home/davis/lib';
        use CGI;

If you are using a version of perl earlier than 5.002 (such as NT perl), use this instead:

        BEGIN {
        use CGI;

The CGI distribution also comes with a cute module called CGI::Carp. It redefines the die(), warn(), confess() and croak() error routines so that they write nicely formatted error messages into the server's error log (or to the output stream of your choice). This avoids long hours of groping through the error and access logs, trying to figure out which CGI script is generating error messages. If you choose, you can even have fatal error messages echoed to the browser to avoid the annoying and uninformative "Server Error" message.



     $query = new CGI;

This will parse the input (from both POST and GET methods) and store it into a perl5 object called $query.


     $query = new CGI(INPUTFILE);

If you provide a file handle to the new() method, it will read parameters from the file (or STDIN, or whatever). The file can be in any of the forms describing below under debugging (i.e. a series of newline delimited TAG=VALUE pairs will work). Conveniently, this type of file is created by the save() method (see below). Multiple records can be saved and restored.

Perl purists will be pleased to know that this syntax accepts references to file handles, or even references to filehandle globs, which is the "official" way to pass a filehandle:

    $query = new CGI(\*STDIN);

You can also initialize the query object from an associative array reference:

    $query = new CGI( {'dinosaur'=>'barney',
                       'song'=>'I love you',
                       'friends'=>[qw/Jessica George Nancy/]}

or from a properly formatted, URL-escaped query string:

    $query = new CGI('dinosaur=barney&color=purple');

To create an empty query, initialize it from an empty string or hash:

        $empty_query = new CGI("");
        $empty_query = new CGI({});


     @keywords = $query->keywords

If the script was invoked as the result of an <ISINDEX> search, the parsed keywords can be obtained as an array using the keywords() method.


     @names = $query->param

If the script was invoked with a parameter list (e.g. "name1=value1&name2=value2&name3=value3"), the param() method will return the parameter names as a list. If the script was invoked as an <ISINDEX> script, there will be a single parameter named 'keywords'.

NOTE: As of version 1.5, the array of parameter names returned will be in the same order as they were submitted by the browser. Usually this order is the same as the order in which the parameters are defined in the form (however, this isn't part of the spec, and so isn't guaranteed).


    @values = $query->param('foo');


    $value = $query->param('foo');

Pass the param() method a single argument to fetch the value of the named parameter. If the parameter is multivalued (e.g. from multiple selections in a scrolling list), you can ask to receive an array. Otherwise the method will return a single value.



This sets the value for the named parameter 'foo' to an array of values. This is one way to change the value of a field AFTER the script has been invoked once before. (Another way is with the -override parameter accepted by all methods that generate form elements.)

param() also recognizes a named parameter style of calling described in more detail later:



    $query->param(-name=>'foo',-value=>'the value');



This adds a value or list of values to the named parameter. The values are appended to the end of the parameter if it already exists. Otherwise the parameter is created. Note that this method only recognizes the named argument calling syntax.



This creates a series of variables in the 'R' namespace. For example, $R::foo, @R:foo. For keyword lists, a variable @R::keywords will appear. If no namespace is given, this method will assume 'Q'. WARNING: don't import anything into 'main'; this is a major security risk!!!!

In older versions, this method was called import(). As of version 2.20, this name has been removed completely to avoid conflict with the built-in Perl module import operator.



This completely clears a parameter. It sometimes useful for resetting parameters that you don't want passed down between script invocations.



This clears the CGI object completely. It might be useful to ensure that all the defaults are taken when you create a fill-out form.



This will write the current state of the form to the provided filehandle. You can read it back in by providing a filehandle to the new() method. Note that the filehandle can be a file, a pipe, or whatever!

The format of the saved file is:


Both name and value are URL escaped. Multi-valued CGI parameters are represented as repeated names. A session record is delimited by a single = symbol. You can write out multiple records and read them back in with several calls to new. You can do this across several sessions by opening the file in append mode, allowing you to create primitive guest books, or to keep a history of users' queries. Here's a short example of creating multiple session records:

   use CGI;

   open (OUT,">>test.out") || die;
   $records = 5;
   foreach (0..$records) {
       my $q = new CGI;
   close OUT;

   # reopen for reading
   open (IN,"test.out") || die;
   while (!eof(IN)) {
       my $q = new CGI(IN);
       print $q->param('counter'),"\n";

The file format used for save/restore is identical to that used by the Whitehead Genome Center's data exchange format "Boulderio", and can be manipulated and even databased using Boulderio utilities. See

for further details.


    $myself = $query->self_url;
    print "<A HREF=$myself>I'm talking to myself.</A>";

self_url() will return a URL, that, when selected, will reinvoke this script with all its state information intact. This is most useful when you want to jump around within the document using internal anchors but you don't want to disrupt the current contents of the form(s). Something like this will do the trick.

     $myself = $query->self_url;
     print "<A HREF=$myself#table1>See table 1</A>";
     print "<A HREF=$myself#table2>See table 2</A>";
     print "<A HREF=$myself#yourself>See for yourself</A>";

If you don't want to get the whole query string, call the method url() to return just the URL for the script:

    $myself = $query->url;
    print "<A HREF=$myself>No query string in this baby!</A>\n";

You can also retrieve the unprocessed query string with query_string():

    $the_string = $query->query_string;


To make it easier to port existing programs that use the compatibility routine "ReadParse" is provided. Porting is simple:

OLD VERSION require ""; &ReadParse; print "The value of the antique is $in{antique}.\n";

NEW VERSION use CGI; CGI::ReadParse print "The value of the antique is $in{antique}.\n";'s ReadParse() routine creates a tied variable named %in, which can be accessed to obtain the query variables. Like ReadParse, you can also provide your own variable. Infrequently used features of ReadParse, such as the creation of @in and $in variables, are not supported.

Once you use ReadParse, you can retrieve the query object itself this way:

    $q = $in{CGI};
    print $q->textfield(-name=>'wow',
                        -value=>'does this really work?');

This allows you to start using the more interesting features of without rewriting your old scripts from scratch.


In versions of prior to 2.0, it could get difficult to remember the proper order of arguments in CGI function calls that accepted five or six different arguments. As of 2.0, there's a better way to pass arguments to the various CGI functions. In this style, you pass a series of name=>argument pairs, like this:

   $field = $query->radio_group(-name=>'OS',

The advantages of this style are that you don't have to remember the exact order of the arguments, and if you leave out a parameter, in most cases it will default to some reasonable value. If you provide a parameter that the method doesn't recognize, it will usually do something useful with it, such as incorporating it into the HTML form tag. For example if Netscape decides next week to add a new JUSTIFICATION parameter to the text field tags, you can start using the feature without waiting for a new version of

   $field = $query->textfield(-name=>'State',

This will result in an HTML tag that looks like this:

        <INPUT TYPE="textfield" NAME="State" VALUE="gaseous"

Parameter names are case insensitive: you can use -name, or -Name or -NAME. You don't have to use the hyphen if you don't want to. After creating a CGI object, call the use_named_parameters() method with a nonzero value. This will tell that you intend to use named parameters exclusively:

   $query = new CGI;
   $field = $query->radio_group('name'=>'OS',

Actually, only looks for a hyphen in the first parameter. So you can leave it off subsequent parameters if you like. Something to be wary of is the potential that a string constant like "values" will collide with a keyword (and in fact it does!) While Perl usually figures out when you're referring to a function and when you're referring to a string, you probably should put quotation marks around all string constants just to play it safe.


        print $query->header;


        print $query->header('image/gif');


        print $query->header('text/html','204 No response');


        print $query->header(-type=>'image/gif',
                             -status=>'402 Payment required',

header() returns the Content-type: header. You can provide your own MIME type if you choose, otherwise it defaults to text/html. An optional second parameter specifies the status code and a human-readable message. For example, you can specify 204, "No response" to create a script that tells the browser to do nothing at all. If you want to add additional fields to the header, just tack them on to the end:

    print $query->header('text/html','200 OK','Content-Length: 3002');

The last example shows the named argument style for passing arguments to the CGI methods using named parameters. Recognized parameters are -type, -status, -expires, and -cookie. Any other parameters will be stripped of their initial hyphens and turned into header fields, allowing you to specify any HTTP header you desire.

Most browsers will not cache the output from CGI scripts. Every time the browser reloads the page, the script is invoked anew. You can change this behavior with the -expires parameter. When you specify an absolute or relative expiration interval with this parameter, some browsers and proxy servers will cache the script's output until the indicated expiration date. The following forms are all valid for the -expires field:

        +30s                              30 seconds from now
        +10m                              ten minutes from now
        +1h                               one hour from now
        -1d                               yesterday (i.e. "ASAP!")
        now                               immediately
        +3M                               in three months
        +10y                              in ten years time
        Thursday, 25-Apr-96 00:40:33 GMT  at the indicated time & date

(CGI::expires() is the static function call used internally that turns relative time intervals into HTTP dates. You can call it directly if you wish.)

The -cookie parameter generates a header that tells the browser to provide a "magic cookie" during all subsequent transactions with your script. Netscape cookies have a special format that includes interesting attributes such as expiration time. Use the cookie() method to create and retrieve session cookies.

The -nph parameter, if set to a true value, will issue the correct headers to work with a NPH (no-parse-header) script. This is important to use with certain servers, such as Microsoft Internet Explorer, which expect all their scripts to be NPH.


   print $query->redirect('http://somewhere.else/in/movie/land');

redirects the browser elsewhere. If you use redirection like this, you should not print out a header as well. As of version 2.0, we produce both the unofficial Location: header and the official URI: header. This should satisfy most servers and browsers.

One hint I can offer is that relative links may not work correctly when you generate a redirection to another document on your site. This is due to a well-intentioned optimization that some servers use. The solution to this is to use the full URL (including the http: part) of the document you are redirecting to.

You can use named parameters:

    print $query->redirect(-uri=>'http://somewhere.else/in/movie/land',

The -nph parameter, if set to a true value, will issue the correct headers to work with a NPH (no-parse-header) script. This is important to use with certain servers, such as Microsoft Internet Explorer, which expect all their scripts to be NPH.


   print $query->start_html(-title=>'Secrets of the Pyramids',
                            -meta=>{'keywords'=>'pharaoh secret mummy',
                                    'copyright'=>'copyright 1996 King Tut'},


   print $query->start_html('Secrets of the Pyramids',

This will return a canned HTML header and the opening <BODY> tag. All parameters are optional. In the named parameter form, recognized parameters are -title, -author, -base, -xbase and -target (see below for the explanation). Any additional parameters you provide, such as the Netscape unofficial BGCOLOR attribute, are added to the <BODY> tag.

The argument -xbase allows you to provide an HREF for the <BASE> tag different from the current location, as in


All relative links will be interpreted relative to this tag.

The argument -target allows you to provide a default target frame for all the links and fill-out forms on the page. See the Netscape documentation on frames for details of how to manipulate this.


All relative links will be interpreted relative to this tag. You add arbitrary meta information to the header with the -meta argument. This argument expects a reference to an associative array containing name/value pairs of meta information. These will be turned into a series of header <META> tags that look something like this:

    <META NAME="keywords" CONTENT="pharaoh secret mummy">
    <META NAME="description" CONTENT="copyright 1996 King Tut">

There is no support for the HTTP-EQUIV type of <META> tag. This is because you can modify the HTTP header directly with the header() method. For example, if you want to send the Refresh: header, do it in the header() method:

    print $q->header(-Refresh=>'10; URL=');

The -style tag is used to incorporate cascading stylesheets into your code. See the section on CASCADING STYLESHEETS for more information.

You can place other arbitrary HTML elements to the <HEAD> section with the -head tag. For example, to place the rarely-used <LINK> element in the head section, use this:

    print $q->header(-head=>link({-rel=>'next',

To incorporate multiple HTML elements into the <HEAD> section, just pass an array reference:

    print $q->header(-head=>[ link({-rel=>'next',

JAVASCRIPTING: The -script, -noScript, -onLoad and -onUnload parameters are used to add Netscape JavaScript calls to your pages. -script should point to a block of text containing JavaScript function definitions. This block will be placed within a <SCRIPT> block inside the HTML (not HTTP) header. The block is placed in the header in order to give your page a fighting chance of having all its JavaScript functions in place even if the user presses the stop button before the page has loaded completely. attempts to format the script in such a way that JavaScript-naive browsers will not choke on the code: unfortunately there are some browsers, such as Chimera for Unix, that get confused by it nevertheless.

The -onLoad and -onUnload parameters point to fragments of JavaScript code to execute when the page is respectively opened and closed by the browser. Usually these parameters are calls to functions defined in the -script field:

      $query = new CGI;
      print $query->header;
      // Ask a silly question
      function riddle_me_this() {
         var r = prompt("What walks on four legs in the morning, " +
                       "two legs in the afternoon, " +
                       "and three legs in the evening?");
      // Get a silly answer
      function response(answer) {
         if (answer == "man")
            alert("Right you are!");
            alert("Wrong!  Guess again.");
      print $query->start_html(-title=>'The Riddle of the Sphinx',

Use the -noScript parameter to pass some HTML text that will be displayed on browsers that do not have JavaScript (or browsers where JavaScript is turned off).

Netscape 3.0 recognizes several attributes of the <SCRIPT> tag, including LANGUAGE and SRC. The latter is particularly interesting, as it allows you to keep the JavaScript code in a file or CGI script rather than cluttering up each page with the source. To use these attributes pass a HASH reference in the -script parameter containing one or more of -language, -src, or -code:

    print $q->start_html(-title=>'The Riddle of the Sphinx',

    print $q->(-title=>'The Riddle of the Sphinx',
                         -code=>'print "hello world!\n;"'


for more information about JavaScript.

The old-style positional parameters are as follows:


The title


The author's e-mail address (will create a <LINK REV="MADE"> tag if present


A 'true' flag if you want to include a <BASE> tag in the header. This helps resolve relative addresses to absolute ones when the document is moved, but makes the document hierarchy non-portable. Use with care!

4, 5, 6...

Any other parameters you want to include in the <BODY> tag. This is a good place to put Netscape extensions, such as colors and wallpaper patterns.


        print $query->end_html

This ends an HTML document by printing the </BODY></HTML> tags.


General note The various form-creating methods all return strings to the caller, containing the tag or tags that will create the requested form element. You are responsible for actually printing out these strings. It's set up this way so that you can place formatting tags around the form elements.

Another note The default values that you specify for the forms are only used the first time the script is invoked (when there is no query string). On subsequent invocations of the script (when there is a query string), the former values are used even if they are blank.

If you want to change the value of a field from its previous value, you have two choices:

(1) call the param() method to set it.

(2) use the -override (alias -force) parameter (a new feature in version 2.15). This forces the default value to be used, regardless of the previous value:

   print $query->textfield(-name=>'field_name',
                           -default=>'starting value',

Yet another note By default, the text and labels of form elements are escaped according to HTML rules. This means that you can safely use "<CLICK ME>" as the label for a button. However, it also interferes with your ability to incorporate special HTML character sequences, such as &Aacute;, into your fields. If you wish to turn off automatic escaping, call the autoEscape() method with a false value immediately after creating the CGI object:

   $query = new CGI;


   print $query->isindex(-action=>$action);


   print $query->isindex($action);

Prints out an <ISINDEX> tag. Not very exciting. The parameter -action specifies the URL of the script to process the query. The default is to process the query with the current script.


    print $query->startform(-method=>$method,
      <... various form stuff ...>
    print $query->endform;


    print $query->startform($method,$action,$encoding);
      <... various form stuff ...>
    print $query->endform;

startform() will return a <FORM> tag with the optional method, action and form encoding that you specify. The defaults are:

    method: POST
    action: this script
    encoding: application/x-www-form-urlencoded

endform() returns the closing </FORM> tag.

Startform()'s encoding method tells the browser how to package the various fields of the form before sending the form to the server. Two values are possible:


This is the older type of encoding used by all browsers prior to Netscape 2.0. It is compatible with many CGI scripts and is suitable for short fields containing text data. For your convenience, stores the name of this encoding type in $CGI::URL_ENCODED.


This is the newer type of encoding introduced by Netscape 2.0. It is suitable for forms that contain very large fields or that are intended for transferring binary data. Most importantly, it enables the "file upload" feature of Netscape 2.0 forms. For your convenience, stores the name of this encoding type in $CGI::MULTIPART

Forms that use this type of encoding are not easily interpreted by CGI scripts unless they use or another library designed to handle them.

For compatibility, the startform() method uses the older form of encoding by default. If you want to use the newer form of encoding by default, you can call start_multipart_form() instead of startform().

JAVASCRIPTING: The -name and -onSubmit parameters are provided for use with JavaScript. The -name parameter gives the form a name so that it can be identified and manipulated by JavaScript functions. -onSubmit should point to a JavaScript function that will be executed just before the form is submitted to your server. You can use this opportunity to check the contents of the form for consistency and completeness. If you find something wrong, you can put up an alert box or maybe fix things up yourself. You can abort the submission by returning false from this function.

Usually the bulk of JavaScript functions are defined in a <SCRIPT> block in the HTML header and -onSubmit points to one of these function call. See start_html() for details.


    print $query->textfield(-name=>'field_name',
                            -default=>'starting value',

    print $query->textfield('field_name','starting value',50,80);

textfield() will return a text input field.


The first parameter is the required name for the field (-name).


The optional second parameter is the default starting value for the field contents (-default).


The optional third parameter is the size of the field in characters (-size).


The optional fourth parameter is the maximum number of characters the field will accept (-maxlength).

As with all these methods, the field will be initialized with its previous contents from earlier invocations of the script. When the form is processed, the value of the text field can be retrieved with:

       $value = $query->param('foo');

If you want to reset it from its initial value after the script has been called once, you can do so like this:

       $query->param('foo',"I'm taking over this value!");

NEW AS OF VERSION 2.15: If you don't want the field to take on its previous value, you can force its current value by using the -override (alias -force) parameter:

    print $query->textfield(-name=>'field_name',
                            -default=>'starting value',

JAVASCRIPTING: You can also provide -onChange, -onFocus, -onBlur and -onSelect parameters to register JavaScript event handlers. The onChange handler will be called whenever the user changes the contents of the text field. You can do text validation if you like. onFocus and onBlur are called respectively when the insertion point moves into and out of the text field. onSelect is called when the user changes the portion of the text that is selected.


   print $query->textarea(-name=>'foo',
                          -default=>'starting value',


   print $query->textarea('foo','starting value',10,50);

textarea() is just like textfield, but it allows you to specify rows and columns for a multiline text entry box. You can provide a starting value for the field, which can be long and contain multiple lines.

JAVASCRIPTING: The -onChange, -onFocus, -onBlur and -onSelect parameters are recognized. See textfield().


   print $query->password_field(-name=>'secret',
                                -value=>'starting value',

   print $query->password_field('secret','starting value',50,80);

password_field() is identical to textfield(), except that its contents will be starred out on the web page.

JAVASCRIPTING: The -onChange, -onFocus, -onBlur and -onSelect parameters are recognized. See textfield().


    print $query->filefield(-name=>'uploaded_file',
                            -default=>'starting value',

    print $query->filefield('uploaded_file','starting value',50,80);

filefield() will return a file upload field for Netscape 2.0 browsers. In order to take full advantage of this you must use the new multipart encoding scheme for the form. You can do this either by calling startform() with an encoding type of $CGI::MULTIPART, or by calling the new method start_multipart_form() instead of vanilla startform().


The first parameter is the required name for the field (-name).


The optional second parameter is the starting value for the field contents to be used as the default file name (-default).

The beta2 version of Netscape 2.0 currently doesn't pay any attention to this field, and so the starting value will always be blank. Worse, the field loses its "sticky" behavior and forgets its previous contents. The starting value field is called for in the HTML specification, however, and possibly later versions of Netscape will honor it.


The optional third parameter is the size of the field in characters (-size).


The optional fourth parameter is the maximum number of characters the field will accept (-maxlength).

When the form is processed, you can retrieve the entered filename by calling param().

       $filename = $query->param('uploaded_file');

In Netscape Gold, the filename that gets returned is the full local filename on the remote user's machine. If the remote user is on a Unix machine, the filename will follow Unix conventions:


On an MS-DOS/Windows and OS/2 machines, the filename will follow DOS conventions:


On a Macintosh machine, the filename will follow Mac conventions:

        HD 40:Desktop Folder:Sort Through:Reminders

The filename returned is also a file handle. You can read the contents of the file using standard Perl file reading calls:

        # Read a text file and print it out
        while (<$filename>) {

        # Copy a binary file to somewhere safe
        open (OUTFILE,">>/usr/local/web/users/feedback");
        while ($bytesread=read($filename,$buffer,1024)) {
           print OUTFILE $buffer;

When a file is uploaded the browser usually sends along some information along with it in the format of headers. The information usually includes the MIME content type. Future browsers may send other information as well (such as modification date and size). To retrieve this information, call uploadInfo(). It returns a reference to an associative array containing all the document headers.

       $filename = $query->param('uploaded_file');
       $type = $query->uploadInfo($filename)->{'Content-Type'};
       unless ($type eq 'text/html') {
          die "HTML FILES ONLY!";

If you are using a machine that recognizes "text" and "binary" data modes, be sure to understand when and how to use them (see the Camel book). Otherwise you may find that binary files are corrupted during file uploads.

JAVASCRIPTING: The -onChange, -onFocus, -onBlur and -onSelect parameters are recognized. See textfield() for details.


   print $query->popup_menu('menu_name',


   %labels = ('eenie'=>'your first choice',
              'meenie'=>'your second choice',
              'minie'=>'your third choice');
   print $query->popup_menu('menu_name',

        -or (named parameter style)-

   print $query->popup_menu(-name=>'menu_name',

popup_menu() creates a menu.

  1. The required first argument is the menu's name (-name).
  2. The required second argument (-values) is an array reference containing the list of menu items in the menu. You can pass the method an anonymous array, as shown in the example, or a reference to a named array, such as "\@foo".
  3. The optional third parameter (-default) is the name of the default menu choice. If not specified, the first item will be the default. The values of the previous choice will be maintained across queries.
  4. The optional fourth parameter (-labels) is provided for people who want to use different values for the user-visible label inside the popup menu nd the value returned to your script. It's a pointer to an associative array relating menu values to user-visible labels. If you leave this parameter blank, the menu values will be displayed by default. (You can also leave a label undefined if you want to).

When the form is processed, the selected value of the popup menu can be retrieved using:

      $popup_menu_value = $query->param('menu_name');

JAVASCRIPTING: popup_menu() recognizes the following event handlers: -onChange, -onFocus, and -onBlur. See the textfield() section for details on when these handlers are called.


   print $query->scrolling_list('list_name',

   print $query->scrolling_list('list_name',


   print $query->scrolling_list(-name=>'list_name',

scrolling_list() creates a scrolling list.


The first and second arguments are the list name (-name) and values (-values). As in the popup menu, the second argument should be an array reference.


The optional third argument (-default) can be either a reference to a list containing the values to be selected by default, or can be a single value to select. If this argument is missing or undefined, then nothing is selected when the list first appears. In the named parameter version, you can use the synonym "-defaults" for this parameter.


The optional fourth argument is the size of the list (-size).


The optional fifth argument can be set to true to allow multiple simultaneous selections (-multiple). Otherwise only one selection will be allowed at a time.


The optional sixth argument is a pointer to an associative array containing long user-visible labels for the list items (-labels). If not provided, the values will be displayed.

When this form is processed, all selected list items will be returned as a list under the parameter name 'list_name'. The values of the selected items can be retrieved with:

      @selected = $query->param('list_name');

JAVASCRIPTING: scrolling_list() recognizes the following event handlers: -onChange, -onFocus, and -onBlur. See textfield() for the description of when these handlers are called.


   print $query->checkbox_group(-name=>'group_name',

   print $query->checkbox_group('group_name',


   print $query->checkbox_group(-name=>'group_name',

checkbox_group() creates a list of checkboxes that are related by the same name.


The first and second arguments are the checkbox name and values, respectively (-name and -values). As in the popup menu, the second argument should be an array reference. These values are used for the user-readable labels printed next to the checkboxes as well as for the values passed to your script in the query string.


The optional third argument (-default) can be either a reference to a list containing the values to be checked by default, or can be a single value to checked. If this argument is missing or undefined, then nothing is selected when the list first appears.


The optional fourth argument (-linebreak) can be set to true to place line breaks between the checkboxes so that they appear as a vertical list. Otherwise, they will be strung together on a horizontal line.


The optional fifth argument is a pointer to an associative array relating the checkbox values to the user-visible labels that will be printed next to them (-labels). If not provided, the values will be used as the default.


HTML3-compatible browsers (such as Netscape) can take advantage of the optional parameters -rows, and -columns. These parameters cause checkbox_group() to return an HTML3 compatible table containing the checkbox group formatted with the specified number of rows and columns. You can provide just the -columns parameter if you wish; checkbox_group will calculate the correct number of rows for you.

To include row and column headings in the returned table, you can use the -rowheader and -colheader parameters. Both of these accept a pointer to an array of headings to use. The headings are just decorative. They don't reorganize the interpretation of the checkboxes -- they're still a single named unit.

When the form is processed, all checked boxes will be returned as a list under the parameter name 'group_name'. The values of the "on" checkboxes can be retrieved with:

      @turned_on = $query->param('group_name');

The value returned by checkbox_group() is actually an array of button elements. You can capture them and use them within tables, lists, or in other creative ways:

    @h = $query->checkbox_group(-name=>'group_name',-values=>\@values);

JAVASCRIPTING: checkbox_group() recognizes the -onClick parameter. This specifies a JavaScript code fragment or function call to be executed every time the user clicks on any of the buttons in the group. You can retrieve the identity of the particular button clicked on using the "this" variable.


    print $query->checkbox(-name=>'checkbox_name',
                           -label=>'CLICK ME');


    print $query->checkbox('checkbox_name','checked','ON','CLICK ME');

checkbox() is used to create an isolated checkbox that isn't logically related to any others.


The first parameter is the required name for the checkbox (-name). It will also be used for the user-readable label printed next to the checkbox.


The optional second parameter (-checked) specifies that the checkbox is turned on by default. Synonyms are -selected and -on.


The optional third parameter (-value) specifies the value of the checkbox when it is checked. If not provided, the word "on" is assumed.


The optional fourth parameter (-label) is the user-readable label to be attached to the checkbox. If not provided, the checkbox name is used.

The value of the checkbox can be retrieved using:

    $turned_on = $query->param('checkbox_name');

JAVASCRIPTING: checkbox() recognizes the -onClick parameter. See checkbox_group() for further details.


   print $query->radio_group(-name=>'group_name',


   print $query->radio_group('group_name',['eenie','meenie','minie'],


   print $query->radio_group(-name=>'group_name',

radio_group() creates a set of logically-related radio buttons (turning one member of the group on turns the others off)


The first argument is the name of the group and is required (-name).


The second argument (-values) is the list of values for the radio buttons. The values and the labels that appear on the page are identical. Pass an array reference in the second argument, either using an anonymous array, as shown, or by referencing a named array as in "\@foo".


The optional third parameter (-default) is the name of the default button to turn on. If not specified, the first item will be the default. You can provide a nonexistent button name, such as "-" to start up with no buttons selected.


The optional fourth parameter (-linebreak) can be set to 'true' to put line breaks between the buttons, creating a vertical list.


The optional fifth parameter (-labels) is a pointer to an associative array relating the radio button values to user-visible labels to be used in the display. If not provided, the values themselves are displayed.


HTML3-compatible browsers (such as Netscape) can take advantage of the optional parameters -rows, and -columns. These parameters cause radio_group() to return an HTML3 compatible table containing the radio group formatted with the specified number of rows and columns. You can provide just the -columns parameter if you wish; radio_group will calculate the correct number of rows for you.

To include row and column headings in the returned table, you can use the -rowheader and -colheader parameters. Both of these accept a pointer to an array of headings to use. The headings are just decorative. They don't reorganize the interpetation of the radio buttons -- they're still a single named unit.

When the form is processed, the selected radio button can be retrieved using:

      $which_radio_button = $query->param('group_name');

The value returned by radio_group() is actually an array of button elements. You can capture them and use them within tables, lists, or in other creative ways:

    @h = $query->radio_group(-name=>'group_name',-values=>\@values);


   print $query->submit(-name=>'button_name',


   print $query->submit('button_name','value');

submit() will create the query submission button. Every form should have one of these.


The first argument (-name) is optional. You can give the button a name if you have several submission buttons in your form and you want to distinguish between them. The name will also be used as the user-visible label. Be aware that a few older browsers don't deal with this correctly and never send back a value from a button.


The second argument (-value) is also optional. This gives the button a value that will be passed to your script in the query string.

You can figure out which button was pressed by using different values for each one:

     $which_one = $query->param('button_name');

JAVASCRIPTING: radio_group() recognizes the -onClick parameter. See checkbox_group() for further details.


   print $query->reset

reset() creates the "reset" button. Note that it restores the form to its value from the last time the script was called, NOT necessarily to the defaults.


   print $query->defaults('button_label')

defaults() creates a button that, when invoked, will cause the form to be completely reset to its defaults, wiping out all the changes the user ever made.


        print $query->hidden(-name=>'hidden_name',


        print $query->hidden('hidden_name','value1','value2'...);

hidden() produces a text field that can't be seen by the user. It is useful for passing state variable information from one invocation of the script to the next.


The first argument is required and specifies the name of this field (-name).


The second argument is also required and specifies its value (-default). In the named parameter style of calling, you can provide a single value here or a reference to a whole list

Fetch the value of a hidden field this way:

     $hidden_value = $query->param('hidden_name');

Note, that just like all the other form elements, the value of a hidden field is "sticky". If you want to replace a hidden field with some other values after the script has been called once you'll have to do it manually:



     print $query->image_button(-name=>'button_name',


     print $query->image_button('button_name','/source/URL','MIDDLE');

image_button() produces a clickable image. When it's clicked on the position of the click is returned to your script as "button_name.x" and "button_name.y", where "button_name" is the name you've assigned to it.

JAVASCRIPTING: image_button() recognizes the -onClick parameter. See checkbox_group() for further details.


The first argument (-name) is required and specifies the name of this field.


The second argument (-src) is also required and specifies the URL

3. The third option (-align, optional) is an alignment type, and may be TOP, BOTTOM or MIDDLE

Fetch the value of the button this way: $x = $query->param('button_name.x'); $y = $query->param('button_name.y');


     print $query->button(-name=>'button_name',
                          -value=>'user visible label',


     print $query->button('button_name',"do_something()");

button() produces a button that is compatible with Netscape 2.0's JavaScript. When it's pressed the fragment of JavaScript code pointed to by the -onClick parameter will be executed. On non-Netscape browsers this form element will probably not even display.


Netscape browsers versions 1.1 and higher support a so-called "cookie" designed to help maintain state within a browser session. has several methods that support cookies.

A cookie is a name=value pair much like the named parameters in a CGI query string. CGI scripts create one or more cookies and send them to the browser in the HTTP header. The browser maintains a list of cookies that belong to a particular Web server, and returns them to the CGI script during subsequent interactions.

In addition to the required name=value pair, each cookie has several optional attributes:

1. an expiration time

This is a time/date string (in a special GMT format) that indicates when a cookie expires. The cookie will be saved and returned to your script until this expiration date is reached if the user exits Netscape and restarts it. If an expiration date isn't specified, the cookie will remain active until the user quits Netscape.

2. a domain

This is a partial or complete domain name for which the cookie is valid. The browser will return the cookie to any host that matches the partial domain name. For example, if you specify a domain name of "", then Netscape will return the cookie to Web servers running on any of the machines "", "", "", etc. Domain names must contain at least two periods to prevent attempts to match on top level domains like ".edu". If no domain is specified, then the browser will only return the cookie to servers on the host the cookie originated from.

3. a path

If you provide a cookie path attribute, the browser will check it against your script's URL before returning the cookie. For example, if you specify the path "/cgi-bin", then the cookie will be returned to each of the scripts "/cgi-bin/", "/cgi-bin/", and "/cgi-bin/customer_service/", but not to the script "/cgi-private/". By default, path is set to "/", which causes the cookie to be sent to any CGI script on your site.

4. a "secure" flag

If the "secure" attribute is set, the cookie will only be sent to your script if the CGI request is occurring on a secure channel, such as SSL.

The interface to Netscape cookies is the cookie() method:

    $cookie = $query->cookie(-name=>'sessionID',
    print $query->header(-cookie=>$cookie);

cookie() creates a new cookie. Its parameters include:


The name of the cookie (required). This can be any string at all. Although Netscape limits its cookie names to non-whitespace alphanumeric characters, removes this restriction by escaping and unescaping cookies behind the scenes.


The value of the cookie. This can be any scalar value, array reference, or even associative array reference. For example, you can store an entire associative array into a cookie this way:

        $cookie=$query->cookie(-name=>'family information',

The optional partial path for which this cookie will be valid, as described above.


The optional partial domain for which this cookie will be valid, as described above.


The optional expiration date for this cookie. The format is as described in the section on the header() method:

        "+1h"  one hour from now

If set to true, this cookie will only be used within a secure SSL session.

The cookie created by cookie() must be incorporated into the HTTP header within the string returned by the header() method:

        print $query->header(-cookie=>$my_cookie);

To create multiple cookies, give header() an array reference:

        $cookie1 = $query->cookie(-name=>'riddle_name',
                                  -value=>"The Sphynx's Question");
        $cookie2 = $query->cookie(-name=>'answers',
        print $query->header(-cookie=>[$cookie1,$cookie2]);

To retrieve a cookie, request it by name by calling cookie() method without the -value parameter:

        use CGI;
        $query = new CGI;
        %answers = $query->cookie(-name=>'answers');
        # $query->cookie('answers') will work too!

The cookie and CGI namespaces are separate. If you have a parameter named 'answers' and a cookie named 'answers', the values retrieved by param() and cookie() are independent of each other. However, it's simple to turn a CGI parameter into a cookie, and vice-versa:

   # turn a CGI parameter into a cookie
   # vice-versa

See the cookie.cgi example script for some ideas on how to use cookies effectively.

NOTE: There appear to be some (undocumented) restrictions on Netscape cookies. In Netscape 2.01, at least, I haven't been able to set more than three cookies at a time. There may also be limits on the length of cookies. If you need to store a lot of information, it's probably better to create a unique session ID, store it in a cookie, and use the session ID to locate an external file/database saved on the server's side of the connection.


It's possible for scripts to write into several browser panels and windows using Netscape's frame mechanism. There are three techniques for defining new frames programmatically:

1. Create a <Frameset> document

After writing out the HTTP header, instead of creating a standard HTML document using the start_html() call, create a <FRAMESET> document that defines the frames on the page. Specify your script(s) (with appropriate parameters) as the SRC for each of the frames.

There is no specific support for creating <FRAMESET> sections in, but the HTML is very simple to write. See the frame documentation in Netscape's home pages for details
2. Specify the destination for the document in the HTTP header

You may provide a -target parameter to the header() method:

    print $q->header(-target=>'ResultsWindow');

This will tell Netscape to load the output of your script into the frame named "ResultsWindow". If a frame of that name doesn't already exist, Netscape will pop up a new window and load your script's document into that. There are a number of magic names that you can use for targets. See the frame documents on Netscape's home pages for details.

3. Specify the destination for the document in the <FORM> tag

You can specify the frame to load in the FORM tag itself. With it looks like this:

    print $q->startform(-target=>'ResultsWindow');

When your script is reinvoked by the form, its output will be loaded into the frame named "ResultsWindow". If one doesn't already exist a new window will be created.

The script "frameset.cgi" in the examples directory shows one way to create pages in which the fill-out form and the response live in side-by-side frames.

LIMITED SUPPORT FOR CASCADING STYLE SHEETS ^ has limited support for HTML3's cascading style sheets (css). To incorporate a stylesheet into your document, pass the start_html() method a -style parameter. The value of this parameter may be a scalar, in which case it is incorporated directly into a <STYLE> section, or it may be a hash reference. In the latter case you should provide the hash with one or more of -src or -code. -src points to a URL where an externally-defined stylesheet can be found. -code points to a scalar value to be incorporated into a <STYLE> section. Style definitions in -code override similarly-named ones in -src, hence the name "cascading."

To refer to a style within the body of your document, add the -class parameter to any HTML element:

    print h1({-class=>'Fancy'},'Welcome to the Party');

Or define styles on the fly with the -style parameter:

    print h1({-style=>'Color: red;'},'Welcome to Hell');

You may also use the new span() element to apply a style to a section of text:

    print span({-style=>'Color: red;'},
               h1('Welcome to Hell'),
               "Where did that handbasket get to?"

Note that you must import the ":html3" definitions to have the span() method available. Here's a quick and dirty example of using CSS's. See the CSS specification at for more information.

    use CGI qw/:standard :html3/;

    #here's a stylesheet incorporated directly into the page
    P.Tip {
        margin-right: 50pt;
        margin-left: 50pt;
        color: red;
    P.Alert {
        font-size: 30pt;
        font-family: sans-serif;
      color: red;
    print header();
    print start_html( -title=>'CGI with Style',
    print h1('CGI with Style'),
            "Better read the cascading style sheet spec before playing with this!"),
          span({-style=>'color: magenta'},
               "Look Mom, no hands!",
               "Whooo wee!"
    print end_html;


If you are running the script from the command line or in the perl debugger, you can pass the script a list of keywords or parameter=value pairs on the command line or from standard input (you don't have to worry about tricking your script into reading from environment variables). You can pass keywords like this: keyword1 keyword2 keyword3

or this: keyword1+keyword2+keyword3

or this: name1=value1 name2=value2

or this: name1=value1&name2=value2

or even as newline-delimited parameters on standard input.

When debugging, you can use quotes and backslashes to escape characters in the familiar shell manner, letting you place spaces and other funny characters in your parameter=value pairs: "name1='I am a long value'" "name2=two\ words"


The dump() method produces a string consisting of all the query's name/value pairs formatted nicely as a nested list. This is useful for debugging purposes:

    print $query->dump

Produces something that looks like:


You can pass a value of 'true' to dump() in order to get it to print the results out as plain text, suitable for incorporating into a <PRE> section.

As a shortcut, as of version 1.56 you can interpolate the entire CGI object into a string and it will be replaced with the a nice HTML dump shown above:

    $query=new CGI;
    print "<H2>Current Values</H2> $query\n";


Some of the more useful environment variables can be fetched through this interface. The methods are as follows:


Return a list of MIME types that the remote browser accepts. If you give this method a single argument corresponding to a MIME type, as in $query->accept('text/html'), it will return a floating point value corresponding to the browser's preference for this type from 0.0 (don't want) to 1.0. Glob types (e.g. text/*) in the browser's accept list are handled correctly.


Returns the HTTP_COOKIE variable, an HTTP extension implemented by Netscape browsers version 1.1 and higher. Cookies have a special format, and this method call just returns the raw form (?cookie dough). See cookie() for ways of setting and retrieving cooked cookies.


Returns the HTTP_USER_AGENT variable. If you give this method a single argument, it will attempt to pattern match on it, allowing you to do something like $query->user_agent(netscape);


Returns additional path information from the script URL. E.G. fetching /cgi-bin/your_script/additional/stuff will result in $query->path_info() returning "additional/stuff".

NOTE: The Microsoft Internet Information Server is broken with respect to additional path information. If you use the Perl DLL library, the IIS server will attempt to execute the additional path information as a Perl script. If you use the ordinary file associations mapping, the path information will be present in the environment, but incorrect. The best thing to do is to avoid using additional path information in CGI scripts destined for use with IIS.


As per path_info() but returns the additional path information translated into a physical path, e.g. "/usr/local/etc/httpd/htdocs/additional/stuff".

The Microsoft IIS is broken with respect to the translated path as well.


Returns either the remote host name or IP address. if the former is unavailable.

script_name() Return the script name as a partial URL, for self-refering scripts.

Return the URL of the page the browser was viewing prior to fetching your script. Not available for all browsers.

auth_type ()

Return the authorization/verification method in use for this script, if any.

server_name ()

Returns the name of the server, usually the machine's host name.

virtual_host ()

When using virtual hosts, returns the name of the host that the browser attempted to contact

server_software ()

Returns the server software and version number.

remote_user ()

Return the authorization/verification name used for user verification, if this script is protected.

user_name ()

Attempt to obtain the remote user's name, using a variety of different techniques. This only works with older browsers such as Mosaic. Netscape does not reliably report the user name!


Returns the method used to access your script, usually one of 'POST', 'GET' or 'HEAD'.


In addition to its shortcuts for creating form elements, defines general HTML shortcut methods as well. HTML shortcuts are named after a single HTML element and return a fragment of HTML text that you can then print or manipulate as you like.

This example shows how to use the HTML methods:

        $q = new CGI;
        print $q->blockquote(
                             "Many years ago on the island of",
                             "there lived a minotaur named",

This results in the following HTML code (extra newlines have been added for readability):

        Many years ago on the island of
        <a HREF="">Crete</a> there lived
        a minotaur named <strong>Fred.</strong> 

If you find the syntax for calling the HTML shortcuts awkward, you can import them into your namespace and dispense with the object syntax completely (see the next section for more details):

        use CGI shortcuts;      # IMPORT HTML SHORTCUTS
        print blockquote(
                     "Many years ago on the island of",
                     "there lived a minotaur named",


The HTML methods will accept zero, one or multiple arguments. If you provide no arguments, you get a single tag:

        print hr;  
        #  gives "<hr>"

If you provide one or more string arguments, they are concatenated together with spaces and placed between opening and closing tags:

        print h1("Chapter","1"); 
        # gives "<h1>Chapter 1</h1>"

If the first argument is an associative array reference, then the keys and values of the associative array become the HTML tag's attributes:

        print a({href=>'fred.html',target=>'_new'},
                "Open a new frame");
        # gives <a href="fred.html",target="_new">Open a new frame</a>

You are free to use dashes in front of the attribute names if you prefer:

        print img {-src=>'fred.gif',-align=>'LEFT'};
        # gives <img ALIGN="LEFT" SRC="fred.gif">

Generating new HTML tags

Since no mere mortal can keep up with Netscape and Microsoft as they battle it out for control of HTML, the code that generates HTML tags is general and extensible. You can create new HTML tags freely just by referring to them on the import line:

        use CGI shortcuts,winkin,blinkin,nod;

Now, in addition to the standard CGI shortcuts, you've created HTML tags named "winkin", "blinkin" and "nod". You can use them like this:

        print blinkin {color=>'blue',rate=>'fast'},"Yahoo!";
        # <blinkin COLOR="blue" RATE="fast">Yahoo!</blinkin>


As a convenience, you can import most of the CGI method calls directly into your name space. The syntax for doing this is:

        use CGI <list of methods>;

The listed methods will be imported into the current package; you can call them directly without creating a CGI object first. This example shows how to import the param() and header() methods, and then use them directly:

        use CGI param,header;
        print header('text/plain');
        $zipcode = param('zipcode');

You can import groups of methods by referring to a number of special names:


Import all CGI-handling methods, such as param(), path_info() and the like.


Import all fill-out form generating methods, such as textfield().


Import all methods that generate HTML 2.0 standard elements.


Import all methods that generate HTML 3.0 proposed elements (such as <table>, <super> and <sub>).


Import all methods that generate Netscape-specific HTML extensions.


Import all HTML-generating shortcuts (i.e. 'html2' + 'html3' + 'netscape')...


Import "standard" features, 'html2', 'form' and 'cgi'.


Import all the available methods. For the full list, see the code, where the variable %TAGS is defined.

Note that in the interests of execution speed does not use the standard Exporter syntax for specifying load symbols. This may change in the future.

If you import any of the state-maintaining CGI or form-generating methods, a default CGI object will be created and initialized automatically the first time you use any of the methods that require one to be present. This includes param(), textfield(), submit() and the like. (If you need direct access to the CGI object, you can find it in the global variable $CGI::Q). By importing methods, you can create visually elegant scripts:

   use CGI standard,html2;
       start_html('Simple Script'),
       h1('Simple Script'),
       "What's your name? ",textfield('name'),p,
       "What's the combination?",
       "What's your favorite color?",

    if (param) {
           "Your name is ",em(param('name')),p,
           "The keywords are: ",em(join(", ",param('words'))),p,
           "Your favorite color is ",em(param('color')),".\n";
    print end_html;


NPH, or "no-parsed-header", scripts bypass the server completely by sending the complete HTTP header directly to the browser. This has slight performance benefits, but is of most use for taking advantage of HTTP extensions that are not directly supported by your server, such as server push and PICS headers.

Servers use a variety of conventions for designating CGI scripts as NPH. Many Unix servers look at the beginning of the script's name for the prefix "nph-". The Macintosh WebSTAR server and Microsoft's Internet Information Server, in contrast, try to decide whether a program is an NPH script by examining the first line of script output. supports NPH scripts with a special NPH mode. When in this mode, will output the necessary extra header information when the header() and redirect() methods are called.

The Microsoft Internet Information Server requires NPH mode. As of version 2.30, will automatically detect when the script is running under IIS and put itself into this mode. You do not need to do this manually, although it won't hurt anything if you do.

There are a number of ways to put into NPH mode:

In the use statement Simply add ":nph" to the list of symbols to be imported into your script:
      use CGI qw(:standard :nph)
By calling the nph() method:

Call nph() with a non-zero parameter at any point after using in your program.

By using -nph parameters in the header() and redirect() statements:
      print $q->header(-nph=&gt;1);


Copyright 1995,1996, Lincoln D. Stein. All rights reserved. It may be used and modified freely, but I do request that this copyright notice remain attached to the file. You may modify this module as you wish, but if you redistribute a modified version, please attach a note listing the modifications you have made.

Address bug reports and comments to:


Thanks very much to:

Matt Heffron (
James Taylor (
Scott Anguish <>
Mike Jewell (
Timothy Shimmin (
Joergen Haegg (
Laurent Delfosse (
Richard Resnick (
Craig Bishop (
Tony Curtis (
Tim Bunce (
Tom Christiansen (
Andreas Koenig (k@franz.ww.TU-Berlin.DE)
Tim MacKenzie (
Kevin B. Hendricks (
Stephen Dahmen (
Ed Jordan (
David Alan Pisoni (
...and many many more...

for suggestions and bug fixes.


        use CGI;
        $query = new CGI;

        print $query->header;
        print $query->start_html("Example Form");
        print "<H1> Example Form</H1>\n";
        print $query->end_html;
        sub print_prompt {
           my($query) = @_;
           print $query->startform;
           print "<EM>What's your name?</EM><BR>";
           print $query->textfield('name');
           print $query->checkbox('Not my real name');
           print "<P><EM>Where can you find English Sparrows?</EM><BR>";
           print $query->checkbox_group(
                                 -name=>'Sparrow locations',
           print "<P><EM>How far can they fly?</EM><BR>",
                        -name=>'how far',
                        -values=>['10 ft','1 mile','10 miles','real far'],
                        -default=>'1 mile');
           print "<P><EM>What's your favorite color?</EM>  ";
           print $query->popup_menu(-name=>'Color',
           print $query->hidden('Reference','Monty Python and the Holy Grail');
           print "<P><EM>What have you got there?</EM><BR>";
           print $query->scrolling_list(
                         -values=>['A Coconut','A Grail','An Icon',
                                   'A Sword','A Ticket'],
           print "<P><EM>Any parting comments?</EM><BR>";
           print $query->textarea(-name=>'Comments',
           print "<P>",$query->reset;
           print $query->submit('Action','Shout');
           print $query->submit('Action','Scream');
           print $query->endform;
           print "<HR>\n";
        sub do_work {
           my($query) = @_;

           print "<H2>Here are the current settings in this form</H2>";

           foreach $key ($query->param) {
              print "<STRONG>$key</STRONG> -> ";
              @values = $query->param($key);
              print join(", ",@values),"<BR>\n";
        sub print_tail {
           print <<END;
        <ADDRESS>Lincoln D. Stein</ADDRESS><BR>
        <A HREF="/">Home Page</A>


This module has grown large and monolithic. Furthermore it's doing many things, such as handling URLs, parsing CGI input, writing HTML, etc., that are also done in the LWP modules. It should be discarded in favor of the CGI::* modules, but somehow I continue to work on it.

Note that the code is truly contorted in order to avoid spurious warnings when programs are run with the -w switch.


CGI::Carp, URI::URL, CGI::Request, CGI::MiniSvr, CGI::Base, CGI::Form, CGI::Apache, CGI::Switch, CGI::Push, CGI::Fast

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