[logo] CGI.pm - a Perl5 CGI Library

Version 2.39, 3/24/98, L. Stein


This perl 5 library uses objects to create Web fill-out forms on the fly and to parse their contents. It provides a simple interface for parsing and interpreting query strings passed to CGI scripts. However, it also offers a rich set of functions for creating fill-out forms. Instead of remembering the syntax for HTML form elements, you just make a series of perl function calls. An important fringe benefit of this is that the value of the previous query is used to initialize the form, so that the state of the form is preserved from invocation to invocation.

Everything is done through a ``CGI'' object. When you create one of these objects it examines the environment for a query string, parses it, and stores the results. You can then ask the CGI object to return or modify the query values. CGI objects handle POST and GET methods correctly, and correctly distinguish between scripts called from <ISINDEX> documents and form-based documents. In fact you can debug your script from the command line without worrying about setting up environment variables.

A script to create a fill-out form that remembers its state each time it's invoked is very easy to write with CGI.pm:


use CGI qw(:standard);

print header;
print start_html('A Simple Example'),
    h1('A Simple Example'),
    "What's your name? ",textfield('name'),
    "What's the combination?",
    "What's your favorite color? ",

if (param()) {
	"Your name is",em(param('name')),
	"The keywords are: ",em(join(", ",param('words'))),
	"Your favorite color is ",em(param('color')),
print a({href=>'../cgi_docs.html'},'Go to the documentation');
Select this link to try the script
More scripting examples


  • Downloading & Installation
  • Creating a new CGI query object
  • Saving the state of the form
  • CGI Functions that Take Multiple Arguments
  • Creating the HTTP header
  • HTML shortcuts
  • Creating forms
  • Importing CGI methods
  • Debugging
  • HTTP session variables
  • Netscape Cookies
  • Support for Netscape frames
  • Support for JavaScript
  • Limited Support for Cascading Style Sheets
  • Using NPH Scripts
  • Advanced techniques
  • Subclassing CGI.pm
  • Using CGI.pm with mod_perl and FastCGI
  • Migrating from cgi-lib.pl
  • Using the File Upload Feature
  • Avoiding Denial of Service Attacks
  • Using CGI.pm on non-Unix Platforms
  • The Relationship of CGI.pm to the CGI::* Modules
  • Distribution information
  • CGI-perl mailing list
  • What's new in version 2.39?

  • Downloading & Installation

    This package requires perl 5.003 patch level 7 or higher. Earlier versions of Perl may work, but CGI.pm has not been tested with them. If you're really stuck, edit the source code to remove the line that says "require 5.00307", but don't be surprised if you run into problems.

    If you are using a Unix system, you should have perl do the installation for you. Move to the directory containing CGI.pm and type the following commands:

       % perl Makefile.PL
       % make
       % make install
    You may need to be root to do the last step.

    This will create two new files in your Perl library. CGI.pm is the main library file. Carp.pm (in the subdirectory "CGI") contains some optional utility routines for writing nicely formatted error messages into your server logs. See the Carp.pm man page for more details.

    If you get error messages when you try to install, then you are either:

    1. Running a Windows NT port of Perl (or another port) that doesn't have make or the MakeMaker program built into it.
    2. Have an old version of Perl. Upgrade to 5.003_7 or higher.
    In the former case don't panic. Here's a recipe that will work (commands are given in MS-DOS/Windows form):
      > cd CGI.pm-2.38
      > copy CGI.pm C:\Perl\lib
      > mkdir C:\Perl\lib\CGI
      > copy CGI\*.pm C:\Perl\lib\CGI
    Modify this if your Perl library has a different location.

    If you do not have sufficient privileges to install into /usr/local/lib/perl5, you can still use CGI.pm. Modify the installation recipe as follows:

       % perl Makefile.PL INSTALLDIRS=site INSTALLSITELIB=/home/your/private/dir
       % make
       % make install
    Replace /home/your/private/dir with the full path to the directory you want the library placed in. Now preface your CGI scripts with a preamble something like the following:
    use lib '/home/your/private/dir';
    use CGI;
    Be sure to replace /home/your/private/dir with the true location of CGI.pm.

    Notes on using CGI.pm in NT and other non-Unix platforms

    Creating a new CGI object

    The most basic use of CGI.pm is to get at the query parameters submitted to your script. To create a new CGI object that contains the parameters passed to your script, put the following at the top of your perl CGI programs:
        use CGI;
        $query = new CGI;
    In the object-oriented world of Perl 5, this code calls the new() method of the CGI class and stores a new CGI object into the variable named $query. The new() method does all the dirty work of parsing the script parameters and environment variables and stores its results in the new object. You'll now make method calls with this object to get at the parameters, generate form elements, and do other useful things.

    An alternative form of the new() method allows you to read script parameters from a previously-opened file handle:

        $query = new CGI(FILEHANDLE)
    The filehandle can contain a URL-encoded query string, or can be a series of newline delimited TAG=VALUE pairs. This is compatible with the save() method. This lets you save the state of a CGI script to a file and reload it later. It's also possible to save the contents of several query objects to the same file, either within a single script or over a period of time. You can then reload the multiple records into an array of query objects with something like this:
    open (IN,"test.in") || die;
    while (!eof(IN)) {
        my $q = new CGI(IN);
    You can make simple databases this way, or create a guestbook. If you're a Perl purist, you can pass a reference to the filehandle glob instead of the filehandle name. This is the "official" way to pass filehandles in Perl5:
        my $q = new CGI(\*IN);
    (If you don't know what I'm talking about, then you're not a Perl purist and you needn't worry about it.)

    If you are using the function-oriented interface and want to initialize CGI state from a file handle, the way to do this is with restore_parameters(). This will (re)initialize the default CGI object from the indicated file handle.

    open (IN,"test.in") || die;
    close IN;

    You can initialize a CGI object from an associative-array reference. Values can be either single- or multivalued:

    $query = new CGI({'dinosaur'=>'barney',
                      'song'=>'I love you',
                      'friends'=>[qw/Jessica George Nancy/]});
    You can initialize a CGI object by passing a URL-style query string to the new() method like this:
    $query = new CGI('dinosaur=barney&color=purple');
    Or you can clone a CGI object from an existing one. The parameter lists of the clone will be identical, but other fields, such as autoescaping, are not:
    $old_query = new CGI; $new_query = new CGI($old_query);

    This form also allows you to create a CGI object that is initially empty:

    $empty_query = new CGI('');
    See advanced techniques for more information.

    Fetching A List Of Keywords From The Query

        @keywords = $query->keywords
    If the script was invoked as the result of an <ISINDEX> search, the parsed keywords can be obtained with the keywords() method. This method will return the keywords as a perl array.

    Fetching The Names Of All The Parameters Passed To Your Script

        @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. For backwards compatability, this method will work even if the script was invoked as an <ISINDEX> script: in this case there will be a single parameter name returned named 'keywords'.

    Fetching The Value(s) Of A Named Parameter

       @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.

    As of version 1.50 of this library, the array of parameter names returned will be in the same order in which the browser sent them. Although this is not guaranteed to be identical to the order in which the parameters were defined in the fill-out form, this is usually the case.

    Setting The Value(s) Of A Named Parameter

    This sets the value for the named parameter 'foo' to one or more values. These values will be used to initialize form elements, if you so desire. Note that this is the one way to forcibly change the value of a form field after it has previously been set.

    The second example shows an alternative "named parameter" style of function call that is accepted by most of the CGI methods. See Calling CGI functions that Take Multiple Arguments for an explanation of this style.

    Appending a Parameter

    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.

    Deleting a Named Parameter Entirely

    This deletes a named parameter entirely. This is useful when you want to reset the value of the parameter so that it isn't passed down between invocations of the script.

    Deleting all Parameters

    This deletes all the parameters and leaves you with an empty CGI object. This may be useful to restore all the defaults produced by the form element generating methods.

    Importing parameters into a namespace

       print "Your name is $R::name\n"
       print "Your favorite colors are @R::colors\n";
    This imports all parameters into the given name space. For example, if there were parameters named 'foo1', 'foo2' and 'foo3', after executing $query->import_names('R'), the variables @R::foo1, $R::foo1, @R::foo2, $R::foo2, etc. would conveniently spring into existence. Since CGI has no way of knowing whether you expect a multi- or single-valued parameter, it creates two variables for each parameter. One is an array, and contains all the values, and the other is a scalar containing the first member of the array. Use whichever one is appropriate. For keyword (a+b+c+d) lists, the variable @R::keywords will be created.

    If you don't specify a name space, this method assumes namespace "Q".

    An optional second argument to import_names, if present and non-zero, will delete the contents of the namespace before loading it. This may be useful for environments like mod_perl in which the script does not exit after processing a request.

    Warning: do not import into namespace 'main'. This represents a major security risk, as evil people could then use this feature to redefine central variables such as @INC. CGI.pm will exit with an error if you try to do this.

    Direct Access to the Parameter List

    $q->param_fetch('address')->[1] = '1313 Mockingbird Lane';
    unshift @{$q->param_fetch(-name=>'address')},'George Munster';
    If you need access to the parameter list in a way that isn't covered by the methods above, you can obtain a direct reference to it by calling the param_fetch() method with the name of the parameter you want. This will return an array reference to the named parameters, which you then can manipulate in any way you like.

    You may call param_fetch() with the name of the CGI parameter, or with the -name argument, which has the same meaning as elsewhere. Table of contents

    Saving the Current State of a Form

    Saving the State to a File

    This writes the current query out to the file handle of your choice. The file handle must already be open and be writable, but other than that it can point to a file, a socket, a pipe, or whatever. The contents of the form are written out as TAG=VALUE pairs, which can be reloaded with the new() method at some later time. You can write out multiple queries to the same file and later read them into query objects one by one.

    If you wish to use this method from the function-oriented (non-OO) interface, the exported name for this method is save_parameters(). See advanced techniques for more information.

    Saving the State in a Self-Referencing URL

    This call returns a URL that, when selected, reinvokes this script with all its state information intact. This is most useful when you want to jump around within a script-generated document using internal anchors, but don't want to disrupt the current contents of the form(s). See advanced techniques for an example.

    If you'd like to get the URL without the entire query string appended to it, use the url() method:


    Mixing POST and URL Parameters

       $color = $query->url_param('color');
    It is possible for a script to receive CGI parameters in the URL as well as in the fill-out form by creating a form that POSTs to a URL containing a query string (a "?" mark followed by arguments). The param() method will always return the contents of the POSTed fill-out form, ignoring the URL's query string. To retrieve URL parameters, call the url_param() method. Use it in the same way as param(). The main difference is that it allows you to read the parameters, but not set them.

    Under no circumstances will the contents of the URL query string interfere with similarly-named CGI parameters in POSTed forms. If you try to mix a URL query string with a form submitted with the GET method, the results will not be what you expect. Table of contents

    Calling CGI Functions that Take Multiple Arguments

    In versions of CGI.pm 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, it will usually 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 tag as an attribute. 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 CGI.pm:
       $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 CGI.pm that you intend to use named parameters exclusively:
       $query = new CGI;
       $field = $query->radio_group('name'=>'OS',
    Actually, CGI.pm 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.

    HTML/HTTP parameters that contain internal hyphens, such as -Content-language can be passed by putting quotes around them, or by using an underscore for the second hyphen, e.g. -Content_language.

    The fact that you must use curly {} braces around the attributes passed to functions that create simple HTML tags but don't use them around the arguments passed to all other functions has many people, including myself, confused. As of 2.37b7, the syntax is extended to allow you to use curly braces for all function calls:

       $field = $query->radio_group({-name=>'OS',
    Table of contents

    Creating the HTTP Header

    Creating the Standard Header for a Virtual Document

       print $query->header('image/gif');
    This prints out the required HTTP Content-type: header and the requisite blank line beneath it. If no parameter is specified, it will default to 'text/html'.

    An extended form of this method allows you to specify a status code and a message to pass back to the browser:

       print $query->header(-type=>'image/gif',
                            -status=>'204 No Response');
    This presents the browser with a status code of 204 (No response). Properly-behaved browsers will take no action, simply remaining on the current page. (This is appropriate for a script that does some processing but doesn't need to display any results, or for a script called when a user clicks on an empty part of a clickable image map.)

    Several other named parameters are recognized. Here's a contrived example that uses them all:

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


    Some browsers, such as Internet Explorer, cache the output of CGI scripts. Others, such as Netscape Navigator do not. This leads to annoying and inconsistent behavior when going from one browser to another. You can force the behavior to be consistent by using the -expires parameter. When you specify an absolute or relative expiration interval with this parameter, 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
    	Thu, 25-Apr-96 00:40:33 GMT  at the indicated time & date
    When you use -expires, the script also generates a correct time stamp for the generated document to ensure that your clock and the browser's clock agree. This allows you to create documents that are reliably cached for short periods of time.

    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 Netscape browsers to return 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 value of this parameter can be either a scalar value or an array reference. You can use the latter to generate multiple cookies. (You can use the alias -cookies for readability.)


    The -nph parameter, if set to a non-zero value, will generate a valid header for use in no-parsed-header scripts. For example:
    print $query->header(-nph=>1,
                            -status=>'200 OK',
    You will need to use this if:
    1. You are using Microsoft Internet Information Server.
    2. If you need to create unbuffered output, for example for use in a "server push" script.
    3. To take advantage of HTTP extensions not supported by your server.
    See Using NPH Scripts for more information.

    Other header fields

    Any other parameters that you pass to header() will be turned into correctly formatted HTTP header fields, even if they aren't called for in the current HTTP spec. For example, the example that appears a few paragraphs above creates a field that looks like this:
       Cost: $0.02
    You can use this to take advantage of new HTTP header fields without waiting for the next release of CGI.pm.

    Creating the Header for a Redirection Request

       print $query->redirect('http://somewhere.else/in/the/world');
    This generates a redirection request for the remote browser. It will immediately go to the indicated URL. You should exit soon after this. Nothing else will be displayed.

    You can add your own headers to this as in the header() method.

    You should always use absolute or full URLs in redirection requests. Relative URLs will not work correctly.

    An alternative syntax for redirect() is:

    print $query->redirect(-location=>'http://somewhere.else/',
    The -location parameter gives the destination URL. You may also use -uri or -url if you prefer.

    The -nph parameter, if non-zero tells CGI.pm that this script is running as a no-parsed-header script. See Using NPH Scripts for more information.

    The -method parameter tells the browser what method to use for redirection. This is handy if, for example, your script was called from a fill-out form POST operation, but you want to redirect the browser to a static page that requires a GET.

    All other parameters recognized by the header() method are also valid in redirect. Table of contents

    HTML Shortcuts

    Creating an HTML Header

       named parameter style
       print $query->start_html(-title=>'Secrets of the Pyramids',
    			    -meta=>{'keywords'=>'pharoah secret mummy',
                                        'copyright'=>'copyright 1996 King Tut'},
       old style
       print $query->start_html('Secrets of the Pyramids',
    This will return a canned HTML header and the opening <BODY> tag. All parameters are optional:

    Ending an HTML Document

      print $query->end_html
    This ends an HTML document by printing the </BODY> </HTML> tags.

    Other HTML Tags

    CGI.pm provides shortcut methods for many other HTML tags. All HTML2 tags and the Netscape extensions are supported, as well as the HTML3 tags that are in common usage (including tables). Unpaired tags, paired tags, and tags that contain attributes are all supported using a simple syntax.

    To see the list of HTML tags that are supported, open up the CGI.pm file and look at the functions defined in the %EXPORT_TAGS array.

    Unpaired Tags

    Unpaired tags include <P>, <HR> and <BR>. The syntax for creating them is:
       print $query->hr;
    This prints out the text "<hr>".

    Paired Tags

    Paired tags include <EM>, <I> and the like. The syntax for creating them is:
       print $query->em("What a silly art exhibit!");
    This prints out the text "<em>What a silly art exhibit!</em>".

    You can pass as many text arguments as you like: they'll be concatenated together with spaces. This allows you to create nested tags easily:

       print $query->h3("The",$query->em("silly"),"art exhibit");
    This creates the text:
       <h3>The <em>silly</em> art exhibit</h3>

    When used in conjunction with the import facility, the HTML shortcuts can make CGI scripts easier to read. For example:

       use CGI qw/:standard/;
       print h1("Road Guide"),
              li(a({href=>"start.html"},"The beginning")),
              li(a({href=>"middle.html"},"The middle")),
              li(a({href=>"end.html"},"The end"))

    Most HTML tags are represented as lowercase function calls. There are a few exceptions:

    1. The <tr> tag used to start a new table row conflicts with the perl translate function tr(). Use TR() or Tr() instead.
    2. The <param> tag used to pass parameters to an applet conflicts with CGI's own param() method. Use PARAM() instead.
    3. The <select> tag used to create selection lists conflicts with perl's select() function. Use Select() instead.

    Tags with Attributes

    To add attributes to an HTML tag, simply pass a reference to an associative array as the first argument. The keys and values of the associative array become the names and values of the attributes. You can use an initial hyphen (-name) for readability if you wish:
       use CGI qw/:standard/;
       print a({-href=>"bad_art.html"},"Jump to the silly exhibit");

    Distributive HTML Tags and Tables

    All HTML tags are distributive. If you give them an argument consisting of a reference to a list, the tag will be distributed across each element of the list. For example, here's one way to make an ordered list:
    print ul(
    This example will result in HTML output that looks like this:
      <LI TYPE="disc">Sneezy</LI>
      <LI TYPE="disc">Doc</LI>
      <LI TYPE="disc">Sleepy</LI>
      <LI TYPE="disc">Happy</LI>
    You can take advantage of this to create HTML tables easily and naturally. Here is some code and the HTML it outputs:
    use CGI qw/:standard :html3 -no_debug/;
    print table({-border=>''},
            caption(strong('When Should You Eat Your Vegetables?')),
    When Should You Eat Your Vegetables?
    Breakfast Lunch Dinner
    Tomatoesno yes yes
    Broccolino no yes
    Onionsyes yes yes

    Notice the use of -no_debug in a program that we intend to call from the command line.

    If you want to produce tables programatically, you can do it this way:

    use CGI qw/:standard :html3 -no_debug/;
    @values = (1..5);
    @headings = ('N','N'.sup('2'),'N'.sup('3'));
    @rows = th(\@headings);
    foreach $n (@values) {
    print table({-border=>'',-width=>'25%'},
                caption(b('Wow.  I can multiply!')),
    Wow. I can multiply!
    N N2 N3
    1 1 1
    2 4 8
    3 9 27
    4 16 64
    5 25 125
    Table of contents

    Creating Forms

    General note 1. The various form-creating methods all return strings to the caller. These strings will contain the HTML code 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.

    General note 2. The default values that you specify for the forms are only used the first time the script is invoked. If there are already values present in the query string, they are used, even if 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. (This is a new feature in 2.15) This forces the default value to be used, regardless of the previous value of the field:
             print $query->textfield(-name=>'favorite_color',
    If you want to reset all fields to their defaults, you can:
    1. Create a special defaults button using the defaults() method.
    2. Create a hypertext link that calls your script without any parameters.
    General note 3. You can put multiple forms on the same page if you wish. However, be warned that it isn't always easy to preserve state information for more than one form at a time. See advanced techniques for some hints.

    General note 4. By popular demand, the text and labels that you provide for form elements are escaped according to HTML rules. This means that you can safely use "<CLICK ME>" as the label for a button. However, this behavior may interfere with your ability to incorporate special HTML character sequences, such as &Aacute; (Á) 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;
    You can turn autoescaping back on at any time with $query->autoEscape('yes')

    Form Elements

  • Opening a form
  • Text entry fields
  • Big text entry fields
  • Password fields
  • File upload fields
  • Popup menus
  • Scrolling lists
  • Checkbox groups
  • Individual checkboxes
  • Radio button groups
  • Submission buttons
  • Reset buttons
  • Reset to defaults button
  • Hidden fields
  • Clickable Images
  • JavaScript Buttons
  • Autoescaping HTML
  • Up to table of contents

    Creating An Isindex Tag

       print $query->isindex($action);
    isindex() without any arguments returns an <ISINDEX> tag that designates your script as the URL to call. If you want the browser to call a different URL to handle the search, pass isindex() the URL you want to be called.

    Starting And Ending A Form

       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. endform() returns a </FORM> tag.

    The form encoding is a new feature introduced in version 1.57 in order to support the "file upload" feature of Netscape 2.0. The form encoding tells the browser how to package up the contents of the form in order to transmit it across the Internet. There are two types of encoding that you can specify:

    This is the 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, CGI.pm 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, CGI.pm 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 CGI.pm or another library that knows how to handle them. Unless you are using the file upload feature, there's no particular reason to use this type of encoding.

    For compatability, 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().

    If you plan to make use of the JavaScript features of Netscape 2.0, you can provide startform() with the optional -name and/or -onSubmit parameters. -name has no effect on the display of the form, but can be used to give the form an identifier so that it can be manipulated by JavaScript functions. Provide the -onSubmit parameter in order to register some JavaScript code to be performed just before the form is submitted. This is useful for checking the validity of a form before submitting it. Your JavaScript code should return a value of "true" to let Netscape know that it can go ahead and submit the form, and "false" to abort the submission.

    Starting a Form that Uses the Netscape 2.0 "File Upload" Feature

       print $query->start_multipart_form($method,$action,$encoding);
         ...various form stuff...
       print $query->endform;
    This has exactly the same usage as startform(), but it specifies form encoding type multipart/form-data as the default.

    Creating A Text Field

      Named parameter style
      print $query->textfield(-name=>'field_name',
    	                    -default=>'starting value',
       Old style
      print $query->textfield('foo','starting value',50,80);
    textfield() will return a text input field. As with all these methods, the field will be initialized with its previous contents from earlier invocations of the script. If you want to force in the new value, overriding the existing one, see General note 2.

    When the form is processed, the value of the text field can be retrieved with:

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

    JavaScripting: You can also provide -onChange, -onFocus, -onBlur and -onSelect parameters to register JavaScript event handlers.

    Creating A Big Text Field

       Named parameter style
       print $query->textarea(-name=>'foo',
    	 		  -default=>'starting value',
       Old style
       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: Like textfield(), you can provide -onChange, -onFocus, -onBlur and -onSelect parameters to register JavaScript event handlers.

    Creating A Password Field

       Named parameter style
       print $query->password_field(-name=>'secret',
    				-value=>'starting value',
       Old style
       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.

    Creating a File Upload Field

        Named parameters style
        print $query->filefield(-name=>'uploaded_file',
    	                    -default=>'starting value',
        Old style
        print $query->filefield('uploaded_file','starting value',50,80);
    filefield() will return a form field that prompts the user to upload a file. filefield() will return a file upload field for use with Netscape 2.0 browsers. Netscape will prompt the remote user to select a file to transmit over the Internet to the server. Other browsers currently ignore this field.

    In order to take full advantage of the file upload facility you must use the new multipart form encoding scheme. You can do this either by calling startform() and specify an encoding type of $CGI::MULTIPART or by using the new start_multipart_form() method. If you don't use multipart encoding, then you'll be able to retreive the name of the file selected by the remote user, but you won't be able to access its contents.

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

           $filename = $query->param('uploaded_file');
    where "uploaded_file" is whatever you named the file upload field. Under Netscape 2.0beta1 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 machine, the filename will follow DOS conventions:
    On a Macintosh machine, the filename will follow Mac conventions:
    	HD 40:Desktop Folder:Sort Through:Reminders
    Netscape 2.0beta2 changes this behavior and only returns the name of the file itself. Who knows what the behavior of the release browser will be?

    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;
           close $filename;
    You can have several file upload fields in the same form, and even give them the same name if you like (in the latter case param() will return a list of file names).

    When processing an uploaded file, CGI.pm creates a temporary file on your hard disk and passes you a file handle to that file. After you are finished with the file handle, CGI.pm unlinks (deletes) the temporary file. If you need to you can access the temporary file directly. Its name is stored inside the CGI object's "private" data, and you can access it by passing the file name to the tmpFileName() method:

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

    The temporary file will be deleted automatically when your program exits unless you manually rename it. On some operating systems (such as Windows NT), you will need to close the temporary file's filehandle before your program exits. Otherwise the attempt to delete the temporary file will fail.

    A potential problem with the temporary file upload feature is that the temporary file is accessible to any local user on the system. In previous versions of this module, the temporary file was world readable, meaning that anyone could peak at what was being uploaded. As of version 2.36, the modes on the temp file have been changed to read/write by owner only. Only the Web server and its CGI scripts can access the temp file. Unfortunately this means that one CGI script can spy on another! To make the temporary files really private, set the CGI global variable $CGI::PRIVATE_TEMPFILES to 1. Alternatively, call the built-in function CGI::private_tempfiles(1), or just use CGI qw/-private_tempfiles. The temp file will now be unlinked as soon as it is created, making it inaccessible to other users. The downside of this is that you will be unable to access this temporary file directly (tmpFileName() will continue to return a string, but you will find no file at that location.) Further, since PRIVATE_TEMPFILES is a global variable, its setting will affect all instances of CGI.pm if you are running mod_perl. You can work around this limitation by declaring $CGI::PRIVATE_TEMPFILES as a local at the top of your script.

    On Windows NT, it is impossible to make a temporary file private. This is because Windows doesn't allow you to delete a file before closing it.

    Usually the browser sends along some header information along with the text of the file itself. Currently the headers contain only the original file name and the MIME content type (if known). Future browsers might 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. For example, this code fragment retrieves the MIME type of the uploaded file (be careful to use the proper capitalization for "Content-Type"!):

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

    JavaScripting: Like textfield(), filefield() accepts -onChange, -onFocus, -onBlur and -onSelect parameters to register JavaScript event handlers. Caveats and potential problems in the file upload feature.

    Creating A Popup Menu

      Named parameter style
      print $query->popup_menu(-name=>'menu_name',
                                -values=>[qw/eenie meenie minie/], 
      print $query->popup_menu(-name=>'menu_name',
      Old style
      print $query->popup_menu('menu_name',
    popup_menu() creates a menu. When the form is processed, the selected value of the popup menu can be retrieved using:
         $popup_menu_value = $query->param('menu_name');
    JavaScripting: You can provide -onChange, -onFocus, and -onBlur parameters to register JavaScript event handlers.

    Creating A Scrolling List

       Named parameter style
       print $query->scrolling_list(-name=>'list_name',
       Old style
       print $query->scrolling_list('list_name',
    scrolling_list() creates a scrolling list. 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: You can provide -onChange, -onFocus, and -onBlur parameters to register JavaScript event handlers.

    Creating A Group Of Related Checkboxes

       Named parameter style
       print $query->checkbox_group(-name=>'group_name',
       Old Style
       print $query->checkbox_group('group_name',
       HTML3 Browsers Only
       print $query->checkbox_group(-name=>'group_name',
    checkbox_group() creates a list of checkboxes that are related by the same name. When the form is processed, the list of checked buttons in the group can be retrieved like this:
         @turned_on = $query->param('group_name');
    This function actually returns an array of button elements. You can capture the array and do interesting things with it, such as incorporating it into your own tables or lists. The -nolabels option is also useful in this regard:
           @h = $query->checkbox_group(-name=>'choice',
    JavaScripting: You can provide an -onClick parameter to register some JavaScript code to be performed every time the user clicks on any of the buttons in the group.

    Creating A Standalone Checkbox

       Named parameter list
       print $query->checkbox(-name=>'checkbox_name',
    		           -value=>'TURNED ON',
    		           -label=>'Turn me on');
       Old style
       print $query->checkbox('checkbox_name',1,'TURNED ON','Turn me on');
    checkbox() is used to create an isolated checkbox that isn't logically related to any others. The value of the checkbox can be retrieved using:
         $turned_on = $query->param('checkbox_name');
    JavaScripting: You can provide an -onClick parameter to register some JavaScript code to be performed every time the user clicks on the button.

    Creating A Radio Button Group

       Named parameter style
       print $query->radio_group(-name=>'group_name',
       Old style
       print $query->radio_group('group_name',['eenie','meenie','minie'],
       HTML3-compatible browsers only
       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. When the form is processed, the selected radio button can be retrieved using:
           $which_radio_button = $query->param('group_name');
    This function actually returns an array of button elements. You can capture the array and do interesting things with it, such as incorporating it into your own tables or lists The -nolabels option is useful in this regard.:
           @h = $query->radio_group(-name=>'choice',

    JavaScripting: You can provide an -onClick parameter to register some JavaScript code to be performed every time the user clicks on any of the buttons in the group.

    Creating A Submit Button

       Named parameter style
       print $query->submit(-name=>'button_name',
      Old style
      print $query->submit('button_name','value');
    submit() will create the query submission button. Every form should have one of these. JavaScripting: You can provide an -onClick parameter to register some JavaScript code to be performed every time the user clicks on the button. You can't prevent a form from being submitted, however. You must provide an -onSubmit handler to the form itself to do that.

    Creating A Reset Button

      print $query->reset
    reset() creates the "reset" button. It undoes whatever changes the user has recently made to the form, but does not necessarily reset the form all the way to the defaults. See defaults() for that. It takes the optional label for the button ("Reset" by default). JavaScripting: You can provide an -onClick parameter to register some JavaScript code to be performed every time the user clicks on the button.

    Creating A Defaults Button

      print $query->defaults('button_label')
    defaults() creates "reset to defaults" button. It takes the optional label for the button ("Defaults" by default). When the user presses this button, the form will automagically be cleared entirely and set to the defaults you specify in your script, just as it was the first time it was called.

    Creating A Hidden Field

       Named parameter style
       print $query->hidden(-name=>'hidden_name',
       Old style
       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. [CAUTION] As of version 2.0 I have changed the behavior of hidden fields once again. Read this if you use hidden fields.

    Hidden fields used to behave differently from all other fields: the provided default values always overrode the "sticky" values. This was the behavior people seemed to expect, however it turns out to make it harder to write state-maintaining forms such as shopping cart programs. Therefore I have made the behavior consistent with other fields.

    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 before writing out the form element:

         print $query->hidden('hidden_name');
    Fetch the value of a hidden field this way:
        $hidden_value = $query->param('hidden_name');
                -or (for values created with arrays)-
        @hidden_values = $query->param('hidden_name');

    Creating a Clickable Image Button

       Named parameter style
       print $query->image_button(-name=>'button_name',
       Old style
       print $query->image_button('button_name','/source/URL','MIDDLE');
    image_button() produces an inline image that acts as a submission button. When selected, the form is submitted and the clicked (x,y) coordinates are submitted as well. When the image is clicked, the results are passed to your script in two parameters named "button_name.x" and "button_name.y", where "button_name" is the name of the image button.
        $x = $query->param('button_name.x');
        $y = $query->param('button_name.y');
    JavaScripting: Current versions of JavaScript do not honor the -onClick handler, unlike other buttons.

    Creating a JavaScript Button

       Named parameter style
       print $query->button(-name=>'button1',
                               -value=>'Click Me',
       Old style
       print $query->image_button('button1','Click Me','doButton(this)');
    button() creates a JavaScript button. When the button is pressed, the JavaScript code pointed to by the -onClick parameter is executed. This only works with Netscape 2.0 and higher. Other browsers do not recognize JavaScript and probably won't even display the button. See JavaScripting for more information.

    Controlling HTML Autoescaping

    By default, if you use a special HTML character such as >, < or & as the label or value of a button, it will be escaped using the appropriate HTML escape sequence (e.g. &gt;). This lets you use anything at all for the text of a form field without worrying about breaking the HTML document. However, it may also interfere with your ability to use special characters, such as Á as default contents of fields. You can turn this feature on and off with the method autoEscape().


    to turn automatic HTML escaping off, and
    to turn it back on.

    Importing CGI Methods

    A large number of scripts allocate only a single query object, use it to read parameters or to create a fill-out form, and then discard it. For this type of script, it may be handy to import CGI module methods into your name space. The most common syntax for this is:
    use CGI qw(:standard);
    This imports the standard methods into your namespace. Now instead of getting parameters like this:
    use CGI;
    $dinner = $query->param('entree');
    You can do it like this:
    use CGI qw(:standard);
    $dinner = param('entree');
    Similarly, instead of creating a form like this:
    print $query->start_form,
          "Check here if you're happy: ",
    You can create it like this:
    print start_form,
          "Check here if you're happy: ",
    Even though there's no CGI object in view in the second example, state is maintained using an implicit CGI object that's created automatically. The form elements created this way are sticky, just as before. If you need to get at the implicit CGI object directly, you can refer to it as:

    The use CGI statement is used to import method names into the current name space. There is a slight overhead for each name you import, but ordinarily is nothing to worry about. You can import selected method names like this:

       use CGI qw(header start_html end_html);
    Ordinarily, however, you'll want to import groups of methods using export tags. Export tags refer to sets of logically related methods which are imported as a group with use. Tags are distinguished from ordinary methods by beginning with a ":" character. This example imports the methods dealing with the CGI protocol (param() and the like) as well as shortcuts that generate HTML2-compliant tags:
    use CGI qw(:cgi :html2);
    Currently there are 8 method families defined in CGI.pm. They are:
    These are all the tags that support one feature or another of the CGI protocol, including param(), path_info(), cookie(), request_method(), header() and the like.
    These are all the form element-generating methods, including start_form(), textfield(), etc.
    These are HTML2-defined shortcuts such as br(), p() and head(). It also includes such things as start_html() and end_html() that aren't exactly HTML2, but are close enough.
    These are a few HTML3 extensions that are in common enough usage to be worth including.
    These are Netscape extensions not included in the HTML3 category, including frameset(), blink() and center().
    These are all the HTML generating shortcuts, comprising the union of html2, html3, and netscape.
    This is the union of html2, form, and :cgi (everything except the HTML3 and Netscape extensions).
    This imports all the public methods into your namespace!


    In addition to importing individual methods and method families, use CGI recognizes several pragmas, all proceeded by dashes.
    When you use CGI -any, then any method that the query object doesn't recognize will be interpreted as a new HTML tag. This allows you to support the next ad hoc Netscape or Microsoft HTML extension. For example, to support Netscape's latest tag, <GRADIENT> (which causes the user's desktop to be flooded with a rotating gradient fill until his machine reboots), you can use something like this:
          use CGI qw(-any);
          $q=new CGI;
          print $q->gradient({speed=>'fast',start=>'red',end=>'blue'});
    Since using any causes any mistyped method name to be interpreted as an HTML tag, use it with care or not at all.

    This causes the indicated autoloaded methods to be compiled up front, rather than deferred to later. This is useful for scripts that run for an extended period of time under FastCGI or mod_perl, and for those destined to be crunched by Malcom Beattie's Perl compiler. Use it in conjunction with the methods or method familes you plan to use.
          use CGI qw(-compile :standard :html3);
    or even
          use CGI qw(-compile :all);

    Note that using the -compile pragma in this way will always have the effect of importing the compiled functions into the current namespace. If you want to compile without importing use the compile() method instead.

    Overrides the autoloader so that any function in your program that is not recognized is referred to CGI.pm for possible evaluation. This allows you to use all the CGI.pm functions without adding them to your symbol table, which is of concern for mod_perl users who are worried about memory consumption. Warning: when -autoload is in effect, you cannot use "poetry mode" (functions without the parenthesis). Use hr() rather than hr, or add something like use subs qw/hr p header/ to the top of your script.

    This makes CGI.pm produce a header appropriate for an NPH (no parsed header) script. You may need to do other things as well to tell the server that the script is NPH. See the discussion of NPH scripts below.

    This turns off the command-line processing features. If you want to run a CGI.pm script from the command line to produce HTML, and you don't want it pausing to request CGI parameters from standard input, then use this pragma:
          use CGI qw(-no_debug :standard);
    See debugging for more details.

    CGI.pm can process uploaded file. Ordinarily it spools the uploaded file to a temporary directory, then deletes the file when done. However, this opens the risk of eavesdropping as described in the file upload section. Another CGI script author could peek at this data during the upload, even if it is confidential information. On Unix systems, the -private_tempfiles pragma will cause the temporary file to be unlinked as soon as it is opened and before any data is written into it, eliminating the risk of eavesdropping.

    Optional Utility Functions

    In addition to the standard imported functions, there are a few optional functions that you must request by name if you want them. They were originally intended for internal use only, but are now made available by popular request.

    escape(), unescape()

    use CGI qw/escape unescape/;
    $q = escape('This $string contains ~wonderful~ characters');
    $u = unescape($q);
    These functions escape and unescape strings according to the URL hex escape rules. For example, the space character will be converted into the string "%20".

    escapeHTML(), unescapeHTML()

    use CGI qw/escapeHTML unescapeHTML/;
    $q = escapeHTML('This string is <illegal> html!');
    $u = unescapeHTML($q);
    These functions escape and unescape strings according to the HTML character entity rules. For example, the character < will be escaped as &lt;.


    Ordinarily CGI.pm autoloads most of its functions on an as-needed basis. This speeds up the loading time by deferring the compilation phase. However, if you are using mod_perl, FastCGI or another system that uses a persistent Perl interpreter, you will want to precompile the methods at initialization time. To accomplish this, call the package function compile() like this:
    use CGI ();
    The arguments to compile() are a list of method names or sets, and are identical to those accepted by the use operator.


    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:
       my_script.pl keyword1 keyword2 keyword3
    or this:
       my_script.pl keyword1+keyword2+keyword3
    or this:
       my_script.pl name1=value1 name2=value2
    or this:
       my_script.pl name1=value1&name2=value2
    or even by sending newline-delimited parameters to standard input:
       % my_script.pl
       occupation='granite miner'

    When debugging, you can use quotation marks and the backslash character to escape spaces and other funny characters in exactly the way you would in the shell (which isn't surprising since CGI.pm uses "shellwords.pl" internally). This lets you do this sort of thing:

        my_script.pl 'name 1=I am a long value' name\ 2=two\ words

    If you run a script that uses CGI.pm from the command line and fail to provide it with any arguments, it will print out the line

    (offline mode: enter name=value pairs on standard input)
    then appear to hang. In fact, the library is waiting for you to give it some parameters to process on its standard input. If you want to give it some parameters, enter them as shown above, then indicate that you're finished with input by pressing ^D (^Z on NT/DOS systems). If you don't want to give CGI.pm parameters, just press ^D.

    You can suppress this behavior in any of the following ways:

    1. Call the script with an empty parameter.
          my_script.pl ''

    2. Redirect standard input from /dev/null or an empty file.
          my_script.pl </dev/null

    3. Include "-no_debug" in the list of symbols to import on the "use" line.
          use CGI qw/:standard -no_debug/;
    Table of contents

    Dumping Out All The Name/Value Pairs

    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 $query->dump
    Produces something that looks like this:
    You can achieve the same effect by incorporating the CGI object directly into a string, as in:
       print "<H2>Current Contents:</H2>\n$query\n";

    HTTP Session Variables

    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.
    Return the authorization type, if protection is active. Example "Basic".
    Returns the "magic cookie" maintained by Netscape 1.1 and higher in a raw state. You'll probably want to use cookie() instead, which gives you a high-level interface to the cookie functions. Called with no parameters, raw_cookie() returns the entire cookie structure, which may consist of several cookies appended together (you can recover individual cookies by splitting on the "; " sequence. Called with the name of a cookie, returns the unescaped value of the cookie as set by the server. This may be useful for retrieving cookies that your script did not set.
    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". In addition to reading the path information, you can set it by giving path_info() an optional string argument. The argument is expected to begin with a "/". If not present, one will be added for you. The new path information will be returned by subsequent calls to path_info(), and will be incorporated into the URL generated by self_url().
    As per path_info() but returns the additional path information translated into a physical path, e.g. "/usr/local/etc/httpd/htdocs/additional/stuff". You cannot change the path_translated, nor will setting the additional path information change this value. The reason for this restriction is that the translation of path information into a physical path is ordinarily done by the server in a layer that is inaccessible to CGI scripts.
    Returns a query string suitable for maintaining state.
    Return the URL of the page the browser was viewing prior to fetching your script. Not available for all browsers.
    Return the dotted IP address of the remote host.
    Return the identity-checking information from the remote host. Only available if the remote host has the identd daemon turned on.
    Returns either the remote host name or IP address. if the former is unavailable.
    Return the name given by the remote user during password authorization.
    Return the HTTP method used to request your script's URL, usually one of GET, POST, or HEAD.
    Return the script name as a partial URL, for self-refering scripts.
    Return the name of the WWW server the script is running under.
    Return the name and version of the server software.
    When using the virtual host feature of some servers, returns the name of the virtual host the browser is accessing.
    Return the communications port the server is using.
    Returns the identity of the remote user's browser software, e.g. "Mozilla/1.1N (Macintosh; I; 68K)"
    Attempts to obtain the remote user's name, using a variety of environment variables. This only works with older browsers such as Mosaic. Netscape does not reliably report the user name!
    Table of contents

    Netscape Cookies

    Netscape browsers versions 1.1 and higher support a so-called "cookie" designed to help maintain state within a browser session. CGI.pm 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:

    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.

    Negative expiration times (e.g. "-1d") cause some browsers to delete the cookie from its persistent store. This is a poorly documented feature.

    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 ".capricorn.com", then Netscape will return the cookie to Web servers running on any of the machines "www.capricorn.com", "www2.capricorn.com", "feckless.capricorn.com", 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.

    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/tally.pl", "/cgi-bin/order.pl", and "/cgi-bin/customer_service/complain.pl", but not to the script "/cgi-private/site_admin.pl". By default, path is set to "/", which causes the cookie to be sent to any CGI script on your site.
    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, CGI.pm 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('answers');
    	# $query->cookie(-name=>'answers') works too!
    To retrieve the names of all cookies passed to your script, call cookie() without any parameters. This allows you to iterate through all cookies:
    	foreach $name ($query->cookie()) {
                print $query->cookie($name);

    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.

    Table of contents

    Support for Netscape Frames

    CGI.pm contains support for Netscape frames, a new feature in version 2.0 and higher. Frames are supported in two ways:
    1. You can direct the output of a script into a new window or into a preexisting named frame by providing the name of the frame as a -target argument in the header method. For example, the following code will pop up a new Netscape window and display the script's output:
            $query = new CGI;
            print $query->header(-target=>'_blank');
    2. You can provide the name of a new or preexisting frame in the startform() and start_multipart_form() methods using the -target parameter. When the form is submitted, the output will be redirected to the indicated frame:
            print $query->start_form(-target=>'result_frame');
    Using frames effectively can be tricky. To create a proper frameset in which the query and response are displayed side-by-side requires you to divide the script into three functional sections. The first section should create the <frameset> declaration and exit. The second section is responsible for creating the query form and directing it into the one frame. The third section is responsible for creating the response and directing it into a different frame.

    The examples directory contains a script called popup.cgi that demonstrates a simple popup window. frameset.cgi provides a skeleton script for creating side-by-side query/result frame sets.

    Support for JavaScript

    Netscape versions 2.0 and higher incorporate an interpreted language called JavaScript. It isn't the same as Java, and certainly isn't at all the same as Perl, which is a great pity. JavaScript allows you to programatically change the contents of fill-out forms, create new windows, and pop up dialog box from within Netscape itself. From the point of view of CGI scripting, JavaScript is quite useful for validating fill-out forms prior to submitting them.

    You'll need to know JavaScript in order to use it. The Netscape JavaScript manual contains a good tutorial and reference guide to the JavaScript programming language.

    The usual way to use JavaScript is to define a set of functions in a <SCRIPT> block inside the HTML header and then to register event handlers in the various elements of the page. Events include such things as the mouse passing over a form element, a button being clicked, the contents of a text field changing, or a form being submitted. When an event occurs that involves an element that has registered an event handler, its associated JavaScript code gets called.

    The elements that can register event handlers include the <BODY> of an HTML document, hypertext links, all the various elements of a fill-out form, and the form itself. There are a large number of events, and each applies only to the elements for which it is relevant:

    The browser is loading the current document. Valid in:
    The browser is closing the current page or frame. Valid for:
    The user has pressed the submit button of a form. This event happens just before the form is submitted, and your function can return a value of false in order to abort the submission. Valid for:
    The mouse has clicked on an item in a fill-out form. Valid for:
    The user has changed the contents of a field. Valid for:
    The user has selected a field to work with. Valid for:
    The user has deselected a field (gone to work somewhere else). Valid for:
    The user has changed the part of a text field that is selected. Valid for:
    In order to register a JavaScript event handler with an HTML element, just use the event name as a parameter when you call the corresponding CGI method. For example, to have your validateAge() JavaScript code executed every time the textfield named "age" changes, generate the field like this:
       print $q->textfield(-name=>'age',-onChange=>"validateAge(this)");
    This example assumes that you've already declared the validateAge() function by incorporating it into a <SCRIPT> block. The CGI.pm start_html() method provides a convenient way to create this section.

    Similarly, you can create a form that checks itself over for consistency and alerts the user if some essential value is missing by creating it this way:

       print $q->startform(-onSubmit=>"validateMe(this)");
    See the javascript.cgi script for a demonstration of how this all works.

    Table of contents

    Limited Support for Cascading Style Sheets

    CGI.pm 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 get the span() and style() methods.

    You won't be able to do much with this unless you understand the CSS specification. A more intuitive subclassable library for cascading style sheets in Perl is in the works, but until then, please read the CSS specification at http://www.w3.org/pub/WWW/Style/ to find out how to use these features. Here's a final example to get you started.

    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;

    Table of contents

    Using NPH Scripts

    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.

    CGI.pm supports NPH scripts with a special NPH mode. When in this mode, CGI.pm will output the necessary extra header information when the header() and redirect() methods are called.

    Important: If you use the Microsoft Internet Information Server, you must designate your script as an NPH script. Otherwise many of CGI.pm's features, such as redirection and the ability to output non-HTML files, will fail.

    There are a number of ways to put CGI.pm 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 CGI.pm in your program.

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

    Advanced Techniques

    A Script that Saves Some Information to a File and Restores It

    This script will save its state to a file of the user's choosing when the "save" button is pressed, and will restore its state when the "restore" button is pressed. Notice that it's very important to check the file name for shell metacharacters so that the script doesn't inadvertently open up a command or overwrite someone's file. For this to work, the script's current directory must be writable by "nobody".
    use CGI;
    $query = new CGI;
    print $query->header;
    print $query->start_html("Save and Restore Example");
    print "<H1>Save and Restore Example</H1>\n";
    # Here's where we take action on the previous request
    &save_parameters($query)              if $query->param('action') eq 'save';
    $query = &restore_parameters($query)  if $query->param('action') eq 'restore';
    # Here's where we create the form
    print $query->startform;
    print "Popup 1: ",$query->popup_menu('popup1',['eenie','meenie','minie']),"\n";
    print "Popup 2: ",$query->popup_menu('popup2',['et','lux','perpetua']),"\n";
    print "<P>";
    print "Save/restore state from file: ",$query->textfield('savefile','state.sav'),"\n";
    print "<P>";
    print $query->submit('action','save'),$query->submit('action','restore');
    print $query->submit('action','usual query');
    print $query->endform;
    # Here we print out a bit at the end
    print $query->end_html;
    sub save_parameters {
        local($query) = @_;
        local($filename) = &clean_name($query->param('savefile'));
        if (open(FILE,">$filename")) {
    	close FILE;
    	print "<STRONG>State has been saved to file $filename</STRONG>\n";
        } else {
    	print "<STRONG>Error:</STRONG> couldn't write to file $filename: $!\n";
    sub restore_parameters {
        local($query) = @_;
        local($filename) = &clean_name($query->param('savefile'));
        if (open(FILE,$filename)) {
    	$query = new CGI(FILE);  # Throw out the old query, replace it with a new one
    	close FILE;
    	print "<STRONG>State has been restored from file $filename</STRONG>\n";
        } else {
    	print "<STRONG>Error:</STRONG> couldn't restore file $filename: $!\n";
        return $query;
    # Very important subroutine -- get rid of all the naughty
    # metacharacters from the file name. If there are, we
    # complain bitterly and die.
    sub clean_name {
       local($name) = @_;
       unless ($name=~/^[\w\._-]+$/) {
          print "<STRONG>$name has naughty characters.  Only ";
          print "alphanumerics are allowed.  You can't use absolute names.</STRONG>";
          die "Attempt to use naughty characters";
       return $name;
    If you use the CGI save() and restore() methods a lot, you might be interested in the Whitehead Genome Center's Boulderio file format. It's a way of transferring semi-strucured data from the standard output of one program to the standard input of the next. It comes with a simple Perl database that allows you to store and retrieve records from a DBM or DB_File database, and is compatible with the format used by save() and restore(). You can get more information on Boulderio from:

    A Script that Uses Self-Referencing URLs to Jump to Internal Links

    (Without losing form information).

    Many people have experienced problems with internal links on pages that have forms. Jumping around within the document causes the state of the form to be reset. A partial solution is to use the self_url() method to generate a link that preserves state information. This script illustrates how this works.

    use CGI;
    $query = new CGI;
    # We generate a regular HTML file containing a very long list
    # and a popup menu that does nothing except to show that we
    # don't lose the state information.
    print $query->header;
    print $query->start_html("Internal Links Example");
    print "<H1>Internal Links Example</H1>\n";
    print "<A NAME=\"start\"></A>\n"; # an anchor point at the top
    # pick a default starting value;
    $query->param('amenu','FOO1') unless $query->param('amenu');
    print $query->startform;
    print $query->popup_menu('amenu',[('FOO1'..'FOO9')]);
    print $query->submit,$query->endform;
    # We create a long boring list for the purposes of illustration.
    $myself = $query->self_url;
    print "<OL>\n";
    for (1..100) {
        print qq{<LI>List item #$_<A HREF="$myself#start">Jump to top</A>\n};
    print "</OL>\n";
    print $query->end_html;

    Multiple forms on the same page

    There's no particular trick to this. Just remember to close one form before you open another one. You can reuse the same query object or create a new one. Either technique works.

    There is, however, a problem with maintaining the states of multiple forms. Because the browser only sends your script the parameters from the form in which the submit button was pressed, the state of all the other forms will be lost. One way to get around this, suggested in this example, is to use hidden fields to pass as much information as possible regardless of which form the user submits.

    use CGI;
    $query=new CGI;
    print $query->header;
    print $query->start_html('Multiple forms');
    print "<H1>Multiple forms</H1>\n";
    # form 1
    print "<HR>\n";
    print $query->startform;
    print $query->textfield('text1'),$query->submit('submit1');
    print $query->hidden('text2');  # pass information from the other form
    print $query->endform;
    print "<HR>\n";
    # form 2
    print $query->startform;
    print $query->textfield('text2'),$query->submit('submit2');
    print $query->hidden('text1');  # pass information from the other form
    print $query->endform;
    print "<HR>\n";
    print $query->end_html;

    Table of contents

    Subclassing CGI.pm

    CGI.pm uses various tricks to work in both an object-oriented and function-oriented fashion. It uses even more tricks to load quickly, despite the fact that it is a humungous module. These tricks may get in your way when you attempt to subclass CGI.pm.

    If you use standard subclassing techniques and restrict yourself to using CGI.pm and its subclasses in the object-oriented manner, you'll have no problems. However, if you wish to use the function-oriented calls with your subclass, follow this model:

    package MySubclass;
    use vars qw(@ISA $VERSION);
    require CGI;
    @ISA = qw(CGI);
    $VERSION = 1.0;
    $CGI::DefaultClass = __PACKAGE__;
    $AutoloadClass = 'CGI';
    sub new {
    The first special trick is to set the CGI package variable $CGI::DefaultClass to the name of the module you are defining. If you are using perl 5.004 or higher, you can use the special token "__PACKAGE__" to retrieve the name of the current module. Otherwise, just hard code the name of the module. This variable tells CGI what type of default object to create when called in the function-oriented manner.

    The second trick is to set the package variable $AutoloadClass to the string "CGI". This tells the CGI autoloader where to look for functions that are not defined. If you wish to override CGI's autoloader, set this to the name of your own package.

    More information on extending CGI.pm can be found in my forthcoming book, Lincoln Stein's Guide to CGI.pm, to be published to Wiley & Sons in January 1998.

    Table of contents

    Using CGI.pm with mod_perl and FastCGI


    FastCGI is a protocol invented by OpenMarket that markedly speeds up CGI scripts under certain circumstances. It works by opening up the script at server startup time and redirecting the script's IO to a Unix domain socket. Every time a new CGI request comes in, the script is passed new parameters to work on. This allows the script to perform all its time-consuming operations at initialization time (including loading CGI.pm!) and then respond quickly to new requests.

    FastCGI modules are available for the Apache and NCSA servers as well as for OpenMarket's own server. In order to use FastCGI with Perl you have to run a specially-modified version of the Perl interpreter. Precompiled Binaries and a patch kit are all available on OpenMarket's FastCGI web site.

    To use FastCGI with CGI.pm, change your scripts as follows:

    Old Script

    use CGI qw(:standard);
    print header,
          start_html("CGI Script"),
          h1("CGI Script"),
          "Not much to see here",
          address(a({href=>'/'},"home page"),  

    New Script

    use CGI::Fast qw(:standard);
    # Do time-consuming initialization up here.
    while (new CGI::Fast) {
       print header,
          start_html("CGI Script"),
          h1("CGI Script"),
          "Not much to see here",
          address(a({href=>'/'},"home page"),  
    That's all there is to it. The param() method, form-generation, HTML shortcuts, etc., all work the way you expect.


    mod_perl is a module for the Apache Web server that embeds a Perl interpreter into the Web server. It can be run in either of two modes:
    1. Server launches a new Perl interpreter every time it needs to interpret a Perl script. This speeds CGI scripts significantly because there's no overhead for launching a new Perl process.
    2. A "fast" mode in which the server launches your script at initialization time. You can load all your favorite modules (like CGI.pm!) at initialization time, greatly speeding things up.
    CGI.pm works with mod_perl, versions 0.95 and higher. If you use Perl 5.003_93 or higher, your scripts should run without any modifications. Users with earlier versions of Perl should use the CGI::Apache module instead. This example shows the change needed:

    Old Script

    use CGI qw(:standard);
    print header,
          start_html("CGI Script"),
          h1("CGI Script"),
          "Not much to see here",
          address(a({href=>'/'},"home page"),  

    New Script

    use CGI::Apache qw(:standard);
    print header,
        start_html("CGI Script"),
        h1("CGI Script"),
        "Not much to see here",
        address(a({href=>'/'},"home page"),  
    Important configuration note: When using CGI.pm with mod_perl be careful not to enable either the PerlSendHeader or PerlSetupEnv directives. This is handled automatically by CGI.pm and by Apache::Registry.

    mod_perl comes with a small wrapper library named CGI::Switch that selects dynamically between using CGI and CGI::Apache. This library is no longer needed. However users of CGI::Switch can continue to use it without risk. Note that the "simple" interface to the CGI.pm functions does not work with CGI::Switch. You'll have to use the object-oriented versions (or use the sfio version of Perl!)

    If you use CGI.pm in many of your mod_perl scripts, you may want to preload CGI.pm and its methods at server startup time. To do this, add the following line to httpd.conf:

    PerlScript /home/httpd/conf/startup.pl
    Create the file /home/httpd/conf/startup.pl and put in it all the modules you want to load. Include CGI.pm among them and call its compile() method to precompile its autoloaded methods.
    use CGI ();
    Change the path to the startup script according to your preferences.

    Table of contents

    Migrating from cgi-lib.pl

    To make it easier to convert older scripts that use cgi-lib.pl, CGI.pm provides a CGI::ReadParse() call that is compatible with cgi-lib.pl's ReadParse() subroutine.

    When you call ReadParse(), CGI.pm creates an associative array named %in that contains the named CGI parameters. Multi-valued parameters are separated by "\0" characters in exactly the same way cgi-lib.pl does it. The function result is the number of parameters parsed. You can use this to determine whether the script is being called from a fill out form or not.

    To port an old script to CGI.pm, you have to make just two changes:

    Old Script

        require "cgi-lib.pl";
        print "The price of your purchase is $in{price}.\n";

    New Script

        use CGI qw(:cgi-lib);
        print "The price of your purchase is $in{price}.\n";
    Like cgi-lib's ReadParse, pass a variable glob in order to use a different variable than the default "%in":
       @partners = split("\0",$Q{'golf_partners'});

    The associative array created by CGI::ReadParse() contains a special key 'CGI', which returns the CGI query object itself:

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

    This allows you to add the more interesting features of CGI.pm to your old scripts without rewriting them completely. As an added benefit, the %in variable is actually tie()'d to the CGI object. Changing the CGI object using param() will dynamically change %in, and vice-versa.

    cgi-lib.pl's @in and $in variables are not supported. In addition, the extended version of ReadParse() that allows you to spool uploaded files to disk is not available. You are strongly encouraged to use CGI.pm's file upload interface instead.

    See cgi-lib_porting.html for more details on porting cgi-lib.pl scripts to CGI.pm.

    Using the File Upload Feature

    The file upload feature doesn't work with every combination of browser and server. The various versions of Netscape on the Macintosh, Unix and Windows platforms don't all seem to implement file uploading in exactly the same way. I've tried to make CGI.pm work with all versions on all platforms, but I keep getting reports from people of instances that break the file upload feature.

    Known problems include:

    1. Large file uploads may fail when using SSL version 2.0. This affects the Netscape servers and possibly others that use the SSL library. I have received reports that WebSite Pro suffers from this problem. This is a documented bug in the Netscape implementation of SSL and not a problem with CGI.pm.
    2. If you try to upload a directory path with Unix Netscape, the browser will hang until you hit the "stop" button. I haven't tried to figure this one out since I think it's dumb of Netscape to allow this to happen at all.
    3. If you create the CGI object in one package (e.g. "main") and then obtain the filehandle in a different package (e.g. "foo"), the filehandle will be accessible through "main" but not "foo". In order to use the filehandle, try the following contortion:
            $file = $query->param('file to upload');
            $file = "main::$file";
      I haven't found a way to determine the correct caller in this situation. I might add a readFile() method to CGI if this problem bothers enough people.
    The main technical challenge of handling file uploads is that it potentially involves sending more data to the CGI script than the script can hold in main memory. For this reason CGI.pm creates temporary files in either the /usr/tmp or the /tmp directory. These temporary files have names like CGItemp125421, and should be deleted automatically.

    Frequent Problems

    When you run a script from the command line, it says "offline mode: enter name=value pairs on standard input". What do I do now?

    This is a prompt to enter some CGI parameters for the purposes of debugging. You can now type in some parameters like this:
    End the list by typing a control-D (or control-Z on DOS/Windows systems).

    If you want to run a CGI script from a script or batch file, and don't want this behavior, just pass it an empty parameter list like this:

         my_script.pl ''
    This will work too on Unix systems:
         my_script.pl </dev/null
    Another option is to use the "-no_debug" pragma when you "use" CGI.pm. This will suppress command-line debugging completely:
    use CGI qw/:standard -no_debug/;

    You can't retrieve the name of the uploaded file using the param() method

    Most likely the remote user isn't using version 2.0 (or higher) of Netscape. Alternatively she just isn't filling in the form completely.

    When you accidentally try to upload a directory name, the browser hangs

    This seems to be a Netscape browser problem. It starts to upload junk to the script, then hangs. You can abort by hitting the "stop" button.

    You can read the name of the uploaded file, but can't retrieve the data

    First check that you've told CGI.pm to use the new multipart/form-data scheme. If it still isn't working, there may be a problem with the temporary files that CGI.pm needs to create in order to read in the (potentially very large) uploaded files. Internally, CGI.pm tries to create temporary files with names similar to CGITemp123456 in a temporary directory. To find a suitable directory it first looks for /usr/tmp and then for /tmp. If it can't find either of these directories, it tries for the current directory, which is usually the same directory that the script resides in.

    If you're on a non-Unix system you may need to modify CGI.pm to point at a suitable temporary directory. This directory must be writable by the user ID under which the server runs (usually "nobody") and must have sufficient capacity to handle large file uploads. Open up CGI.pm, and find the line:

          package TempFile;
          foreach ('/usr/tmp','/tmp') {
             do {$TMPDIRECTORY = $_; last} if -d $_ && -w _;
    Modify the foreach() line to contain a series of one or more directories to store temporary files in.

    Alternatively, you can just skip the search entirely and force CGI.pm to store its temporary files in some logical location. Do this at the top of your script with a line like this one: $TempFile::TMPDIRECTORY='/WWW_ROOT';

    On Windows Systems, the temporary file is never deleted, but hangs around in \temp, taking up space.

    Be sure to close the filehandle before your program exits. In fact, close the file as soon as you're finished with it, because the file will end up hanging around if the script later crashes.

    Unix users don't have this problem, because well designed operating systems make it possible to delete a file without closing it.

    When you press the "back" button, the same page is loaded, not the previous one.

    Netscape 2.0's history list gets confused when processing multipart forms. If the script generates different pages for the form and the results, hitting the "back" button doesn't always return you to the previous page; instead Netscape reloads the current page. This happens even if you don't use an upload file field in your form.

    A workaround for this is to use additional path information to trick Netscape into thinking that the form and the response have different URLs. I recommend giving each form a sequence number and bumping the sequence up by one each time the form is accessed:

       my($s) = $query->path_info=~/(\d+)/; # get sequence
       $s++;                                #bump it up
       # Trick Netscape into thinking it's loading a new script:
       print $q->start_multipart_form(-action=>$q->script_name . "/$s");

    You can't find the temporary file that CGI.pm creates

    You're encouraged to copy the data into your own file by reading from the file handle that CGI.pm provides you with. In the future there may be no temporary file at all, just a pipe. However, for now, if you really want to get at the temp file, you can retrieve its path using the tmpFileName() method. Be sure to move the temporary file elsewhere in the file system if you don't want it to be automatically deleted when CGI.pm exits.

    Avoiding Denial of Service Attacks

    A potential problem with CGI.pm is that, by default, it attempts to process form POSTings no matter how large they are. A wily hacker could attack your site by sending a CGI script a huge POST of many megabytes. CGI.pm will attempt to read the entire POST into a variable, growing hugely in size until it runs out of memory. While the script attempts to allocate the memory the system may slow down dramatically. This is a form of denial of service attack.

    Another possible attack is for the remote user to force CGI.pm to accept a huge file upload. CGI.pm will accept the upload and store it in a temporary directory even if your script doesn't expect to receive an uploaded file. CGI.pm will delete the file automatically when it terminates, but in the meantime the remote user may have filled up the server's disk space, causing problems for other programs.

    The best way to avoid denial of service attacks is to limit the amount of memory, CPU time and disk space that CGI scripts can use. Some Web servers come with built-in facilities to accomplish this. In other cases, you can use the shell limit or ulimit commands to put ceilings on CGI resource usage.

    CGI.pm also has some simple built-in protections against denial of service attacks, but you must activate them before you can use them. These take the form of two global variables in the CGI name space:

    If set to a non-negative integer, this variable puts a ceiling on the size of POSTings, in bytes. If CGI.pm detects a POST that is greater than the ceiling, it will immediately exit with an error message. This value will affect both ordinary POSTs and multipart POSTs, meaning that it limits the maximum size of file uploads as well. You should set this to a reasonably high value, such as 1 megabyte.

    If set to a non-zero value, this will disable file uploads completely. Other fill-out form values will work as usual.
    You can use these variables in either of two ways.
    1. On a script-by-script basis. Set the variable at the top of the script, right after the "use" statement:
            use CGI qw/:standard/;
            use CGI::Carp 'fatalsToBrowser';
            $CGI::POST_MAX=1024 * 100;  # max 100K posts
            $CGI::DISABLE_UPLOADS = 1;  # no uploads

    2. Globally for all scripts. Open up CGI.pm, find the definitions for $POST_MAX and $DISABLE_UPLOADS, and set them to the desired values. You'll find them towards the top of the file in a subroutine named initialize_globals.
    Since an attempt to send a POST larger than $POST_MAX bytes will cause a fatal error, you might want to use CGI::Carp to echo the fatal error message to the browser window as shown in the example above. Otherwise the remote user will see only a generic "Internal Server" error message. See the manual page for CGI::Carp for more details.

    Table of contents

    Using CGI.pm on non-Unix Platforms

    I don't have access to all the combinations of hardware and software that I really need to make sure that CGI.pm works consistently for all Web servers, so I rely heavily on helpful reports from users like yourself.

    There are a number of differences in file name and text processing conventions on different platforms. By default, CGI.pm is set up to work properly on a Unix (or Linux) system. During load, it will attempt to guess the correct operating system using the Config module. Currently it guesses correctly; however if the operating system names change it may not work right. The main symptom will be that file upload does not work correctly. If this happens, find the place at the top of the script where the OS is defined, and uncomment the correct definition:

       # $OS = 'UNIX';
       # $OS = 'MACINTOSH';
       # $OS = 'WINDOWS';
       # $OS = 'VMS';
    Other notes follow:

    Windows NT

    CGI.pm works well with WebSite, the EMWACS server, Purveyor and the Microsoft IIS server. CGI.pm must be put in the perl5 library directory, and all CGI scripts that use it should be placed in cgi-bin directory. You also need to associate the .pl suffix with perl5 using the NT file manager (Website, Purveyor), or install the correct script mapping registry keys for IIS. There are two ports of Perl for Windows, one done by the ActiveWare company, and the other by Gurusamy Sarathy. I have only tested CGI.pm with the former. The home site for the ActiveWare port is:

    The ActiveWare port comes in two parts. The first part is a standard standalone Perl interpreter. The second part is a small DLL library that implements a Perl ISAPI interface for IIS and other Web servers. As of build 307, the DLL library is seriously broken. It is seriously unreliable when used for any Perl CGI script, with or without CGI.pm. Symptoms include truncated CGI parameters, missing parameters, scrambled output, and failed file uploads. I strongly recommend that you use the standalone interpreter instead.

    The Microsoft IIS server is broken with respect to the handling of additional path information. If you use the DLL version of ActiveWare Perl, IIS will attempt to execute the additional path information as a script. If you use the external Perl interpreter, the additional path information may contain incorrect information. This is not a bug in CGI.pm.

    WebSite uses a slightly different cgi-bin directory structure than the standard. For this server, place the scripts in the cgi-shl directory. CGI.pm appears to work correctly in both the Windows95 and WindowsNT versions of WebSite.

    Old Netscape Communications Server technical notes recommended placing perl.exe in cgi-bin. This a very bad idea because it opens up a gaping security hole. Put a C .exe wrapper around the perl script until such time as Netscape recognizes NT file manager associations, or provides a Perl-compatible DLL library for its servers.

    If you find that binary files get slightly larger when uploaded but that text files remain the same, then binary made is not correctly activated. Be sure to set the $OS variable to 'NT' or 'WINDOWS'. If you continue to have problems, make sure you're calling binmode() on the filehandle that you use to write the uploaded file to disk.


    I don't have access to a VMS machine, and I'm not sure whether file upload works correctly. Other features are known to work.


    Most CGI.pm features work with MacPerl version 5.0.6r1 or higher under the WebStar and MacHTTP servers. In order to install a Perl program to use with the Web, you'll need Matthias Nuuracher's PCGI extension, available at:
    Known incompatibilities between CGI.pm and MacPerl include:
    1. The perl compiler will object to the use of -values in named parameters. Put single quotes around this parameter ('-values') or use the singular form ('-value') instead.
    2. File upload isn't working in my hands (Perl goes into an endless loop). Other people have gotten it to work.

    The Relation of this Library to the CGI Modules

    This library is maintained in parallel with the full featured CGI, URL, and HTML modules. I use this library to test out new ideas before incorporating them into the CGI hierarchy. I am continuing to maintain and improve this library in order to satisfy people who are looking for an easy-to-use introduction to the world of CGI scripting.

    The CGI::* modules are being reworked to be interoperable with the excellent LWP modules. Stay tuned.

    The current version of CGI.pm can be found at:


    You are encouraged to look at these other Web-related modules:

    A module that simplifies the creation of HTML documents programatically.
    CGI::Base,CGI::Form,CGI::MiniSrv,CGI::Request and CGI::URI::URL
    Modules for parsing script input, manipulating URLs, creating forms and even launching a miniature Web server.
    Modules for fetching Web resources from within Perl, writing Web robots, and much more.
    You might also be interested in two packages for creating graphics on the fly:
    A module for creating GIF images on the fly, using Tom Boutell's gd graphics library.
    A library for creating Macintosh PICT files on the fly (which can be converted to GIF or JPEG using NetPBM).

    For a collection of CGI scripts of various levels of complexity, see the companion pages for my book How to Set Up and Maintain a World Wide Web Site

    Distribution Information:

    This code is copyright 1995-1997 by Lincoln Stein. 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.

    The CGI-perl mailing list

    The CGI Perl mailing list is defunct and is unlikely to be resurrected. Please address your questions to comp.lang.perl.modules and to comp.lang.perl.misc.

    Bug Reports

    Address bug reports and comments to:

    Up to table of contents

    Revision History

    Version 2.39

    1. file uploads failing because of VMS patch; fixed.
    2. -dtd parameter was not being properly processed.

    Version 2.38

    I finally got tired of all the 2.37 betas and released 2.38. The main difference between this version and the last 2.37 beta (2.37b30) are some fixes for VMS. This should allow file upload to work properly on all VMS Web servers.

    Version 2.37, various beta versions

    1. Added a CGI::Cookie::parse() method for lucky mod_perl users.
    2. No longer need separate -values and -labels arguments for multi-valued form elements.
    3. Added better interface to raw cookies (fix courtesy Ken Fox, kfox@ford.com)
    4. Added param_fetch() function for direct access to parameter list.
    5. Fix to checkbox() to allow for multi-valued single checkboxes (weird problem).
    6. Added a compile() method for those who want to compile without importing.
    7. Documented the import pragmas a little better.
    8. Added a -compile switch to the use clause for the long-suffering mod_perl and Perl compiler users.
    9. Fixed initialization routines so that FileHandle and type globs work correctly (and hash initialization doesn't fail!).
    10. Better deletion of temporary files on NT systems.
    11. Added documentation on escape(), unescape(), unescapeHTML() and unescapeHTML() subroutines.
    12. Added documentation on creating subclasses.
    13. Fixed problem when calling $self->SUPER::foo() from inheriting subclasses.
    14. Fixed problem using filehandles from within subroutines.
    15. Fixed inability to use the string "CGI" as a parameter.
    16. Fixed exponentially growing $FILLUNIT bug
    17. Check for undef filehandle in read_from_client()
    18. Now requires the UNIVERSAL.pm module, present in Perl 5.003_7 or higher.
    19. Fixed problem with uppercase-only parameters being ignored.
    20. Fixed vanishing cookie problem.
    21. Fixed warning in initialize_globals() under mod_perl.
    22. File uploads from Macintosh versions of MSIE should now work.
    23. Pragmas now preceded by dashes (-nph) rather than colons (:nph). Old style is supported for backward compatability.
    24. Can now pass arguments to all functions using {} brackets, resolving historical inconsistencies.
    25. Removed autoloader warnings about absent MultipartBuffer::DESTROY.
    26. Fixed non-sticky checkbox() when -name used without -value.
    27. Hack to fix path_info() in IIS 2.0. Doesn't help with IIS 3.0.
    28. Parameter syntax for debugging from command line now more straightforward.
    29. Added $DISABLE_UPLOAD to disable file uploads.
    30. Added $POST_MAX to error out if POSTings exceed some ceiling.
    31. Fixed url_param(), which wasn't working at all.
    32. Fixed variable suicide problem in s///e expressions, where the autoloader was needed during evaluation.
    33. Removed excess spaces between elements of checkbox and radio groups
    34. Can now create "valueless" submit buttons
    35. Can now set path_info as well as read it.
    36. ReadParse() now returns a useful function result.
    37. import_names() now allows you to optionally clear out the namespace before importing (for mod_perl users)
    38. Made it possible to have a popup menu or radio button with a value of "0".
    39. link() changed to Link() to avoid overriding native link function.
    40. Takes advantage of mod_perl's register_cleanup() function to clear globals.
    41. <LAYER> and <ILAYER> added to :html3 functions.
    42. Fixed problems with private tempfiles and NT/IIS systems.
    43. No longer prints the DTD by default (I bet no one will complain).
    44. Allow underscores to replace internal hyphens in parameter names.
    45. CGI::Push supports heterogeneous MIME types and adjustable delays between pages.
    46. url_param() method added for retrieving URL parameters even when a fill-out form is POSTed.
    47. Got rid of warnings when radio_group() is called.
    48. Cookies now moved to their very own module.
    49. Fixed documentation bug in CGI::Fast.
    50. Added a :no_debug pragma to the import list.

    Version 2.36

    1. Expanded JavaScript functionality
    2. Preliminary support for cascading stylesheets
    3. Security fixes for file uploads:
    4. use CGI qw/:nph/ wasn't working correctly. Now it is.
    5. Cookie and HTTP date formats didn't meet spec. Thanks to Mark Fisher (fisherm@indy.tce.com) for catching and fixing this.

    Version 2.35

    1. Robustified multipart file upload against incorrect syntax in POST.
    2. Fixed more problems with mod_perl.
    3. Added -noScript parameter to start_html().
    4. Documentation fixes.

    Version 2.34

    1. Stupid typo fix

    Version 2.33

    1. Fixed a warning about an undefined environment variable.
    2. Doug's patch for redirect() under mod_perl
    3. Partial fix for busted inheritence from CGI::Apache
    4. Documentation fixes.

    Version 2.32

    1. Improved support for Apache's mod_perl.
    2. Changes to better support inheritance.
    3. Support for OS/2.

    Version 2.31

    1. New uploadInfo() method to obtain header information from uploaded files.
    2. cookie() without any arguments returns all the cookies passed to a script.
    3. Removed annoying warnings about $ENV{NPH} when running with the -w switch.
    4. Removed operator overloading throughout to make compatible with new versions of perl.
    5. -expires now implies the -date header, to avoid clock skew.
    6. WebSite passes cookies in $ENV{COOKIE} rather than $ENV{HTTP_COOKIE}. We now handle this, even though it's O'Reilly's fault.
    7. Tested successfully against new sfio I/O layer.
    8. Documentation fixes.

    Version 2.30

    1. Automatic detection of operating system at load time.
    2. Changed select() function to Select() in order to avoid conflict with Perl built-in.
    3. Added Tr() as an alternative to TR(); some people think it looks better that way.
    4. Fixed problem with autoloading of MultipartBuffer::DESTROY code.
    5. Added the following methods:
    6. Automatic NPH mode when running under Microsoft IIS server.

    Version 2.29

    1. Fixed cookie bugs
    2. Fixed problems that cropped up when useNamedParameters was set to 1.
    3. Prevent CGI::Carp::fatalsToBrowser() from crapping out when encountering a die() within an eval().
    4. Fixed problems with filehandle initializers.

    Version 2.28

    1. Added support for NPH scripts; also fixes problems with Microsoft IIS.
    2. Fixed a problem with checkbox() values not being correctly saved and restored.
    3. Fixed a bug in which CGI objects created with empty string initializers took on default values from earlier CGI objects.
    4. Documentation fixes.

    Version 2.27

    1. Small but important bug fix: the automatic capitalization of tag attributes was accidentally capitalizing the VALUES as well as the ATTRIBUTE names (oops).

    Version 2.26

    1. Changed behavior of scrolling_list(), checkbox() and checkbox_group() methods so that defaults are honored correctly. The "fix" causes endform() to generate additional <INPUT TYPE="HIDDEN"> tags -- don't be surpised.
    2. Fixed bug involving the detection of the SSL protocol.
    3. Fixed documentation error in position of the -meta argument in start_html().
    4. HTML shortcuts now generate tags in ALL UPPERCASE.
    5. start_html() now generates correct SGML header:
    6. CGI::Carp no longer fails "use strict refs" pragma.

    Version 2.25

    1. Fixed bug that caused bad redirection on destination URLs with arguments.
    2. Fixed bug involving use_named_parameters() followed by start_multipart_form()
    3. Fixed bug that caused incorrect determination of binmode for Macintosh.
    4. Spelling fixes on documentation.

    Version 2.24

    1. Fixed bug that caused generation of lousy HTML for some form elements
    2. Fixed uploading bug in Windows NT
    3. Some code cleanup (not enough)

    Version 2.23

    1. Fixed an obscure bug that caused scripts to fail mysteriously.
    2. Fixed auto-caching bug.
    3. Fixed bug that prevented HTML shortcuts from passing taint checks.
    4. Fixed some -w warning problems.

    Version 2.22

    1. New CGI::Fast module for use with FastCGI protocol. See pod documentation for details.
    2. Fixed problems with inheritance and autoloading.
    3. Added TR() (<tr>) and PARAM() (<param>) methods to list of exported HTML tag-generating functions.
    4. Moved all CGI-related I/O to a bottleneck method so that this can be overridden more easily in mod_perl (thanks to Doug MacEachern).
    5. put() method as substitute for print() for use in mod_perl.
    6. Fixed crash in tmpFileName() method.
    7. Added tmpFileName(), startform() and endform() to export list.
    8. Fixed problems with attributes in HTML shortcuts.
    9. Functions that don't actually need access to the CGI object now no longer generate a default one. May speed things up slightly.
    10. Aesthetic improvements in generated HTML.
    11. New examples.

    Version 2.21

    1. Added the -meta argument to start_html().
    2. Fixed hidden fields (again).
    3. Radio_group() and checkbox_group() now return an appropriate scalar value when called in a scalar context, rather than returning a numeric value!
    4. Cleaned up the formatting of form elements to avoid unesthetic extra spaces within the attributes.
    5. HTML elements now correctly include the closing tag when parameters are present but null: em('')
    6. Added password_field() to the export list.

    Version 2.20

    1. Dumped the SelfLoader because of problems with running with taint checks and rolled my own. Performance is now significantly improved.
    2. Added HTML shortcuts.
    3. import() now adheres to the Perl module conventions, allowing CGI.pm to import any or all method names into the user's name space.
    4. Added the ability to initialize CGI objects from strings and associative arrays.
    5. Made it possible to initialize CGI objects with filehandle references rather than filehandle strings.
    6. Added the delete_all() and append() methods.
    7. CGI objects correctly initialize from filehandles on NT/95 systems now.
    8. Fixed the problem with binary file uploads on NT/95 systems.
    9. Fixed bug in redirect().
    10. Added '-Window-target' parameter to redirect().
    11. Fixed import_names() so that parameter names containing funny characters work.
    12. Broke the unfortunate connection between cookie and CGI parameter name space.
    13. Fixed problems with hidden fields whose values are 0.
    14. Cleaned up the documentation somewhat.

    Version 2.19

    1. Added cookie() support routines.
    2. Added -expires parameter to header().
    3. Added cgi-lib.pl compatability mode.
    4. Made the module more configurable for different operating systems.
    5. Fixed a dumb bug in JavaScript button() method.

    Version 2.18

    1. Fixed a bug that corrects a hang that occurs on some platforms when processing file uploads. Unfortunately this disables the check for bad Netscape uploads.
    2. Fixed bizarre problem involving the inability to process uploaded files that begin with a non alphabetic character in the file name.
    3. Fixed a bug in the hidden fields involving the -override directive being ignored when scalar defaults were passed.
    4. Added documentation on how to disable the SelfLoader features.

    Version 2.17

    1. Added support for the SelfLoader module.
    2. Added oodles of JavaScript support routines.
    3. Fixed bad bug in query_string() method that caused some parameters to be silently dropped.
    4. Robustified file upload code to handle premature termination by the client.
    5. Exported temporary file names on file upload.
    6. Removed spurious "uninitialized variable" warnings that appeared when running under 5.002.
    7. Added the Carp.pm library to the standard distribution.
    8. Fixed a number of errors in this documentation, and probably added a few more.
    9. Checkbox_group() and radio_group() now return the buttons as arrays, so that you can incorporate the individual buttons into specialized tables.
    10. Added the '-nolabels' option to checkbox_group() and radio_group(). Probably should be added to all the other HTML-generating routines.
    11. Added the url() method to recover the URL without the entire query string appended.
    12. Added request_method() to list of environment variables available.
    13. Would you believe it? Fixed hidden fields again!

    Version 2.16

    1. Fixed hidden fields yet again.
    2. Fixed subtle problems in the file upload method that caused intermittent failures (thanks to Keven Hendrick for this one).
    3. Made file upload more robust in the face of bizarre behavior by the Macintosh and Windows Netscape clients.
    4. Moved the POD documentation to the bottom of the module at the request of Stephen Dahmen.
    5. Added the -xbase parameter to the start_html() method, also at the request of Stephen Dahmen.
    6. Added JavaScript form buttons at Stephen's request. I'm not sure how to use this Netscape extension correctly, however, so for now the form() method is in the module as an undocumented feature. Use at your own risk!

    Version 2.15

    1. Added the -override parameter to all field-generating methods.
    2. Documented the user_name() and remote_user() methods.
    3. Fixed bugs that prevented empty strings from being recognized as valid textfield contents.
    4. Documented the use of framesets and added a frameset example.

    Version 2.14

    This was an internal experimental version that was never released.

    Version 2.13

    1. Fixed a bug that interfered with the value "0" being entered into text fields.

    Version 2.01

    1. Added -rows and -columns to the radio and checkbox groups. No doubt this will cause much grief because it seems to promise a level of meta-organization that it doesn't actually provide.
    2. Fixed a bug in the redirect() method -- it was not truly HTTP/1.0 compliant.

    Version 2.0

    The changes seemed to touch every line of code, so I decided to bump up the major version number.
    1. Support for named parameter style method calls. This turns out to be a big win for extending CGI.pm when Netscape adds new HTML "features".
    2. Changed behavior of hidden fields back to the correct "sticky" behavior. This is going to break some programs, but it is for the best in the long run.
    3. Netscape 2.0b2 broke the file upload feature. CGI.pm now handles both 2.0b1 and 2.0b2-style uploading. It will probably break again in 2.0b3.
    4. There were still problems with library being unable to distinguish between a form being loaded for the first time, and a subsequent loading with all fields blank. We now forcibly create a default name for the Submit button (if not provided) so that there's always at least one parameter.
    5. More workarounds to prevent annoying spurious warning messages when run under the -w switch. -w is seriously broken in perl 5.001!

    Version 1.57

    1. Support for the Netscape 2.0 "File upload" field.
    2. The handling of defaults for selected items in scrolling lists and multiple checkboxes is now consistent.

    Version 1.56

    1. Created true "pod" documentation for the module.
    2. Cleaned up the code to avoid many of the spurious "use of uninitialized variable" warnings when running with the -w switch.
    3. Added the autoEscape() method. v
    4. Added string interpolation of the CGI object.
    5. Added the ability to pass additional parameters to the <BODY> tag.
    6. Added the ability to specify the status code in the HTTP header.

    Bug fixes in version 1.55

    1. Every time self_url() was called, the parameter list would grow. This was a bad "feature".
    2. Documented the fact that you can pass "-" to radio_group() in order to prevent any button from being highlighted by default.

    Bug fixes in version 1.54

    1. The user_agent() method is now documented;
    2. A potential security hole in import() is now plugged.
    3. Changed name of import() to import_names() for compatability with CGI:: modules.

    Bug fixes in version 1.53

    1. Fixed several typos in the code that were causing the following subroutines to fail in some circumstances
      1. checkbox()
      2. hidden()
    2. No features added

    New features added in version 1.52

    1. Added backslashing, quotation marks, and other shell-style escape sequences to the parameters passed in during debugging off-line.
    2. Changed the way that the hidden() method works so that the default value always overrides the current one.
    3. Improved the handling of sticky values in forms. It's now less likely that sticky values will get stuck.
    4. If you call server_name(), script_name() and several other methods when running offline, the methods now create "dummy" values to work with.

    Bugs fixed in version 1.51

    1. param() when called without arguments was returning an array of length 1 even when there were no parameters to be had. Bad bug! Bad!
    2. The HTML code generated would break if input fields contained the forbidden characters ">< or &. You can now use these characters freely.

    New features added in version 1.50

    1. import() method allows all the parameters to be imported into a namespace in one fell swoop.
    2. Parameters are now returned in the same order in which they were defined.

    Bugs fixed in version 1.45

    1. delete() method didn't work correctly. This is now fixed.
    2. reset() method didn't allow you to set the name of the button. Fixed.

    Bugs fixed in version 1.44

    1. self_url() didn't include the path information. This is now fixed.

    New features added in version 1.43

    1. Added the delete() method.

    New features added in version 1.42

    1. The image_button() method to create clickable images.
    2. A few bug fixes involving forms embedded in <PRE> blocks.

    New features added in version 1.4

    1. New header shortcut methods
    2. A new save() method that allows you to write out the state of an script to a file or pipe.
    3. An improved version of the new() method that allows you to restore the state of a script from a file or pipe. With (2) this gives you dump and restore capabilities! (Wow, you can put a "121,931 customers served" banner at the bottom of your pages!)
    4. A self_url() method that allows you to create state-maintaining hypertext links. In addition to allowing you to maintain the state of your scripts between invocations, this lets you work around a problem that some browsers have when jumping to internal links in a document that contains a form -- the form information gets lost.
    5. The user-visible labels in checkboxes, radio buttons, popup menus and scrolling lists have now been decoupled from the values sent to your CGI script. Your script can know a checkbox by the name of "cb1" while the user knows it by a more descriptive name. I've also added some parameters that were missing from the text fields, such as MAXLENGTH.
    6. A whole bunch of methods have been added to get at environment variables involved in user verification and other obscure features.

    Bug fixes

    1. The problems with the hidden fields have (I hope at last) been fixed.
    2. You can create multiple query objects and they will all be initialized correctly. This simplifies the creation of multiple forms on one page.
    3. The URL unescaping code works correctly now.
    Table of Contents
    Lincoln D. Stein, lstein@genome.wi.mit.edu
    Whitehead Institute/MIT Center for Genome Research

    Last modified: Tue Mar 24 17:08:36 EST 1998