CGI - Simple Common Gateway Interface Class

- NAME
- SYNOPSIS
- ABSTRACT
- DESCRIPTION

- PROGRAMMING STYLE
- CALLING CGI.PM ROUTINES
- CREATING A NEW QUERY OBJECT (OBJECT-ORIENTED STYLE):
- CREATING A NEW QUERY OBJECT FROM AN INPUT FILE
- FETCHING A LIST OF KEYWORDS FROM THE QUERY:
- FETCHING THE NAMES OF ALL THE PARAMETERS PASSED TO YOUR SCRIPT:
- FETCHING THE VALUE OR VALUES OF A SINGLE NAMED PARAMETER:
- SETTING THE `VALUE(S)` OF A NAMED PARAMETER:
- APPENDING ADDITIONAL VALUES TO A NAMED PARAMETER:
- IMPORTING ALL PARAMETERS INTO A NAMESPACE:
- DELETING A PARAMETER COMPLETELY:
- DELETING ALL PARAMETERS:
- DIRECT ACCESS TO THE PARAMETER LIST:
- FETCHING THE PARAMETER LIST AS A HASH:
- SAVING THE STATE OF THE SCRIPT TO A FILE:
- RETRIEVING CGI ERRORS
- USING THE FUNCTION-ORIENTED INTERFACE
- PRAGMAS
- SPECIAL FORMS FOR IMPORTING HTML-TAG FUNCTIONS

- GENERATING DYNAMIC DOCUMENTS

- CREATING A STANDARD HTTP HEADER:
- GENERATING A REDIRECTION HEADER
- CREATING THE HTML DOCUMENT HEADER
- ENDING THE HTML DOCUMENT:
- CREATING A SELF-REFERENCING URL THAT PRESERVES STATE INFORMATION:
- OBTAINING THE SCRIPT'S URL
- MIXING POST AND URL PARAMETERS

- CREATING STANDARD HTML ELEMENTS:

- PROVIDING ARGUMENTS TO HTML SHORTCUTS
- THE DISTRIBUTIVE PROPERTY OF HTML SHORTCUTS
- HTML SHORTCUTS AND LIST INTERPOLATION
- NON-STANDARD HTML SHORTCUTS
- AUTOESCAPING HTML
- PRETTY-PRINTING HTML

- CREATING FILL-OUT FORMS:

- CREATING AN ISINDEX TAG
- STARTING AND ENDING A FORM
- CREATING A TEXT FIELD
- CREATING A BIG TEXT FIELD
- CREATING A PASSWORD FIELD
- CREATING A FILE UPLOAD FIELD
- CREATING A POPUP MENU
- CREATING A SCROLLING LIST
- CREATING A GROUP OF RELATED CHECKBOXES
- CREATING A STANDALONE CHECKBOX
- CREATING A RADIO BUTTON GROUP
- CREATING A SUBMIT BUTTON
- CREATING A RESET BUTTON
- CREATING A DEFAULT BUTTON
- CREATING A HIDDEN FIELD
- CREATING A CLICKABLE IMAGE BUTTON
- CREATING A JAVASCRIPT ACTION BUTTON

- HTTP COOKIES
- WORKING WITH FRAMES
- LIMITED SUPPORT FOR CASCADING STYLE SHEETS
- DEBUGGING

- DUMPING OUT ALL THE NAME/VALUE PAIRS

- FETCHING ENVIRONMENT VARIABLES
- USING NPH SCRIPTS
- Server Push
- Avoiding Denial of Service Attacks
- COMPATIBILITY WITH CGI-LIB.PL
- AUTHOR INFORMATION
- CREDITS
- A COMPLETE EXAMPLE OF A SIMPLE FORM-BASED SCRIPT
- BUGS
- SEE ALSO

# NAME

CGI - Simple Common Gateway Interface Class

# SYNOPSIS

      # CGI script that creates a fill-out form
      # and echoes back its values.

      use CGI qw/:standard/;
      print header,
            start_html('A Simple Example'),
            h1('A Simple Example'),
            start_form,
            "What's your name? ",textfield('name'),p,
            "What's the combination?", p,
            checkbox_group(-name=>'words',
                           -values=>['eenie','meenie','minie','moe'],
                           -defaults=>['eenie','minie']), p,
            "What's your favorite color? ",
            popup_menu(-name=>'color',
                       -values=>['red','green','blue','chartreuse']),p,
            submit,
            end_form,
            hr;

       if (param()) {
           print "Your name is",em(param('name')),p,
                 "The keywords are: ",em(join(", ",param('words'))),p,
                 "Your favorite color is ",em(param('color')),
                 hr;
       }

# ABSTRACT

This perl library uses perl5 objects to make it easy to create Web fill-out forms and parse their contents. This package defines CGI objects, entities that contain the values of the current query string and other state variables. Using a CGI object's methods, you can examine keywords and parameters passed to your script, and create forms whose initial values are taken from the current query (thereby preserving state information). The module provides shortcut functions that produce boilerplate HTML, reducing typing and coding errors. It also provides functionality for some of the more advanced features of CGI scripting, including support for file uploads, cookies, cascading style sheets, server push, and frames.

CGI.pm also provides a simple function-oriented programming style for those who don't need its object-oriented features.

The current version of CGI.pm is available at

      http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html
      ftp://ftp-genome.wi.mit.edu/pub/software/WWW/

# DESCRIPTION

## PROGRAMMING STYLE

There are two styles of programming with CGI.pm, an object-oriented style and a function-oriented style. In the object-oriented style you create one or more CGI objects and then use object methods to create the various elements of the page. Each CGI object starts out with the list of named parameters that were passed to your CGI script by the server. You can modify the objects, save them to a file or database and recreate them. Because each object corresponds to the ``state'' of the CGI script, and because each object's parameter list is independent of the others, this allows you to save the state of the script and restore it later.

For example, using the object oriented style, here is how you create a simple ``Hello World'' HTML page:

       #!/usr/local/bin/perl -w
       use CGI;                             # load CGI routines
       $q = new CGI;                        # create new CGI object
       print $q->header,                    # create the HTTP header
             $q->start_html('hello world'), # start the HTML
             $q->h1('hello world'),         # level 1 header
             $q->end_html;                  # end the HTML

In the function-oriented style, there is one default CGI object that you rarely deal with directly. Instead you just call functions to retrieve CGI parameters, create HTML tags, manage cookies, and so on. This provides you with a cleaner programming interface, but limits you to using one CGI object at a time. The following example prints the same page, but uses the function-oriented interface. The main differences are that we now need to import a set of functions into our name space (usually the ``standard'' functions), and we don't need to create the CGI object.

       #!/usr/local/bin/perl
       use CGI qw/:standard/;           # load standard CGI routines
       print header,                    # create the HTTP header
             start_html('hello world'), # start the HTML
             h1('hello world'),         # level 1 header
             end_html;                  # end the HTML

The examples in this document mainly use the object-oriented style. See HOW TO IMPORT FUNCTIONS for important information on function-oriented programming in CGI.pm

## CALLING CGI.PM ROUTINES

Most CGI.pm routines accept several arguments, sometimes as many as 20 optional ones! To simplify this interface, all routines use a named argument calling style that looks like this:

       print $q->header(-type=>'image/gif',-expires=>'+3d');

Each argument name is preceded by a dash. Neither case nor order matters in the argument list. -type, -Type, and -TYPE are all acceptable. In fact, only the first argument needs to begin with a dash. If a dash is present in the first argument, CGI.pm assumes dashes for the subsequent ones.

Several routines are commonly called with just one argument. In the case of these routines you can provide the single argument without an argument name. `header()` happens to be one of these routines. In this case, the single argument is the document type.

       print $q->header('text/html');

Other such routines are documented below.

Sometimes named arguments expect a scalar, sometimes a reference to an array, and sometimes a reference to a hash. Often, you can pass any type of argument and the routine will do whatever is most appropriate. For example, the `param()` routine is used to set a CGI parameter to a single or a multi-valued value. The two cases are shown below:

       $q->param(-name=>'veggie',-value=>'tomato');
       $q->param(-name=>'veggie',-value=>['tomato','tomahto','potato','potahto']);

A large number of routines in CGI.pm actually aren't specifically defined in the module, but are generated automatically as needed. These are the ``HTML shortcuts,'' routines that generate HTML tags for use in dynamically-generated pages. HTML tags have both attributes (the attribute=``value'' pairs within the tag itself) and contents (the part between the opening and closing pairs.) To distinguish between attributes and contents, CGI.pm uses the convention of passing HTML attributes as a hash reference as the first argument, and the contents, if any, as any subsequent arguments. It works out like this:

       Code                           Generated HTML
       ----                           --------------
       h1()                           <H1>
       h1('some','contents');         <H1>some contents</H1>
       h1({-align=>left});            <H1 ALIGN="LEFT">
       h1({-align=>left},'contents'); <H1 ALIGN="LEFT">contents</H1>

HTML tags are described in more detail later.

Many newcomers to CGI.pm are puzzled by the difference between the calling conventions for the HTML shortcuts, which require curly braces around the HTML tag attributes, and the calling conventions for other routines, which manage to generate attributes without the curly brackets. Don't be confused. As a convenience the curly braces are optional in all but the HTML shortcuts. If you like, you can use curly braces when calling any routine that takes named arguments. For example:

       print $q->header( {-type=>'image/gif',-expires=>'+3d'} );

If you use the -w switch, you will be warned that some CGI.pm argument names conflict with built-in Perl functions. The most frequent of these is the -values argument, used to create multi-valued menus, radio button clusters and the like. To get around this warning, you have several choices:

1. Use another name for the argument, if one is available. For example, -value is an alias for -values.

2. Change the capitalization, e.g. -Values

3. Put quotes around the argument name, e.g. '-values'

Many routines will do something useful with a named argument that it doesn't recognize. For example, you can produce non-standard HTTP header fields by providing them as named arguments:

      print $q->header(-type  =>  'text/html',
                       -cost  =>  'Three smackers',
                       -annoyance_level => 'high',
                       -complaints_to   => 'bit bucket');

This will produce the following nonstandard HTTP header:

       HTTP/1.0 200 OK
       Cost: Three smackers
       Annoyance-level: high
       Complaints-to: bit bucket
       Content-type: text/html

Notice the way that underscores are translated automatically into hyphens. HTML-generating routines perform a different type of translation.

This feature allows you to keep up with the rapidly changing HTTP and HTML ``standards''.

## CREATING A NEW QUERY OBJECT (OBJECT-ORIENTED STYLE):

         $query = new CGI;

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

## CREATING A NEW QUERY OBJECT FROM AN INPUT FILE

         $query = new CGI(INPUTFILE);

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

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

        $query = new CGI(\*STDIN);

You can also initialize the CGI object with a FileHandle or IO::File object.

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;
        restore_parameters(IN);
        close IN;

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

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

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

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

or from a previously existing CGI object (currently this clones the parameter list, but none of the other object-specific fields, such as autoescaping):

        $old_query = new CGI;
        $new_query = new CGI($old_query);

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

       $empty_query = new CGI("");

           -or-

       $empty_query = new CGI({});

## 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 as an array using the `keywords()` method.

## 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. If the script was invoked as an <ISINDEX> script and contains a string without ampersands (e.g. ``value1+value2+value3'') , there will be a single parameter named ``keywords'' containing the ``+''-delimited keywords.

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

## FETCHING THE VALUE OR VALUES OF A SINGLE NAMED PARAMETER:

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

                  -or-

        $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.

If a value is not given in the query string, as in the queries ``name1=&name2='' or ``name1&name2'', it will be returned as an empty string. This feature is new in 2.63.

## SETTING THE `VALUE(S)` OF A NAMED PARAMETER:

        $query->param('foo','an','array','of','values');

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

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

        $query->param(-name=>'foo',-values=>['an','array','of','values']);

                                  -or-

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

## APPENDING ADDITIONAL VALUES TO A NAMED PARAMETER:

       $query->append(-name=>'foo',-values=>['yet','more','values']);

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

## IMPORTING ALL PARAMETERS INTO A NAMESPACE:

       $query->import_names('R');

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

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

## DELETING A PARAMETER COMPLETELY:

        $query->delete('foo');

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

If you are using the function call interface, use ``Delete()'' instead to avoid conflicts with Perl's built-in delete operator.

## DELETING ALL PARAMETERS:

       $query->delete_all();

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

Use `Delete_all()` instead if you are using the function call interface.

## 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 . This will return an array reference to the named parameters, which you then can manipulate in any way you like.

You can also use a named argument style using the -name argument.

## FETCHING THE PARAMETER LIST AS A HASH:

        $params = $q->Vars;
        print $params->{'address'};
        @foo = split("\0",$params->{'foo'});
        %params = $q->Vars;

        use CGI ':cgi-lib';
        $params = Vars;

Many people want to fetch the entire parameter list as a hash in which the keys are the names of the CGI parameters, and the values are the parameters' values. The `Vars()` method does this. Called in a scalar context, it returns the parameter list as a tied hash reference. Changing a key changes the value of the parameter in the underlying CGI parameter list. Called in a list context, it returns the parameter list as an ordinary hash. This allows you to read the contents of the parameter list, but not to change it.

When using this, the thing you must watch out for are multivalued CGI parameters. Because a hash cannot distinguish between scalar and list context, multivalued parameters will be returned as a packed string, separated by the ``\0'' (null) character. You must split this packed string in order to get at the individual values. This is the convention introduced long ago by Steve Brenner in his cgi-lib.pl module for Perl version 4.

If you wish to use `Vars()` as a function, import the :cgi-lib set of function calls (also see the section on CGI-LIB compatibility).

## SAVING THE STATE OF THE SCRIPT TO A FILE:

        $query->save(FILEHANDLE)

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

The format of the saved file is:

            NAME1=VALUE1
            NAME1=VALUE1'
            NAME2=VALUE2
            NAME3=VALUE3
            =

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

       use CGI;

       open (OUT,">>test.out") || die;
       $records = 5;
       foreach (0..$records) {
           my $q = new CGI;
           $q->param(-name=>'counter',-value=>$_);
           $q->save(OUT);
       }
       close OUT;

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

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

      http://stein.cshl.org/boulder/

for further details.

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

## RETRIEVING CGI ERRORS

Errors can occur while processing user input, particularly when processing uploaded files. When these errors occur, CGI will stop processing and return an empty parameter list. You can test for the existence and nature of errors using the cgi_error() function. The error messages are formatted as HTTP status codes. You can either incorporate the error text into an HTML page, or use it as the value of the HTTP status:

        my $error = $q->cgi_error;
        if ($error) {
            print $q->header(-status=>$error),
                  $q->start_html('Problems'),
                  $q->h2('Request not processed'),
                  $q->strong($error);
            exit 0;
        }

When using the function-oriented interface (see the next section), errors may only occur the first time you call param(). Be ready for this!

## USING THE FUNCTION-ORIENTED INTERFACE

To use the function-oriented interface, you must specify which CGI.pm routines or sets of routines to import into your script's namespace. There is a small overhead associated with this importation, but it isn't much.

       use CGI <list of methods>;

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

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

More frequently, you'll import common sets of functions by referring to the groups by name. All function sets are preceded with a ``:'' character as in ``:html3'' (for tags defined in the HTML 3 standard).

Here is a list of the function sets you can import:

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

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

:html2
  Import all methods that generate HTML 2.0 standard elements.

:html3
  Import all methods that generate HTML 3.0 proposed elements (such as <table>, <super> and <sub>).

:netscape
  Import all methods that generate Netscape-specific HTML extensions.

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

:standard
  Import ``standard'' features, 'html2', 'html3', 'form' and 'cgi'.

:all
  Import all the available methods. For the full list, see the CGI.pm code, where the variable %EXPORT_TAGS is defined.

If you import a function name that is not part of CGI.pm, the module will treat it as a new HTML tag and generate the appropriate subroutine. You can then use it like any other HTML tag. This is to provide for the rapidly-evolving HTML ``standard.'' For example, say Microsoft comes out with a new tag called <GRADIENT> (which causes the user's desktop to be flooded with a rotating gradient fill until his machine reboots). You don't need to wait for a new version of CGI.pm to start using it immediately:

       use CGI qw/:standard :html3 gradient/;
       print gradient({-start=>'red',-end=>'blue'});

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

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

       use CGI qw/:standard/;
       print
           header,
           start_html('Simple Script'),
           h1('Simple Script'),
           start_form,
           "What's your name? ",textfield('name'),p,
           "What's the combination?",
           checkbox_group(-name=>'words',
                          -values=>['eenie','meenie','minie','moe'],
                          -defaults=>['eenie','moe']),p,
           "What's your favorite color?",
           popup_menu(-name=>'color',
                      -values=>['red','green','blue','chartreuse']),p,
           submit,
           end_form,
           hr,"\n";

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

## PRAGMAS

In addition to the function sets, there are a number of pragmas that you can import. Pragmas, which are always preceded by a hyphen, change the way that CGI.pm functions in various ways. Pragmas, function sets, and individual functions can all be imported in the same `use()` line. For example, the following use statement imports the standard set of functions and enables debugging mode (pragma -debug):

       use CGI qw/:standard -debug/;

The current list of pragmas is as follows:

-any
  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. This lets you go wild with new and unsupported tags:

         use CGI qw(-any);
         $q=new CGI;
         print $q->gradient({speed=>'fast',start=>'red',end=>'blue'});

  Since using <cite>any</cite> causes any mistyped method name to be interpreted as an HTML tag, use it with care or not at all.

-compile
  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 families 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 (see below).

-nosticky
  This makes CGI.pm not generating the hidden fields .submit and .cgifields. It is very useful if you don't want to have the hidden fields appear in the querystring in a GET method. For example, a search script generated this way will have a very nice url with search parameters for bookmarking.

-no_xhtml
  By default, CGI.pm versions 2.69 and higher emit XHTML (http://www.w3.org/TR/xhtml1/). The -no_xhtml pragma disables this feature. Thanks to Michalis Kabrianis <kabrianis@hellug.gr> for this feature.

-nph
  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.

-newstyle_urls
  Separate the name=value pairs in CGI parameter query strings with semicolons rather than ampersands. For example:

         ?name=fred;age=24;favorite_color=3

  Semicolon-delimited query strings are always accepted, but will not be emitted by `self_url()` and `query_string()` unless the -newstyle_urls pragma is specified.

  This became the default in version 2.64.

-oldstyle_urls
  Separate the name=value pairs in CGI parameter query strings with ampersands rather than semicolons. This is no longer the default.

-autoload
  This 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.

-no_debug
  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 to read CGI parameters from the command line or STDIN, then use this pragma:

         use CGI qw(-no_debug :standard);

-debug
  This turns on full debugging. In addition to reading CGI arguments from the command-line processing, CGI.pm will pause and try to read arguments from STDIN, producing the message ``(offline mode: enter name=value pairs on standard input)'' features.

  See the section on debugging for more details.

-private_tempfiles
  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, reducing, but not eliminating the risk of eavesdropping (there is still a potential race condition). To make life harder for the attacker, the program chooses tempfile names by calculating a 32 bit checksum of the incoming HTTP headers.

  To ensure that the temporary file cannot be read by other CGI scripts, use suEXEC or a CGI wrapper program to run your script. The temporary file is created with mode 0600 (neither world nor group readable).

  The temporary directory is selected using the following algorithm:

          1. if the current user (e.g. "nobody") has a directory named
          "tmp" in its home directory, use that (Unix systems only).

          2. if the environment variable TMPDIR exists, use the location
          indicated.

          3. Otherwise try the locations /usr/tmp, /var/tmp, C:\temp,
          /tmp, /temp, ::Temporary Items, and \WWW_ROOT.

  Each of these locations is checked that it is a directory and is writable. If not, the algorithm tries the next choice.

## SPECIAL FORMS FOR IMPORTING HTML-TAG FUNCTIONS

Many of the methods generate HTML tags. As described below, tag functions automatically generate both the opening and closing tags. For example:

      print h1('Level 1 Header');

produces

      <H1>Level 1 Header</H1>

There will be some times when you want to produce the start and end tags yourself. In this case, you can use the form start_tag_name and end_tag_name, as in:

      print start_h1,'Level 1 Header',end_h1;

With a few exceptions (described below), start_tag_name and end_tag_name functions are not generated automatically when you use CGI. However, you can specify the tags you want to generate start/end functions for by putting an asterisk in front of their name, or, alternatively, requesting either ``start_tag_name'' or ``end_tag_name'' in the import list.

Example:

      use CGI qw/:standard *table start_ul/;

In this example, the following functions are generated in addition to the standard ones:

1. `start_table()` (generates a <TABLE> tag)
2. `end_table()` (generates a </TABLE> tag)
3. `start_ul()` (generates a <UL> tag)
4. `end_ul()` (generates a </UL> tag)

# GENERATING DYNAMIC DOCUMENTS

Most of CGI.pm's functions deal with creating documents on the fly. Generally you will produce the HTTP header first, followed by the document itself. CGI.pm provides functions for generating HTTP headers of various types as well as for generating HTML. For creating GIF images, see the GD.pm module.

Each of these functions produces a fragment of HTML or HTTP which you can print out directly so that it displays in the browser window, append to a string, or save to a file for later use.

## CREATING A STANDARD HTTP HEADER:

Normally the first thing you will do in any CGI script is print out an HTTP header. This tells the browser what type of document to expect, and gives other optional information, such as the language, expiration date, and whether to cache the document. The header can also be manipulated for special purposes, such as server push and pay per view pages.

            print $query->header;

                 -or-

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

                 -or-

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

                 -or-

            print $query->header(-type=>'image/gif',
                                 -nph=>1,
                                 -status=>'402 Payment required',
                                 -expires=>'+3d',
                                 -cookie=>$cookie,
                                 -charset=>'utf-7',
                                 -attachment=>'foo.gif',
                                 -Cost=>'$2.00');

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

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

        print $query->header(-Content_length=>3002);

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

            +30s                              30 seconds from now
            +10m                              ten minutes from now
            +1h                               one hour from now
            -1d                               yesterday (i.e. "ASAP!")
            now                               immediately
            +3M                               in three months
            +10y                              in ten years time
            Thursday, 25-Apr-1999 00:40:33 GMT  at the indicated time & date

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

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

The -charset parameter can be used to control the character set sent to the browser. If not provided, defaults to ISO-8859-1. As a side effect, this sets the `charset()` method as well.

The -attachment parameter can be used to turn the page into an attachment. Instead of displaying the page, some browsers will prompt the user to save it to disk. The value of the argument is the suggested name for the saved file. In order for this to work, you may have to set the -type to ``application/octet-stream''.

## GENERATING A REDIRECTION HEADER

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

Sometimes you don't want to produce a document yourself, but simply redirect the browser elsewhere, perhaps choosing a URL based on the time of day or the identity of the user.

The `redirect()` function redirects the browser to a different URL. If you use redirection like this, you should not print out a header as well.

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

You can also use named arguments:

        print $query->redirect(-uri=>'http://somewhere.else/in/movie/land',
                               -nph=>1);

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

## CREATING THE HTML DOCUMENT HEADER

       print $query->start_html(-title=>'Secrets of the Pyramids',
                                -author=>'fred@capricorn.org',
                                -base=>'true',
                                -target=>'_blank',
                                -meta=>{'keywords'=>'pharaoh secret mummy',
                                        'copyright'=>'copyright 1996 King Tut'},
                                -style=>{'src'=>'/styles/style1.css'},
                                -BGCOLOR=>'blue');

After creating the HTTP header, most CGI scripts will start writing out an HTML document. The `start_html()` routine creates the top of the page, along with a lot of optional information that controls the page's appearance and behavior.

This method returns a canned HTML header and the opening <BODY> tag. All parameters are optional. In the named parameter form, recognized parameters are -title, -author, -base, -xbase, -dtd, -lang and -target (see below for the explanation). Any additional parameters you provide, such as the Netscape unofficial BGCOLOR attribute, are added to the <BODY> tag. Additional parameters must be proceeded by a hyphen.

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

        -xbase=>"http://home.mcom.com/";

All relative links will be interpreted relative to this tag.

The argument -target allows you to provide a default target frame for all the links and fill-out forms on the page. This is a non-standard HTTP feature which only works with Netscape browsers! See the Netscape documentation on frames for details of how to manipulate this.

        -target=>"answer_window"

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

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

To create an HTTP-EQUIV type of <META> tag, use -head, described below.

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

The -lang argument is used to incorporate a language attribute into the <HTML> tag. The default if not specified is ``en-US'' for US English. For example:

        print $q->start_html(-lang=>'fr-CA');

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

        print start_html(-head=>Link({-rel=>'next',
                                      -href=>'http://www.capricorn.com/s2.html'}));

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

        print start_html(-head=>[
                                 Link({-rel=>'next',
                                       -href=>'http://www.capricorn.com/s2.html'}),
                                 Link({-rel=>'previous',
                                       -href=>'http://www.capricorn.com/s1.html'})
                                 ]
                         );

And here's how to create an HTTP-EQUIV <META> tag:

          print start_html(-head=>meta({-http_equiv => 'Content-Type',
                                        -content    => 'text/html'}))

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

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

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

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

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

        print $q->start_html(-title=>'The Riddle of the Sphinx',
                             -script=>{-language=>'JAVASCRIPT',
                                       -src=>'/javascript/sphinx.js'}
                             );

        print $q->(-title=>'The Riddle of the Sphinx',
                   -script=>{-language=>'PERLSCRIPT',
                             -code=>'print "hello world!\n;"'}
                   );

A final feature allows you to incorporate multiple <SCRIPT> sections into the header. Just pass the list of script sections as an array reference. this allows you to specify different source files for different dialects of JavaScript. Example:

         print $q->start_html(-title=>'The Riddle of the Sphinx',
                              -script=>[
                                        { -language => 'JavaScript1.0',
                                          -src      => '/javascript/utilities10.js'
                                        },
                                        { -language => 'JavaScript1.1',
                                          -src      => '/javascript/utilities11.js'
                                        },
                                        { -language => 'JavaScript1.2',
                                          -src      => '/javascript/utilities12.js'
                                        },
                                        { -language => 'JavaScript28.2',
                                          -src      => '/javascript/utilities219.js'
                                        }
                                     ]
                                 );
         </pre>

If this looks a bit extreme, take my advice and stick with straight CGI scripting.

See

       http://home.netscape.com/eng/mozilla/2.0/handbook/javascript/

for more information about JavaScript.

The old-style positional parameters are as follows:

Parameters:
  - The title

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

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

  - , 5, 6...
    Any other parameters you want to include in the <BODY> tag. This is a good place to put Netscape extensions, such as colors and wallpaper patterns.

## ENDING THE HTML DOCUMENT:

            print $query->end_html

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

## CREATING A SELF-REFERENCING URL THAT PRESERVES STATE INFORMATION:

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

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

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

If you want more control over what's returned, using the url() method instead.

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

        $the_string = $query->query_string;

## OBTAINING THE SCRIPT'S URL

        $full_url      = $query->url();
        $full_url      = $query->url(-full=>1);  #alternative syntax
        $relative_url  = $query->url(-relative=>1);
        $absolute_url  = $query->url(-absolute=>1);
        $url_with_path = $query->url(-path_info=>1);
        $url_with_path_and_query = $query->url(-path_info=>1,-query=>1);
        $netloc        = $query->url(-base => 1);

url() returns the script's URL in a variety of formats. Called without any arguments, it returns the full form of the URL, including host name and port number

        http://your.host.com/path/to/script.cgi

You can modify this format with the following named arguments:

-absolute
  If true, produce an absolute URL, e.g.

          /path/to/script.cgi

-relative
  Produce a relative URL. This is useful if you want to reinvoke your script with different parameters. For example:

          script.cgi

-full
  Produce the full URL, exactly as if called without any arguments. This overrides the -relative and -absolute arguments.

-path (-path_info)
  Append the additional path information to the URL. This can be combined with -full, -absolute or -relative. -path_info is provided as a synonym.

-query (-query_string)
  Append the query string to the URL. This can be combined with -full, -absolute or -relative. -query_string is provided as a synonym.

-base
  Generate just the protocol and net location, as in http://www.foo.com:8000

## MIXING POST AND URL PARAMETERS

       $color = $query-&gt;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.

# CREATING STANDARD HTML ELEMENTS:

CGI.pm defines general HTML shortcut methods for most, if not all of the HTML 3 and HTML 4 tags. HTML shortcuts are named after a single HTML element and return a fragment of HTML text that you can then print or manipulate as you like. Each shortcut returns a fragment of HTML code that you can append to a string, save to a file, or, most commonly, print out so that it displays in the browser window.

This example shows how to use the HTML methods:

       $q = new CGI;
       print $q->blockquote(
                         "Many years ago on the island of",
                         $q->a({href=>"http://crete.org/";},"Crete"),
                         "there lived a Minotaur named",
                         $q->strong("Fred."),
                        ),
           $q->hr;

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

       <blockquote>
       Many years ago on the island of
       <a HREF="http://crete.org/";>Crete</a> there lived
       a minotaur named <strong>Fred.</strong>
       </blockquote>
       <hr>

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

       use CGI ':standard';
       print blockquote(
          "Many years ago on the island of",
          a({href=>"http://crete.org/";},"Crete"),
          "there lived a minotaur named",
          strong("Fred."),
          ),
          hr;

## PROVIDING ARGUMENTS TO HTML SHORTCUTS

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

       print hr;    #  <HR>

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

       print h1("Chapter","1"); # <H1>Chapter 1</H1>"

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

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

                <A HREF="fred.html",TARGET="_new">Open a new frame</A>

You may dispense with the dashes in front of the attribute names if you prefer:

       print img {src=>'fred.gif',align=>'LEFT'};

               <IMG ALIGN="LEFT" SRC="fred.gif">

Sometimes an HTML tag attribute has no argument. For example, ordered lists can be marked as COMPACT. The syntax for this is an argument that that points to an undef string:

       print ol({compact=>undef},li('one'),li('two'),li('three'));

Prior to CGI.pm version 2.41, providing an empty ('') string as an attribute argument was the same as providing undef. However, this has changed in order to accommodate those who want to create tags of the form <IMG ALT=``''>. The difference is shown in these two pieces of code:

       CODE                   RESULT
       img({alt=>undef})      <IMG ALT>
       img({alt=>''})         <IMT ALT="">

## THE DISTRIBUTIVE PROPERTY OF HTML SHORTCUTS

One of the cool features of the HTML shortcuts is that they 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(
                 li({-type=>'disc'},['Sneezy','Doc','Sleepy','Happy'])
               );

This example will result in HTML output that looks like this:

       <UL>
         <LI TYPE="disc">Sneezy</LI>
         <LI TYPE="disc">Doc</LI>
         <LI TYPE="disc">Sleepy</LI>
         <LI TYPE="disc">Happy</LI>
       </UL>

This is extremely useful for creating tables. For example:

       print table({-border=>undef},
               caption('When Should You Eat Your Vegetables?'),
               Tr({-align=>CENTER,-valign=>TOP},
               [
                  th(['Vegetable', 'Breakfast','Lunch','Dinner']),
                  td(['Tomatoes' , 'no', 'yes', 'yes']),
                  td(['Broccoli' , 'no', 'no',  'yes']),
                  td(['Onions'   , 'yes','yes', 'yes'])
               ]
               )
            );

## HTML SHORTCUTS AND LIST INTERPOLATION

Consider this bit of code:

       print blockquote(em('Hi'),'mom!'));

It will ordinarily return the string that you probably expect, namely:

       <BLOCKQUOTE><EM>Hi</EM> mom!</BLOCKQUOTE>

Note the space between the element ``Hi'' and the element ``mom!''. CGI.pm puts the extra space there using array interpolation, which is controlled by the magic $`` variable. Sometimes this extra space is not what you want, for example, when you are trying to align a series of images. In this case, you can simply change the value of $'' to an empty string.

       {
          local($") = '';
          print blockquote(em('Hi'),'mom!'));
        }

I suggest you put the code in a block as shown here. Otherwise the change to $`` will affect all subsequent code until you explicitly reset it.

## NON-STANDARD HTML SHORTCUTS

A few HTML tags don't follow the standard pattern for various reasons.

comment() generates an HTML comment (<!-- comment -->). Call it like

        print comment('here is my comment');

Because of conflicts with built-in Perl functions, the following functions begin with initial caps:

        Select
        Tr
        Link
        Delete
        Accept
        Sub

In addition, start_html(), end_html(), start_form(), end_form(), `start_multipart_form()` and all the fill-out form tags are special. See their respective sections.

## AUTOESCAPING HTML

By default, all HTML that is emitted by the form-generating functions is passed through a function called escapeHTML():

$escaped_string = escapeHTML(``unescaped string'');
  Escape HTML formatting characters in a string.

Provided that you have specified a character set of ISO-8859-1 (the default), the standard HTML escaping rules will be used. The ``<'' character becomes ``&lt;'', ``>'' becomes ``&gt;'', ``&'' becomes ``&amp;'', and the quote character becomes ``&quot;''. In addition, the hexadecimal 0x8b and 0x9b characters, which many windows-based browsers interpret as the left and right angle-bracket characters, are replaced by their numeric HTML entities (``&#139'' and ``&#155;''). If you manually change the charset, either by calling the `charset()` method explicitly or by passing a -charset argument to header(), then all characters will be replaced by their numeric entities, since CGI.pm has no lookup table for all the possible encodings.

The automatic escaping does not apply to other shortcuts, such as h1(). You should call `escapeHTML()` yourself on untrusted data in order to protect your pages against nasty tricks that people may enter into guestbooks, etc.. To change the character set, use charset(). To turn autoescaping off completely, use autoescape():

$charset = charset([$charset]);
  Get or set the current character set.

$flag = autoEscape([$flag]);
  Get or set the value of the autoescape flag.

## PRETTY-PRINTING HTML

By default, all the HTML produced by these functions comes out as one long line without carriage returns or indentation. This is yuck, but it does reduce the size of the documents by 10-20%. To get pretty-printed output, please use the CGI::Pretty manpage, a subclass contributed by Brian Paulsen.

# CREATING FILL-OUT FORMS:

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

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

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

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

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

       print $query->textfield(-name=>'field_name',
                               -default=>'starting value',
                               -override=>1,
                               -size=>50,
                               -maxlength=>80);

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

       $query = new CGI;
       $query->autoEscape(undef);

## CREATING AN ISINDEX TAG

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

             -or-

       print $query->isindex($action);

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

## STARTING AND ENDING A FORM

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

            -or-

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

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

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

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

Start_form()'s enctype argument tells the browser how to package the various fields of the form before sending the form to the server. Two values are possible:

Note: This method was previously named startform(), and `startform()` is still recognized as an alias.

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

multipart/form-data
  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 designed to handle them.

For compatibility, the `start_form()` 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 start_form().

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

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

## CREATING A TEXT FIELD

        print $query->textfield(-name=>'field_name',
                                -default=>'starting value',
                                -size=>50,
                                -maxlength=>80);
            -or-

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

`textfield()` will return a text input field.

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

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

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

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

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

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

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

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

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

        print $query->textfield(-name=>'field_name',
                                -default=>'starting value',
                                -override=>1,
                                -size=>50,
                                -maxlength=>80);

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

## CREATING A BIG TEXT FIELD

       print $query->textarea(-name=>'foo',
                              -default=>'starting value',
                              -rows=>10,
                              -columns=>50);

            -or

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

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

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

## CREATING A PASSWORD FIELD

       print $query->password_field(-name=>'secret',
                                    -value=>'starting value',
                                    -size=>50,
                                    -maxlength=>80);
            -or-

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

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

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

## CREATING A FILE UPLOAD FIELD

        print $query->filefield(-name=>'uploaded_file',
                                -default=>'starting value',
                                -size=>50,
                                -maxlength=>80);
            -or-

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

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

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

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

    For security reasons, browsers don't pay any attention to this field, and so the starting value will always be blank. Worse, the field loses its ``sticky'' behavior and forgets its previous contents. The starting value field is called for in the HTML specification, however, and possibly some browser will eventually provide support for it.

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

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

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

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

Different browsers will return slightly different things for the name. Some browsers return the filename only. Others return the full path to the file, using the path conventions of the user's machine. Regardless, the name returned is always the name of the file on the user's machine, and is unrelated to the name of the temporary file that CGI.pm creates during upload spooling (see below).

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>) {
               print;
            }

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

However, there are problems with the dual nature of the upload fields. If you `use strict`, then Perl will complain when you try to use a string as a filehandle. You can get around this by placing the file reading code in a block containing the `no strict` pragma. More seriously, it is possible for the remote user to type garbage into the upload field, in which case what you get from `param()` is not a filehandle at all, but a string.

To be safe, use the upload() function (new in version 2.47). When called with the name of an upload field, upload() returns a filehandle, or undef if the parameter is not a valid filehandle.

         $fh = $query->upload('uploaded_file');
         while (<$fh>) {
               print;
         }

This is the recommended idiom.

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

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

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

There are occasionally problems involving parsing the uploaded file. This usually happens when the user presses ``Stop'' before the upload is finished. In this case, CGI.pm will return undef for the name of the uploaded file and set cgi_error() to the string ``400 Bad request (malformed multipart POST)''. This error message is designed so that you can incorporate it into a status code to be sent to the browser. Example:

       $file = $query->upload('uploaded_file');
       if (!$file && $query->cgi_error) {
          print $query->header(-status=>$query->cgi_error);
          exit 0;
       }

You are free to create a custom HTML page to complain about the error, if you wish.

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

## CREATING A POPUP MENU

       print $query->popup_menu('menu_name',
                                ['eenie','meenie','minie'],
                                'meenie');

          -or-

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

            -or (named parameter style)-

       print $query->popup_menu(-name=>'menu_name',
                                -values=>['eenie','meenie','minie'],
                                -default=>'meenie',
                                -labels=>\%labels);

`popup_menu()` creates a menu.

1. The required first argument is the menu's name (-name).

2. The required second argument (-values) is an array reference containing the list of menu items in the menu. You can pass the method an anonymous array, as shown in the example, or a reference to a named array, such as ``\@foo''.

3. The optional third parameter (-default) is the name of the default menu choice. If not specified, the first item will be the default. The values of the previous choice will be maintained across queries.

4. The optional fourth parameter (-labels) is provided for people who want to use different values for the user-visible label inside the popup menu nd the value returned to your script. It's a pointer to an associative array relating menu values to user-visible labels. If you leave this parameter blank, the menu values will be displayed by default. (You can also leave a label undefined if you want to).

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

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

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

## CREATING A SCROLLING LIST

       print $query->scrolling_list('list_name',
                                    ['eenie','meenie','minie','moe'],
                                    ['eenie','moe'],5,'true');
          -or-

       print $query->scrolling_list('list_name',
                                    ['eenie','meenie','minie','moe'],
                                    ['eenie','moe'],5,'true',
                                    \%labels);

            -or-

       print $query->scrolling_list(-name=>'list_name',
                                    -values=>['eenie','meenie','minie','moe'],
                                    -default=>['eenie','moe'],
                                    -size=>5,
                                    -multiple=>'true',
                                    -labels=>\%labels);

`scrolling_list()` creates a scrolling list.

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

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

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

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

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

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

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

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

## CREATING A GROUP OF RELATED CHECKBOXES

       print $query->checkbox_group(-name=>'group_name',
                                    -values=>['eenie','meenie','minie','moe'],
                                    -default=>['eenie','moe'],
                                    -linebreak=>'true',
                                    -labels=>\%labels);

       print $query->checkbox_group('group_name',
                                    ['eenie','meenie','minie','moe'],
                                    ['eenie','moe'],'true',\%labels);

       HTML3-COMPATIBLE BROWSERS ONLY:

       print $query->checkbox_group(-name=>'group_name',
                                    -values=>['eenie','meenie','minie','moe'],
                                    -rows=2,-columns=>2);

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

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

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

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

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

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

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

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

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

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

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

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

## CREATING A STANDALONE CHECKBOX

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

            -or-

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

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

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

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

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

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

The value of the checkbox can be retrieved using:

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

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

## CREATING A RADIO BUTTON GROUP

       print $query->radio_group(-name=>'group_name',
                                 -values=>['eenie','meenie','minie'],
                                 -default=>'meenie',
                                 -linebreak=>'true',
                                 -labels=>\%labels);

            -or-

       print $query->radio_group('group_name',['eenie','meenie','minie'],
                                              'meenie','true',\%labels);

       HTML3-COMPATIBLE BROWSERS ONLY:

       print $query->radio_group(-name=>'group_name',
                                 -values=>['eenie','meenie','minie','moe'],
                                 -rows=2,-columns=>2);

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

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

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

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

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

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

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

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

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

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

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

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

## CREATING A SUBMIT BUTTON

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

            -or-

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

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

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

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

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

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

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

## CREATING A RESET BUTTON

       print $query->reset

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

Note that this conflicts with the Perl `reset()` built-in. Use CORE::reset() to get the original reset function.

## CREATING A DEFAULT BUTTON

       print $query->defaults('button_label')

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

## CREATING A HIDDEN FIELD

            print $query->hidden(-name=>'hidden_name',
                                 -default=>['value1','value2'...]);

                    -or-

            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.

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

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

Fetch the value of a hidden field this way:

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

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

         $query->param('hidden_name','new','values','here');

## CREATING A CLICKABLE IMAGE BUTTON

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

            -or-

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

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

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

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

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

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

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

## CREATING A JAVASCRIPT ACTION BUTTON

         print $query->button(-name=>'button_name',
                              -value=>'user visible label',
                              -onClick=>"do_something()");

            -or-

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

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

# HTTP COOKIES

Netscape browsers versions 1.1 and higher, and all versions of Internet Explorer, 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:

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

2. a domain
   This is a partial or complete domain name for which the cookie is valid. The browser will return the cookie to any host that matches the partial domain name. For example, if you specify a domain name of ``.capricorn.com'', then the browser 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.

3. a path
   If you provide a cookie path attribute, the browser will check it against your script's URL before returning the cookie. For example, if you specify the path ``/cgi-bin'', then the cookie will be returned to each of the scripts ``/cgi-bin/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.

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

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

        $cookie = $query->cookie(-name=>'sessionID',
                                 -value=>'xyzzy',
                                 -expires=>'+1h',
                                 -path=>'/cgi-bin/database',
                                 -domain=>'.capricorn.org',
                                 -secure=>1);
        print $query->header(-cookie=>$cookie);

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

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

-value
  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',
                                     -value=>\%childrens_ages);

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

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

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

              "+1h"  one hour from now

-secure
  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',
                                      -value=>\%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;
            $riddle = $query->cookie('riddle_name');
            %answers = $query->cookie('answers');

Cookies created with a single scalar value, such as the ``riddle_name'' cookie, will be returned in that form. Cookies with array and hash values can also be retrieved.

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
       $c=$q->cookie(-name=>'answers',-value=>[$q->param('answers')]);
       # vice-versa
       $q->param(-name=>'answers',-value=>[$q->cookie('answers')]);

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

# WORKING WITH FRAMES

It's possible for CGI.pm scripts to write into several browser panels and windows using the HTML 4 frame mechanism. There are three techniques for defining new frames programmatically:

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

   There is no specific support for creating <FRAMESET> sections in CGI.pm, but the HTML is very simple to write. See the frame documentation in Netscape's home pages for details

         http://home.netscape.com/assist/net_sites/frames.html

2. Specify the destination for the document in the HTTP header
   You may provide a -target parameter to the `header()` method:

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

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

3. Specify the destination for the document in the <FORM> tag
   You can specify the frame to load in the FORM tag itself. With CGI.pm it looks like this:

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

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

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

# LIMITED SUPPORT FOR CASCADING STYLE SHEETS

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.''

You may also specify the type of the stylesheet by adding the optional -type parameter to the hash pointed to by -style. If not specified, the style defaults to 'text/css'.

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

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

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

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

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

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

Note that you must import the ``:html3'' definitions to have the span() method available. Here's a quick and dirty example of using CSS's. See the CSS specification at http://www.w3.org/pub/WWW/TR/Wd-css-1.html for more information.

        use CGI qw/:standard :html3/;

        #here's a stylesheet incorporated directly into the page
        $newStyle=<<END;
        <!--
        P.Tip {
            margin-right: 50pt;
            margin-left: 50pt;
            color: red;
        }
        P.Alert {
            font-size: 30pt;
            font-family: sans-serif;
          color: red;
        }
        -->
        END
        print header();
        print start_html( -title=>'CGI with Style',
                          -style=>{-src=>'http://www.capricorn.com/style/st1.css',
                                   -code=>$newStyle}
                         );
        print h1('CGI with Style'),
              p({-class=>'Tip'},
                "Better read the cascading style sheet spec before playing with this!"),
              span({-style=>'color: magenta'},
                   "Look Mom, no hands!",
                   p(),
                   "Whooo wee!"
                   );
        print end_html;

Pass an array reference to -style in order to incorporate multiple stylesheets into your document.

# DEBUGGING

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:

        your_script.pl keyword1 keyword2 keyword3

or this:

       your_script.pl keyword1+keyword2+keyword3

or this:

        your_script.pl name1=value1 name2=value2

or this:

        your_script.pl name1=value1&name2=value2

To turn off this feature, use the -no_debug pragma.

To test the POST method, you may enable full debugging with the -debug pragma. This will allow you to feed newline-delimited name=value pairs to the script on standard input.

When debugging, you can use quotes and backslashes to escape characters in the familiar shell manner, letting you place spaces and other funny characters in your parameter=value pairs:

       your_script.pl "name1='I am a long value'" "name2=two\ words"

## 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:

        <UL>
        <LI>name1
            <UL>
            <LI>value1
            <LI>value2
            </UL>
        <LI>name2
            <UL>
            <LI>value1
            </UL>
        </UL>

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

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

# FETCHING ENVIRONMENT VARIABLES

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

Accept()
  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.

  Note that the capitalization changed between version 2.43 and 2.44 in order to avoid conflict with Perl's `accept()` function.

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

  Called with no parameters, `raw_cookie()` returns the packed cookie structure. You can separate it into individual cookies by splitting on the character sequence ``; ''. Called with the name of a cookie, retrieves the unescaped form of the cookie. You can use the regular `cookie()` method to get the names, or use the `raw_fetch()` method from the CGI::Cookie module.

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

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

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

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

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

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

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

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

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

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

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

server_port ()
  Return the port that the server is listening on.

server_software ()
  Returns the server software and version number.

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

user_name ()
  Attempt to obtain the remote user's name, using a variety of different techniques. This only works with older browsers such as Mosaic. Newer browsers do not report the user name for privacy reasons!

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

content_type()
  Returns the content_type of data submitted in a POST, generally multipart/form-data or application/x-www-form-urlencoded

http()
  Called with no arguments returns the list of HTTP environment variables, including such things as HTTP_USER_AGENT, HTTP_ACCEPT_LANGUAGE, and HTTP_ACCEPT_CHARSET, corresponding to the like-named HTTP header fields in the request. Called with the name of an HTTP header field, returns its value. Capitalization and the use of hyphens versus underscores are not significant.

  For example, all three of these examples are equivalent:

         $requested_language = $q->http('Accept-language');
         $requested_language = $q->http('Accept_language');
         $requested_language = $q->http('HTTP_ACCEPT_LANGUAGE');

https()
  The same as http(), but operates on the HTTPS environment variables present when the SSL protocol is in effect. Can be used to determine whether SSL is turned on.

# 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.

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

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

In the use statement
  Simply add the ``-nph'' pragmato 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.

            CGI->nph(1)

By using -nph parameters
  in the header() and redirect() statements:

            print $q->header(-nph=>1);

# Server Push

CGI.pm provides four simple functions for producing multipart documents of the type needed to implement server push. These functions were graciously provided by Ed Jordan <ed@fidalgo.net>. To import these into your namespace, you must import the ``:push'' set. You are also advised to put the script into NPH mode and to set $| to 1 to avoid buffering problems.

Here is a simple script that demonstrates server push:

      #!/usr/local/bin/perl
      use CGI qw/:push -nph/;
      $| = 1;
      print multipart_init(-boundary=>'----here we go!');
      foreach (0 .. 4) {
          print multipart_start(-type=>'text/plain'),
                "The current time is ",scalar(localtime),"\n";
          if ($_ < 4) {
                  print multipart_end;
          } else {
                  print multipart_final;
          }
          sleep 1;
      }

This script initializes server push by calling multipart_init(). It then enters a loop in which it begins a new multipart section by calling multipart_start(), prints the current local time, and ends a multipart section with multipart_end(). It then sleeps a second, and begins again. On the final iteration, it ends the multipart section with multipart_final() rather than with multipart_end().

`multipart_init()`

        multipart_init(-boundary=>$boundary);

  Initialize the multipart system. The -boundary argument specifies what MIME boundary string to use to separate parts of the document. If not provided, CGI.pm chooses a reasonable boundary for you.

`multipart_start()`

        multipart_start(-type=>$type)

  Start a new part of the multipart document using the specified MIME type. If not specified, text/html is assumed.

`multipart_end()`

        multipart_end()

  End a part. You must remember to call `multipart_end()` once for each multipart_start(), except at the end of the last part of the multipart document when `multipart_final()` should be called instead of multipart_end().

`multipart_final()`

        multipart_final()

  End all parts. You should call `multipart_final()` rather than `multipart_end()` at the end of the last part of the multipart document.

Users interested in server push applications should also have a look at the CGI::Push module.

Only Netscape Navigator supports server push. Internet Explorer browsers do not.

# 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:

$CGI::POST_MAX
  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.

$CGI::DISABLE_UPLOADS
  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. 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. 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().

An attempt to send a POST larger than $POST_MAX bytes will cause param() to return an empty CGI parameter list. You can test for this event by checking cgi_error(), either after you create the CGI object or, if you are using the function-oriented interface, call <param()> for the first time. If the POST was intercepted, then `cgi_error()` will return the message ``413 POST too large''.

This error message is actually defined by the HTTP protocol, and is designed to be returned to the browser as the CGI script's status code. For example:

       $uploaded_file = param('upload');
       if (!$uploaded_file && cgi_error()) {
          print header(-status=>cgi_error());
          exit 0;
       }

However it isn't clear that any browser currently knows what to do with this status code. It might be better just to create an HTML page that warns the user of the problem.

# COMPATIBILITY WITH CGI-LIB.PL

To make it easier to port existing programs that use cgi-lib.pl the compatibility routine ``ReadParse'' is provided. Porting is simple:

OLD VERSION require ``cgi-lib.pl''; &ReadParse; print ``The value of the antique is $in{antique}.\n'';

NEW VERSION use CGI; CGI::ReadParse print ``The value of the antique is $in{antique}.\n'';

CGI.pm's `ReadParse()` routine creates a tied variable named %in, which can be accessed to obtain the query variables. Like ReadParse, you can also provide your own variable. Infrequently used features of ReadParse, such as the creation of @in and $in variables, are not supported.

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

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

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

# AUTHOR INFORMATION

Copyright 1995-1998, Lincoln D. Stein. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Address bug reports and comments to: lstein@cshl.org. When sending bug reports, please provide the version of CGI.pm, the version of Perl, the name and version of your Web server, and the name and version of the operating system you are using. If the problem is even remotely browser dependent, please provide information about the affected browers as well.

# CREDITS

Thanks very much to:

Matt Heffron (heffron@falstaff.css.beckman.com)
James Taylor (james.taylor@srs.gov)
Scott Anguish <sanguish@digifix.com>
Mike Jewell (mlj3u@virginia.edu)
Timothy Shimmin (tes@kbs.citri.edu.au)
Joergen Haegg (jh@axis.se)
Laurent Delfosse (delfosse@delfosse.com)
Richard Resnick (applepi1@aol.com)
Craig Bishop (csb@barwonwater.vic.gov.au)
Tony Curtis (tc@vcpc.univie.ac.at)
Tim Bunce (Tim.Bunce@ig.co.uk)
Tom Christiansen (tchrist@convex.com)
Andreas Koenig (k@franz.ww.TU-Berlin.DE)
Tim MacKenzie (Tim.MacKenzie@fulcrum.com.au)
Kevin B. Hendricks (kbhend@dogwood.tyler.wm.edu)
Stephen Dahmen (joyfire@inxpress.net)
Ed Jordan (ed@fidalgo.net)
David Alan Pisoni (david@cnation.com)
Doug MacEachern (dougm@opengroup.org)
Robin Houston (robin@oneworld.org)
...and many many more...
  for suggestions and bug fixes.

# A COMPLETE EXAMPLE OF A SIMPLE FORM-BASED SCRIPT

            #!/usr/local/bin/perl

            use CGI;

            $query = new CGI;

            print $query->header;
            print $query->start_html("Example CGI.pm Form");
            print "<H1> Example CGI.pm Form</H1>\n";
            &print_prompt($query);
            &do_work($query);
            &print_tail;
            print $query->end_html;

            sub print_prompt {
               my($query) = @_;

               print $query->start_form;
               print "<EM>What's your name?</EM><BR>";
               print $query->textfield('name');
               print $query->checkbox('Not my real name');

               print "<P><EM>Where can you find English Sparrows?</EM><BR>";
               print $query->checkbox_group(
                                     -name=>'Sparrow locations',
                                     -values=>[England,France,Spain,Asia,Hoboken],
                                     -linebreak=>'yes',
                                     -defaults=>[England,Asia]);

               print "<P><EM>How far can they fly?</EM><BR>",
                    $query->radio_group(
                            -name=>'how far',
                            -values=>['10 ft','1 mile','10 miles','real far'],
                            -default=>'1 mile');

               print "<P><EM>What's your favorite color?</EM>  ";
               print $query->popup_menu(-name=>'Color',
                                        -values=>['black','brown','red','yellow'],
                                        -default=>'red');

               print $query->hidden('Reference','Monty Python and the Holy Grail');

               print "<P><EM>What have you got there?</EM><BR>";
               print $query->scrolling_list(
                             -name=>'possessions',
                             -values=>['A Coconut','A Grail','An Icon',
                                       'A Sword','A Ticket'],
                             -size=>5,
                             -multiple=>'true');

               print "<P><EM>Any parting comments?</EM><BR>";
               print $query->textarea(-name=>'Comments',
                                      -rows=>10,
                                      -columns=>50);

               print "<P>",$query->reset;
               print $query->submit('Action','Shout');
               print $query->submit('Action','Scream');
               print $query->endform;
               print "<HR>\n";
            }

            sub do_work {
               my($query) = @_;
               my(@values,$key);

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

               foreach $key ($query->param) {
                  print "<STRONG>$key</STRONG> -> ";
                  @values = $query->param($key);
                  print join(", ",@values),"<BR>\n";
              }
            }

            sub print_tail {
               print <<END;
            <HR>
            <ADDRESS>Lincoln D. Stein</ADDRESS><BR>
            <A HREF="/">Home Page</A>
            END
            }

# BUGS

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

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

# SEE ALSO

the CGI::Carp manpage, the URI::URL manpage, the CGI::Request manpage, the CGI::MiniSvr manpage, the CGI::Base manpage, the CGI::Form manpage, the CGI::Push manpage, the CGI::Fast manpage, the CGI::Pretty manpage

CGI - Simple Common Gateway Interface Class