Provided by: libcgi-pm-perl_4.57-1_all bug

NAME

       CGI - Handle Common Gateway Interface requests and responses

SYNOPSIS

           use strict;
           use warnings;

           use CGI;

               # create a CGI object (query) for use
           my $q = CGI->new;

           # Process an HTTP request
           my @values  = $q->multi_param('form_field');
           my $value   = $q->param('param_name');

           my $fh      = $q->upload('file_field');

           my $riddle  = $q->cookie('riddle_name');
           my %answers = $q->cookie('answers');

           # Prepare various HTTP responses
           print $q->header();
           print $q->header('application/json');

           my $cookie1 = $q->cookie(
               -name  => 'riddle_name',
               -value => "The Sphynx's Question"
           );

           my $cookie2 = $q->cookie(
               -name  => 'answers',
               -value => \%answers
           );

           print $q->header(
               -type    => 'image/gif',
               -expires => '+3d',
               -cookie  => [ $cookie1,$cookie2 ]
           );

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

DESCRIPTION

       CGI.pm is a stable, complete and mature solution for processing and preparing HTTP
       requests and responses. Major features including processing form submissions, file
       uploads, reading and writing cookies, query string generation and manipulation, and
       processing and preparing HTTP headers.

       CGI.pm performs very well in a vanilla CGI.pm environment and also comes with built-in
       support for mod_perl and mod_perl2 as well as FastCGI.

       It has the benefit of having developed and refined over 20 years with input from dozens of
       contributors and being deployed on thousands of websites.  CGI.pm was included in the perl
       distribution from perl v5.4 to v5.20, however is has now been removed from the perl
       core...

CGI.pm HAS BEEN REMOVED FROM THE PERL CORE

       <http://perl5.git.perl.org/perl.git/commitdiff/e9fa5a80>

       If you upgrade to a new version of perl or if you rely on a system or vendor perl and get
       an updated version of perl through a system update, then you will have to install CGI.pm
       yourself with cpan/cpanm/a vendor package/manually. To make this a little easier the
       CGI::Fast module has been split into its own distribution, meaning you do not need access
       to a compiler to install CGI.pm

       The rationale for this decision is that CGI.pm is no longer considered good practice for
       developing web applications, including quick prototyping and small web scripts. There are
       far better, cleaner, quicker, easier, safer, more scalable, more extensible, more modern
       alternatives available at this point in time. These will be documented with
       CGI::Alternatives.

       For more discussion on the removal of CGI.pm from core please see:

       <http://www.nntp.perl.org/group/perl.perl5.porters/2013/05/msg202130.html>

       Note that the v4 releases of CGI.pm will retain back compatibility as much as possible,
       however you may need to make some minor changes to your code if you are using deprecated
       methods or some of the more obscure features of the module. If you plan to upgrade to
       v4.00 and beyond you should read the Changes file for more information and test your code
       against CGI.pm before deploying it.

HTML Generation functions should no longer be used

       All HTML generation functions within CGI.pm are no longer being maintained. Any issues,
       bugs, or patches will be rejected unless they relate to fundamentally broken page
       rendering.

       The rationale for this is that the HTML generation functions of CGI.pm are an obfuscation
       at best and a maintenance nightmare at worst. You should be using a template engine for
       better separation of concerns.  See CGI::Alternatives for an example of using CGI.pm with
       the Template::Toolkit module.

       These functions, and perldoc for them, are considered deprecated, they are no longer being
       maintained and no fixes or features for them will be accepted. They will, however,
       continue to exist in CGI.pm without any deprecation warnings ("soft" deprecation) so you
       can continue to use them if you really want to. All documentation for these functions has
       been moved to CGI::HTML::Functions.

Programming style

       There are two styles of programming with CGI.pm, an object-oriented (OO) style and a
       function-oriented style. You are recommended to use the OO style as CGI.pm will create an
       internal default object when the functions are called procedurally and you will not have
       to worry about method names clashing with perl builtins.

       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:

           #!/usr/bin/env perl

           use strict;
           use warnings;

           use CGI;                             # load CGI routines

           my $q = CGI->new;                    # create new CGI object
           print $q->header;                    # create the HTTP header

       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, manage cookies, and
       so on. The following example is identical to above, in terms of output, 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/bin/env perl

           use strict;
           use warnings;

           use CGI qw/:standard/;           # load standard CGI routines
           print header();                  # create the HTTP header

       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 => [ qw/tomato tomahto potato potahto/ ],
           );

       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.

   Creating a new query object (object-oriented style)
           my $q = CGI->new;

       This will parse the input (from POST, GET and DELETE methods) and store it into a perl5
       object called $q. Note that because the input parsing happens at object instantiation you
       have to set any CGI package variables that control parsing before you call CGI->new.

       Any filehandles from file uploads will have their position reset to the beginning of the
       file.

   Creating a new query object from an input file
           my $q = CGI->new( $input_filehandle );

       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.
       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( my $in_fh,'<',"test.in") || die "Couldn't open test.in for read: $!";
           restore_parameters( $in_fh );
           close( $in_fh );

       You can also initialize the query object from a hash reference:

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

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

           my $q = CGI->new('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):

           my $old_query = CGI->new;
           my $new_query = CGI->new($old_query);

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

           my $empty_query = CGI->new("");


              -or-
           my $empty_query = CGI->new({});

   Fetching a list of keywords from the query
           my @keywords = $q->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
           my @names = $q->multi_param

           my @names = $q->param

       If the script was invoked with a parameter list (e.g.
       "name1=value1&name2=value2&name3=value3"), the param() / multi_param() methods 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.

       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
           my @values = $q->multi_param('foo');


               -or-
           my $value = $q->param('foo');


               -or-
           my @values = $q->param('foo'); # list context, discouraged and will raise
                                          # a warning (use ->multi_param instead)

       Pass the param() / multi_param() method a single argument to fetch the value of the named
       parameter. When calling param() 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 the first value.

       Warning - calling param() in list context can lead to vulnerabilities if you do not
       sanitise user input as it is possible to inject other param keys and values into your
       code. This is why the multi_param() method exists, to make it clear that a list is being
       returned, note that param() can still be called in list context and will return a list for
       back compatibility.

       The following code is an example of a vulnerability as the call to param will be evaluated
       in list context and thus possibly inject extra keys and values into the hash:

           my %user_info = (
               id   => 1,
               name => $q->param('name'),
           );

       The fix for the above is to force scalar context on the call to ->param by prefixing it
       with "scalar"

           name => scalar $q->param('name'),

       If you call param() in list context with an argument a warning will be raised by CGI.pm,
       you can disable this warning by setting $CGI::LIST_CONTEXT_WARN to 0 or by using the
       multi_param() method instead

       If a value is not given in the query string, as in the queries "name1=&name2=", it will be
       returned as an empty string.

       If the parameter does not exist at all, then param() will return undef in scalar context,
       and the empty list in a list context.

   Setting the value(s) of a named parameter
           $q->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.

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

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


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

   Appending additional values to a named parameter
           $q->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
           $q->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!

       NOTE 1: Variable names are transformed as necessary into legal perl variable names. All
       non-legal characters are transformed into underscores. If you need to keep the original
       names, you should use the param() method instead to access CGI variables by name.

       In fact, you should probably not use this method at all given the above caveats and
       security risks.

   Deleting a parameter completely
           $q->delete('foo','bar','baz');

       This completely clears a list of parameters. 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
           $q->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.

   Handling non-urlencoded arguments
       If POSTed data is not of type application/x-www-form-urlencoded or multipart/form-data,
       then the POSTed data will not be processed, but instead be returned as-is in a parameter
       named POSTDATA. To retrieve it, use code like this:

           my $data = $q->param('POSTDATA');

       Likewise if PUTed and PATCHed data can be retrieved with code like this:

           my $data = $q->param('PUTDATA');

           my $data = $q->param('PATCHDATA');

       (If you don't know what the preceding means, worry not. It only affects people trying to
       use CGI for XML processing and other specialized tasks)

       PUTDATA/POSTDATA/PATCHDATA are also available via upload_hook, and as file uploads via
       "-putdata_upload" option.

   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 given
       in the previous sections, you can obtain a direct reference to it by calling the
       param_fetch() method with the name of the parameter. This will return an array reference
       to the named parameter, 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
           my $params = $q->Vars;
           print $params->{'address'};
           my @foo = split("\0",$params->{'foo'});
           my %params = $q->Vars;

           use CGI ':cgi-lib';
           my $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, and may be replaced
       in future versions with array references.

       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
           $q->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 strict;
           use warnings;
           use CGI;

           open (my $out_fh,'>>','test.out') || die "Can't open test.out: $!";
           my $records = 5;
           for ( 0 .. $records ) {
               my $q = CGI->new;
               $q->param( -name => 'counter',-value => $_ );
               $q->save( $out_fh );
           }
           close( $out_fh );

           # reopen for reading
           open (my $in_fh,'<','test.out') || die "Can't open test.out: $!";
           while (!eof($in_fh)) {
               my $q = CGI->new($in_fh);
               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 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 a page, or use it as the value of the HTTP status:

           if ( my $error = $q->cgi_error ) {
               print $q->header( -status => $error );
               print "Error: $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 strict;
           use warnings;

           use CGI qw/ 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 strict;
           use warnings;

           use CGI qw/ param header /;
           print header('text/plain');
           my $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 ":cgi" (for CGI protocol
       handling methods).

       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.

       :all
           Import all the available methods. For the full list, see the CGI.pm code, where the
           variable %EXPORT_TAGS is defined. (N.B. the :cgi-lib imports will not be included in
           the :all import, you will have to import :cgi-lib to get those)

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

   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 cgi set of functions
       and enables debugging mode (pragma -debug):

           use strict;
           use warninigs;
           use CGI qw/ :cgi -debug /;

       The current list of pragmas is as follows:

       -no_undef_params
           This keeps CGI.pm from including undef params in the parameter list.

       -utf8
           This makes CGI.pm treat all parameters as text strings rather than binary strings (see
           perlunitut for the distinction), assuming UTF-8 for the encoding.

           CGI.pm does the decoding from the UTF-8 encoded input data, restricting this decoding
           to input text as distinct from binary upload data which are left untouched. Therefore,
           a ':utf8' layer must not be used on STDIN.

           If you do not use this option you can manually select which fields are expected to
           return utf-8 strings and convert them using code like this:

               use strict;
               use warnings;

               use CGI;
               use Encode qw/ decode /;

               my $cgi   = CGI->new;
               my $param = $cgi->param('foo');
               $param    = decode( 'UTF-8',$param );

       -putdata_upload / -postdata_upload / -patchdata_upload
           Makes "$cgi->param('PUTDATA');", "$cgi->param('PATCHDATA');", and
           "$cgi->param('POSTDATA');" act like file uploads named PUTDATA, PATCHDATA, and
           POSTDATA. See "Handling non-urlencoded arguments" and "Processing a file upload field"
           PUTDATA/POSTDATA/PATCHDATA are also available via upload_hook.

       -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, and will be emitted by
           self_url() and query_string(). newstyle_urls 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.

       -no_debug
           This turns off the command-line processing features. If you want to run a CGI.pm
           script from the command line, 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.

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.

       Each of these functions produces a fragment of HTTP which you can print out directly so
       that it is processed by the browser, appended to a string, or saved 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.

           use strict;
           use warnings;

           use CGI;

           my $cgi = CGI->new;

           print $cgi->header;


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


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


               -or-
           print $cgi->header(
               -type       => 'image/gif',
               -nph        => 1,
               -status     => '402 Payment required',
               -expires    => '+3d',
               -cookie     => $cookie,
               -charset    => 'utf-8',
               -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. Note that RFC 2616 expects
       the human-readable phase to be there as well as the numeric status code.

       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 $cgi->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-2018 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. Some 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. Note that the default being ISO-8859-1 may not make sense for all content types,
       e.g.:

           Content-Type: image/gif; charset=ISO-8859-1

       In the above case you need to pass -charset => '' to prevent the default being used.

       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".

       The -p3p parameter will add a P3P tag to the outgoing header. The parameter can be an
       arrayref or a space-delimited string of P3P tags. For example:

           print $cgi->header( -p3p => [ qw/ CAO DSP LAW CURa / ] );
           print $cgi->header( -p3p => 'CAO DSP LAW CURa' );

       In either case, the outgoing header will be formatted as:

           P3P: policyref="/w3c/p3p.xml" cp="CAO DSP LAW CURa"

       CGI.pm will accept valid multi-line headers when each line is separated with a CRLF value
       ("\r\n" on most platforms) followed by at least one space. For example:

           print $cgi->header( -ingredients => "ham\r\n\seggs\r\n\sbacon" );

       Invalid multi-line header input will trigger in an exception. When multi-line headers are
       received, CGI.pm will always output them back as a single line, according to the folding
       rules of RFC 2616: the newlines will be removed, while the white space remains.

   Generating a redirection header
           print $q->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() method redirects the browser to a different URL. If you use redirection
       like this, you should not print out a header as well.

       You are advised to use full URLs (absolute with respect to current URL or even including
       the http: or ftp: part) in redirection requests as relative URLs are resolved by the user
       agent of the client so may not do what you want or expect them to do.

       You can also use named arguments:

           print $q->redirect(
               -uri    => 'http://somewhere.else/in/movie/land',
               -nph    => 1,
               -status => '301 Moved Permanently'
           );

       All names arguments recognized by header() are also recognized by redirect().  However,
       most HTTP headers, including those generated by -cookie and -target, are ignored by the
       browser.

       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 IIS, which expect all their scripts to be NPH.

       The -status parameter will set the status of the redirect. HTTP defines several different
       possible redirection status codes, and the default if not specified is 302, which means
       "moved temporarily." You may change the status to another status code if you wish.

       Note that the human-readable phrase is also expected to be present to conform with RFC
       2616, section 6.1.

   Creating a self-referencing url that preserves state information
           my $myself = $q->self_url;
           print qq(<a href="$myself">I'm talking to myself.</a>);

       self_url() will return a URL, that, when selected, will re-invoke 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:

            my $myself = $q->self_url;
            print "<a href=\"$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 a query string representation of the current object state with
       query_string():

           my $the_string = $q->query_string();

       The behavior of calling query_string is currently undefined when the HTTP method is
       something other than GET.

       If you want to retrieved the query string as set in the webserver, namely the environment
       variable, you can call env_query_string()

   Obtaining the script's url
           my $full_url      = url();
           my $full_url      = url( -full =>1 );  # alternative syntax
           my $relative_url  = url( -relative => 1 );
           my $absolute_url  = url( -absolute =>1 );
           my $url_with_path = url( -path_info => 1 );
           my $url_path_qry  = url( -path_info => 1, -query =>1 );
           my $netloc        = 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 re-invoke 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

       -rewrite
           If Apache's mod_rewrite is turned on, then the script name and path info probably
           won't match the request that the user sent. Set -rewrite => 1 (default) to return URLs
           that match what the user sent (the original request URI). Set -rewrite => 0 to return
           URLs that match the URL after the mod_rewrite rules have run.

   Mixing post and url parameters
           my $color = 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.

       If running from the command line, "url_param" will not pick up any parameters given on the
       command line.

   Processing a file upload field
       Basics

       When the form is processed, you can retrieve an IO::File compatible handle for a file
       upload field like this:

           use autodie;

           # undef may be returned if it's not a valid file handle
           if ( my $io_handle = $q->upload('field_name') ) {
               open ( my $out_file,'>>','/usr/local/web/users/feedback' );
               while ( my $bytesread = $io_handle->read($buffer,1024) ) {
                   print $out_file $buffer;
               }
           }

       In a list context, upload() will return an array of filehandles. This makes it possible to
       process forms that use the same name for multiple upload fields.

       If you want the entered file name for the file, you can just call param():

           my $filename = $q->param('field_name');

       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).

       When a file is uploaded the browser usually sends along some information along with it in
       the Content-Type (MIME type) and Content-Disposition (filename) headers.  To retrieve this
       information, call uploadInfo(). It returns a reference to a hash containing all the
       document headers.

           my $filehandle = $q->upload( 'uploaded_file' );
           my $type       = $q->uploadInfo( $filehandle )->{'Content-Type'};
           if ( $type ne 'text/html' ) {
               die "HTML FILES ONLY!";
           }

       Note that you must use ->upload or ->param to get the file-handle to pass into uploadInfo
       as internally this is represented as a File::Temp object (which is what will be returned
       by ->upload or ->param). When using ->Vars you will get the literal filename rather than
       the File::Temp object, which will not return anything when passed to uploadInfo. So don't
       use ->Vars.

       When uploading multiple files, call ->param() in list context to retrieve a list of
       filehandles that you can use when calling ->uploadInfo.

           my @filehandles = $q->param('uploaded_file');

           for my $fh (@filehandles) {
             my $info = $q->uploadInfo($fh);
             ...
           }

       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.

       Accessing the temp files directly

       When processing an uploaded file, CGI.pm creates a temporary file on your hard disk and
       passes you a file handle to that file. After you are finished with the file handle, CGI.pm
       unlinks (deletes) the temporary file. If you need to you can access the temporary file
       directly. You can access the temp file for a file upload by passing the file name to the
       tmpFileName() method:

           my $filehandle  = $q->upload( 'uploaded_file' );
           my $tmpfilename = $q->tmpFileName( $filehandle );

       As with ->uploadInfo, using the reference returned by ->upload or ->param is preferred,
       although unlike ->uploadInfo, plain filenames also work if possible for backwards
       compatibility.

       The temporary file will be deleted automatically when your program exits unless you
       manually rename it or set $CGI::UNLINK_TMP_FILES to 0. On some operating systems (such as
       Windows NT), you will need to close the temporary file's filehandle before your program
       exits. Otherwise the attempt to delete the temporary file will fail.

       Changes in temporary file handling (v4.05+)

       CGI.pm had its temporary file handling significantly refactored, this logic is now all
       deferred to File::Temp (which is wrapped in a compatibility object, CGI::File::Temp - DO
       NOT USE THIS PACKAGE DIRECTLY). As a consequence the PRIVATE_TEMPFILES variable has been
       removed along with deprecation of the private_tempfiles routine and complete removal of
       the CGITempFile package.  The $CGITempFile::TMPDIRECTORY is no longer used to set the temp
       directory, refer to the perldoc for File::Temp if you want to override the default
       settings in that package (the TMPDIR env variable is still available on some platforms).
       For Windows platforms the temporary directory order remains as before: TEMP > TMP > WINDIR
       ( > TMPDIR ) so if you have any of these in use in existing scripts they should still
       work.

       The Fh package still exists but does nothing, the CGI::File::Temp class is a subclass of
       both File::Temp and the empty Fh package, so if you have any code that checks that the
       filehandle isa Fh this should still work.

       When you get the internal file handle you will receive a File::Temp object, this should be
       transparent as File::Temp isa IO::Handle and isa IO::Seekable meaning it behaves as
       previously. If you are doing anything out of the ordinary with regards to temp files you
       should test your code before deploying this update and refer to the File::Temp
       documentation for more information.

       Handling interrupted 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:

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

       Progress bars for file uploads and avoiding temp files

       CGI.pm gives you low-level access to file upload management through a file upload hook.
       You can use this feature to completely turn off the temp file storage of file uploads, or
       potentially write your own file upload progress meter.

       This is much like the UPLOAD_HOOK facility available in Apache::Request, with the
       exception that the first argument to the callback is an Apache::Upload object, here it's
       the remote filename.

           my $q = CGI->new( \&hook [,$data [,$use_tempfile]] );

           sub hook {
               my ( $filename, $buffer, $bytes_read, $data ) = @_;
               print "Read $bytes_read bytes of $filename\n";
           }

       The $data field is optional; it lets you pass configuration information (e.g. a database
       handle) to your hook callback.

       The $use_tempfile field is a flag that lets you turn on and off CGI.pm's use of a
       temporary disk-based file during file upload. If you set this to a FALSE value (default
       true) then "$q->param('uploaded_file')" will still return a typeglob that can be used to
       access a filehandle and the filename of the uploaded file, however the filehandle will be
       a handle to an empty file. Existence of your hook causes CGI.pm to bypass writing to that
       filehandle (which is probably what you intended when you set $use_tempfile off).

       The "uploadInfo()" method can be used on the typeglob returned to you when you called
       "$q->param('upload_file')" to return information about the uploaded file(s). For multiple
       file uploads, use the " param() " method in list context to retrieve all of the typeglobs.

           my (@filehandles) = $cgi->param('upfile');

           foreach my $fh (@filehandles) {
             my $info = $cgi->uploadInfo($fh);
             ...
           }

       If using the function-oriented interface, call the CGI::upload_hook() method before
       calling param() or any other CGI functions:

           CGI::upload_hook( \&hook [,$data [,$use_tempfile]] );

       This method is not exported by default. You will have to import it explicitly if you wish
       to use it without the CGI:: prefix.

       Troubleshooting file uploads on Windows

       If you are using CGI.pm on a Windows platform and find that binary files get slightly
       larger when uploaded but that text files remain the same, then you have forgotten to
       activate binary mode on the output filehandle. Be sure to call binmode() on any handle
       that you create to write the uploaded file to disk.

       Older ways to process file uploads

       This section is here for completeness. if you are building a new application with CGI.pm,
       you can skip it.

       The original way to process file uploads with CGI.pm was to use param(). The value it
       returns has a dual nature as both a file name and a lightweight filehandle. This dual
       nature is problematic if you following the recommended practice of having "use strict" in
       your code. perl will complain when you try to use a string as a filehandle. 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 solve this problem the upload() method was added, which always returns a lightweight
       filehandle. This generally works well, but will have trouble interoperating with some
       other modules because the file handle is not derived from IO::File. So that brings us to
       current recommendation given above, which is to call the handle() method on the file
       handle returned by upload().  That upgrades the handle to an IO::File. It's a big win for
       compatibility for a small penalty of loading IO::File the first time you call it.

HTTP COOKIES

       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:

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

           print $q->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 hash
           reference. For example, you can store an entire hash into a cookie this way:

               my $cookie = $q->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:

           use strict;
           use warnings;

           use CGI;

           my $q      = CGI->new;
           my $cookie = ...
           print $q->header( -cookie => $cookie );

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

           my $cookie1 = $q->cookie(
               -name  => 'riddle_name',
               -value => "The Sphynx's Question"
           );

           my $cookie2 = $q->cookie(
               -name  => 'answers',
               -value => \%answers
           );

           print $q->header( -cookie => [ $cookie1,$cookie2 ] );

       To retrieve a cookie, request it by name by calling cookie() method without the -value
       parameter. This example uses the object-oriented form:

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

       If you call cookie() without any parameters, it will return a list of the names of all
       cookies passed to your script:

           my @cookies = $q->cookie();

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

       $CGI::COOKIE_CACHE
           If set to a non-negative integer, this variable will cause CGI.pm to use the cached
           cookie details from the previous call to cookie(). By default this cache is off to
           retain backwards compatibility.

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"

       Finally, you can set the path info for the script by prefixing the first name/value
       parameter with the path followed by a question mark (?):

           your_script.pl /your/path/here?name1=value1&name2=value2

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 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. 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.

       env_query_string()
           Returns the QUERY_STRING variable, note that this is the original value as set in the
           environment by the webserver and (possibly) not the same value as returned by
           query_string(), which represents the object state

       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
           user_agent(Mozilla);

       path_info()
           Returns additional path information from the script URL. E.G. fetching
           /cgi-bin/your_script/additional/stuff will result in 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. A best attempt has been made to make CGI.pm do the
           right thing.

       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.

       remote_ident()
           Returns the name of the remote user (as returned by identd) or undef if not set

       remote_addr()
           Returns the remote host IP address, or 127.0.0.1 if the address is unavailable.

       request_uri()
           Returns the interpreted pathname of the requested document or CGI (relative to the
           document root). Or undef if not set.

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

       referer()
           Return the URL of the page the browser was viewing prior to fetching your script.

       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_protocol()
           Returns the protocol and revision of the incoming request, or defaults to HTTP/1.0 if
           this is not set

       virtual_port()
           Like server_port() except that it takes virtual hosts into account. Use this when
           running with virtual hosts.

       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. May
           not work in all browsers.

       request_method()
           Returns the method used to access your script, usually one of 'POST', 'GET' or 'HEAD'.
           If running from the command line it will be undef.

       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:

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

               my $requested_language = $q->http('Accept_language');

               my $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.

       In the use statement
           Simply add the "-nph" pragma to the list of symbols to be imported into your script:

               use CGI qw(:standard -nph)

       By calling the nph() method:
           Call nph() with a non-zero parameter at any point after using CGI.pm in your program.

               CGI->nph(1)

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

               print 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/bin/env perl

           use strict;
           use warnings;

           use CGI qw/:push -nph/;

           $| = 1;
           print multipart_init( -boundary=>'----here we go!' );
           for (0 .. 4) {
               print multipart_start( -type=>'text/plain' ),
                   "The current time is ",scalar( localtime ),"\n";
               if ($_ < 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, -charset => $charset );

           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.

           The -charset provides the character set, if not provided this will default to
           ISO-8859-1

       multipart_start()
               multipart_start( -type => $type, -charset => $charset );

           Start a new part of the multipart document using the specified MIME type and charset.
           If not specified, text/html ISO-8859-1 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.

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 gigabytes. 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 10 megabytes.

       $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.

       To use these variables, set the variable at the top of the script, right after the "use"
       statement:

           #!/usr/bin/env perl

           use strict;
           use warnings;

           use CGI;

           $CGI::POST_MAX = 1024 * 1024 * 10;  # max 10MB posts
           $CGI::DISABLE_UPLOADS = 1;          # no uploads

       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:

           my $uploaded_file = $q->param('upload');
           if ( !$uploaded_file && $q->cgi_error() ) {
               print $q->header( -status => $q->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 a page that warns the user of the problem.

MODULE FLAGS

       There are a number of global module flags which affect how CGI.pm operates.

       $CGI::APPEND_QUERY_STRING
           If set to a non-zero value, this will add query string parameters to a POST forms
           parameters hence allowing param() to return values from the query string as well as
           from the decoded POST request instead of having to use url_param instead. This makes
           it easier to get the value of a parameter when you don't know the source.

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:

           my $q = $in{CGI};

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

       An even simpler way to mix cgi-lib calls with CGI.pm calls is to import both the
       ":cgi-lib" and ":standard" method:

           use CGI qw(:cgi-lib :standard);
           &ReadParse;
           print "The price of your purchase is $in{price}.\n";
           print textfield(-name=>'price', -default=>'$1.99');

   Cgi-lib functions that are available in CGI.pm
       In compatibility mode, the following cgi-lib.pl functions are available for your use:

           ReadParse()
           PrintHeader()
           SplitParam()
           MethGet()
           MethPost()

LICENSE

       The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is distributed under
       the Artistic License 2.0. It is currently maintained by Lee Johnson (LEEJO) with help from
       many contributors.

CREDITS

       Thanks very much to:

       Mark Stosberg (mark@stosberg.com)
       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.

BUGS

       Address bug reports and comments to: <https://github.com/leejo/CGI.pm/issues>

       See the <https://github.com/leejo/CGI.pm/blob/master/CONTRIBUTING.md> file for information
       on raising issues and contributing

       The original bug tracker can be found at:
       <https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm>

SEE ALSO

       CGI::Carp - provides Carp implementation tailored to the CGI environment.

       CGI::Fast - supports running CGI applications under FastCGI