NAME
    CGI - Handle Common Gateway Interface requests and responses

SYNOPSIS
        use strict;
        use warnings;

        use CGI;

        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  = $query->cookie('riddle_name');
        my %answers = $query->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, will continue to exist in the v4
    releases of CGI.pm but may be deprecated (soft) in v5 and beyond. 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 $query = CGI->new;

    This will parse the input (from POST, GET and DELETE methods) and store
    it into a perl5 object called $query. 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 $query = 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 $query = CGI->new( {
            'dinosaur' => 'barney',
            'song'     => 'I love you',
            'friends'  => [ qw/ Jessica George Nancy / ]
        } );

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

        my $query = 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 = $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
        my @names = $query->multi_param

        my @names = $query->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 = $query->multi_param('foo');

            -or-

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

    Pass the param() / multi_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.

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

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

        name => scalar $query->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
        $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.

    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!

    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
        $query->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
        $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.

  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 = $query->param('POSTDATA');

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

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

    (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 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
        $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 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
        Makes `$cgi->param('PUTDATA');' and `$cgi->param('POSTDATA');' act
        like file uploads named PUTDATA and POSTDATA. See Handling
        non-urlencoded arguments and Processing a file upload field
        PUTDATA/POSTDATA 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 should always use full URLs (including the http: or ftp: part) in
    redirection requests. Relative URLs will not work correctly.

    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.

  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 format of headers. The information usually includes
    the MIME content type. To retrieve this information, call uploadInfo().
    It returns a reference to a hash containing all the document headers.

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

    Note that you must use ->param to get the filename to pass into
    uploadInfo as internally this is represented as a File::Temp object
    (which is what will be returned by ->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.

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

    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 no longer work, and the only way to get at the uploaded data is via
    the hook you provide.

    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 = $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
        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.

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'.

    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.

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 GPL and 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

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

    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 browsers as well.

    Failing tests cases are appreciated with issues, and if you submit a
    patch then it will *not* be accepted unless you provide a reasonable
    automated test case with it (please see the existing tests in t/ for
    examples).

    Please note the CGI.pm is now considered "done". See also "mature" and
    "legacy". Features requests and none critical issues will be outright
    rejected. The module is now in maintenance mode for critical issues
    only.

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

    CGI::Fast - supports running CGI applications under FastCGI

