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Updated: Thursday, June 13, 2019
 
 

CGI (3)

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

User Contributed Perl Documentation                                     CGI(3)



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 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 $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.

       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 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 = $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.

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.

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>

       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>


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------------+
       |ATTRIBUTE TYPE |    ATTRIBUTE VALUE     |
       +---------------+------------------------+
       |Availability   | library/perl-5/CGI-526 |
       +---------------+------------------------+
       |Stability      | Committed              |
       +---------------+------------------------+
SEE ALSO
       CGI::Carp - provides Carp implementation tailored to the CGI
       environment.

       CGI::Fast - supports running CGI applications under FastCGI



NOTES
       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from
       http://search.cpan.org/CPAN/authors/id/L/LE/LEEJO/CGI-4.37.tar.gz

       Further information about this software can be found on the open source
       community website at http://search.cpan.org/~leejo/CGI.



perl v5.26.2                      2017-03-29                            CGI(3)