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CGI(3pm) User Contributed Perl Documentation CGI(3pm)
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.
$CGI::COOKIE_CACHE
If set to a non-negative integer, this variable will cause CGI.pm to use the cached
cookie details from the previous call to cookie(). By default this cache is off to
retain backwards compatibility.
DEBUGGING
If you are running the script from the command line or in the perl debugger, you can pass
the script a list of keywords or parameter=value pairs on the command line or from
standard input (you don't have to worry about tricking your script into reading from
environment variables). You can pass keywords like this:
your_script.pl keyword1 keyword2 keyword3
or this:
your_script.pl keyword1+keyword2+keyword3
or this:
your_script.pl name1=value1 name2=value2
or this:
your_script.pl name1=value1&name2=value2
To turn off this feature, use the -no_debug pragma.
To test the POST method, you may enable full debugging with the -debug pragma. This will
allow you to feed newline-delimited name=value pairs to the script on standard input.
When debugging, you can use quotes and backslashes to escape characters in the familiar
shell manner, letting you place spaces and other funny characters in your parameter=value
pairs:
your_script.pl "name1='I am a long value'" "name2=two\ words"
Finally, you can set the path info for the script by prefixing the first name/value
parameter with the path followed by a question mark (?):
your_script.pl /your/path/here?name1=value1&name2=value2
FETCHING ENVIRONMENT VARIABLES
Some of the more useful environment variables can be fetched through this interface. The
methods are as follows:
Accept()
Return a list of MIME types that the remote browser accepts. If you give this method a
single argument corresponding to a MIME type, as in Accept('text/html'), it will
return a floating point value corresponding to the browser's preference for this type
from 0.0 (don't want) to 1.0. Glob types (e.g. text/*) in the browser's accept list
are handled correctly.
Note that the capitalization changed between version 2.43 and 2.44 in order to avoid
conflict with perl's accept() function.
raw_cookie()
Returns the HTTP_COOKIE variable. Cookies have a special format, and this method call
just returns the raw form (?cookie dough). See cookie() for ways of setting and
retrieving cooked cookies.
Called with no parameters, raw_cookie() returns the packed cookie structure. You can
separate it into individual cookies by splitting on the character sequence "; ".
Called with the name of a cookie, retrieves the unescaped form of the cookie. You can
use the regular cookie() method to get the names, or use the raw_fetch() method from
the CGI::Cookie module.
env_query_string()
Returns the QUERY_STRING variable, note that this is the original value as set in the
environment by the webserver and (possibly) not the same value as returned by
query_string(), which represents the object state
user_agent()
Returns the HTTP_USER_AGENT variable. If you give this method a single argument, it
will attempt to pattern match on it, allowing you to do something like
user_agent(Mozilla);
path_info()
Returns additional path information from the script URL. E.G. fetching
/cgi-bin/your_script/additional/stuff will result in path_info() returning
"/additional/stuff".
NOTE: The Microsoft Internet Information Server is broken with respect to additional
path information. If you use the perl DLL library, the IIS server will attempt to
execute the additional path information as a perl script. If you use the ordinary file
associations mapping, the path information will be present in the environment, but
incorrect. The best thing to do is to avoid using additional path information in CGI
scripts destined for use with IIS. A best attempt has been made to make CGI.pm do the
right thing.
path_translated()
As per path_info() but returns the additional path information translated into a
physical path, e.g. "/usr/local/etc/httpd/htdocs/additional/stuff".
The Microsoft IIS is broken with respect to the translated path as well.
remote_host()
Returns either the remote host name or IP address if the former is unavailable.
remote_ident()
Returns the name of the remote user (as returned by identd) or undef if not set
remote_addr()
Returns the remote host IP address, or 127.0.0.1 if the address is unavailable.
request_uri()
Returns the interpreted pathname of the requested document or CGI (relative to the
document root). Or undef if not set.
script_name()
Return the script name as a partial URL, for self-referring scripts.
referer()
Return the URL of the page the browser was viewing prior to fetching your script.
auth_type()
Return the authorization/verification method in use for this script, if any.
server_name()
Returns the name of the server, usually the machine's host name.
virtual_host()
When using virtual hosts, returns the name of the host that the browser attempted to
contact
server_port()
Return the port that the server is listening on.
server_protocol()
Returns the protocol and revision of the incoming request, or defaults to HTTP/1.0 if
this is not set
virtual_port()
Like server_port() except that it takes virtual hosts into account. Use this when
running with virtual hosts.
server_software()
Returns the server software and version number.
remote_user()
Return the authorization/verification name used for user verification, if this script
is protected.
user_name()
Attempt to obtain the remote user's name, using a variety of different techniques. May
not work in all browsers.
request_method()
Returns the method used to access your script, usually one of 'POST', 'GET' or 'HEAD'.
If running from the command line it will be undef.
content_type()
Returns the content_type of data submitted in a POST, generally multipart/form-data or
application/x-www-form-urlencoded
http()
Called with no arguments returns the list of HTTP environment variables, including
such things as HTTP_USER_AGENT, HTTP_ACCEPT_LANGUAGE, and HTTP_ACCEPT_CHARSET,
corresponding to the like-named HTTP header fields in the request. Called with the
name of an HTTP header field, returns its value. Capitalization and the use of
hyphens versus underscores are not significant.
For example, all three of these examples are equivalent:
my $requested_language = $q->http('Accept-language');
my $requested_language = $q->http('Accept_language');
my $requested_language = $q->http('HTTP_ACCEPT_LANGUAGE');
https()
The same as http(), but operates on the HTTPS environment variables present when the
SSL protocol is in effect. Can be used to determine whether SSL is turned on.
USING NPH SCRIPTS
NPH, or "no-parsed-header", scripts bypass the server completely by sending the complete
HTTP header directly to the browser. This has slight performance benefits, but is of most
use for taking advantage of HTTP extensions that are not directly supported by your
server, such as server push and PICS headers.
Servers use a variety of conventions for designating CGI scripts as NPH. Many Unix servers
look at the beginning of the script's name for the prefix "nph-". The Macintosh WebSTAR
server and Microsoft's Internet Information Server, in contrast, try to decide whether a
program is an NPH script by examining the first line of script output.
CGI.pm supports NPH scripts with a special NPH mode. When in this mode, CGI.pm will output
the necessary extra header information when the header() and redirect() methods are
called.
The Microsoft Internet Information Server requires NPH mode. As of version 2.30, CGI.pm
will automatically detect when the script is running under IIS and put itself into this
mode. You do not need to do this manually, although it won't hurt anything if you do.
In the use statement
Simply add the "-nph" pragma to the list of symbols to be imported into your script:
use CGI qw(:standard -nph)
By calling the nph() method:
Call nph() with a non-zero parameter at any point after using CGI.pm in your program.
CGI->nph(1)
By using -nph parameters
in the header() and redirect() statements:
print header(-nph=>1);
SERVER PUSH
CGI.pm provides four simple functions for producing multipart documents of the type needed
to implement server push. These functions were graciously provided by Ed Jordan
<ed AT fidalgo.net>. To import these into your namespace, you must import the ":push" set.
You are also advised to put the script into NPH mode and to set $| to 1 to avoid buffering
problems.
Here is a simple script that demonstrates server push:
#!/usr/bin/env perl
use strict;
use warnings;
use CGI qw/:push -nph/;
$| = 1;
print multipart_init( -boundary=>'----here we go!' );
for (0 .. 4) {
print multipart_start( -type=>'text/plain' ),
"The current time is ",scalar( localtime ),"\n";
if ($_ < 4) {
print multipart_end();
} else {
print multipart_final();
}
sleep 1;
}
This script initializes server push by calling multipart_init(). It then enters a loop in
which it begins a new multipart section by calling multipart_start(), prints the current
local time, and ends a multipart section with multipart_end(). It then sleeps a second,
and begins again. On the final iteration, it ends the multipart section with
multipart_final() rather than with multipart_end().
multipart_init()
multipart_init( -boundary => $boundary, -charset => $charset );
Initialize the multipart system. The -boundary argument specifies what MIME boundary
string to use to separate parts of the document. If not provided, CGI.pm chooses a
reasonable boundary for you.
The -charset provides the character set, if not provided this will default to
ISO-8859-1
multipart_start()
multipart_start( -type => $type, -charset => $charset );
Start a new part of the multipart document using the specified MIME type and charset.
If not specified, text/html ISO-8859-1 is assumed.
multipart_end()
multipart_end()
End a part. You must remember to call multipart_end() once for each multipart_start(),
except at the end of the last part of the multipart document when multipart_final()
should be called instead of multipart_end().
multipart_final()
multipart_final()
End all parts. You should call multipart_final() rather than multipart_end() at the
end of the last part of the multipart document.
Users interested in server push applications should also have a look at the CGI::Push
module.
AVOIDING DENIAL OF SERVICE ATTACKS
A potential problem with CGI.pm is that, by default, it attempts to process form POSTings
no matter how large they are. A wily hacker could attack your site by sending a CGI script
a huge POST of many gigabytes. CGI.pm will attempt to read the entire POST into a
variable, growing hugely in size until it runs out of memory. While the script attempts to
allocate the memory the system may slow down dramatically. This is a form of denial of
service attack.
Another possible attack is for the remote user to force CGI.pm to accept a huge file
upload. CGI.pm will accept the upload and store it in a temporary directory even if your
script doesn't expect to receive an uploaded file. CGI.pm will delete the file
automatically when it terminates, but in the meantime the remote user may have filled up
the server's disk space, causing problems for other programs.
The best way to avoid denial of service attacks is to limit the amount of memory, CPU time
and disk space that CGI scripts can use. Some Web servers come with built-in facilities to
accomplish this. In other cases, you can use the shell limit or ulimit commands to put
ceilings on CGI resource usage.
CGI.pm also has some simple built-in protections against denial of service attacks, but
you must activate them before you can use them. These take the form of two global
variables in the CGI name space:
$CGI::POST_MAX
If set to a non-negative integer, this variable puts a ceiling on the size of
POSTings, in bytes. If CGI.pm detects a POST that is greater than the ceiling, it will
immediately exit with an error message. This value will affect both ordinary POSTs and
multipart POSTs, meaning that it limits the maximum size of file uploads as well. You
should set this to a reasonably high value, such as 10 megabytes.
$CGI::DISABLE_UPLOADS
If set to a non-zero value, this will disable file uploads completely. Other fill-out
form values will work as usual.
To use these variables, set the variable at the top of the script, right after the "use"
statement:
#!/usr/bin/env perl
use strict;
use warnings;
use CGI;
$CGI::POST_MAX = 1024 * 1024 * 10; # max 10MB posts
$CGI::DISABLE_UPLOADS = 1; # no uploads
An attempt to send a POST larger than $POST_MAX bytes will cause param() to return an
empty CGI parameter list. You can test for this event by checking cgi_error(), either
after you create the CGI object or, if you are using the function-oriented interface, call
<param()> for the first time. If the POST was intercepted, then cgi_error() will return
the message "413 POST too large".
This error message is actually defined by the HTTP protocol, and is designed to be
returned to the browser as the CGI script's status code. For example:
my $uploaded_file = $q->param('upload');
if ( !$uploaded_file && $q->cgi_error() ) {
print $q->header( -status => $q->cgi_error() );
exit 0;
}
However it isn't clear that any browser currently knows what to do with this status code.
It might be better just to create a page that warns the user of the problem.
MODULE FLAGS
There are a number of global module flags which affect how CGI.pm operates.
$CGI::APPEND_QUERY_STRING
If set to a non-zero value, this will add query string parameters to a POST forms
parameters hence allowing param() to return values from the query string as well as
from the decoded POST request instead of having to use url_param instead. This makes
it easier to get the value of a parameter when you don't know the source.
COMPATIBILITY WITH CGI-LIB.PL
To make it easier to port existing programs that use cgi-lib.pl the compatibility routine
"ReadParse" is provided. Porting is simple:
OLD VERSION
require "cgi-lib.pl";
&ReadParse;
print "The value of the antique is $in{antique}.\n";
NEW VERSION
use CGI;
CGI::ReadParse();
print "The value of the antique is $in{antique}.\n";
CGI.pm's ReadParse() routine creates a tied variable named %in, which can be accessed to
obtain the query variables. Like ReadParse, you can also provide your own variable.
Infrequently used features of ReadParse, such as the creation of @in and $in variables,
are not supported.
Once you use ReadParse, you can retrieve the query object itself this way:
my $q = $in{CGI};
This allows you to start using the more interesting features of CGI.pm without rewriting
your old scripts from scratch.
An even simpler way to mix cgi-lib calls with CGI.pm calls is to import both the
":cgi-lib" and ":standard" method:
use CGI qw(:cgi-lib :standard);
&ReadParse;
print "The price of your purchase is $in{price}.\n";
print textfield(-name=>'price', -default=>'$1.99');
Cgi-lib functions that are available in CGI.pm
In compatibility mode, the following cgi-lib.pl functions are available for your use:
ReadParse()
PrintHeader()
SplitParam()
MethGet()
MethPost()
LICENSE
The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is distributed under
the Artistic License 2.0. It is currently maintained by Lee Johnson (LEEJO) with help from
many contributors.
CREDITS
Thanks very much to:
Mark Stosberg (mark AT stosberg.com)
Matt Heffron (heffron AT falstaff.com)
James Taylor (james.taylor AT srs.gov)
Scott Anguish (sanguish AT digifix.com)
Mike Jewell (mlj3u AT virginia.edu)
Timothy Shimmin (tes AT kbs.au)
Joergen Haegg (jh AT axis.se)
Laurent Delfosse (delfosse AT delfosse.com)
Richard Resnick (applepi1 AT aol.com)
Craig Bishop (csb AT barwonwater.au)
Tony Curtis (tc AT vcpc.at)
Tim Bunce (Tim.Bunce AT ig.uk)
Tom Christiansen (tchrist AT convex.com)
Andreas Koenig (k AT franz.DE)
Tim MacKenzie (Tim.MacKenzie AT fulcrum.au)
Kevin B. Hendricks (kbhend AT dogwood.edu)
Stephen Dahmen (joyfire AT inxpress.net)
Ed Jordan (ed AT fidalgo.net)
David Alan Pisoni (david AT cnation.com)
Doug MacEachern (dougm AT opengroup.org)
Robin Houston (robin AT oneworld.org)
...and many many more...
for suggestions and bug fixes.
BUGS
Address bug reports and comments to: <https://github.com/leejo/CGI.pm/issues>
See the <https://github.com/leejo/CGI.pm/blob/master/CONTRIBUTING.md> file for information
on raising issues and contributing
The original bug tracker can be found at:
<https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm>
SEE ALSO
CGI::Carp - provides Carp implementation tailored to the CGI environment.
CGI::Fast - supports running CGI applications under FastCGI
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