CGI(3) 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.
Since v5.00 parameters named POSTDATA, PUTDATA, PATCHDATA or XForms:Model
sent by the client (in the query string, a form field, or a multipart
part) are ignored, so these parameters only ever contain the request
body. Prior to this a client could set them, e.g. with "?POSTDATA=..." or
a plain HTML form, and an application could not tell that apart from the
body. You should still check the request's content type is what you
expect.
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 ccggii_eerrrroorr(()) 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 ppaarraamm(()). 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". Any """ or "\" in the name is
backslash escaped (since v5.00) as required for the quoted filename
parameter.
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.
The URL is used exactly as given. Prior to v5.00 HTML entities in it (and
in any other header values) were decoded, so "//evil.example/" became
"//evil.example/" after any validation your application had done. If you
were relying on this to pass an HTML escaped URL (e.g. "/x?a=1&b=2")
you should pass the unescaped URL instead.
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.
The request URI is supplied by the client, so since v5.00 it is reduced
to a path on this host before it is used: any scheme and host (an
absolute-form request such as "GET http://other.example/x") are removed,
and leading slashes or backslashes are collapsed to a single slash, so
that an absolute or relative URL can never point at another host. A
relative URL that would otherwise look like it has a scheme (e.g.
"javascript:...") is prefixed with "./". The same applies to the default
action of start_form(). request_uri() still returns the literal value.
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 = $q->param('field_name');
The name returned is the name of the file on the user's machine, and is
unrelated to the name of the temporary file that CGI.pm creates during
upload spooling (see below).
As the name is supplied by the client it cannot be trusted. Since v5.00
CGI.pm removes any directory part from it (splitting on both "/" and "\",
as some browsers send the full path to the file using the path
conventions of the user's machine) along with any control characters. If
nothing usable remains (e.g. the name was "..") the name "upload" is used
instead. The name may still contain other characters that are unsafe for
your use, so you should validate it, or better generate your own name,
before using it to save the file.
The raw value sent by the client is still available in the Content-
Disposition header returned by uploadInfo() (see below). If you need the
previous behaviour of returning the raw value you can set
"$CGI::SANITIZE_UPLOAD_FILENAMES" to 0, but you should then make sure you
never use it as a path.
When a file is uploaded the browser usually sends along some information
along with it in the Content-Type (MIME type) and Content-Disposition
(filename) headers. To retrieve this information, call uploadInfo(). It
returns a reference to a hash containing all the document headers.
When running under taint mode ("-T") the header values, like the uploaded
file's name and all other request data, are tainted (prior to v5.00 the
filename and header values were not). Note that the header names are hash
keys, which perl never taints, so must be treated with care if you use
them.
my $filehandle = $q->upload( 'uploaded_file' );
my $type = $q->uploadInfo( $filehandle )->{'Content-Type'};
if ( $type ne 'text/html' ) {
die "HTML FILES ONLY!";
}
Note that you must use ->upload or ->param to get the file-handle to pass
into uploadInfo as internally this is represented as a File::Temp object
(which is what will be returned by ->upload or ->param). When using
->Vars you will get the literal filename rather than the File::Temp
object, which will not return anything when passed to uploadInfo. So
don't use ->Vars.
When uploading multiple files, call ->param() in list context to retrieve
a list of filehandles that you can use when calling ->uploadInfo.
my @filehandles = $q->param('uploaded_file');
for my $fh (@filehandles) {
my $info = $q->uploadInfo($fh);
...
}
If you are using a machine that recognizes "text" and "binary" data
modes, be sure to understand when and how to use them (see the Camel
book). Otherwise you may find that binary files are corrupted during file
uploads.
Accessing the temp files directly
When processing an uploaded file, CGI.pm creates a temporary file on your
hard disk and passes you a file handle to that file. After you are
finished with the file handle, CGI.pm unlinks (deletes) the temporary
file. If you need to you can access the temporary file directly. You can
access the temp file for a file upload by passing the file handle 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 ccggii_eerrrroorr(()) to the string "400 Bad request
(malformed multipart POST)". This error message is designed so that you
can incorporate it into a status code to be sent to the browser. Example:
my $file = $q->upload( 'uploaded_file' );
if ( !$file && $q->cgi_error ) {
print $q->header( -status => $q->cgi_error );
exit 0;
}
Progress bars for file uploads and avoiding temp files
CGI.pm gives you low-level access to file upload management through a
file upload hook. You can use this feature to completely turn off the
temp file storage of file uploads, or potentially write your own file
upload progress meter.
This is much like the UPLOAD_HOOK facility available in Apache::Request,
with the exception that the first argument to the callback is an
Apache::Upload object, here it's the remote filename.
my $q = CGI->new( \&hook [,$data [,$use_tempfile]] );
sub hook {
my ( $filename, $buffer, $bytes_read, $data ) = @_;
print "Read $bytes_read bytes of $filename\n";
}
The $data field is optional; it lets you pass configuration information
(e.g. a database handle) to your hook callback.
The $use_tempfile field is a flag that lets you turn on and off CGI.pm's
use of a temporary disk-based file during file upload. If you set this to
a FALSE value (default true) then "$q->param('uploaded_file')" will still
return a typeglob that can be used to access a filehandle and the
filename of the uploaded file, however the filehandle will be a handle to
an empty file. Existence of your hook causes CGI.pm to bypass writing to
that filehandle (which is probably what you intended when you set
$use_tempfile off).
The "uploadInfo()" method can be used on the typeglob returned to you
when you called "$q->param('upload_file')" to return information about
the uploaded file(s). For multiple file uploads, use the " param() "
method in list context to retrieve all of the typeglobs.
my (@filehandles) = $cgi->param('upfile');
foreach my $fh (@filehandles) {
my $info = $cgi->uploadInfo($fh);
...
}
If using the function-oriented interface, call the CGI::upload_hook()
method before calling param() or any other CGI functions:
CGI::upload_hook( \&hook [,$data [,$use_tempfile]] );
This method is not exported by default. You will have to import it
explicitly if you wish to use it without the CGI:: prefix.
Troubleshooting file uploads on Windows
If you are using CGI.pm on a Windows platform and find that binary files
get slightly larger when uploaded but that text files remain the same,
then you have forgotten to activate binary mode on the output filehandle.
Be sure to call binmode() on any handle that you create to write the
uploaded file to disk.
Older ways to process file uploads
This section is here for completeness. if you are building a new
application with CGI.pm, you can skip it.
The original way to process file uploads with CGI.pm was to use param().
The value it returns has a dual nature as both a file name and a
lightweight filehandle. This dual nature is problematic if you following
the recommended practice of having "use strict" in your code. perl will
complain when you try to use a string as a filehandle. More seriously, it
is possible for the remote user to type garbage into the upload field, in
which case what you get from param() is not a filehandle at all, but a
string.
To solve this problem the upload() method was added, which always returns
a lightweight filehandle. This generally works well, but will have
trouble interoperating with some other modules because the file handle is
not derived from IO::File. So that brings us to current recommendation
given above, which is to call the handle() method on the file handle
returned by upload(). That upgrades the handle to an IO::File. It's a
big win for compatibility for a small penalty of loading IO::File the
first time you call it.
HTTP COOKIES
CGI.pm has several methods that support cookies.
A cookie is a name=value pair much like the named parameters in a CGI
query string. CGI scripts create one or more cookies and send them to the
browser in the HTTP header. The browser maintains a list of cookies that
belong to a particular Web server, and returns them to the CGI script
during subsequent interactions.
In addition to the required name=value pair, each cookie has several
optional attributes:
1. an expiration time
This is a time/date string (in a special GMT format) that indicates
when a cookie expires. The cookie will be saved and returned to your
script until this expiration date is reached if the user exits the
browser and restarts it. If an expiration date isn't specified, the
cookie will remain active until the user quits the browser.
2. a domain
This is a partial or complete domain name for which the cookie is
valid. The browser will return the cookie to any host that matches
the partial domain name. For example, if you specify a domain name
of ".capricorn.com", then the browser will return the cookie to Web
servers running on any of the machines "www.capricorn.com",
"www2.capricorn.com", "feckless.capricorn.com", etc. Domain names
must contain at least two periods to prevent attempts to match on top
level domains like ".edu". If no domain is specified, then the
browser will only return the cookie to servers on the host the cookie
originated from.
3. a path
If you provide a cookie path attribute, the browser will check it
against your script's URL before returning the cookie. For example,
if you specify the path "/cgi-bin", then the cookie will be returned
to each of the scripts "/cgi-bin/tally.pl", "/cgi-bin/order.pl", and
"/cgi-bin/customer_service/complain.pl", but not to the script
"/cgi-private/site_admin.pl". By default, path is set to "/", which
causes the cookie to be sent to any CGI script on your site.
4. a "secure" flag
If the "secure" attribute is set, the cookie will only be sent to
your script if the CGI request is occurring on a secure channel, such
as SSL.
The interface to HTTP cookies is the cookie() method:
my $cookie = $q->cookie(
-name => 'sessionID',
-value => 'xyzzy',
-expires => '+1h',
-path => '/cgi-bin/database',
-domain => '.capricorn.org',
-secure => 1
);
print $q->header( -cookie => $cookie );
cookie() creates a new cookie. Its parameters include:
-name
The name of the cookie (required). This can be any string at all.
Although browsers limit their cookie names to non-whitespace
alphanumeric characters, CGI.pm removes this restriction by escaping
and unescaping cookies behind the scenes.
-value
The value of the cookie. This can be any scalar value, array
reference, or even hash reference. For example, you can store an
entire hash into a cookie this way:
my $cookie = $q->cookie(
-name => 'family information',
-value => \%childrens_ages
);
-path
The optional partial path for which this cookie will be valid, as
described above.
-domain
The optional partial domain for which this cookie will be valid, as
described above.
-expires
The optional expiration date for this cookie. The format is as
described in the section on the header() method:
"+1h" one hour from now
-secure
If set to true, this cookie will only be used within a secure SSL
session.
The cookie created by cookie() must be incorporated into the HTTP header
within the string returned by the header() method:
use strict;
use warnings;
use CGI;
my $q = CGI->new;
my $cookie = ...
print $q->header( -cookie => $cookie );
To create multiple cookies, give header() an array reference:
my $cookie1 = $q->cookie(
-name => 'riddle_name',
-value => "The Sphynx's Question"
);
my $cookie2 = $q->cookie(
-name => 'answers',
-value => \%answers
);
print $q->header( -cookie => [ $cookie1,$cookie2 ] );
To retrieve a cookie, request it by name by calling cookie() method
without the -value parameter. This example uses the object-oriented form:
my $riddle = $q->cookie('riddle_name');
my %answers = $q->cookie('answers');
Cookies created with a single scalar value, such as the "riddle_name"
cookie, will be returned in that form. Cookies with array and hash values
can also be retrieved.
The cookie and CGI namespaces are separate. If you have a parameter named
'answers' and a cookie named 'answers', the values retrieved by param()
and cookie() are independent of each other. However, it's simple to turn
a CGI parameter into a cookie, and vice-versa:
# turn a CGI parameter into a cookie
my $c = cookie( -name => 'answers',-value => [$q->param('answers')] );
# vice-versa
$q->param( -name => 'answers',-value => [ $q->cookie('answers')] );
If you call cookie() without any parameters, it will return a list of the
names of all cookies passed to your script:
my @cookies = $q->cookie();
See the cookie.cgi example script for some ideas on how to use cookies
effectively.
$CGI::COOKIE_CACHE
If set to a non-negative integer, this variable will cause CGI.pm to
use the cached cookie details from the previous call to cookie(). By
default this cache is off to retain backwards compatibility.
DEBUGGING
If you are running the script from the command line or in the perl
debugger, you can pass the script a list of keywords or parameter=value
pairs on the command line or from standard input (you don't have to worry
about tricking your script into reading from environment variables). You
can pass keywords like this:
your_script.pl keyword1 keyword2 keyword3
or this:
your_script.pl keyword1+keyword2+keyword3
or this:
your_script.pl name1=value1 name2=value2
or this:
your_script.pl name1=value1&name2=value2
To turn off this feature, use the -no_debug pragma.
To test the POST method, you may enable full debugging with the -debug
pragma. This will allow you to feed newline-delimited name=value pairs
to the script on standard input.
When debugging, you can use quotes and backslashes to escape characters
in the familiar shell manner, letting you place spaces and other funny
characters in your parameter=value pairs:
your_script.pl "name1='I am a long value'" "name2=two\ words"
Finally, you can set the path info for the script by prefixing the first
name/value parameter with the path followed by a question mark (?):
your_script.pl /your/path/here?name1=value1&name2=value2
FETCHING ENVIRONMENT VARIABLES
Some of the more useful environment variables can be fetched through this
interface. The methods are as follows:
Accept()
Return a list of MIME types that the remote browser accepts. If you
give this method a single argument corresponding to a MIME type, as
in Accept('text/html'), it will return a floating point value
corresponding to the browser's preference for this type from 0.0
(don't want) to 1.0. Glob types (e.g. text/*) in the browser's accept
list are handled correctly.
Note that the capitalization changed between version 2.43 and 2.44 in
order to avoid conflict with perl's accept() function.
raw_cookie()
Returns the HTTP_COOKIE variable. Cookies have a special format, and
this method call just returns the raw form (?cookie dough). See
cookie() for ways of setting and retrieving cooked cookies.
Called with no parameters, raw_cookie() returns the packed cookie
structure. You can separate it into individual cookies by splitting
on the character sequence "; ". Called with the name of a cookie,
retrieves the unescaped form of the cookie. You can use the regular
cookie() method to get the names, or use the raw_fetch() method from
the CGI::Cookie module.
env_query_string()
Returns the QUERY_STRING variable, note that this is the original
value as set in the environment by the webserver and (possibly) not
the same value as returned by query_string(), which represents the
object state
user_agent()
Returns the HTTP_USER_AGENT variable. If you give this method a
single argument, it will attempt to pattern match on it, allowing you
to do something like user_agent(Mozilla);
path_info()
Returns additional path information from the script URL. E.G.
fetching /cgi-bin/your_script/additional/stuff will result in
path_info() returning "/additional/stuff".
NOTE: The Microsoft Internet Information Server is broken with
respect to additional path information. If you use the perl DLL
library, the IIS server will attempt to execute the additional path
information as a perl script. If you use the ordinary file
associations mapping, the path information will be present in the
environment, but incorrect. The best thing to do is to avoid using
additional path information in CGI scripts destined for use with IIS.
A best attempt has been made to make CGI.pm do the right thing.
path_translated()
As per path_info() but returns the additional path information
translated into a physical path, e.g.
"/usr/local/etc/httpd/htdocs/additional/stuff".
The Microsoft IIS is broken with respect to the translated path as
well.
remote_host()
Returns either the remote host name or IP address if the former is
unavailable.
remote_ident()
Returns the name of the remote user (as returned by identd) or undef
if not set
remote_addr()
Returns the remote host IP address, or 127.0.0.1 if the address is
unavailable.
request_uri()
Returns the interpreted pathname of the requested document or CGI
(relative to the document root). Or undef if not set.
script_name()
Return the script name as a partial URL, for self-referring scripts.
referer()
Return the URL of the page the browser was viewing prior to fetching
your script.
auth_type()
Return the authorization/verification method in use for this script,
if any.
server_name()
Returns the name of the server, usually the machine's host name.
virtual_host()
When using virtual hosts, returns the name of the host that the
browser attempted to contact
This is taken from the Host header if it is a syntactically valid
"host[:port]", otherwise from server_name(). The X-Forwarded-Host
header is not used (since v5.00) as it can be set by any client; if
you are behind a reverse proxy, configure the proxy or web server to
pass the correct Host header or SERVER_NAME instead. If that is not
possible, and all requests come through a proxy that sets the header,
you can opt back in by setting "$CGI::TRUST_X_FORWARDED_HOST". The
same applies to url(), self_url() and virtual_port().
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 hhttttpp(()), 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. These take the form of two global variables in the CGI
name space:
$CGI::POST_MAX
If set to a positive 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 discard it and set an error (see below).
This value will affect both ordinary POSTs and multipart POSTs,
meaning that it limits the maximum size of file uploads as well. The
limit is also enforced while reading multipart POSTs that have no
Content-Length (i.e. chunked transfer encoding).
The default is 128 megabytes (since v5.00, previously there was no
limit). You should set this to a value appropriate to your
application, or to -1 to remove the limit entirely.
$CGI::MAX_PARAMS
The maximum number of parameter values in a request, counting those
in the query string, a form encoded body, and every part of a
multipart body. A request exceeding it is discarded with the same
error as for $CGI::POST_MAX. Without a limit a body within
$CGI::POST_MAX can contain millions of tiny parameters, taking many
seconds and gigabytes of memory to parse.
The default is 10,000 (since v5.00, previously there was no limit),
set it to -1 to remove the limit.
$CGI::MAX_UPLOADS
The maximum number of uploaded files in a request, as each one is
saved to a temporary file (and its filehandle kept open, unless
$CGI::CLOSE_UPLOAD_FILES or close_upload_files(1) is used). A request
exceeding it is discarded with the same error as for $CGI::POST_MAX.
Note that your system may limit the number of open files per process
to fewer than this.
The default is 1,000 (since v5.00, previously there was no limit),
set it to -1 to remove the limit.
$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 (or with more than
$MAX_PARAMS parameters or $MAX_UPLOADS uploads) will cause ppaarraamm(()) to
return an empty CGI parameter list. You can test for this event by
checking ccggii_eerrrroorr(()), 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 Request entity 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::SANITIZE_UPLOAD_FILENAMES
Defaults to 1, which removes any directory part and control
characters from the client supplied filename of file uploads (see
"Processing a file upload field"). Set this to 0 to get the raw value
sent by the client, which was the behaviour prior to v5.00. Doing so
is not recommended as the raw value can contain a path, such as
"../../etc/passwd".
$CGI::APPEND_QUERY_STRING
If set to a non-zero value, this will add query string parameters to
a POST forms parameters hence allowing ppaarraamm(()) 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.
$CGI::TRUST_X_FORWARDED_HOST
Defaults to 0, meaning the X-Forwarded-Host header is ignored when
determining the host name for url(), self_url(), virtual_host() and
virtual_port() (see "virtual_host()"). Set this to 1 to use it in
preference to the Host header, which was the behaviour prior to
v5.00. If it contains a list of hosts the last one is used, and it
must still be a valid "host[:port]".
Only do this if all requests reach your application through a reverse
proxy that sets (or removes) this header, as otherwise any client can
set it to control the host name in generated URLs.
COMPATIBILITY WITH CGI-LIB.PL
To make it easier to port existing programs that use cgi-lib.pl the
compatibility routine "ReadParse" is provided. Porting is simple:
OLD VERSION
require "cgi-lib.pl";
&ReadParse;
print "The value of the antique is $in{antique}.\n";
NEW VERSION
use CGI;
CGI::ReadParse();
print "The value of the antique is $in{antique}.\n";
CGI.pm's ReadParse() routine creates a tied variable named %in, which can
be accessed to obtain the query variables. Like ReadParse, you can also
provide your own variable. Infrequently used features of ReadParse, such
as the creation of @in and $in variables, are not supported.
Once you use ReadParse, you can retrieve the query object itself this
way:
my $q = $in{CGI};
This allows you to start using the more interesting features of CGI.pm
without rewriting your old scripts from scratch.
An even simpler way to mix cgi-lib calls with CGI.pm calls is to import
both the ":cgi-lib" and ":standard" method:
use CGI qw(:cgi-lib :standard);
&ReadParse;
print "The price of your purchase is $in{price}.\n";
print textfield(-name=>'price', -default=>'$1.99');
Cgi-lib functions that are available in CGI.pm
In compatibility mode, the following cgi-lib.pl functions are available
for your use:
ReadParse()
PrintHeader()
SplitParam()
MethGet()
MethPost()
LICENSE
The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is
distributed under the Artistic License 2.0. It is currently maintained by
Lee Johnson (LEEJO) with help from many contributors.
CREDITS
Thanks very much to:
Mark Stosberg (mark@stosberg.com)
Matt Heffron (heffron@falstaff.css.beckman.com)
James Taylor (james.taylor@srs.gov)
Scott Anguish (sanguish@digifix.com)
Mike Jewell (mlj3u@virginia.edu)
Timothy Shimmin (tes@kbs.citri.edu.au)
Joergen Haegg (jh@axis.se)
Laurent Delfosse (delfosse@delfosse.com)
Richard Resnick (applepi1@aol.com)
Craig Bishop (csb@barwonwater.vic.gov.au)
Tony Curtis (tc@vcpc.univie.ac.at)
Tim Bunce (Tim.Bunce@ig.co.uk)
Tom Christiansen (tchrist@convex.com)
Andreas Koenig (k@franz.ww.TU-Berlin.DE)
Tim MacKenzie (Tim.MacKenzie@fulcrum.com.au)
Kevin B. Hendricks (kbhend@dogwood.tyler.wm.edu)
Stephen Dahmen (joyfire@inxpress.net)
Ed Jordan (ed@fidalgo.net)
David Alan Pisoni (david@cnation.com)
Doug MacEachern (dougm@opengroup.org)
Robin Houston (robin@oneworld.org)
...and many many more...
for suggestions and bug fixes.
BUGS
Address bug reports and comments to:
<https://github.com/leejo/CGI.pm/issues>
See the <https://github.com/leejo/CGI.pm/blob/master/CONTRIBUTING.md>
file for information on raising issues and contributing
The original bug tracker can be found at:
<https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm>
SEE ALSO
CGI::Carp(3) - provides Carp implementation tailored to the CGI environment.
CGI::Fast(3) - supports running CGI applications under FastCGI
perl v5.34.3 2026-11-09 CGI(3)
cgi 5.20.0 - Generated Tue Nov 10 07:40:49 CST 2026