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CGI(3)
NAME
CGI - Simple Common Gateway Interface Class
SYNOPSIS
# CGI script that creates a fill-out form
# and echoes back its values.
use CGI qw/:standard/;
print header,
start_html('A Simple Example'),
h1('A Simple Example'),
start_form,
"What's your name? ",textfield('name'),p,
"What's the combination?", p,
checkbox_group(-name=>'words',
-values=>['eenie','meenie','minie','moe'],
-defaults=>['eenie','minie']), p,
"What's your favorite color? ",
popup_menu(-name=>'color',
-values=>['red','green','blue','chartreuse']),p,
submit,
end_form,
hr;
if (param()) {
print "Your name is",em(param('name')),p,
"The keywords are: ",em(join(", ",param('words'))),p,
"Your favorite color is ",em(param('color')),
hr;
}
ABSTRACT
This perl library uses perl5 objects to make it easy to create Web fill-out
forms and parse their contents. This package defines CGI objects, entities
that contain the values of the current query string and other state
variables. Using a CGI object's methods, you can examine keywords and
parameters passed to your script, and create forms whose initial values are
taken from the current query (thereby preserving state information). The
module provides shortcut functions that produce boilerplate HTML, reducing
typing and coding errors. It also provides functionality for some of the
more advanced features of CGI scripting, including support for file
uploads, cookies, cascading style sheets, server push, and frames.
CGI.pm also provides a simple function-oriented programming style for those
who don't need its object-oriented features.
The current version of CGI.pm is available at
http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html
ftp://ftp-genome.wi.mit.edu/pub/software/WWW/
DESCRIPTION
PROGRAMMING STYLE
There are two styles of programming with CGI.pm, an object-oriented style
and a function-oriented style. 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, here is how you create a
simple "Hello World" HTML page:
#!/usr/local/bin/perl -w
use CGI; # load CGI routines
$q = new CGI; # create new CGI object
print $q->header, # create the HTTP header
$q->start_html('hello world'), # start the HTML
$q->h1('hello world'), # level 1 header
$q->end_html; # end the HTML
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, create HTML tags, manage cookies, and so on. This provides you
with a cleaner programming interface, but limits you to using one CGI
object at a time. The following example prints the same page, 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/local/bin/perl
use CGI qw/:standard/; # load standard CGI routines
print header, # create the HTTP header
start_html('hello world'), # start the HTML
h1('hello world'), # level 1 header
end_html; # end the HTML
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=>['tomato','tomahto','potato','potahto']);
A large number of routines in CGI.pm actually aren't specifically defined
in the module, but are generated automatically as needed. These are the
"HTML shortcuts," routines that generate HTML tags for use in dynamically-
generated pages. HTML tags have both attributes (the attribute="value"
pairs within the tag itself) and contents (the part between the opening and
closing pairs.) To distinguish between attributes and contents, CGI.pm
uses the convention of passing HTML attributes as a hash reference as the
first argument, and the contents, if any, as any subsequent arguments. It
works out like this:
Code Generated HTML
---- --------------
h1() <h1>
h1('some','contents'); <h1>some contents</h1>
h1({-align=>left}); <h1 ALIGN="LEFT">
h1({-align=>left},'contents'); <h1 ALIGN="LEFT">contents</h1>
HTML tags are described in more detail later.
Many newcomers to CGI.pm are puzzled by the difference between the calling
conventions for the HTML shortcuts, which require curly braces around the
HTML tag attributes, and the calling conventions for other routines, which
manage to generate attributes without the curly brackets. Don't be
confused. As a convenience the curly braces are optional in all but the
HTML shortcuts. If you like, you can use curly braces when calling any
routine that takes named arguments. For example:
print $q->header( {-type=>'image/gif',-expires=>'+3d'} );
If you use the -w switch, you will be warned that some CGI.pm argument
names conflict with built-in Perl functions. The most frequent of these is
the -values argument, used to create multi-valued menus, radio button
clusters and the like. To get around this warning, you have several
choices:
1. Use another name for the argument, if one is available. For example,
-value is an alias for -values.
2. Change the capitalization, e.g. -Values
3. Put quotes around the argument name, e.g. '-values'
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.
HTML-generating routines perform a different type of translation.
This feature allows you to keep up with the rapidly changing HTTP and HTML
"standards".
CREATING A NEW QUERY OBJECT (OBJECT-ORIENTED STYLE):
$query = new CGI;
This will parse the input (from both POST and GET methods) and store it
into a perl5 object called $query.
CREATING A NEW QUERY OBJECT FROM AN INPUT FILE
$query = new CGI(INPUTFILE);
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:
$query = new CGI(\*STDIN);
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 (IN,"test.in") || die;
restore_parameters(IN);
close IN;
You can also initialize the query object from an associative array
reference:
$query = new CGI( {'dinosaur'=>'barney',
'song'=>'I love you',
'friends'=>[qw/Jessica George Nancy/]}
);
or from a properly formatted, URL-escaped query string:
$query = new CGI('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):
$old_query = new CGI;
$new_query = new CGI($old_query);
To create an empty query, initialize it from an empty string or hash:
$empty_query = new CGI("");
-or-
$empty_query = new CGI({});
FETCHING A LIST OF KEYWORDS FROM THE QUERY:
@keywords = $query->keywords
If the script was invoked as the result of an <ISINDEX> search, the parsed
keywords can be obtained as an array using the keywords() method.
FETCHING THE NAMES OF ALL THE PARAMETERS PASSED TO YOUR SCRIPT:
@names = $query->param
If the script was invoked with a parameter list (e.g.
"name1=value1&name2=value2&name3=value3"), the param() method 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.
NOTE: As of version 1.5, 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:
@values = $query->param('foo');
-or-
$value = $query->param('foo');
Pass the param() method a single argument to fetch the value of the named
parameter. If the parameter is multivalued (e.g. from multiple selections
in a scrolling list), you can ask to receive an array. Otherwise the
method will return a single value.
If a value is not given in the query string, as in the queries
"name1=&name2=" or "name1&name2", it will be returned as an empty string.
This feature is new in 2.63.
SETTING THE VALUE(S) OF A NAMED PARAMETER:
$query->param('foo','an','array','of','values');
This sets the value for the named parameter 'foo' to an array of values.
This is one way to change the value of a field AFTER the script has been
invoked once before. (Another way is with the -override parameter accepted
by all methods that generate form elements.)
param() also recognizes a named parameter style of calling described in
more detail later:
$query->param(-name=>'foo',-values=>['an','array','of','values']);
-or-
$query->param(-name=>'foo',-value=>'the value');
APPENDING ADDITIONAL VALUES TO A NAMED PARAMETER:
$query->append(-name=>'foo',-values=>['yet','more','values']);
This adds a value or list of values to the named parameter. The values are
appended to the end of the parameter if it already exists. Otherwise the
parameter is created. Note that this method only recognizes the named
argument calling syntax.
IMPORTING ALL PARAMETERS INTO A NAMESPACE:
$query->import_names('R');
This creates a series of variables in the 'R' namespace. For example,
$R::foo, @R:foo. For keyword lists, a variable @R::keywords will appear.
If no namespace is given, this method will assume 'Q'. WARNING: don't
import anything into 'main'; this is a major security risk!!!!
In older versions, this method was called import(). As of version 2.20,
this name has been removed completely to avoid conflict with the built-in
Perl module import operator.
DELETING A PARAMETER COMPLETELY:
$query->delete('foo');
This completely clears a parameter. It sometimes useful for resetting
parameters that you don't want passed down between script invocations.
If you are using the function call interface, use "Delete()" instead to
avoid conflicts with Perl's built-in delete operator.
DELETING ALL PARAMETERS:
$query->delete_all();
This clears the CGI object completely. It might be useful to ensure that
all the defaults are taken when you create a fill-out form.
Use Delete_all() instead if you are using the function call interface.
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 above, you can obtain a direct reference to it by calling the
param_fetch() method with the name of the . This will return an array
reference to the named parameters, 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:
$params = $q->Vars;
print $params->{'address'};
@foo = split("\0",$params->{'foo'});
%params = $q->Vars;
use CGI ':cgi-lib';
$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.
If you wish to use Vars() as a function, import the :cgi-lib set of
function calls (also see the section on CGI-LIB compatibility).
SAVING THE STATE OF THE SCRIPT TO A FILE:
$query->save(FILEHANDLE)
This will write the current state of the form to the provided filehandle.
You can read it back in by providing a filehandle to the new() method.
Note that the filehandle can be a file, a pipe, or whatever!
The format of the saved file is:
NAME1=VALUE1
NAME1=VALUE1'
NAME2=VALUE2
NAME3=VALUE3
=
Both name and value are URL escaped. Multi-valued CGI parameters are
represented as repeated names. A session record is delimited by a single =
symbol. You can write out multiple records and read them back in with
several calls to new. You can do this across several sessions by opening
the file in append mode, allowing you to create primitive guest books, or
to keep a history of users' queries. Here's a short example of creating
multiple session records:
use CGI;
open (OUT,">>test.out") || die;
$records = 5;
foreach (0..$records) {
my $q = new CGI;
$q->param(-name=>'counter',-value=>$_);
$q->save(OUT);
}
close OUT;
# reopen for reading
open (IN,"test.out") || die;
while (!eof(IN)) {
my $q = new CGI(IN);
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
http://stein.cshl.org/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 an
HTML page, or use it as the value of the HTTP status:
my $error = $q->cgi_error;
if ($error) {
print $q->header(-status=>$error),
$q->start_html('Problems'),
$q->h2('Request not processed'),
$q->strong($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 CGI <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 CGI 'param','header';
print header('text/plain');
$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
":html3" (for tags defined in the HTML 3 standard).
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.
:form
Import all fill-out form generating methods, such as textfield().
:html2
Import all methods that generate HTML 2.0 standard elements.
:html3
Import all methods that generate HTML 3.0 elements (such as <table>,
<super> and <sub>).
:html4
Import all methods that generate HTML 4 elements (such as <abbrev>,
<acronym> and <thead>).
:netscape
Import all methods that generate Netscape-specific HTML extensions.
:html
Import all HTML-generating shortcuts (i.e. 'html2' + 'html3' +
'netscape')...
:standard
Import "standard" features, 'html2', 'html3', 'html4', 'form' and
'cgi'.
:all
Import all the available methods. For the full list, see the CGI.pm
code, where the variable %EXPORT_TAGS is defined.
If you import a function name that is not part of CGI.pm, the module will
treat it as a new HTML tag and generate the appropriate subroutine. You
can then use it like any other HTML tag. This is to provide for the
rapidly-evolving HTML "standard." For example, say Microsoft comes out
with a new tag called <gradient> (which causes the user's desktop to be
flooded with a rotating gradient fill until his machine reboots). You
don't need to wait for a new version of CGI.pm to start using it
immediately:
use CGI qw/:standard :html3 gradient/;
print gradient({-start=>'red',-end=>'blue'});
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.
If you import any of the state-maintaining CGI or form-generating methods,
a default CGI object will be created and initialized automatically the
first time you use any of the methods that require one to be present. This
includes param(), textfield(), submit() and the like. (If you need direct
access to the CGI object, you can find it in the global variable $CGI::Q).
By importing CGI.pm methods, you can create visually elegant scripts:
use CGI qw/:standard/;
print
header,
start_html('Simple Script'),
h1('Simple Script'),
start_form,
"What's your name? ",textfield('name'),p,
"What's the combination?",
checkbox_group(-name=>'words',
-values=>['eenie','meenie','minie','moe'],
-defaults=>['eenie','moe']),p,
"What's your favorite color?",
popup_menu(-name=>'color',
-values=>['red','green','blue','chartreuse']),p,
submit,
end_form,
hr,"\n";
if (param) {
print
"Your name is ",em(param('name')),p,
"The keywords are: ",em(join(", ",param('words'))),p,
"Your favorite color is ",em(param('color')),".\n";
}
print end_html;
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 standard set of functions
and enables debugging mode (pragma -debug):
use CGI qw/:standard -debug/;
The current list of pragmas is as follows:
-any
When you use CGI -any, then any method that the query object doesn't
recognize will be interpreted as a new HTML tag. This allows you to
support the next ad hoc Netscape or Microsoft HTML extension. This
lets you go wild with new and unsupported tags:
use CGI qw(-any);
$q=new CGI;
print $q->gradient({speed=>'fast',start=>'red',end=>'blue'});
Since using <cite>any</cite> causes any mistyped method name to be
interpreted as an HTML tag, use it with care or not at all.
-compile
This causes the indicated autoloaded methods to be compiled up front,
rather than deferred to later. This is useful for scripts that run for
an extended period of time under FastCGI or mod_perl, and for those
destined to be crunched by Malcom Beattie's Perl compiler. Use it in
conjunction with the methods or method families you plan to use.
use CGI qw(-compile :standard :html3);
or even
use CGI qw(-compile :all);
Note that using the -compile pragma in this way will always have the
effect of importing the compiled functions into the current namespace.
If you want to compile without importing use the compile() method
instead (see below).
-nosticky
This makes CGI.pm not generating the hidden fields .submit and
.cgifields. It is very useful if you don't want to have the hidden
fields appear in the querystring in a GET method. For example, a
search script generated this way will have a very nice url with search
parameters for bookmarking.
-no_undef_params
This keeps CGI.pm from including undef params in the parameter list.
-no_xhtml
By default, CGI.pm versions 2.69 and higher emit XHTML
(http://www.w3.org/TR/xhtml1/). The -no_xhtml pragma disables this
feature. Thanks to Michalis Kabrianis <kabrianis@hellug.gr> for this
feature.
-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, but will not be
emitted by self_url() and query_string() unless the -newstyle_urls
pragma is specified.
This 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.
-autoload
This overrides the autoloader so that any function in your program that
is not recognized is referred to CGI.pm for possible evaluation. This
allows you to use all the CGI.pm functions without adding them to your
symbol table, which is of concern for mod_perl users who are worried
about memory consumption. Warning: when -autoload is in effect, you
cannot use "poetry mode" (functions without the parenthesis). Use hr()
rather than hr, or add something like use subs qw/hr p header/ to the
top of your script.
-no_debug
This turns off the command-line processing features. If you want to
run a CGI.pm script from the command line to produce HTML, 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.
-private_tempfiles
CGI.pm can process uploaded file. Ordinarily it spools the uploaded
file to a temporary directory, then deletes the file when done.
However, this opens the risk of eavesdropping as described in the file
upload section. Another CGI script author could peek at this data
during the upload, even if it is confidential information. On Unix
systems, the -private_tempfiles pragma will cause the temporary file to
be unlinked as soon as it is opened and before any data is written into
it, reducing, but not eliminating the risk of eavesdropping (there is
still a potential race condition). To make life harder for the
attacker, the program chooses tempfile names by calculating a 32 bit
checksum of the incoming HTTP headers.
To ensure that the temporary file cannot be read by other CGI scripts,
use suEXEC or a CGI wrapper program to run your script. The temporary
file is created with mode 0600 (neither world nor group readable).
The temporary directory is selected using the following algorithm:
1. if the current user (e.g. "nobody") has a directory named
"tmp" in its home directory, use that (Unix systems only).
2. if the environment variable TMPDIR exists, use the location
indicated.
3. Otherwise try the locations /usr/tmp, /var/tmp, C:\temp,
/tmp, /temp, ::Temporary Items, and \WWW_ROOT.
Each of these locations is checked that it is a directory and is
writable. If not, the algorithm tries the next choice.
SPECIAL FORMS FOR IMPORTING HTML-TAG FUNCTIONS
Many of the methods generate HTML tags. As described below, tag functions
automatically generate both the opening and closing tags. For example:
print h1('Level 1 Header');
produces
<h1>Level 1 Header</h1>
There will be some times when you want to produce the start and end tags
yourself. In this case, you can use the form start_tag_name and
end_tag_name, as in:
print start_h1,'Level 1 Header',end_h1;
With a few exceptions (described below), start_tag_name and end_tag_name
functions are not generated automatically when you use CGI. However, you
can specify the tags you want to generate start/end functions for by
putting an asterisk in front of their name, or, alternatively, requesting
either "start_tag_name" or "end_tag_name" in the import list.
Example:
use CGI qw/:standard *table start_ul/;
In this example, the following functions are generated in addition to the
standard ones:
1. start_table() (generates a <table> tag)
2. end_table() (generates a </table> tag)
3. start_ul() (generates a <ul> tag)
4. end_ul() (generates a </ul> tag)
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 as well as for generating HTML. For creating GIF images, see the
GD.pm module.
Each of these functions produces a fragment of HTML or HTTP which you can
print out directly so that it displays in the browser window, append to a
string, or save 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.
print $query->header;
-or-
print $query->header('image/gif');
-or-
print $query->header('text/html','204 No response');
-or-
print $query->header(-type=>'image/gif',
-nph=>1,
-status=>'402 Payment required',
-expires=>'+3d',
-cookie=>$cookie,
-charset=>'utf-7',
-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.
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 $query->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-1999 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.
Netscape 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 an 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.
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".
GENERATING A REDIRECTION HEADER
print $query->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() function redirects the browser to a different URL. If you
use redirection like this, you should not print out a header as well.
One hint I can offer is that relative links may not work correctly when you
generate a redirection to another document on your site. This is due to a
well-intentioned optimization that some servers use. The solution to this
is to use the full URL (including the http: part) of the document you are
redirecting to.
You can also use named arguments:
print $query->redirect(-uri=>'http://somewhere.else/in/movie/land',
-nph=>1);
The -nph parameter, if set to a true value, will issue the correct headers
to work with an NPH (no-parse-header) script. This is important to use
with certain servers, such as Microsoft Internet Explorer, which expect all
their scripts to be NPH.
CREATING THE HTML DOCUMENT HEADER
print $query->start_html(-title=>'Secrets of the Pyramids',
-author=>'fred@capricorn.org',
-base=>'true',
-target=>'_blank',
-meta=>{'keywords'=>'pharaoh secret mummy',
'copyright'=>'copyright 1996 King Tut'},
-style=>{'src'=>'/styles/style1.css'},
-BGCOLOR=>'blue');
After creating the HTTP header, most CGI scripts will start writing out an
HTML document. The start_html() routine creates the top of the page, along
with a lot of optional information that controls the page's appearance and
behavior.
This method returns a canned HTML header and the opening <body> tag. All
parameters are optional. In the named parameter form, recognized
parameters are -title, -author, -base, -xbase, -dtd, -lang and -target (see
below for the explanation). Any additional parameters you provide, such as
the Netscape unofficial BGCOLOR attribute, are added to the <body> tag.
Additional parameters must be proceeded by a hyphen.
The argument -xbase allows you to provide an HREF for the <base> tag
different from the current location, as in
-xbase=>"http://home.mcom.com/"
All relative links will be interpreted relative to this tag.
The argument -target allows you to provide a default target frame for all
the links and fill-out forms on the page. This is a non-standard HTTP
feature which only works with Netscape browsers! See the Netscape
documentation on frames for details of how to manipulate this.
-target=>"answer_window"
All relative links will be interpreted relative to this tag. You add
arbitrary meta information to the header with the -meta argument. This
argument expects a reference to an associative array containing name/value
pairs of meta information. These will be turned into a series of header
<meta> tags that look something like this:
<meta name="keywords" content="pharaoh secret mummy">
<meta name="description" content="copyright 1996 King Tut">
To create an HTTP-EQUIV type of <meta> tag, use -head, described below.
The -style argument is used to incorporate cascading stylesheets into your
code. See the section on CASCADING STYLESHEETS for more information.
The -lang argument is used to incorporate a language attribute into the
<html> tag. The default if not specified is "en-US" for US English. For
example:
print $q->start_html(-lang=>'fr-CA');
The -encoding argument can be used to specify the character set for XHTML.
It defaults to iso-8859-1 if not specified.
You can place other arbitrary HTML elements to the <head> section with the
-head tag. For example, to place the rarely-used <link> element in the
head section, use this:
print start_html(-head=>Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}));
To incorporate multiple HTML elements into the <head> section, just pass an
array reference:
print start_html(-head=>[
Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}),
Link({-rel=>'previous',
-href=>'http://www.capricorn.com/s1.html'})
]
);
And here's how to create an HTTP-EQUIV <meta> tag:
print start_html(-head=>meta({-http_equiv => 'Content-Type',
-content => 'text/html'}))
JAVASCRIPTING: The -script, -noScript, -onLoad, -onMouseOver, -onMouseOut
and -onUnload parameters are used to add Netscape JavaScript calls to your
pages. -script should point to a block of text containing JavaScript
function definitions. This block will be placed within a <script> block
inside the HTML (not HTTP) header. The block is placed in the header in
order to give your page a fighting chance of having all its JavaScript
functions in place even if the user presses the stop button before the page
has loaded completely. CGI.pm attempts to format the script in such a way
that JavaScript-naive browsers will not choke on the code: unfortunately
there are some browsers, such as Chimera for Unix, that get confused by it
nevertheless.
The -onLoad and -onUnload parameters point to fragments of JavaScript code
to execute when the page is respectively opened and closed by the browser.
Usually these parameters are calls to functions defined in the -script
field:
$query = new CGI;
print $query->header;
$JSCRIPT=<<END;
// Ask a silly question
function riddle_me_this() {
var r = prompt("What walks on four legs in the morning, " +
"two legs in the afternoon, " +
"and three legs in the evening?");
response(r);
}
// Get a silly answer
function response(answer) {
if (answer == "man")
alert("Right you are!");
else
alert("Wrong! Guess again.");
}
END
print $query->start_html(-title=>'The Riddle of the Sphinx',
-script=>$JSCRIPT);
Use the -noScript parameter to pass some HTML text that will be displayed
on browsers that do not have JavaScript (or browsers where JavaScript is
turned off).
Netscape 3.0 recognizes several attributes of the <script> tag, including
LANGUAGE and SRC. The latter is particularly interesting, as it allows you
to keep the JavaScript code in a file or CGI script rather than cluttering
up each page with the source. To use these attributes pass a HASH
reference in the -script parameter containing one or more of -language,
-src, or -code:
print $q->start_html(-title=>'The Riddle of the Sphinx',
-script=>{-language=>'JAVASCRIPT',
-src=>'/javascript/sphinx.js'}
);
print $q->(-title=>'The Riddle of the Sphinx',
-script=>{-language=>'PERLSCRIPT',
-code=>'print "hello world!\n;"'}
);
A final feature allows you to incorporate multiple <script> sections into
the header. Just pass the list of script sections as an array reference.
this allows you to specify different source files for different dialects of
JavaScript. Example:
print $q->start_html(-title=>'The Riddle of the Sphinx',
-script=>[
{ -language => 'JavaScript1.0',
-src => '/javascript/utilities10.js'
},
{ -language => 'JavaScript1.1',
-src => '/javascript/utilities11.js'
},
{ -language => 'JavaScript1.2',
-src => '/javascript/utilities12.js'
},
{ -language => 'JavaScript28.2',
-src => '/javascript/utilities219.js'
}
]
);
If this looks a bit extreme, take my advice and stick with straight CGI
scripting.
See
http://home.netscape.com/eng/mozilla/2.0/handbook/javascript/
for more information about JavaScript.
The old-style positional parameters are as follows:
Parameters:
1. The title
2. The author's e-mail address (will create a <link rev="MADE"> tag if
present
3. A 'true' flag if you want to include a <base> tag in the header. This
helps resolve relative addresses to absolute ones when the document is
moved, but makes the document hierarchy non-portable. Use with care!
4, 5, 6...
Any other parameters you want to include in the <body> tag. This is a
good place to put Netscape extensions, such as colors and wallpaper
patterns.
ENDING THE HTML DOCUMENT:
print $query->end_html
This ends an HTML document by printing the </body></html> tags.
CREATING A SELF-REFERENCING URL THAT PRESERVES STATE INFORMATION:
$myself = $query->self_url;
print q(<a href="$myself">I'm talking to myself.</a>);
self_url() will return a URL, that, when selected, will reinvoke 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.
$myself = $query->self_url;
print "<a href=$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 the unprocessed query string with query_string():
$the_string = $query->query_string;
OBTAINING THE SCRIPT'S URL
$full_url = $query->url();
$full_url = $query->url(-full=>1); #alternative syntax
$relative_url = $query->url(-relative=>1);
$absolute_url = $query->url(-absolute=>1);
$url_with_path = $query->url(-path_info=>1);
$url_with_path_and_query = $query->url(-path_info=>1,-query=>1);
$netloc = $query->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 reinvoke 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
MIXING POST AND URL PARAMETERS
$color = $query->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.
CREATING STANDARD HTML ELEMENTS:
CGI.pm defines general HTML shortcut methods for most, if not all of the
HTML 3 and HTML 4 tags. HTML shortcuts are named after a single HTML
element and return a fragment of HTML text that you can then print or
manipulate as you like. Each shortcut returns a fragment of HTML code that
you can append to a string, save to a file, or, most commonly, print out so
that it displays in the browser window.
This example shows how to use the HTML methods:
$q = new CGI;
print $q->blockquote(
"Many years ago on the island of",
$q->a({href=>"http://crete.org/"},"Crete"),
"there lived a Minotaur named",
$q->strong("Fred."),
),
$q->hr;
This results in the following HTML code (extra newlines have been added for
readability):
<blockquote>
Many years ago on the island of
<a href="http://crete.org/">Crete</a> there lived
a minotaur named <strong>Fred.</strong>
</blockquote>
<hr>
If you find the syntax for calling the HTML shortcuts awkward, you can
import them into your namespace and dispense with the object syntax
completely (see the next section for more details):
use CGI ':standard';
print blockquote(
"Many years ago on the island of",
a({href=>"http://crete.org/"},"Crete"),
"there lived a minotaur named",
strong("Fred."),
),
hr;
PROVIDING ARGUMENTS TO HTML SHORTCUTS
The HTML methods will accept zero, one or multiple arguments. If you
provide no arguments, you get a single tag:
print hr; # <hr>
If you provide one or more string arguments, they are concatenated together
with spaces and placed between opening and closing tags:
print h1("Chapter","1"); # <h1>Chapter 1</h1>"
If the first argument is an associative array reference, then the keys and
values of the associative array become the HTML tag's attributes:
print a({-href=>'fred.html',-target=>'_new'},
"Open a new frame");
<a href="fred.html",target="_new">Open a new frame</a>
You may dispense with the dashes in front of the attribute names if you
prefer:
print img {src=>'fred.gif',align=>'LEFT'};
<img align="LEFT" src="fred.gif">
Sometimes an HTML tag attribute has no argument. For example, ordered
lists can be marked as COMPACT. The syntax for this is an argument that
points to an undef string:
print ol({compact=>undef},li('one'),li('two'),li('three'));
Prior to CGI.pm version 2.41, providing an empty ('') string as an
attribute argument was the same as providing undef. However, this has
changed in order to accommodate those who want to create tags of the form
<img alt="">. The difference is shown in these two pieces of code:
CODE RESULT
img({alt=>undef}) <img alt>
img({alt=>''}) <img alt="">
THE DISTRIBUTIVE PROPERTY OF HTML SHORTCUTS
One of the cool features of the HTML shortcuts is that they are
distributive. If you give them an argument consisting of a reference to a
list, the tag will be distributed across each element of the list. For
example, here's one way to make an ordered list:
print ul(
li({-type=>'disc'},['Sneezy','Doc','Sleepy','Happy'])
);
This example will result in HTML output that looks like this:
<ul>
<li type="disc">Sneezy</li>
<li type="disc">Doc</li>
<li type="disc">Sleepy</li>
<li type="disc">Happy</li>
</ul>
This is extremely useful for creating tables. For example:
print table({-border=>undef},
caption('When Should You Eat Your Vegetables?'),
Tr({-align=>CENTER,-valign=>TOP},
[
th(['Vegetable', 'Breakfast','Lunch','Dinner']),
td(['Tomatoes' , 'no', 'yes', 'yes']),
td(['Broccoli' , 'no', 'no', 'yes']),
td(['Onions' , 'yes','yes', 'yes'])
]
)
);
HTML SHORTCUTS AND LIST INTERPOLATION
Consider this bit of code:
print blockquote(em('Hi'),'mom!'));
It will ordinarily return the string that you probably expect, namely:
<blockquote><em>Hi</em> mom!</blockquote>
Note the space between the element "Hi" and the element "mom!". CGI.pm
puts the extra space there using array interpolation, which is controlled
by the magic $" variable. Sometimes this extra space is not what you want,
for example, when you are trying to align a series of images. In this
case, you can simply change the value of $" to an empty string.
{
local($") = '';
print blockquote(em('Hi'),'mom!'));
}
I suggest you put the code in a block as shown here. Otherwise the change
to $" will affect all subsequent code until you explicitly reset it.
NON-STANDARD HTML SHORTCUTS
A few HTML tags don't follow the standard pattern for various reasons.
comment() generates an HTML comment (<!-- comment -->). Call it like
print comment('here is my comment');
Because of conflicts with built-in Perl functions, the following functions
begin with initial caps:
Select
Tr
Link
Delete
Accept
Sub
In addition, start_html(), end_html(), start_form(), end_form(),
start_multipart_form() and all the fill-out form tags are special. See
their respective sections.
AUTOESCAPING HTML
By default, all HTML that is emitted by the form-generating functions is
passed through a function called escapeHTML():
$escaped_string = escapeHTML("unescaped string");
Escape HTML formatting characters in a string.
Provided that you have specified a character set of ISO-8859-1 (the
default), the standard HTML escaping rules will be used. The "<" character
becomes "<", ">" becomes ">", "&" becomes "&", and the quote
character becomes """. In addition, the hexadecimal 0x8b and 0x9b
characters, which many windows-based browsers interpret as the left and
right angle-bracket characters, are replaced by their numeric HTML entities
("‹" and "›"). If you manually change the charset, either by
calling the charset() method explicitly or by passing a -charset argument
to header(), then all characters will be replaced by their numeric
entities, since CGI.pm has no lookup table for all the possible encodings.
The automatic escaping does not apply to other shortcuts, such as h1().
You should call escapeHTML() yourself on untrusted data in order to protect
your pages against nasty tricks that people may enter into guestbooks,
etc.. To change the character set, use charset(). To turn autoescaping
off completely, use autoescape():
$charset = charset([$charset]);
Get or set the current character set.
$flag = autoEscape([$flag]);
Get or set the value of the autoescape flag.
PRETTY-PRINTING HTML
By default, all the HTML produced by these functions comes out as one long
line without carriage returns or indentation. This is yuck, but it does
reduce the size of the documents by 10-20%. To get pretty-printed output,
please use CGI::Pretty, a subclass contributed by Brian Paulsen.
CREATING FILL-OUT FORMS:
General note The various form-creating methods all return strings to the
caller, containing the tag or tags that will create the requested form
element. You are responsible for actually printing out these strings.
It's set up this way so that you can place formatting tags around the form
elements.
Another note The default values that you specify for the forms are only
used the first time the script is invoked (when there is no query string).
On subsequent invocations of the script (when there is a query string), the
former values are used even if they are blank.
If you want to change the value of a field from its previous value, you
have two choices:
(1) call the param() method to set it.
(2) use the -override (alias -force) parameter (a new feature in version
2.15). This forces the default value to be used, regardless of the
previous value:
print $query->textfield(-name=>'field_name',
-default=>'starting value',
-override=>1,
-size=>50,
-maxlength=>80);
Yet another note By default, the text and labels of form elements are
escaped according to HTML rules. This means that you can safely use
"<CLICK ME>" as the label for a button. However, it also interferes with
your ability to incorporate special HTML character sequences, such as
Á, into your fields. If you wish to turn off automatic escaping,
call the autoEscape() method with a false value immediately after creating
the CGI object:
$query = new CGI;
$query->autoEscape(undef);
CREATING AN ISINDEX TAG
print $query->isindex(-action=>$action);
-or-
print $query->isindex($action);
Prints out an <isindex> tag. Not very exciting. The parameter -action
specifies the URL of the script to process the query. The default is to
process the query with the current script.
STARTING AND ENDING A FORM
print $query->start_form(-method=>$method,
-action=>$action,
-enctype=>$encoding);
<... various form stuff ...>
print $query->endform;
-or-
print $query->start_form($method,$action,$encoding);
<... various form stuff ...>
print $query->endform;
start_form() will return a <form> tag with the optional method, action and
form encoding that you specify. The defaults are:
method: POST
action: this script
enctype: application/x-www-form-urlencoded
endform() returns the closing </form> tag.
Start_form()'s enctype argument tells the browser how to package the
various fields of the form before sending the form to the server. Two
values are possible:
Note: This method was previously named startform(), and startform() is
still recognized as an alias.
application/x-www-form-urlencoded
This is the older type of encoding used by all browsers prior to
Netscape 2.0. It is compatible with many CGI scripts and is suitable
for short fields containing text data. For your convenience, CGI.pm
stores the name of this encoding type in &CGI::URL_ENCODED.
multipart/form-data
This is the newer type of encoding introduced by Netscape 2.0. It is
suitable for forms that contain very large fields or that are intended
for transferring binary data. Most importantly, it enables the "file
upload" feature of Netscape 2.0 forms. For your convenience, CGI.pm
stores the name of this encoding type in &CGI::MULTIPART
Forms that use this type of encoding are not easily interpreted by CGI
scripts unless they use CGI.pm or another library designed to handle
them.
For compatibility, the start_form() method uses the older form of encoding
by default. If you want to use the newer form of encoding by default, you
can call start_multipart_form() instead of start_form().
JAVASCRIPTING: The -name and -onSubmit parameters are provided for use with
JavaScript. The -name parameter gives the form a name so that it can be
identified and manipulated by JavaScript functions. -onSubmit should point
to a JavaScript function that will be executed just before the form is
submitted to your server. You can use this opportunity to check the
contents of the form for consistency and completeness. If you find
something wrong, you can put up an alert box or maybe fix things up
yourself. You can abort the submission by returning false from this
function.
Usually the bulk of JavaScript functions are defined in a <script> block in
the HTML header and -onSubmit points to one of these function call. See
start_html() for details.
CREATING A TEXT FIELD
print $query->textfield(-name=>'field_name',
-default=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print $query->textfield('field_name','starting value',50,80);
textfield() will return a text input field.
Parameters
1. The first parameter is the required name for the field (-name).
2. The optional second parameter is the default starting value for the
field contents (-default).
3. The optional third parameter is the size of the field in
characters (-size).
4. The optional fourth parameter is the maximum number of characters the
field will accept (-maxlength).
As with all these methods, the field will be initialized with its previous
contents from earlier invocations of the script. When the form is
processed, the value of the text field can be retrieved with:
$value = $query->param('foo');
If you want to reset it from its initial value after the script has been
called once, you can do so like this:
$query->param('foo',"I'm taking over this value!");
NEW AS OF VERSION 2.15: If you don't want the field to take on its previous
value, you can force its current value by using the -override (alias
-force) parameter:
print $query->textfield(-name=>'field_name',
-default=>'starting value',
-override=>1,
-size=>50,
-maxlength=>80);
JAVASCRIPTING: You can also provide -onChange, -onFocus, -onBlur,
-onMouseOver, -onMouseOut and -onSelect parameters to register JavaScript
event handlers. The onChange handler will be called whenever the user
changes the contents of the text field. You can do text validation if you
like. onFocus and onBlur are called respectively when the insertion point
moves into and out of the text field. onSelect is called when the user
changes the portion of the text that is selected.
CREATING A BIG TEXT FIELD
print $query->textarea(-name=>'foo',
-default=>'starting value',
-rows=>10,
-columns=>50);
-or
print $query->textarea('foo','starting value',10,50);
textarea() is just like textfield, but it allows you to specify rows and
columns for a multiline text entry box. You can provide a starting value
for the field, which can be long and contain multiple lines.
JAVASCRIPTING: The -onChange, -onFocus, -onBlur , -onMouseOver,
-onMouseOut, and -onSelect parameters are recognized. See textfield().
CREATING A PASSWORD FIELD
print $query->password_field(-name=>'secret',
-value=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print $query->password_field('secret','starting value',50,80);
password_field() is identical to textfield(), except that its contents will
be starred out on the web page.
JAVASCRIPTING: The -onChange, -onFocus, -onBlur, -onMouseOver, -onMouseOut
and -onSelect parameters are recognized. See textfield().
CREATING A FILE UPLOAD FIELD
print $query->filefield(-name=>'uploaded_file',
-default=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print $query->filefield('uploaded_file','starting value',50,80);
filefield() will return a file upload field for Netscape 2.0 browsers. In
order to take full advantage of this you must use the new multipart
encoding scheme for the form. You can do this either by calling
start_form() with an encoding type of &CGI::MULTIPART, or by calling the
new method start_multipart_form() instead of vanilla start_form().
Parameters
1. The first parameter is the required name for the field (-name).
2. The optional second parameter is the starting value for the field
contents to be used as the default file name (-default).
For security reasons, browsers don't pay any attention to this field,
and so the starting value will always be blank. Worse, the field loses
its "sticky" behavior and forgets its previous contents. The starting
value field is called for in the HTML specification, however, and
possibly some browser will eventually provide support for it.
3. The optional third parameter is the size of the field in characters
(-size).
4. The optional fourth parameter is the maximum number of characters the
field will accept (-maxlength).
When the form is processed, you can retrieve the entered filename by
calling param():
$filename = $query->param('uploaded_file');
Different browsers will return slightly different things for the name.
Some browsers return the filename only. Others return the full path to the
file, using the path conventions of the user's machine. Regardless, the
name returned is always the name of the file on the user's machine, and is
unrelated to the name of the temporary file that CGI.pm creates during
upload spooling (see below).
The filename returned is also a file handle. You can read the contents of
the file using standard Perl file reading calls:
# Read a text file and print it out
while (<$filename>) {
print;
}
# Copy a binary file to somewhere safe
open (OUTFILE,">>/usr/local/web/users/feedback");
while ($bytesread=read($filename,$buffer,1024)) {
print OUTFILE $buffer;
}
However, there are problems with the dual nature of the upload fields. If
you "use strict", then Perl will complain when you try to use a string as a
filehandle. You can get around this by placing the file reading code in a
block containing the "no strict" pragma. 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 be safe, use the upload() function (new in version 2.47). When called
with the name of an upload field, upload() returns a filehandle, or undef
if the parameter is not a valid filehandle.
$fh = $query->upload('uploaded_file');
while (<$fh>) {
print;
}
In an array context, upload() will return an array of filehandles. This
makes it possible to create forms that use the same name for multiple
upload fields.
This is the recommended idiom.
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. Future browsers may send other information as well
(such as modification date and size). To retrieve this information, call
uploadInfo(). It returns a reference to an associative array containing
all the document headers.
$filename = $query->param('uploaded_file');
$type = $query->uploadInfo($filename)->{'Content-Type'};
unless ($type eq 'text/html') {
die "HTML FILES ONLY!";
}
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.
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:
$file = $query->upload('uploaded_file');
if (!$file && $query->cgi_error) {
print $query->header(-status=>$query->cgi_error);
exit 0;
}
You are free to create a custom HTML page to complain about the error, if
you wish.
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.
JAVASCRIPTING: The -onChange, -onFocus, -onBlur, -onMouseOver, -onMouseOut
and -onSelect parameters are recognized. See textfield() for details.
CREATING A POPUP MENU
print $query->popup_menu('menu_name',
['eenie','meenie','minie'],
'meenie');
-or-
%labels = ('eenie'=>'your first choice',
'meenie'=>'your second choice',
'minie'=>'your third choice');
print $query->popup_menu('menu_name',
['eenie','meenie','minie'],
'meenie',\%labels);
-or (named parameter style)-
print $query->popup_menu(-name=>'menu_name',
-values=>['eenie','meenie','minie'],
-default=>'meenie',
-labels=>\%labels);
popup_menu() creates a menu.
1. The required first argument is the menu's name (-name).
2. The required second argument (-values) is an array reference containing
the list of menu items in the menu. You can pass the method an
anonymous array, as shown in the example, or a reference to a named
array, such as "\@foo".
3. The optional third parameter (-default) is the name of the default menu
choice. If not specified, the first item will be the default. The
values of the previous choice will be maintained across queries.
4. The optional fourth parameter (-labels) is provided for people who want
to use different values for the user-visible label inside the popup
menu nd the value returned to your script. It's a pointer to an
associative array relating menu values to user-visible labels. If you
leave this parameter blank, the menu values will be displayed by
default. (You can also leave a label undefined if you want to).
When the form is processed, the selected value of the popup menu can be
retrieved using:
$popup_menu_value = $query->param('menu_name');
JAVASCRIPTING: popup_menu() recognizes the following event handlers:
-onChange, -onFocus, -onMouseOver, -onMouseOut, and -onBlur. See the
textfield() section for details on when these handlers are called.
CREATING A SCROLLING LIST
print $query->scrolling_list('list_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],5,'true');
-or-
print $query->scrolling_list('list_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],5,'true',
\%labels);
-or-
print $query->scrolling_list(-name=>'list_name',
-values=>['eenie','meenie','minie','moe'],
-default=>['eenie','moe'],
-size=>5,
-multiple=>'true',
-labels=>\%labels);
scrolling_list() creates a scrolling list.
Parameters:
1. The first and second arguments are the list name (-name) and values
(-values). As in the popup menu, the second argument should be an
array reference.
2. The optional third argument (-default) can be either a reference to a
list containing the values to be selected by default, or can be a
single value to select. If this argument is missing or undefined, then
nothing is selected when the list first appears. In the named
parameter version, you can use the synonym "-defaults" for this
parameter.
3. The optional fourth argument is the size of the list (-size).
4. The optional fifth argument can be set to true to allow multiple
simultaneous selections (-multiple). Otherwise only one selection will
be allowed at a time.
5. The optional sixth argument is a pointer to an associative array
containing long user-visible labels for the list items (-labels). If
not provided, the values will be displayed.
When this form is processed, all selected list items will be returned
as a list under the parameter name 'list_name'. The values of the
selected items can be retrieved with:
@selected = $query->param('list_name');
JAVASCRIPTING: scrolling_list() recognizes the following event handlers:
-onChange, -onFocus, -onMouseOver, -onMouseOut and -onBlur. See
textfield() for the description of when these handlers are called.
CREATING A GROUP OF RELATED CHECKBOXES
print $query->checkbox_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-default=>['eenie','moe'],
-linebreak=>'true',
-labels=>\%labels);
print $query->checkbox_group('group_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],'true',\%labels);
HTML3-COMPATIBLE BROWSERS ONLY:
print $query->checkbox_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-rows=2,-columns=>2);
checkbox_group() creates a list of checkboxes that are related by the same
name.
Parameters:
1. The first and second arguments are the checkbox name and values,
respectively (-name and -values). As in the popup menu, the second
argument should be an array reference. These values are used for the
user-readable labels printed next to the checkboxes as well as for the
values passed to your script in the query string.
2. The optional third argument (-default) can be either a reference to a
list containing the values to be checked by default, or can be a single
value to checked. If this argument is missing or undefined, then
nothing is selected when the list first appears.
3. The optional fourth argument (-linebreak) can be set to true to place
line breaks between the checkboxes so that they appear as a vertical
list. Otherwise, they will be strung together on a horizontal line.
4. The optional fifth argument is a pointer to an associative array
relating the checkbox values to the user-visible labels that will be
printed next to them (-labels). If not provided, the values will be
used as the default.
5. HTML3-compatible browsers (such as Netscape) can take advantage of the
optional parameters -rows, and -columns. These parameters cause
checkbox_group() to return an HTML3 compatible table containing the
checkbox group formatted with the specified number of rows and columns.
You can provide just the -columns parameter if you wish; checkbox_group
will calculate the correct number of rows for you.
To include row and column headings in the returned table, you can use
the -rowheaders and -colheaders parameters. Both of these accept a
pointer to an array of headings to use. The headings are just
decorative. They don't reorganize the interpretation of the checkboxes
-- they're still a single named unit.
When the form is processed, all checked boxes will be returned as a list
under the parameter name 'group_name'. The values of the "on" checkboxes
can be retrieved with:
@turned_on = $query->param('group_name');
The value returned by checkbox_group() is actually an array of button
elements. You can capture them and use them within tables, lists, or in
other creative ways:
@h = $query->checkbox_group(-name=>'group_name',-values=>\@values);
&use_in_creative_way(@h);
JAVASCRIPTING: checkbox_group() recognizes the -onClick parameter. This
specifies a JavaScript code fragment or function call to be executed every
time the user clicks on any of the buttons in the group. You can retrieve
the identity of the particular button clicked on using the "this" variable.
CREATING A STANDALONE CHECKBOX
print $query->checkbox(-name=>'checkbox_name',
-checked=>1,
-value=>'ON',
-label=>'CLICK ME');
-or-
print $query->checkbox('checkbox_name','checked','ON','CLICK ME');
checkbox() is used to create an isolated checkbox that isn't logically
related to any others.
Parameters:
1. The first parameter is the required name for the checkbox (-name). It
will also be used for the user-readable label printed next to the
checkbox.
2. The optional second parameter (-checked) specifies that the checkbox is
turned on by default. Synonyms are -selected and -on.
3. The optional third parameter (-value) specifies the value of the
checkbox when it is checked. If not provided, the word "on" is
assumed.
4. The optional fourth parameter (-label) is the user-readable label to be
attached to the checkbox. If not provided, the checkbox name is used.
The value of the checkbox can be retrieved using:
$turned_on = $query->param('checkbox_name');
JAVASCRIPTING: checkbox() recognizes the -onClick parameter. See
checkbox_group() for further details.
CREATING A RADIO BUTTON GROUP
print $query->radio_group(-name=>'group_name',
-values=>['eenie','meenie','minie'],
-default=>'meenie',
-linebreak=>'true',
-labels=>\%labels);
-or-
print $query->radio_group('group_name',['eenie','meenie','minie'],
'meenie','true',\%labels);
HTML3-COMPATIBLE BROWSERS ONLY:
print $query->radio_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-rows=2,-columns=>2);
radio_group() creates a set of logically-related radio buttons (turning one
member of the group on turns the others off)
Parameters:
1. The first argument is the name of the group and is required (-name).
2. The second argument (-values) is the list of values for the radio
buttons. The values and the labels that appear on the page are
identical. Pass an array reference in the second argument, either
using an anonymous array, as shown, or by referencing a named array as
in "\@foo".
3. The optional third parameter (-default) is the name of the default
button to turn on. If not specified, the first item will be the
default. You can provide a nonexistent button name, such as "-" to
start up with no buttons selected.
4. The optional fourth parameter (-linebreak) can be set to 'true' to put
line breaks between the buttons, creating a vertical list.
5. The optional fifth parameter (-labels) is a pointer to an associative
array relating the radio button values to user-visible labels to be
used in the display. If not provided, the values themselves are
displayed.
6. HTML3-compatible browsers (such as Netscape) can take advantage of the
optional parameters -rows, and -columns. These parameters cause
radio_group() to return an HTML3 compatible table containing the radio
group formatted with the specified number of rows and columns. You can
provide just the -columns parameter if you wish; radio_group will
calculate the correct number of rows for you.
To include row and column headings in the returned table, you can use
the -rowheader and -colheader parameters. Both of these accept a
pointer to an array of headings to use. The headings are just
decorative. They don't reorganize the interpretation of the radio
buttons -- they're still a single named unit.
When the form is processed, the selected radio button can be retrieved
using:
$which_radio_button = $query->param('group_name');
The value returned by radio_group() is actually an array of button
elements. You can capture them and use them within tables, lists, or in
other creative ways:
@h = $query->radio_group(-name=>'group_name',-values=>\@values);
&use_in_creative_way(@h);
CREATING A SUBMIT BUTTON
print $query->submit(-name=>'button_name',
-value=>'value');
-or-
print $query->submit('button_name','value');
submit() will create the query submission button. Every form should have
one of these.
Parameters:
1. The first argument (-name) is optional. You can give the button a name
if you have several submission buttons in your form and you want to
distinguish between them. The name will also be used as the user-
visible label. Be aware that a few older browsers don't deal with this
correctly and never send back a value from a button.
2. The second argument (-value) is also optional. This gives the button a
value that will be passed to your script in the query string.
You can figure out which button was pressed by using different values for
each one:
$which_one = $query->param('button_name');
JAVASCRIPTING: radio_group() recognizes the -onClick parameter. See
checkbox_group() for further details.
CREATING A RESET BUTTON
print $query->reset
reset() creates the "reset" button. Note that it restores the form to its
value from the last time the script was called, NOT necessarily to the
defaults.
Note that this conflicts with the Perl reset() built-in. Use CORE::reset()
to get the original reset function.
CREATING A DEFAULT BUTTON
print $query->defaults('button_label')
defaults() creates a button that, when invoked, will cause the form to be
completely reset to its defaults, wiping out all the changes the user ever
made.
CREATING A HIDDEN FIELD
print $query->hidden(-name=>'hidden_name',
-default=>['value1','value2'...]);
-or-
print $query->hidden('hidden_name','value1','value2'...);
hidden() produces a text field that can't be seen by the user. It is
useful for passing state variable information from one invocation of the
script to the next.
Parameters:
1. The first argument is required and specifies the name of this field
(-name).
2. The second argument is also required and specifies its value
(-default). In the named parameter style of calling, you can provide a
single value here or a reference to a whole list
Fetch the value of a hidden field this way:
$hidden_value = $query->param('hidden_name');
Note, that just like all the other form elements, the value of a hidden
field is "sticky". If you want to replace a hidden field with some other
values after the script has been called once you'll have to do it manually:
$query->param('hidden_name','new','values','here');
CREATING A CLICKABLE IMAGE BUTTON
print $query->image_button(-name=>'button_name',
-src=>'/source/URL',
-align=>'MIDDLE');
-or-
print $query->image_button('button_name','/source/URL','MIDDLE');
image_button() produces a clickable image. When it's clicked on the
position of the click is returned to your script as "button_name.x" and
"button_name.y", where "button_name" is the name you've assigned to it.
JAVASCRIPTING: image_button() recognizes the -onClick parameter. See
checkbox_group() for further details.
Parameters:
1. The first argument (-name) is required and specifies the name of this
field.
2. The second argument (-src) is also required and specifies the URL
3. The third option (-align, optional) is an alignment type, and may be
TOP, BOTTOM or MIDDLE
Fetch the value of the button this way:
$x = $query->param('button_name.x');
$y = $query->param('button_name.y');
CREATING A JAVASCRIPT ACTION BUTTON
print $query->button(-name=>'button_name',
-value=>'user visible label',
-onClick=>"do_something()");
-or-
print $query->button('button_name',"do_something()");
button() produces a button that is compatible with Netscape 2.0's
JavaScript. When it's pressed the fragment of JavaScript code pointed to
by the -onClick parameter will be executed. On non-Netscape browsers this
form element will probably not even display.
HTTP COOKIES
Netscape browsers versions 1.1 and higher, and all versions of Internet
Explorer, support a so-called "cookie" designed to help maintain state
within a browser session. 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:
$cookie = $query->cookie(-name=>'sessionID',
-value=>'xyzzy',
-expires=>'+1h',
-path=>'/cgi-bin/database',
-domain=>'.capricorn.org',
-secure=>1);
print $query->header(-cookie=>$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 associative array reference. For example, you can
store an entire associative array into a cookie this way:
$cookie=$query->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:
print $query->header(-cookie=>$my_cookie);
To create multiple cookies, give header() an array reference:
$cookie1 = $query->cookie(-name=>'riddle_name',
-value=>"The Sphynx's Question");
$cookie2 = $query->cookie(-name=>'answers',
-value=>\%answers);
print $query->header(-cookie=>[$cookie1,$cookie2]);
To retrieve a cookie, request it by name by calling cookie() method without
the -value parameter:
use CGI;
$query = new CGI;
$riddle = $query->cookie('riddle_name');
%answers = $query->cookie('answers');
Cookies created with a single scalar value, such as the "riddle_name"
cookie, will be returned in that form. Cookies with array and hash values
can also be retrieved.
The cookie and CGI namespaces are separate. If you have a parameter named
'answers' and a cookie named 'answers', the values retrieved by param() and
cookie() are independent of each other. However, it's simple to turn a CGI
parameter into a cookie, and vice-versa:
# turn a CGI parameter into a cookie
$c=$q->cookie(-name=>'answers',-value=>[$q->param('answers')]);
# vice-versa
$q->param(-name=>'answers',-value=>[$q->cookie('answers')]);
See the cookie.cgi example script for some ideas on how to use cookies
effectively.
WORKING WITH FRAMES
It's possible for CGI.pm scripts to write into several browser panels and
windows using the HTML 4 frame mechanism. There are three techniques for
defining new frames programmatically:
1. Create a <Frameset> document
After writing out the HTTP header, instead of creating a standard HTML
document using the start_html() call, create a <frameset> document that
defines the frames on the page. Specify your script(s) (with
appropriate parameters) as the SRC for each of the frames.
There is no specific support for creating <frameset> sections in
CGI.pm, but the HTML is very simple to write. See the frame
documentation in Netscape's home pages for details
http://home.netscape.com/assist/net_sites/frames.html
2. Specify the destination for the document in the HTTP header
You may provide a -target parameter to the header() method:
print $q->header(-target=>'ResultsWindow');
This will tell the browser to load the output of your script into the
frame named "ResultsWindow". If a frame of that name doesn't already
exist, the browser will pop up a new window and load your script's
document into that. There are a number of magic names that you can use
for targets. See the frame documents on Netscape's home pages for
details.
3. Specify the destination for the document in the <form> tag
You can specify the frame to load in the FORM tag itself. With CGI.pm
it looks like this:
print $q->start_form(-target=>'ResultsWindow');
When your script is reinvoked by the form, its output will be loaded
into the frame named "ResultsWindow". If one doesn't already exist a
new window will be created.
The script "frameset.cgi" in the examples directory shows one way to create
pages in which the fill-out form and the response live in side-by-side
frames.
LIMITED SUPPORT FOR CASCADING STYLE SHEETS
CGI.pm has limited support for HTML3's cascading style sheets (css). To
incorporate a stylesheet into your document, pass the start_html() method a
-style parameter. The value of this parameter may be a scalar, in which
case it is incorporated directly into a <style> section, or it may be a
hash reference. In the latter case you should provide the hash with one or
more of -src or -code. -src points to a URL where an externally-defined
stylesheet can be found. -code points to a scalar value to be incorporated
into a <style> section. Style definitions in -code override similarly-
named ones in -src, hence the name "cascading."
You may also specify the type of the stylesheet by adding the optional
-type parameter to the hash pointed to by -style. If not specified, the
style defaults to 'text/css'.
To refer to a style within the body of your document, add the -class
parameter to any HTML element:
print h1({-class=>'Fancy'},'Welcome to the Party');
Or define styles on the fly with the -style parameter:
print h1({-style=>'Color: red;'},'Welcome to Hell');
You may also use the new span() element to apply a style to a section of
text:
print span({-style=>'Color: red;'},
h1('Welcome to Hell'),
"Where did that handbasket get to?"
);
Note that you must import the ":html3" definitions to have the span()
method available. Here's a quick and dirty example of using CSS's. See
the CSS specification at http://www.w3.org/pub/WWW/TR/Wd-css-1.html for
more information.
use CGI qw/:standard :html3/;
#here's a stylesheet incorporated directly into the page
$newStyle=<<END;
<!--
P.Tip {
margin-right: 50pt;
margin-left: 50pt;
color: red;
}
P.Alert {
font-size: 30pt;
font-family: sans-serif;
color: red;
}
-->
END
print header();
print start_html( -title=>'CGI with Style',
-style=>{-src=>'http://www.capricorn.com/style/st1.css',
-code=>$newStyle}
);
print h1('CGI with Style'),
p({-class=>'Tip'},
"Better read the cascading style sheet spec before playing with this!"),
span({-style=>'color: magenta'},
"Look Mom, no hands!",
p(),
"Whooo wee!"
);
print end_html;
Pass an array reference to -style in order to incorporate multiple
stylesheets into your document.
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"
DUMPING OUT ALL THE NAME/VALUE PAIRS
The Dump() method produces a string consisting of all the query's
name/value pairs formatted nicely as a nested list. This is useful for
debugging purposes:
print $query->Dump
Produces something that looks like:
<ul>
<li>name1
<ul>
<li>value1
<li>value2
</ul>
<li>name2
<ul>
<li>value1
</ul>
</ul>
As a shortcut, you can interpolate the entire CGI object into a string and
it will be replaced with the a nice HTML dump shown above:
$query=new CGI;
print "<h2>Current Values</h2> $query\n";
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
$query->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, an HTTP extension implemented by
Netscape browsers version 1.1 and higher, and all versions of Internet
Explorer. 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.
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 $query->user_agent(netscape);
path_info()
Returns additional path information from the script URL. E.G. fetching
/cgi-bin/your_script/additional/stuff will result in
$query->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.
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.
script_name()
Return the script name as a partial URL, for self-refering scripts.
referer()
Return the URL of the page the browser was viewing prior to fetching
your script. Not available for all browsers.
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_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. This only works with older browsers such as Mosaic. Newer
browsers do not report the user name for privacy reasons!
request_method()
Returns the method used to access your script, usually one of 'POST',
'GET' or 'HEAD'.
content_type()
Returns the content_type of data submitted in a POST, generally
multipart/form-data or application/x-www-form-urlencoded
http()
Called with no arguments returns the list of HTTP environment
variables, including such things as HTTP_USER_AGENT,
HTTP_ACCEPT_LANGUAGE, and HTTP_ACCEPT_CHARSET, corresponding to the
like-named HTTP header fields in the request. Called with the name of
an HTTP header field, returns its value. Capitalization and the use of
hyphens versus underscores are not significant.
For example, all three of these examples are equivalent:
$requested_language = $q->http('Accept-language');
$requested_language = $q->http('Accept_language');
$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. However, note that if you have
applied Service Pack 6, much of the functionality of NPH scripts, including
the ability to redirect while setting a cookie, b<do not work at all> on
IIS without a special patch from Microsoft. See
http://support.microsoft.com/support/kb/articles/Q280/3/41.ASP: Non-Parsed
Headers Stripped From CGI Applications That Have nph- Prefix in Name.
In the use statement
Simply add the "-nph" pragmato 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 $q->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/local/bin/perl
use CGI qw/:push -nph/;
$| = 1;
print multipart_init(-boundary=>'----here we go!');
foreach (0 .. 4) {
print multipart_start(-type=>'text/plain'),
"The current time is ",scalar(localtime),"\n";
if ($_ < 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=>$boundary);
Initialize the multipart system. The -boundary argument specifies what
MIME boundary string to use to separate parts of the document. If not
provided, CGI.pm chooses a reasonable boundary for you.
multipart_start()
multipart_start(-type=>$type)
Start a new part of the multipart document using the specified MIME
type. If not specified, text/html 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.
Only Netscape Navigator supports server push. Internet Explorer browsers
do not.
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 megabytes. 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 1 megabyte.
$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.
You can use these variables in either of two ways.
1. On a script-by-script basis
Set the variable at the top of the script, right after the "use"
statement:
use CGI qw/:standard/;
use CGI::Carp 'fatalsToBrowser';
$CGI::POST_MAX=1024 * 100; # max 100K posts
$CGI::DISABLE_UPLOADS = 1; # no uploads
2. Globally for all scripts
Open up CGI.pm, find the definitions for $POST_MAX and
$DISABLE_UPLOADS, and set them to the desired values. You'll find them
towards the top of the file in a subroutine named initialize_globals().
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:
$uploaded_file = param('upload');
if (!$uploaded_file && cgi_error()) {
print header(-status=>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 an HTML page that
warns the user of the problem.
COMPATIBILITY WITH CGI-LIB.PL
To make it easier to port existing programs that use cgi-lib.pl the
compatibility routine "ReadParse" is provided. Porting is simple:
OLD VERSION
require "cgi-lib.pl";
&ReadParse;
print "The value of the antique is $in{antique}.\n";
NEW VERSION
use CGI;
CGI::ReadParse
print "The value of the antique is $in{antique}.\n";
CGI.pm's ReadParse() routine creates a tied variable named %in, which can
be accessed to obtain the query variables. Like ReadParse, you can also
provide your own variable. Infrequently used features of ReadParse, such
as the creation of @in and $in variables, are not supported.
Once you use ReadParse, you can retrieve the query object itself this way:
$q = $in{CGI};
print $q->textfield(-name=>'wow',
-value=>'does this really work?');
This allows you to start using the more interesting features of CGI.pm
without rewriting your old scripts from scratch.
AUTHOR INFORMATION
Copyright 1995-1998, Lincoln D. Stein. All rights reserved.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
Address bug reports and comments to: lstein@cshl.org. When sending bug
reports, please provide the version of CGI.pm, the version of Perl, the
name and version of your Web server, and the name and version of the
operating system you are using. If the problem is even remotely browser
dependent, please provide information about the affected browers as well.
CREDITS
Thanks very much to:
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.
A COMPLETE EXAMPLE OF A SIMPLE FORM-BASED SCRIPT
#!/usr/local/bin/perl
use CGI;
$query = new CGI;
print $query->header;
print $query->start_html("Example CGI.pm Form");
print "<h1> Example CGI.pm Form</h1>\n";
&print_prompt($query);
&do_work($query);
&print_tail;
print $query->end_html;
sub print_prompt {
my($query) = @_;
print $query->start_form;
print "<em>What's your name?</em><br>";
print $query->textfield('name');
print $query->checkbox('Not my real name');
print "<p><em>Where can you find English Sparrows?</em><br>";
print $query->checkbox_group(
-name=>'Sparrow locations',
-values=>[England,France,Spain,Asia,Hoboken],
-linebreak=>'yes',
-defaults=>[England,Asia]);
print "<p><em>How far can they fly?</em><br>",
$query->radio_group(
-name=>'how far',
-values=>['10 ft','1 mile','10 miles','real far'],
-default=>'1 mile');
print "<p><em>What's your favorite color?</em> ";
print $query->popup_menu(-name=>'Color',
-values=>['black','brown','red','yellow'],
-default=>'red');
print $query->hidden('Reference','Monty Python and the Holy Grail');
print "<p><em>What have you got there?</em><br>";
print $query->scrolling_list(
-name=>'possessions',
-values=>['A Coconut','A Grail','An Icon',
'A Sword','A Ticket'],
-size=>5,
-multiple=>'true');
print "<p><em>Any parting comments?</em><br>";
print $query->textarea(-name=>'Comments',
-rows=>10,
-columns=>50);
print "<p>",$query->reset;
print $query->submit('Action','Shout');
print $query->submit('Action','Scream');
print $query->endform;
print "<hr>\n";
}
sub do_work {
my($query) = @_;
my(@values,$key);
print "<h2>Here are the current settings in this form</h2>";
foreach $key ($query->param) {
print "<strong>$key</strong> -> ";
@values = $query->param($key);
print join(", ",@values),"<br>\n";
}
}
sub print_tail {
print <<END;
<hr>
<address>Lincoln D. Stein</address><br>
<a href="/">Home Page</a>
END
}
BUGS
This module has grown large and monolithic. Furthermore it's doing many
things, such as handling URLs, parsing CGI input, writing HTML, etc., that
are also done in the LWP modules. It should be discarded in favor of the
CGI::* modules, but somehow I continue to work on it.
Note that the code is truly contorted in order to avoid spurious warnings
when programs are run with the -w switch.
SEE ALSO
CGI::Carp, CGI::Fast, CGI::Pretty
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