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 vari
ables. Using a CGI object's methods, you can examine key
words 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 func
tionality 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 program
ming style for those who don't need its object-oriented
features.
The current version of CGI.pm is available at
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-ori
ented style. See HOW TO IMPORT FUNCTIONS for important
information on function-oriented programming in CGI.pm
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 argu
ment needs to begin with a dash. If a dash is present in
the first argument, CGI.pm assumes dashes for the subse
quent ones.
You don't have to use the hyphen at all if you don't want
to. After creating a CGI object, call the
uussee_nnaammeedd_ppaarraammeetteerrss(()) method with a nonzero value. This
will tell CGI.pm that you intend to use named parameters
exclusively:
$query = new CGI;
$query->use_named_parameters(1);
$field = $query->radio_group('name'=>'OS',
'values'=>['Unix','Windows','Macintosh'],
'default'=>'Unix');
Several routines are commonly called with just one argu
ment. In the case of these routines you can provide the
single argument without an argument name. header() hap
pens to be one of these routines. In this case, the sin
gle 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 exam
ple, 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
tents (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 man
age 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 func
tions. The most frequent of these is the -values argu
ment, 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 argu
ment that it doesn't recognize. For example, you can pro
duce 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:
Cost: Three smackers
Annoyance-level: high
Complaints-to: bit bucket
Content-type: text/html
Notice the way that underscores are translated automati
cally into hyphens. HTML-generating routines perform a
different type of translation.
This feature allows you to keep up with the rapidly chang
ing 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 cre
ated 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 rreessttoorree_ppaarraammeetteerrss(()). This will (re)initial
ize 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 associa
tive array reference:
'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, there will be a
single parameter named '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 guar
anteed).
@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 multi
valued (e.g. from multiple selections in a scrolling
list), you can ask to receive an array. Otherwise the
method will return a single value.
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 parame
ter. 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 vari
able @R::keywords will appear. If no namespace is given,
this method will assume 'Q'. WARNING: don't import any
thing into 'main'; this is a major security risk!!!!
version 2.20, this name has been removed completely to
avoid conflict with the built-in Perl module import opera
tor.
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 ppaarraamm_ffeettcchh(()) method
with the name of the . This will return an array refer
ence to the named parameters, which you then can manipu
late 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
ters, 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 an array con
text, 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 mul
tivalued CGI parameters. Because a hash cannot distin
guish between scalar and array context, multivalued param
eters 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 pro
vided 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 ses
sion records:
use CGI;
$records = 5;
foreach (0..$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
ssaavvee_ppaarraammeetteerrss(()).
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!
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 asso
ciated with this importation, but it isn't much.
use CGI <list of methods>;
The listed methods will be imported into the current pack
age; you can call them directly without creating a CGI
object first. This example shows how to import the
ppaarraamm(()) and hheeaaddeerr(()) 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 ppaarraamm(()),
ppaatthh_iinnffoo(()) and the like.
:form
Import all fill-out form generating methods, such as
tteexxttffiieelldd(()).
:html2
Import all methods that generate HTML 2.0 standard
elements.
:html3
Import all methods that generate HTML 3.0 proposed
elements (such as <table>, <super> and <sub>).
: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', 'form'
and 'cgi'.
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-evolv
ing 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 the Exporter manpage syntax for spec
ifying 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 ppaarraamm(()), tteexxttffiieelldd(()), ssuubbmmiitt(()) 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";
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 disables debugging mode (pragma
-no_debug):
use CGI qw/:standard -no_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);
always have the effect of importing the compiled func
tions into the current namespace. If you want to com
pile without importing use the compile() method
instead (see below).
-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.
-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. Warn
ing: 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 pausing to
request CGI parameters from standard input or the com
mand line, then use this pragma:
use CGI qw(-no_debug :standard);
If you'd like to process the command-line parameters
but not standard input, this should work:
use CGI qw(-no_debug :standard);
restore_parameters(join('&',@ARGV));
See the section on debugging for more details.
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 condi
tion). To make life harder for the attacker, the pro
gram 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 follow
ing 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 direc
tory 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 open
ing 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;
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-
-or-
print $query->header(-type=>'image/gif',
-nph=>1,
-status=>'402 Payment required',
-expires=>'+3d',
-cookie=>$cookie,
-Cost=>'$2.00');
header() returns the Content-type: header. You can pro
vide your own MIME type if you choose, otherwise it
defaults to text/html. An optional second parameter spec
ifies 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 pass
ing 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 rela
tive 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
script. This is important to use with certain servers,
such as Microsoft Internet Explorer, which expect all
their scripts to be NPH.
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 choos
ing a URL based on the time of day or the identity of the
user.
The redirect() function redirects the browser to a differ
ent URL. If you use redirection like this, you should not
print out a header as well. As of version 2.0, we produce
both the unofficial Location: header and the official URI:
header. This should satisfy most servers and browsers.
One hint I can offer is that relative links may not work
correctly when you generate a redirection to another docu
ment 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 a 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() rou
tine creates the top of the page, along with a lot of
optional information that controls the page's appearance
and behavior.
<BODY> tag. All parameters are optional. In the named
parameter form, recognized parameters are -title, -author,
-base, -xbase 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 tar
get frame for all the links and fill-out forms on the
page. 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 refer
ence 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">
There is no support for the HTTP-EQUIV type of <META> tag.
This is because you can modify the HTTP header directly
with the hheeaaddeerr(()) method. For example, if you want to
send the Refresh: header, do it in the header() method:
print $q->header(-Refresh=>'10; URL=http://www.capricorn.com');
The -style tag is used to incorporate cascading
stylesheets into your code. See the section on CASCADING
STYLESHEETS for more information.
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> sec
tion, just pass an array reference:
Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}),
Link({-rel=>'previous',
-href=>'http://www.capricorn.com/s1.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 parame
ters 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>
larly 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'
}
]
);
</pre>
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:
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 = $query->self_url;
print "<A HREF=$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
uurrll(()) 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=>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);
uurrll(()) 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 argu
ments:
-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 -rela
tive. -path_info is provided as a synonym.
-query (-query_string)
Append the query string to the URL. This can be com
bined with -full, -absolute or -relative.
-query_string is provided as a synonym.
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 ppaarraamm(()) method will always
return the contents of the POSTed fill-out form, ignoring
the uurrll_ppaarraamm(()) method. Use it in the same way as
ppaarraamm(()). 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 com
monly, print out so that it displays in the browser win
dow.
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 awk
ward, you can import them into your namespace and dispense
with the object syntax completely (see the next section
for more details):
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 argu
ments. If you provide no arguments, you get a single tag:
print hr; # <HR>
If you provide one or more string arguments, they are con
catenated 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 syn
tax for this is an argument that 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:
img({alt=>undef}) <IMG ALT>
img({alt=>''}) <IMT 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 con
sisting of a reference to a list, the tag will be dis
tributed 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 exam
ple:
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>
"mom!". CGI.pm puts the extra space there using array
interpolation, which is controlled by the magic $" vari
able. 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. Oth
erwise 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 var
ious reasons.
ccoommmmeenntt(()) 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.
PRETTY-PRINTING HTML
By default, all the HTML produced by these functions comes
out as one long line without carriage returns or indenta
tion. This is yuck, but it does reduce the size of the
documents by 10-20%. To get pretty-printed output, please
use the CGI::Pretty manpage, 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
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 invoca
tions 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 previ
ous value, you have two choices:
(1) call the param() method to set it.
(2) use the -override (alias -force) parameter (a new fea
ture 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 auto
matic 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 pro
cess the query. The default is to process the query with
the current script.
print $query->startform(-method=>$method,
-action=>$action,
-enctype=>$encoding);
<... various form stuff ...>
print $query->endform;
-or-
print $query->startform($method,$action,$encoding);
<... various form stuff ...>
print $query->endform;
startform() 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.
Startform()'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:
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 con
taining 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 transfer
ring 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 startform() method uses the older
form of encoding by default. If you want to use the newer
form of encoding by default, you can call ssttaarrtt_mmuullttii
ppaarrtt_ffoorrmm(()) instead of ssttaarrttffoorrmm(()).
vided for use with JavaScript. The -name parameter gives
the form a name so that it can be identified and manipu
lated 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 consis
tency 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:
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 parame
ters to register JavaScript event handlers. The onChange
handler will be called whenever the user changes the con
tents 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.
-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 ssttaarrttffoorrmm(()) with an
encoding type of $CGI::MULTIPART, or by calling the new
method ssttaarrtt_mmuullttiippaarrtt_ffoorrmm(()) instead of vanilla ssttaarrtt
ffoorrmm(()).
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" behav
ior 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 = $query->param('uploaded_file');
Different browsers will return slightly different things
for the name. Some browsers return the filename only.
Others return the full path to the file, using the path
conventions of the user's machine. Regardless, the name
machine, and is unrelated to the name of the temporary
file that CGI.pm creates during upload spooling (see
below).
The filename returned is also a file handle. You can read
the contents of the file using standard Perl file reading
calls:
# Read a text file and print it out
while (<$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 com
plain 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;
}
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 informa
tion, 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!";
}
"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 (mal
formed 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.
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).
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 asso
ciative 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.
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 syn
onym "-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 asso
ciative 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 descrip
tion 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:
-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-read
able 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 asso
ciative 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 check
box group formatted with the specified number of rows
and columns. You can provide just the -columns param
eter 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 deco
rative. 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:
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=>'checked',
-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 pro
vided, 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 parame
ter. See checkbox_group() for further details.
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 oth
ers 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 ref
erence in the second argument, either using an anony
mous 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, cre
ating 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
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 deco
rative. 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 but
tons 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 dif
ferent values for each one:
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:\fIs0: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 ref
erence 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
$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 "but
ton_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 speci
fies 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 ele
ment will probably not even display.
Netscape browsers versions 1.1 and higher, and all ver
sions 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 parame
ters 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 expi
ration date is reached if the user exits the browser
and restarts it. If an expiration date isn't speci
fied, 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", "feck
less.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 speci
fied, 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 return
ing 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/com
plain.pl", but not to the script "/cgi-pri
vate/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
The interface to HTTP cookies is the ccooookkiiee(()) method:
$cookie = $query->cookie(-name=>'sessionID',
-value=>'xyzzy',
-expires=>'+1h',
-path=>'/cgi-bin/database',
-domain=>'.capricorn.org',
-secure=>1);
print $query->header(-cookie=>$cookie);
ccooookkiiee(()) 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 ref
erence. For example, you can store an entire associa
tive 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 hheeaaddeerr(())
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:
To create multiple cookies, give header() an array refer
ence:
$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;
%answers = $query->cookie(-name=>'answers');
# $query->cookie('answers') will work too!
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 indepen
dent 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 mecha
nism. 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
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 docu
ment 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->startform(-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 cre
ated.
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 docu
ment, 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 incorpo
rated 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');
print h1({-style=>'Color: red;'},'Welcome to Hell');
You may also use the new ssppaann(()) 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 ssppaann(()) 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 infor
mation.
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;
DEBUGGING
If you are running the script from the command line or in
the perl debugger, you can pass the script a list of
from standard input (you don't have to worry about trick
ing 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
or even as newline-delimited parameters 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 param
eter=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:
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 fol
lows:
AAcccceepptt(())
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.
rraaww_ccooookkiiee(())
Returns the HTTP_COOKIE variable, an HTTP extension
implemented by Netscape browsers version 1.1 and
higher, and all versions of Internet Explorer. Cook
ies 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 mod
ule.
uusseerr_aaggeenntt(())
Returns the HTTP_USER_AGENT variable. If you give
this method a single argument, it will attempt to pat
tern match on it, allowing you to do something like
$query->user_agent(netscape);
ppaatthh_iinnffoo(())
Returns additional path information from the script
URL. E.G. fetching /cgi-bin/your_script/addi
tional/stuff will result in $query->path_info()
returning "additional/stuff".
NOTE: The Microsoft Internet Information Server is
broken with respect to additional path information.
attempt to execute the additional path information as
a Perl script. If you use the ordinary file associa
tions 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.
ppaatthh_ttrraannssllaatteedd(())
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 trans
lated path as well.
rreemmoottee_hhoosstt(())
Returns either the remote host name or IP address. if
the former is unavailable.
ssccrriipptt_nnaammee(()) Return the script name as a partial URL, for
self- refering scripts.
rreeffeerreerr(())
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_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!
Returns the method used to access your script, usually
one of 'POST', 'GET' or 'HEAD'.
ccoonntteenntt_ttyyppee(())
Returns the content_type of data submitted in a POST,
generally multipart/form-data or application/x-www-
form-urlencoded
hhttttpp(())
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. Cap
italization and the use of hyphens versus underscores
are not significant.
For example, all three of these examples are equiva
lent:
$requested_language = $q->http('Accept-language');
$requested_language = $q->http('Accept_language');
$requested_language = $q->http('HTTP_ACCEPT_LANGUAGE');
hhttttppss(())
The same as http(), but operates on the HTTPS environ
ment 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 com
pletely 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() meth
ods are called.
The Microsoft Internet Information Server requires NPH
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.
There are a number of ways to put CGI.pm into NPH mode:
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 nnpphh(()) method:
Call nnpphh(()) with a non-zero parameter at any point
after using CGI.pm in your program.
CGI->nph(1)
By using -nph parameters in the hheeaaddeerr(()) and rreeddiirreecctt(())
state ments:
print $q->header(-nph=>1);
Server Push
CGI.pm provides three simple functions for producing mul
tipart documents of the type needed to implement server
push. These functions were graciously provided by Ed Jor
dan <ed@fidalgo.net>. To import these into your names
pace, 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/;
$| = 1;
print multipart_init(-boundary=>'----------------here we go!');
while (1) {
print multipart_start(-type=>'text/plain'),
"The current time is ",scalar(localtime),"\n",
multipart_end;
sleep 1;
}
This script initializes server push by calling mmuullttii
ppaarrtt_iinniitt(()). It then enters an infinite loop in which it
begins a new multipart section by calling mmuullttii
ppaarrtt_ssttaarrtt(()), prints the current local time, and ends a
multipart section with mmuullttiippaarrtt_eenndd(()). It then sleeps a
second, and begins again.
multipart_init(-boundary=>$boundary);
Initialize the multipart system. The -boundary argu
ment 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().
Users interested in server push applications should also
have a look at the CGI::Push module.
Avoiding Denial of Service Attacks
A potential problem with CGI.pm is that, by default, it
attempts to process form POSTings no matter how large they
are. A wily hacker could attack your site by sending a
CGI script a huge POST of many 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 termi
nates, 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
$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 sub
routine 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 proto
col, 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;
}
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 cre
ation 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 fea
tures 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 sys
tem 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:
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 $query->start_html("Example CGI.pm Form");
print "<H1> Example CGI.pm Form</H1>\n";
&print_prompt($query);
&do_work($query);
&print_tail;
print $query->end_html;
sub print_prompt {
my($query) = @_;
print $query->startform;
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 $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
the CGI::Carp manpage, the URI::URL manpage, the
CGI::Request manpage, the CGI::MiniSvr manpage, the
CGI::Base manpage, the CGI::Form manpage, the CGI::Push
manpage, the CGI::Fast manpage, the CGI::Pretty manpage
Man(1) output converted with
man2html