CGI(3) User Contributed Perl Documentation CGI(3)
NAME
CGI - Handle Common Gateway Interface requests and responses
SYNOPSIS
use CGI;
my $q = CGI->new;
# Process an HTTP request
@values = $q->param('form_field');
$fh = $q->upload('file_field');
$riddle = $query->cookie('riddle_name');
%answers = $query->cookie('answers');
# Prepare various HTTP responses
print $q->header();
print $q->header('application/json');
$cookie1 = $q->cookie(-name=>'riddle_name', -value=>"The Sphynx's Question");
$cookie2 = $q->cookie(-name=>'answers', -value=>\%answers);
print $q->header(
-type => 'image/gif',
-expires => '+3d',
-cookie => [$cookie1,$cookie2]
);
print $q->redirect('http://somewhere.else/in/movie/land');
DESCRIPTION
CGI.pm is a stable, complete and mature solution for processing and
preparing HTTP requests and responses. Major features including
processing form submissions, file uploads, reading and writing cookies,
query string generation and manipulation, and processing and preparing
HTTP headers. Some HTML generation utilities are included as well.
CGI.pm performs very well in in a vanilla CGI.pm environment and also
comes with built-in support for mod_perl and mod_perl2 as well as
FastCGI.
It has the benefit of having developed and refined over 10 years with
input from dozens of contributors and being deployed on thousands of
websites. CGI.pm has been included in the Perl distribution since Perl
5.4, and has become a de-facto standard.
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 = CGI->new; # create new CGI object
print $q->header, # create the HTTP header
$q->start_html('hello world'), # start the HTML
$q->h1('hello world'), # level 1 header
$q->end_html; # end the HTML
In the function-oriented style, there is one default CGI object that
you rarely deal with directly. Instead you just call functions to
retrieve CGI parameters, create HTML tags, manage cookies, and so on.
This provides you with a cleaner programming interface, but limits you
to using one CGI object at a time. The following example prints the
same page, but uses the function-oriented interface. The main
differences are that we now need to import a set of functions into our
name space (usually the "standard" functions), and we don't need to
create the CGI object.
#!/usr/local/bin/perl
use CGI qw/:standard/; # load standard CGI routines
print header, # create the HTTP header
start_html('hello world'), # start the HTML
h1('hello world'), # level 1 header
end_html; # end the HTML
The examples in this document mainly use the object-oriented style.
See HOW TO IMPORT FUNCTIONS for important information on function-
oriented programming in CGI.pm
CALLING CGI.PM ROUTINES
Most CGI.pm routines accept several arguments, sometimes as many as 20
optional ones! To simplify this interface, all routines use a named
argument calling style that looks like this:
print $q->header(-type=>'image/gif',-expires=>'+3d');
Each argument name is preceded by a dash. Neither case nor order
matters in the argument list. -type, -Type, and -TYPE are all
acceptable. In fact, only the first argument needs to begin with a
dash. If a dash is present in the first argument, CGI.pm assumes
dashes for the subsequent ones.
Several routines are commonly called with just one argument. In the
case of these routines you can provide the single argument without an
argument name. header() happens to be one of these routines. In this
case, the single argument is the document type.
print $q->header('text/html');
Other such routines are documented below.
Sometimes named arguments expect a scalar, sometimes a reference to an
array, and sometimes a reference to a hash. Often, you can pass any
type of argument and the routine will do whatever is most appropriate.
For example, the param() routine is used to set a CGI parameter to a
single or a multi-valued value. The two cases are shown below:
$q->param(-name=>'veggie',-value=>'tomato');
$q->param(-name=>'veggie',-value=>['tomato','tomahto','potato','potahto']);
A large number of routines in CGI.pm actually aren't specifically
defined in the module, but are generated automatically as needed.
These are the "HTML shortcuts," routines that generate HTML tags for
use in dynamically-generated pages. HTML tags have both attributes
(the attribute="value" pairs within the tag itself) and contents (the
part between the opening and closing pairs.) To distinguish between
attributes and contents, CGI.pm uses the convention of passing HTML
attributes as a hash reference as the first argument, and the contents,
if any, as any subsequent arguments. It works out like this:
Code Generated HTML
---- --------------
h1() <h1>
h1('some','contents'); <h1>some contents</h1>
h1({-align=>left}); <h1 align="LEFT">
h1({-align=>left},'contents'); <h1 align="LEFT">contents</h1>
HTML tags are described in more detail later.
Many newcomers to CGI.pm are puzzled by the difference between the
calling conventions for the HTML shortcuts, which require curly braces
around the HTML tag attributes, and the calling conventions for other
routines, which manage to generate attributes without the curly
brackets. Don't be confused. As a convenience the curly braces are
optional in all but the HTML shortcuts. If you like, you can use curly
braces when calling any routine that takes named arguments. For
example:
print $q->header( {-type=>'image/gif',-expires=>'+3d'} );
If you use the -w switch, you will be warned that some CGI.pm argument
names conflict with built-in Perl functions. The most frequent of
these is the -values argument, used to create multi-valued menus, radio
button clusters and the like. To get around this warning, you have
several choices:
1. Use another name for the argument, if one is available. For
example, -value is an alias for -values.
2. Change the capitalization, e.g. -Values
3. Put quotes around the argument name, e.g. '-values'
Many routines will do something useful with a named argument that it
doesn't recognize. For example, you can produce non-standard HTTP
header fields by providing them as named arguments:
print $q->header(-type => 'text/html',
-cost => 'Three smackers',
-annoyance_level => 'high',
-complaints_to => 'bit bucket');
This will produce the following nonstandard HTTP header:
HTTP/1.0 200 OK
Cost: Three smackers
Annoyance-level: high
Complaints-to: bit bucket
Content-type: text/html
Notice the way that underscores are translated automatically into
hyphens. HTML-generating routines perform a different type of
translation.
This feature allows you to keep up with the rapidly changing HTTP and
HTML "standards".
CREATING A NEW QUERY OBJECT (OBJECT-ORIENTED STYLE):
$query = CGI->new;
This will parse the input (from POST, GET and DELETE methods) and store
it into a perl5 object called $query.
Any filehandles from file uploads will have their position reset to the
beginning of the file.
CREATING A NEW QUERY OBJECT FROM AN INPUT FILE
$query = CGI->new(INPUTFILE);
If you provide a file handle to the new() method, it will read
parameters from the file (or STDIN, or whatever). The file can be in
any of the forms describing below under debugging (i.e. a series of
newline delimited TAG=VALUE pairs will work). Conveniently, this type
of file is created by the save() method (see below). Multiple records
can be saved and restored.
Perl purists will be pleased to know that this syntax accepts
references to file handles, or even references to filehandle globs,
which is the "official" way to pass a filehandle:
$query = CGI->new(\*STDIN);
You can also initialize the CGI object with a FileHandle or IO::File
object.
If you are using the function-oriented interface and want to initialize
CGI state from a file handle, the way to do this is with
restore_parameters(). This will (re)initialize the default CGI object
from the indicated file handle.
open (IN,"test.in") || die;
restore_parameters(IN);
close IN;
You can also initialize the query object from a hash reference:
$query = CGI->new( {'dinosaur'=>'barney',
'song'=>'I love you',
'friends'=>[qw/Jessica George Nancy/]}
);
or from a properly formatted, URL-escaped query string:
$query = CGI->new('dinosaur=barney&color=purple');
or from a previously existing CGI object (currently this clones the
parameter list, but none of the other object-specific fields, such as
autoescaping):
$old_query = CGI->new;
$new_query = CGI->new($old_query);
To create an empty query, initialize it from an empty string or hash:
$empty_query = CGI->new("");
-or-
$empty_query = CGI->new({});
FETCHING A LIST OF KEYWORDS FROM THE QUERY:
@keywords = $query->keywords
If the script was invoked as the result of an <ISINDEX> search, the
parsed keywords can be obtained as an array using the keywords()
method.
FETCHING THE NAMES OF ALL THE PARAMETERS PASSED TO YOUR SCRIPT:
@names = $query->param
If the script was invoked with a parameter list (e.g.
"name1=value1&name2=value2&name3=value3"), the param() method will
return the parameter names as a list. If the script was invoked as an
<ISINDEX> script and contains a string without ampersands (e.g.
"value1+value2+value3") , there will be a single parameter named
"keywords" containing the "+"-delimited keywords.
NOTE: As of version 1.5, the array of parameter names returned will be
in the same order as they were submitted by the browser. Usually this
order is the same as the order in which the parameters are defined in
the form (however, this isn't part of the spec, and so isn't
guaranteed).
FETCHING THE VALUE OR VALUES OF A SINGLE NAMED PARAMETER:
@values = $query->param('foo');
-or-
$value = $query->param('foo');
Pass the param() method a single argument to fetch the value of the
named parameter. If the parameter is multivalued (e.g. from multiple
selections in a scrolling list), you can ask to receive an array.
Otherwise the method will return a single value.
If a value is not given in the query string, as in the queries
"name1=&name2=", it will be returned as an empty string.
If the parameter does not exist at all, then param() will return undef
in a scalar context, and the empty list in a list context.
SETTING THE VALUE(S) OF A NAMED PARAMETER:
$query->param('foo','an','array','of','values');
This sets the value for the named parameter 'foo' to an array of
values. This is one way to change the value of a field AFTER the
script has been invoked once before. (Another way is with the
-override parameter accepted by all methods that generate form
elements.)
param() also recognizes a named parameter style of calling described in
more detail later:
$query->param(-name=>'foo',-values=>['an','array','of','values']);
-or-
$query->param(-name=>'foo',-value=>'the value');
APPENDING ADDITIONAL VALUES TO A NAMED PARAMETER:
$query->append(-name=>'foo',-values=>['yet','more','values']);
This adds a value or list of values to the named parameter. The values
are appended to the end of the parameter if it already exists.
Otherwise the parameter is created. Note that this method only
recognizes the named argument calling syntax.
IMPORTING ALL PARAMETERS INTO A NAMESPACE:
$query->import_names('R');
This creates a series of variables in the 'R' namespace. For example,
$R::foo, @R:foo. For keyword lists, a variable @R::keywords will
appear. If no namespace is given, this method will assume 'Q'.
WARNING: don't import anything into 'main'; this is a major security
risk!!!!
NOTE 1: Variable names are transformed as necessary into legal Perl
variable names. All non-legal characters are transformed into
underscores. If you need to keep the original names, you should use
the param() method instead to access CGI variables by name.
NOTE 2: In older versions, this method was called import(). As of
version 2.20, this name has been removed completely to avoid conflict
with the built-in Perl module import operator.
DELETING A PARAMETER COMPLETELY:
$query->delete('foo','bar','baz');
This completely clears a list of parameters. It sometimes useful for
resetting parameters that you don't want passed down between script
invocations.
If you are using the function call interface, use "Delete()" instead to
avoid conflicts with Perl's built-in delete operator.
DELETING ALL PARAMETERS:
$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.
HANDLING NON-URLENCODED ARGUMENTS
If POSTed data is not of type application/x-www-form-urlencoded or
multipart/form-data, then the POSTed data will not be processed, but
instead be returned as-is in a parameter named POSTDATA. To retrieve
it, use code like this:
my $data = $query->param('POSTDATA');
Likewise if PUTed data can be retrieved with code like this:
my $data = $query->param('PUTDATA');
(If you don't know what the preceding means, don't worry about it. It
only affects people trying to use CGI for XML processing and other
specialized tasks.)
DIRECT ACCESS TO THE PARAMETER LIST:
$q->param_fetch('address')->[1] = '1313 Mockingbird Lane';
unshift @{$q->param_fetch(-name=>'address')},'George Munster';
If you need access to the parameter list in a way that isn't covered by
the methods given in the previous sections, you can obtain a direct
reference to it by calling the param_fetch() method with the name of
the parameter. This will return an array reference to the named
parameter, which you then can manipulate in any way you like.
You can also use a named argument style using the -name argument.
FETCHING THE PARAMETER LIST AS A HASH:
$params = $q->Vars;
print $params->{'address'};
@foo = split("\0",$params->{'foo'});
%params = $q->Vars;
use CGI ':cgi-lib';
$params = Vars;
Many people want to fetch the entire parameter list as a hash in which
the keys are the names of the CGI parameters, and the values are the
parameters' values. The Vars() method does this. Called in a scalar
context, it returns the parameter list as a tied hash reference.
Changing a key changes the value of the parameter in the underlying CGI
parameter list. Called in a list context, it returns the parameter
list as an ordinary hash. This allows you to read the contents of the
parameter list, but not to change it.
When using this, the thing you must watch out for are multivalued CGI
parameters. Because a hash cannot distinguish between scalar and list
context, multivalued parameters will be returned as a packed string,
separated by the "\0" (null) character. You must split this packed
string in order to get at the individual values. This is the
convention introduced long ago by Steve Brenner in his cgi-lib.pl
module for Perl version 4.
If you wish to use Vars() as a function, import the :cgi-lib set of
function calls (also see the section on CGI-LIB compatibility).
SAVING THE STATE OF THE SCRIPT TO A FILE:
$query->save(\*FILEHANDLE)
This will write the current state of the form to the provided
filehandle. You can read it back in by providing a filehandle to the
new() method. Note that the filehandle can be a file, a pipe, or
whatever!
The format of the saved file is:
NAME1=VALUE1
NAME1=VALUE1'
NAME2=VALUE2
NAME3=VALUE3
=
Both name and value are URL escaped. Multi-valued CGI parameters are
represented as repeated names. A session record is delimited by a
single = symbol. You can write out multiple records and read them back
in with several calls to new. You can do this across several sessions
by opening the file in append mode, allowing you to create primitive
guest books, or to keep a history of users' queries. Here's a short
example of creating multiple session records:
use CGI;
open (OUT,'>>','test.out') || die;
$records = 5;
for (0..$records) {
my $q = CGI->new;
$q->param(-name=>'counter',-value=>$_);
$q->save(\*OUT);
}
close OUT;
# reopen for reading
open (IN,'<','test.out') || die;
while (!eof(IN)) {
my $q = CGI->new(\*IN);
print $q->param('counter'),"\n";
}
The file format used for save/restore is identical to that used by the
Whitehead Genome Center's data exchange format "Boulderio", and can be
manipulated and even databased using Boulderio utilities. See
http://stein.cshl.org/boulder/
for further details.
If you wish to use this method from the function-oriented (non-OO)
interface, the exported name for this method is save_parameters().
RETRIEVING CGI ERRORS
Errors can occur while processing user input, particularly when
processing uploaded files. When these errors occur, CGI will stop
processing and return an empty parameter list. You can test for the
existence and nature of errors using the cgi_error() function. The
error messages are formatted as HTTP status codes. You can either
incorporate the error text into an HTML page, or use it as the value of
the HTTP status:
my $error = $q->cgi_error;
if ($error) {
print $q->header(-status=>$error),
$q->start_html('Problems'),
$q->h2('Request not processed'),
$q->strong($error);
exit 0;
}
When using the function-oriented interface (see the next section),
errors may only occur the first time you call param(). Be ready for
this!
USING THE FUNCTION-ORIENTED INTERFACE
To use the function-oriented interface, you must specify which CGI.pm
routines or sets of routines to import into your script's namespace.
There is a small overhead associated with this importation, but it
isn't much.
use CGI <list of methods>;
The listed methods will be imported into the current package; you can
call them directly without creating a CGI object first. This example
shows how to import the param() and header() methods, and then use them
directly:
use CGI 'param','header';
print header('text/plain');
$zipcode = param('zipcode');
More frequently, you'll import common sets of functions by referring to
the groups by name. All function sets are preceded with a ":"
character as in ":html3" (for tags defined in the HTML 3 standard).
Here is a list of the function sets you can import:
:cgi
Import all CGI-handling methods, such as param(), path_info() and
the like.
:form
Import all fill-out form generating methods, such as textfield().
:html2
Import all methods that generate HTML 2.0 standard elements.
:html3
Import all methods that generate HTML 3.0 elements (such as
<table>, <super> and <sub>).
:html4
Import all methods that generate HTML 4 elements (such as <abbrev>,
<acronym> and <thead>).
:netscape
Import the <blink>, <fontsize> and <center> tags.
:html
Import all HTML-generating shortcuts (i.e. 'html2', 'html3',
'html4' and 'netscape')
:standard
Import "standard" features, 'html2', 'html3', 'html4', 'form' and
'cgi'.
:all
Import all the available methods. For the full list, see the
CGI.pm code, where the variable %EXPORT_TAGS is defined.
If you import a function name that is not part of CGI.pm, the module
will treat it as a new HTML tag and generate the appropriate
subroutine. You can then use it like any other HTML tag. This is to
provide for the rapidly-evolving HTML "standard." For example, say
Microsoft comes out with a new tag called <gradient> (which causes the
user's desktop to be flooded with a rotating gradient fill until his
machine reboots). You don't need to wait for a new version of CGI.pm
to start using it immediately:
use CGI qw/:standard :html3 gradient/;
print gradient({-start=>'red',-end=>'blue'});
Note that in the interests of execution speed CGI.pm does not use the
standard Exporter syntax for specifying load symbols. This may change
in the future.
If you import any of the state-maintaining CGI or form-generating
methods, a default CGI object will be created and initialized
automatically the first time you use any of the methods that require
one to be present. This includes param(), textfield(), submit() and
the like. (If you need direct access to the CGI object, you can find
it in the global variable $CGI::Q). By importing CGI.pm methods, you
can create visually elegant scripts:
use CGI qw/:standard/;
print
header,
start_html('Simple Script'),
h1('Simple Script'),
start_form,
"What's your name? ",textfield('name'),p,
"What's the combination?",
checkbox_group(-name=>'words',
-values=>['eenie','meenie','minie','moe'],
-defaults=>['eenie','moe']),p,
"What's your favorite color?",
popup_menu(-name=>'color',
-values=>['red','green','blue','chartreuse']),p,
submit,
end_form,
hr,"\n";
if (param) {
print
"Your name is ",em(param('name')),p,
"The keywords are: ",em(join(", ",param('words'))),p,
"Your favorite color is ",em(param('color')),".\n";
}
print end_html;
PRAGMAS
In addition to the function sets, there are a number of pragmas that
you can import. Pragmas, which are always preceded by a hyphen, change
the way that CGI.pm functions in various ways. Pragmas, function sets,
and individual functions can all be imported in the same use() line.
For example, the following use statement imports the standard set of
functions and enables debugging mode (pragma -debug):
use CGI qw/:standard -debug/;
The current list of pragmas is as follows:
-any
When you use CGI -any, then any method that the query object
doesn't recognize will be interpreted as a new HTML tag. This
allows you to support the next ad hoc HTML extension. This lets
you go wild with new and unsupported tags:
use CGI qw(-any);
$q=CGI->new;
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 Malcolm Beattie's Perl
compiler. Use it in conjunction with the methods or method
families you plan to use.
use CGI qw(-compile :standard :html3);
or even
use CGI qw(-compile :all);
Note that using the -compile pragma in this way will always have
the effect of importing the compiled functions into the current
namespace. If you want to compile without importing use the
compile() method instead:
use CGI();
CGI->compile();
This is particularly useful in a mod_perl environment, in which you
might want to precompile all CGI routines in a startup script, and
then import the functions individually in each mod_perl script.
-nosticky
By default the CGI module implements a state-preserving behavior
called "sticky" fields. The way this works is that if you are
regenerating a form, the methods that generate the form field
values will interrogate param() to see if similarly-named
parameters are present in the query string. If they find a like-
named parameter, they will use it to set their default values.
Sometimes this isn't what you want. The -nosticky pragma prevents
this behavior. You can also selectively change the sticky behavior
in each element that you generate.
-tabindex
Automatically add tab index attributes to each form field. With
this option turned off, you can still add tab indexes manually by
passing a -tabindex option to each field-generating method.
-no_undef_params
This keeps CGI.pm from including undef params in the parameter
list.
-no_xhtml
By default, CGI.pm versions 2.69 and higher emit XHTML
(http://www.w3.org/TR/xhtml1/). The -no_xhtml pragma disables this
feature. Thanks to Michalis Kabrianis <kabrianis AT hellug.gr> for
this feature.
If start_html()'s -dtd parameter specifies an HTML 2.0, 3.2, 4.0 or
4.01 DTD, XHTML will automatically be disabled without needing to
use this pragma.
-utf8
This makes CGI.pm treat all parameters as UTF-8 strings. Use this
with care, as it will interfere with the processing of binary
uploads. It is better to manually select which fields are expected
to return utf-8 strings and convert them using code like this:
use Encode;
my $arg = decode utf8=>param('foo');
-nph
This makes CGI.pm produce a header appropriate for an NPH (no
parsed header) script. You may need to do other things as well to
tell the server that the script is NPH. See the discussion of NPH
scripts below.
-newstyle_urls
Separate the name=value pairs in CGI parameter query strings with
semicolons rather than ampersands. For example:
?name=fred;age=24;favorite_color=3
Semicolon-delimited query strings are always accepted, and will be
emitted by self_url() and query_string(). newstyle_urls became the
default in version 2.64.
-oldstyle_urls
Separate the name=value pairs in CGI parameter query strings with
ampersands rather than semicolons. This is no longer the default.
-autoload
This overrides the autoloader so that any function in your program
that is not recognized is referred to CGI.pm for possible
evaluation. This allows you to use all the CGI.pm functions
without adding them to your symbol table, which is of concern for
mod_perl users who are worried about memory consumption. Warning:
when -autoload is in effect, you cannot use "poetry mode"
(functions without the parenthesis). Use hr() rather than hr, or
add something like use subs qw/hr p header/ to the top of your
script.
-no_debug
This turns off the command-line processing features. If you want
to run a CGI.pm script from the command line to produce HTML, and
you don't want it to read CGI parameters from the command line or
STDIN, then use this pragma:
use CGI qw(-no_debug :standard);
-debug
This turns on full debugging. In addition to reading CGI arguments
from the command-line processing, CGI.pm will pause and try to read
arguments from STDIN, producing the message "(offline mode: enter
name=value pairs on standard input)" features.
See the section on debugging for more details.
-private_tempfiles
CGI.pm can process uploaded file. Ordinarily it spools the uploaded
file to a temporary directory, then deletes the file when done.
However, this opens the risk of eavesdropping as described in the
file upload section. Another CGI script author could peek at this
data during the upload, even if it is confidential information. On
Unix systems, the -private_tempfiles pragma will cause the
temporary file to be unlinked as soon as it is opened and before
any data is written into it, reducing, but not eliminating the risk
of eavesdropping (there is still a potential race condition). To
make life harder for the attacker, the program chooses tempfile
names by calculating a 32 bit checksum of the incoming HTTP
headers.
To ensure that the temporary file cannot be read by other CGI
scripts, use suEXEC or a CGI wrapper program to run your script.
The temporary file is created with mode 0600 (neither world nor
group readable).
The temporary directory is selected using the following algorithm:
1. if $CGITempFile::TMPDIRECTORY is already set, use that
2. if the environment variable TMPDIR exists, use the location
indicated.
3. Otherwise try the locations /usr/tmp, /var/tmp, C:\temp,
/tmp, /temp, ::Temporary Items, and \WWW_ROOT.
Each of these locations is checked that it is a directory and is
writable. If not, the algorithm tries the next choice.
SPECIAL FORMS FOR IMPORTING HTML-TAG FUNCTIONS
Many of the methods generate HTML tags. As described below, tag
functions automatically generate both the opening and closing tags.
For example:
print h1('Level 1 Header');
produces
<h1>Level 1 Header</h1>
There will be some times when you want to produce the start and end
tags yourself. In this case, you can use the form start_tag_name and
end_tag_name, as in:
print start_h1,'Level 1 Header',end_h1;
With a few exceptions (described below), start_tag_name and
end_tag_name functions are not generated automatically when you use
CGI. However, you can specify the tags you want to generate start/end
functions for by putting an asterisk in front of their name, or,
alternatively, requesting either "start_tag_name" or "end_tag_name" in
the import list.
Example:
use CGI qw/:standard *table start_ul/;
In this example, the following functions are generated in addition to
the standard ones:
1. start_table() (generates a <table> tag)
2. end_table() (generates a </table> tag)
3. start_ul() (generates a <ul> tag)
4. end_ul() (generates a </ul> tag)
GENERATING DYNAMIC DOCUMENTS
Most of CGI.pm's functions deal with creating documents on the fly.
Generally you will produce the HTTP header first, followed by the
document itself. CGI.pm provides functions for generating HTTP headers
of various types as well as for generating HTML. For creating GIF
images, see the GD.pm module.
Each of these functions produces a fragment of HTML or HTTP which you
can print out directly so that it displays in the browser window,
append to a string, or save to a file for later use.
CREATING A STANDARD HTTP HEADER:
Normally the first thing you will do in any CGI script is print out an
HTTP header. This tells the browser what type of document to expect,
and gives other optional information, such as the language, expiration
date, and whether to cache the document. The header can also be
manipulated for special purposes, such as server push and pay per view
pages.
print header;
-or-
print header('image/gif');
-or-
print header('text/html','204 No response');
-or-
print header(-type=>'image/gif',
-nph=>1,
-status=>'402 Payment required',
-expires=>'+3d',
-cookie=>$cookie,
-charset=>'utf-7',
-attachment=>'foo.gif',
-Cost=>'$2.00');
header() returns the Content-type: header. You can provide your own
MIME type if you choose, otherwise it defaults to text/html. An
optional second parameter specifies the status code and a human-
readable message. For example, you can specify 204, "No response" to
create a script that tells the browser to do nothing at all. Note that
RFC 2616 expects the human-readable phase to be there as well as the
numeric status code.
The last example shows the named argument style for passing arguments
to the CGI methods using named parameters. Recognized parameters are
-type, -status, -expires, and -cookie. Any other named parameters will
be stripped of their initial hyphens and turned into header fields,
allowing you to specify any HTTP header you desire. Internal
underscores will be turned into hyphens:
print header(-Content_length=>3002);
Most browsers will not cache the output from CGI scripts. Every time
the browser reloads the page, the script is invoked anew. You can
change this behavior with the -expires parameter. When you specify an
absolute or relative expiration interval with this parameter, some
browsers and proxy servers will cache the script's output until the
indicated expiration date. The following forms are all valid for the
-expires field:
+30s 30 seconds from now
+10m ten minutes from now
+1h one hour from now
-1d yesterday (i.e. "ASAP!")
now immediately
+3M in three months
+10y in ten years time
Thursday, 25-Apr-1999 00:40:33 GMT at the indicated time & date
The -cookie parameter generates a header that tells the browser to
provide a "magic cookie" during all subsequent transactions with your
script. Some cookies have a special format that includes interesting
attributes such as expiration time. Use the cookie() method to create
and retrieve session cookies.
The -nph parameter, if set to a true value, will issue the correct
headers to work with a NPH (no-parse-header) script. This is important
to use with certain servers that expect all their scripts to be NPH.
The -charset parameter can be used to control the character set sent to
the browser. If not provided, defaults to ISO-8859-1. As a side
effect, this sets the charset() method as well.
The -attachment parameter can be used to turn the page into an
attachment. Instead of displaying the page, some browsers will prompt
the user to save it to disk. The value of the argument is the
suggested name for the saved file. In order for this to work, you may
have to set the -type to "application/octet-stream".
The -p3p parameter will add a P3P tag to the outgoing header. The
parameter can be an arrayref or a space-delimited string of P3P tags.
For example:
print header(-p3p=>[qw(CAO DSP LAW CURa)]);
print header(-p3p=>'CAO DSP LAW CURa');
In either case, the outgoing header will be formatted as:
P3P: policyref="/w3c/p3p.xml" cp="CAO DSP LAW CURa"
CGI.pm will accept valid multi-line headers when each line is separated
with a CRLF value ("\r\n" on most platforms) followed by at least one
space. For example:
print header( -ingredients => "ham\r\n\seggs\r\n\sbacon" );
Invalid multi-line header input will trigger in an exception. When
multi-line headers are received, CGI.pm will always output them back as
a single line, according to the folding rules of RFC 2616: the newlines
will be removed, while the white space remains.
GENERATING A REDIRECTION HEADER
print $q->redirect('http://somewhere.else/in/movie/land');
Sometimes you don't want to produce a document yourself, but simply
redirect the browser elsewhere, perhaps choosing a URL based on the
time of day or the identity of the user.
The redirect() method redirects the browser to a different URL. If you
use redirection like this, you should not print out a header as well.
You should always use full URLs (including the http: or ftp: part) in
redirection requests. Relative URLs will not work correctly.
You can also use named arguments:
print $q->redirect(
-uri=>'http://somewhere.else/in/movie/land',
-nph=>1,
-status=>'301 Moved Permanently');
All names arguments recognized by header() are also recognized by
redirect(). However, most HTTP headers, including those generated by
-cookie and -target, are ignored by the browser.
The -nph parameter, if set to a true value, will issue the correct
headers to work with a NPH (no-parse-header) script. This is important
to use with certain servers, such as Microsoft IIS, which expect all
their scripts to be NPH.
The -status parameter will set the status of the redirect. HTTP
defines three different possible redirection status codes:
301 Moved Permanently
302 Found
303 See Other
The default if not specified is 302, which means "moved temporarily."
You may change the status to another status code if you wish. Be
advised that changing the status to anything other than 301, 302 or 303
will probably break redirection.
Note that the human-readable phrase is also expected to be present to
conform with RFC 2616, section 6.1.
CREATING THE HTML DOCUMENT HEADER
print start_html(-title=>'Secrets of the Pyramids',
-author=>'fred AT capricorn.org',
-base=>'true',
-target=>'_blank',
-meta=>{'keywords'=>'pharaoh secret mummy',
'copyright'=>'copyright 1996 King Tut'},
-style=>{'src'=>'/styles/style1.css'},
-BGCOLOR=>'blue');
The start_html() routine creates the top of the page, along with a lot
of optional information that controls the page's appearance and
behavior.
This method returns a canned HTML header and the opening <body> tag.
All parameters are optional. In the named parameter form, recognized
parameters are -title, -author, -base, -xbase, -dtd, -lang and -target
(see below for the explanation). Any additional parameters you
provide, such as the unofficial BGCOLOR attribute, are added to the
<body> tag. Additional parameters must be proceeded by a hyphen.
The argument -xbase allows you to provide an HREF for the <base> tag
different from the current location, as in
-xbase=>"http://home.mcom.com/"
All relative links will be interpreted relative to this tag.
The argument -target allows you to provide a default target frame for
all the links and fill-out forms on the page. This is a non-standard
HTTP feature which only works with some browsers!
-target=>"answer_window"
All relative links will be interpreted relative to this tag. You add
arbitrary meta information to the header with the -meta argument. This
argument expects a reference to a hash containing name/value pairs of
meta information. These will be turned into a series of header <meta>
tags that look something like this:
<meta name="keywords" content="pharaoh secret mummy">
<meta name="description" content="copyright 1996 King Tut">
To create an HTTP-EQUIV type of <meta> tag, use -head, described below.
The -style argument is used to incorporate cascading stylesheets into
your code. See the section on CASCADING STYLESHEETS for more
information.
The -lang argument is used to incorporate a language attribute into the
<html> tag. For example:
print $q->start_html(-lang=>'fr-CA');
The default if not specified is "en-US" for US English, unless the -dtd
parameter specifies an HTML 2.0 or 3.2 DTD, in which case the lang
attribute is left off. You can force the lang attribute to left off in
other cases by passing an empty string (-lang=>'').
The -encoding argument can be used to specify the character set for
XHTML. It defaults to iso-8859-1 if not specified.
The -dtd argument can be used to specify a public DTD identifier
string. For example:
-dtd => '-//W3C//DTD HTML 4.01 Transitional//EN')
Alternatively, it can take public and system DTD identifiers as an
array:
dtd => [ '-//W3C//DTD HTML 4.01 Transitional//EN', 'http://www.w3.org/TR/html4/loose.dtd' ]
For the public DTD identifier to be considered, it must be valid.
Otherwise it will be replaced by the default DTD. If the public DTD
contains 'XHTML', CGI.pm will emit XML.
The -declare_xml argument, when used in conjunction with XHTML, will
put a <?xml> declaration at the top of the HTML header. The sole
purpose of this declaration is to declare the character set encoding.
In the absence of -declare_xml, the output HTML will contain a <meta>
tag that specifies the encoding, allowing the HTML to pass most
validators. The default for -declare_xml is false.
You can place other arbitrary HTML elements to the <head> section with
the -head tag. For example, to place a <link> element in the head
section, use this:
print start_html(-head=>Link({-rel=>'shortcut icon',
-href=>'favicon.ico'}));
To incorporate multiple HTML elements into the <head> section, just
pass an array reference:
print start_html(-head=>[
Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}),
Link({-rel=>'previous',
-href=>'http://www.capricorn.com/s1.html'})
]
);
And here's how to create an HTTP-EQUIV <meta> tag:
print start_html(-head=>meta({-http_equiv => 'Content-Type',
-content => 'text/html'}))
JAVASCRIPTING: The -script, -noScript, -onLoad, -onMouseOver,
-onMouseOut and -onUnload parameters are used to add JavaScript calls
to your pages. -script should point to a block of text containing
JavaScript function definitions. This block will be placed within a
<script> block inside the HTML (not HTTP) header. The block is placed
in the header in order to give your page a fighting chance of having
all its JavaScript functions in place even if the user presses the stop
button before the page has loaded completely. CGI.pm attempts to
format the script in such a way that JavaScript-naive browsers will not
choke on the code: unfortunately there are some browsers, such as
Chimera for Unix, that get confused by it nevertheless.
The -onLoad and -onUnload parameters point to fragments of JavaScript
code to execute when the page is respectively opened and closed by the
browser. Usually these parameters are calls to functions defined in
the -script field:
$query = CGI->new;
print header;
$JSCRIPT=<<END;
// Ask a silly question
function riddle_me_this() {
var r = prompt("What walks on four legs in the morning, " +
"two legs in the afternoon, " +
"and three legs in the evening?");
response(r);
}
// Get a silly answer
function response(answer) {
if (answer == "man")
alert("Right you are!");
else
alert("Wrong! Guess again.");
}
END
print start_html(-title=>'The Riddle of the Sphinx',
-script=>$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).
The <script> tag, has several attributes including "type", "charset"
and "src". "src" allows you to keep JavaScript code in an external
file. To use these attributes pass a HASH reference in the -script
parameter containing one or more of -type, -src, or -code:
print $q->start_html(-title=>'The Riddle of the Sphinx',
-script=>{-type=>'JAVASCRIPT',
-src=>'/javascript/sphinx.js'}
);
print $q->(-title=>'The Riddle of the Sphinx',
-script=>{-type=>'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=>[
{ -type => 'text/javascript',
-src => '/javascript/utilities10.js'
},
{ -type => 'text/javascript',
-src => '/javascript/utilities11.js'
},
{ -type => 'text/jscript',
-src => '/javascript/utilities12.js'
},
{ -type => 'text/ecmascript',
-src => '/javascript/utilities219.js'
}
]
);
The option "-language" is a synonym for -type, and is supported for
backwards compatibility.
The old-style positional parameters are as follows:
Parameters:
1. The title
2. The author's e-mail address (will create a <link rev="MADE"> tag if
present
3. A 'true' flag if you want to include a <base> tag in the header.
This helps resolve relative addresses to absolute ones when the
document is moved, but makes the document hierarchy non-portable.
Use with care!
4, 5, 6...
Any other parameters you want to include in the <body> tag. This
is a good place to put HTML extensions, such as colors and
wallpaper patterns.
ENDING THE HTML DOCUMENT:
print $q->end_html;
This ends an HTML document by printing the </body></html> tags.
CREATING A SELF-REFERENCING URL THAT PRESERVES STATE INFORMATION:
$myself = $q->self_url;
print q(<a href="$myself">I'm talking to myself.</a>);
self_url() will return a URL, that, when selected, will reinvoke this
script with all its state information intact. This is most useful when
you want to jump around within the document using internal anchors but
you don't want to disrupt the current contents of the form(s).
Something like this will do the trick.
$myself = $q->self_url;
print "<a href=\"$myself#table1\">See table 1</a>";
print "<a href=\"$myself#table2\">See table 2</a>";
print "<a href=\"$myself#yourself\">See for yourself</a>";
If you want more control over what's returned, using the url() method
instead.
You can also retrieve the unprocessed query string with query_string():
$the_string = $q->query_string();
The behavior of calling query_string is currently undefined when the
HTTP method is something other than GET.
OBTAINING THE SCRIPT'S URL
$full_url = url();
$full_url = url(-full=>1); #alternative syntax
$relative_url = url(-relative=>1);
$absolute_url = url(-absolute=>1);
$url_with_path = url(-path_info=>1);
$url_with_path_and_query = url(-path_info=>1,-query=>1);
$netloc = url(-base => 1);
url() returns the script's URL in a variety of formats. Called without
any arguments, it returns the full form of the URL, including host name
and port number
http://your.host.com/path/to/script.cgi
You can modify this format with the following named arguments:
-absolute
If true, produce an absolute URL, e.g.
/path/to/script.cgi
-relative
Produce a relative URL. This is useful if you want to reinvoke
your script with different parameters. For example:
script.cgi
-full
Produce the full URL, exactly as if called without any arguments.
This overrides the -relative and -absolute arguments.
-path (-path_info)
Append the additional path information to the URL. This can be
combined with -full, -absolute or -relative. -path_info is
provided as a synonym.
-query (-query_string)
Append the query string to the URL. This can be combined with
-full, -absolute or -relative. -query_string is provided as a
synonym.
-base
Generate just the protocol and net location, as in
http://www.foo.com:8000
-rewrite
If Apache's mod_rewrite is turned on, then the script name and path
info probably won't match the request that the user sent. Set
-rewrite=>1 (default) to return URLs that match what the user sent
(the original request URI). Set -rewrite=>0 to return URLs that
match the URL after mod_rewrite's rules have run.
MIXING POST AND URL PARAMETERS
$color = url_param('color');
It is possible for a script to receive CGI parameters in the URL as
well as in the fill-out form by creating a form that POSTs to a URL
containing a query string (a "?" mark followed by arguments). The
param() method will always return the contents of the POSTed fill-out
form, ignoring the URL's query string. To retrieve URL parameters,
call the url_param() method. Use it in the same way as param(). The
main difference is that it allows you to read the parameters, but not
set them.
Under no circumstances will the contents of the URL query string
interfere with similarly-named CGI parameters in POSTed forms. If you
try to mix a URL query string with a form submitted with the GET
method, the results will not be what you expect.
CREATING STANDARD HTML ELEMENTS:
CGI.pm defines general HTML shortcut methods for many HTML tags. HTML
shortcuts are named after a single HTML element and return a fragment
of HTML text. Example:
print $q->blockquote(
"Many years ago on the island of",
$q->a({href=>"http://crete.org/"},"Crete"),
"there lived a Minotaur named",
$q->strong("Fred."),
),
$q->hr;
This results in the following HTML code (extra newlines have been added
for readability):
<blockquote>
Many years ago on the island of
<a href="http://crete.org/">Crete</a> there lived
a minotaur named <strong>Fred.</strong>
</blockquote>
<hr>
If you find the syntax for calling the HTML shortcuts awkward, you can
import them into your namespace and dispense with the object syntax
completely (see the next section for more details):
use CGI ':standard';
print blockquote(
"Many years ago on the island of",
a({href=>"http://crete.org/"},"Crete"),
"there lived a minotaur named",
strong("Fred."),
),
hr;
PROVIDING ARGUMENTS TO HTML SHORTCUTS
The HTML methods will accept zero, one or multiple arguments. If you
provide no arguments, you get a single tag:
print hr; # <hr>
If you provide one or more string arguments, they are concatenated
together with spaces and placed between opening and closing tags:
print h1("Chapter","1"); # <h1>Chapter 1</h1>"
If the first argument is a hash reference, then the keys and values of
the hash become the HTML tag's attributes:
print a({-href=>'fred.html',-target=>'_new'},
"Open a new frame");
<a href="fred.html",target="_new">Open a new frame</a>
You may dispense with the dashes in front of the attribute names if you
prefer:
print img {src=>'fred.gif',align=>'LEFT'};
<img align="LEFT" src="fred.gif">
Sometimes an HTML tag attribute has no argument. For example, ordered
lists can be marked as COMPACT. The syntax for this is an argument
that that points to an undef string:
print ol({compact=>undef},li('one'),li('two'),li('three'));
Prior to CGI.pm version 2.41, providing an empty ('') string as an
attribute argument was the same as providing undef. However, this has
changed in order to accommodate those who want to create tags of the
form <img alt="">. The difference is shown in these two pieces of
code:
CODE RESULT
img({alt=>undef}) <img alt>
img({alt=>''}) <img alt="">
THE DISTRIBUTIVE PROPERTY OF HTML SHORTCUTS
One of the cool features of the HTML shortcuts is that they are
distributive. If you give them an argument consisting of a reference
to a list, the tag will be distributed across each element of the list.
For example, here's one way to make an ordered list:
print ul(
li({-type=>'disc'},['Sneezy','Doc','Sleepy','Happy'])
);
This example will result in HTML output that looks like this:
<ul>
<li type="disc">Sneezy</li>
<li type="disc">Doc</li>
<li type="disc">Sleepy</li>
<li type="disc">Happy</li>
</ul>
This is extremely useful for creating tables. For example:
print table({-border=>undef},
caption('When Should You Eat Your Vegetables?'),
Tr({-align=>'CENTER',-valign=>'TOP'},
[
th(['Vegetable', 'Breakfast','Lunch','Dinner']),
td(['Tomatoes' , 'no', 'yes', 'yes']),
td(['Broccoli' , 'no', 'no', 'yes']),
td(['Onions' , 'yes','yes', 'yes'])
]
)
);
HTML SHORTCUTS AND LIST INTERPOLATION
Consider this bit of code:
print blockquote(em('Hi'),'mom!'));
It will ordinarily return the string that you probably expect, namely:
<blockquote><em>Hi</em> mom!</blockquote>
Note the space between the element "Hi" and the element "mom!". CGI.pm
puts the extra space there using array interpolation, which is
controlled by the magic $" variable. Sometimes this extra space is not
what you want, for example, when you are trying to align a series of
images. In this case, you can simply change the value of $" to an
empty string.
{
local($") = '';
print blockquote(em('Hi'),'mom!'));
}
I suggest you put the code in a block as shown here. Otherwise the
change to $" will affect all subsequent code until you explicitly reset
it.
NON-STANDARD HTML SHORTCUTS
A few HTML tags don't follow the standard pattern for various reasons.
comment() generates an HTML comment (<!-- comment -->). Call it like
print comment('here is my comment');
Because of conflicts with built-in Perl functions, the following
functions begin with initial caps:
Select
Tr
Link
Delete
Accept
Sub
In addition, start_html(), end_html(), start_form(), end_form(),
start_multipart_form() and all the fill-out form tags are special. See
their respective sections.
AUTOESCAPING HTML
By default, all HTML that is emitted by the form-generating functions
is passed through a function called escapeHTML():
$escaped_string = escapeHTML("unescaped string");
Escape HTML formatting characters in a string.
Provided that you have specified a character set of ISO-8859-1 (the
default), the standard HTML escaping rules will be used. The "<"
character becomes "<", ">" becomes ">", "&" becomes "&", and
the quote character becomes """. In addition, the hexadecimal
0x8b and 0x9b characters, which some browsers incorrectly interpret as
the left and right angle-bracket characters, are replaced by their
numeric character entities ("‹" and "›"). If you manually
change the charset, either by calling the charset() method explicitly
or by passing a -charset argument to header(), then all characters will
be replaced by their numeric entities, since CGI.pm has no lookup table
for all the possible encodings.
"escapeHTML()" expects the supplied string to be a character string.
This means you should Encode::decode data received from "outside" and
Encode::encode your strings before sending them back outside. If your
source code UTF-8 encoded and you want to upgrade string literals in
your source to character strings, you can use "use utf8". See
perlunitut, perlunifaq and perlunicode for more information on how Perl
handles the difference between bytes and characters.
The automatic escaping does not apply to other shortcuts, such as h1().
You should call escapeHTML() yourself on untrusted data in order to
protect your pages against nasty tricks that people may enter into
guestbooks, etc.. To change the character set, use charset(). To turn
autoescaping off completely, use autoEscape(0):
$charset = charset([$charset]);
Get or set the current character set.
$flag = autoEscape([$flag]);
Get or set the value of the autoescape flag.
PRETTY-PRINTING HTML
By default, all the HTML produced by these functions comes out as one
long line without carriage returns or indentation. This is yuck, but it
does reduce the size of the documents by 10-20%. To get pretty-printed
output, please use CGI::Pretty, a subclass contributed by Brian
Paulsen.
CREATING FILL-OUT FORMS:
General note The various form-creating methods all return strings to
the caller, containing the tag or tags that will create the requested
form element. You are responsible for actually printing out these
strings. It's set up this way so that you can place formatting tags
around the form elements.
Another note The default values that you specify for the forms are only
used the first time the script is invoked (when there is no query
string). On subsequent invocations of the script (when there is a
query string), the former values are used even if they are blank.
If you want to change the value of a field from its previous value, you
have two choices:
(1) call the param() method to set it.
(2) use the -override (alias -force) parameter (a new feature in
version 2.15). This forces the default value to be used, regardless of
the previous value:
print textfield(-name=>'field_name',
-default=>'starting value',
-override=>1,
-size=>50,
-maxlength=>80);
Yet another note By default, the text and labels of form elements are
escaped according to HTML rules. This means that you can safely use
"<CLICK ME>" as the label for a button. However, it also interferes
with your ability to incorporate special HTML character sequences, such
as Á, into your fields. If you wish to turn off automatic
escaping, call the autoEscape() method with a false value immediately
after creating the CGI object:
$query = CGI->new;
$query->autoEscape(0);
Note that autoEscape() is exclusively used to effect the behavior of
how some CGI.pm HTML generation functions handle escaping. Calling
escapeHTML() explicitly will always escape the HTML.
A Lurking Trap! Some of the form-element generating methods return
multiple tags. In a scalar context, the tags will be concatenated
together with spaces, or whatever is the current value of the $"
global. In a list context, the methods will return a list of elements,
allowing you to modify them if you wish. Usually you will not notice
this behavior, but beware of this:
printf("%s\n",end_form())
end_form() produces several tags, and only the first of them will be
printed because the format only expects one value.
<p>
CREATING AN ISINDEX TAG
print isindex(-action=>$action);
-or-
print isindex($action);
Prints out an <isindex> tag. Not very exciting. The parameter -action
specifies the URL of the script to process the query. The default is
to process the query with the current script.
STARTING AND ENDING A FORM
print start_form(-method=>$method,
-action=>$action,
-enctype=>$encoding);
<... various form stuff ...>
print end_form;
-or-
print start_form($method,$action,$encoding);
<... various form stuff ...>
print end_form;
start_form() will return a <form> tag with the optional method, action
and form encoding that you specify. The defaults are:
method: POST
action: this script
enctype: application/x-www-form-urlencoded for non-XHTML
multipart/form-data for XHTML, see multipart/form-data below.
end_form() returns the closing </form> tag.
Start_form()'s enctype argument tells the browser how to package the
various fields of the form before sending the form to the server. Two
values are possible:
Note: These methods were previously named startform() and endform().
These methods are now DEPRECATED. Please use start_form() and
end_form() instead.
application/x-www-form-urlencoded
This is the older type of encoding. It is compatible with many CGI
scripts and is suitable for short fields containing text data. For
your convenience, CGI.pm stores the name of this encoding type in
&CGI::URL_ENCODED.
multipart/form-data
This is the newer type of encoding. It is suitable for forms that
contain very large fields or that are intended for transferring
binary data. Most importantly, it enables the "file upload"
feature. 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.
If XHTML is activated (the default), then forms will be
automatically created using this type of encoding.
The start_form() method uses the older form of encoding by default
unless XHTML is requested. If you want to use the newer form of
encoding by default, you can call start_multipart_form() instead of
start_form(). The method end_multipart_form() is an alias to
end_form().
JAVASCRIPTING: The -name and -onSubmit parameters are provided for use
with JavaScript. The -name parameter gives the form a name so that it
can be identified and manipulated by JavaScript functions. -onSubmit
should point to a JavaScript function that will be executed just before
the form is submitted to your server. You can use this opportunity to
check the contents of the form for consistency and completeness. If
you find something wrong, you can put up an alert box or maybe fix
things up yourself. You can abort the submission by returning false
from this function.
Usually the bulk of JavaScript functions are defined in a <script>
block in the HTML header and -onSubmit points to one of these function
call. See start_html() for details.
FORM ELEMENTS
After starting a form, you will typically create one or more
textfields, popup menus, radio groups and other form elements. Each of
these elements takes a standard set of named arguments. Some elements
also have optional arguments. The standard arguments are as follows:
-name
The name of the field. After submission this name can be used to
retrieve the field's value using the param() method.
-value, -values
The initial value of the field which will be returned to the script
after form submission. Some form elements, such as text fields,
take a single scalar -value argument. Others, such as popup menus,
take a reference to an array of values. The two arguments are
synonyms.
-tabindex
A numeric value that sets the order in which the form element
receives focus when the user presses the tab key. Elements with
lower values receive focus first.
-id A string identifier that can be used to identify this element to
JavaScript and DHTML.
-override
A boolean, which, if true, forces the element to take on the value
specified by -value, overriding the sticky behavior described
earlier for the -nosticky pragma.
-onChange, -onFocus, -onBlur, -onMouseOver, -onMouseOut, -onSelect
These are used to assign JavaScript event handlers. See the
JavaScripting section for more details.
Other common arguments are described in the next section. In addition
to these, all attributes described in the HTML specifications are
supported.
CREATING A TEXT FIELD
print textfield(-name=>'field_name',
-value=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print 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 (-value, formerly known as -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 = 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:
param('foo',"I'm taking over this value!");
CREATING A BIG TEXT FIELD
print textarea(-name=>'foo',
-default=>'starting value',
-rows=>10,
-columns=>50);
-or
print 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.
CREATING A PASSWORD FIELD
print password_field(-name=>'secret',
-value=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print 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.
CREATING A FILE UPLOAD FIELD
print filefield(-name=>'uploaded_file',
-default=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print filefield('uploaded_file','starting value',50,80);
filefield() will return a file upload field. In order to take full
advantage of this you must use the new multipart encoding scheme for
the form. You can do this either by calling start_form() with an
encoding type of &CGI::MULTIPART, or by calling the new method
start_multipart_form() instead of vanilla start_form().
Parameters
1. The first parameter is the required name for the field (-name).
2. The optional second parameter is the starting value for the field
contents to be used as the default file name (-default).
For security reasons, browsers don't pay any attention to this
field, and so the starting value will always be blank. Worse, the
field loses its "sticky" behavior and forgets its previous
contents. The starting value field is called for in the HTML
specification, however, and possibly some browser will eventually
provide support for it.
3. The optional third parameter is the size of the field in characters
(-size).
4. The optional fourth parameter is the maximum number of characters
the field will accept (-maxlength).
JAVASCRIPTING: The -onChange, -onFocus, -onBlur, -onMouseOver,
-onMouseOut and -onSelect parameters are recognized. See textfield()
for details.
PROCESSING A FILE UPLOAD FIELD
Basics
When the form is processed, you can retrieve an IO::Handle compatible
handle for a file upload field like this:
$lightweight_fh = $q->upload('field_name');
# undef may be returned if it's not a valid file handle
if (defined $lightweight_fh) {
# Upgrade the handle to one compatible with IO::Handle:
my $io_handle = $lightweight_fh->handle;
open (OUTFILE,'>>','/usr/local/web/users/feedback');
while ($bytesread = $io_handle->read($buffer,1024)) {
print OUTFILE $buffer;
}
}
In a list context, upload() will return an array of filehandles. This
makes it possible to process forms that use the same name for multiple
upload fields.
If you want the entered file name for the file, you can just call
param():
$filename = $q->param('field_name');
Different browsers will return slightly different things for the name.
Some browsers return the filename only. Others return the full path to
the file, using the path conventions of the user's machine.
Regardless, the name returned is always the name of the file on the
user's machine, and is unrelated to the name of the temporary file that
CGI.pm creates during upload spooling (see below).
When a file is uploaded the browser usually sends along some
information along with it in the format of headers. The information
usually includes the MIME content type. To retrieve this information,
call uploadInfo(). It returns a reference to a hash containing all the
document headers.
$filename = $q->param('uploaded_file');
$type = $q->uploadInfo($filename)->{'Content-Type'};
unless ($type eq 'text/html') {
die "HTML FILES ONLY!";
}
If you are using a machine that recognizes "text" and "binary" data
modes, be sure to understand when and how to use them (see the Camel
book). Otherwise you may find that binary files are corrupted during
file uploads.
Accessing the temp files directly
When processing an uploaded file, CGI.pm creates a temporary file on
your hard disk and passes you a file handle to that file. After you are
finished with the file handle, CGI.pm unlinks (deletes) the temporary
file. If you need to you can access the temporary file directly. You
can access the temp file for a file upload by passing the file name to
the tmpFileName() method:
$filename = $query->param('uploaded_file');
$tmpfilename = $query->tmpFileName($filename);
The temporary file will be deleted automatically when your program
exits unless you manually rename it. On some operating systems (such as
Windows NT), you will need to close the temporary file's filehandle
before your program exits. Otherwise the attempt to delete the
temporary file will fail.
Handling interrupted file uploads
There are occasionally problems involving parsing the uploaded file.
This usually happens when the user presses "Stop" before the upload is
finished. In this case, CGI.pm will return undef for the name of the
uploaded file and set cgi_error() to the string "400 Bad request
(malformed multipart POST)". This error message is designed so that
you can incorporate it into a status code to be sent to the browser.
Example:
$file = $q->upload('uploaded_file');
if (!$file && $q->cgi_error) {
print $q->header(-status=>$q->cgi_error);
exit 0;
}
You are free to create a custom HTML page to complain about the error,
if you wish.
Progress bars for file uploads and avoiding temp files
CGI.pm gives you low-level access to file upload management through a
file upload hook. You can use this feature to completely turn off the
temp file storage of file uploads, or potentially write your own file
upload progress meter.
This is much like the UPLOAD_HOOK facility available in
Apache::Request, with the exception that the first argument to the
callback is an Apache::Upload object, here it's the remote filename.
$q = CGI->new(\&hook [,$data [,$use_tempfile]]);
sub hook {
my ($filename, $buffer, $bytes_read, $data) = @_;
print "Read $bytes_read bytes of $filename\n";
}
The $data field is optional; it lets you pass configuration information
(e.g. a database handle) to your hook callback.
The $use_tempfile field is a flag that lets you turn on and off
CGI.pm's use of a temporary disk-based file during file upload. If you
set this to a FALSE value (default true) then
$q->param('uploaded_file') will no longer work, and the only way to get
at the uploaded data is via the hook you provide.
If using the function-oriented interface, call the CGI::upload_hook()
method before calling param() or any other CGI functions:
CGI::upload_hook(\&hook [,$data [,$use_tempfile]]);
This method is not exported by default. You will have to import it
explicitly if you wish to use it without the CGI:: prefix.
Troubleshooting file uploads on Windows
If you are using CGI.pm on a Windows platform and find that binary
files get slightly larger when uploaded but that text files remain the
same, then you have forgotten to activate binary mode on the output
filehandle. Be sure to call binmode() on any handle that you create to
write the uploaded file to disk.
Older ways to process file uploads
( This section is here for completeness. if you are building a new
application with CGI.pm, you can skip it. )
The original way to process file uploads with CGI.pm was to use
param(). The value it returns has a dual nature as both a file name and
a lightweight filehandle. This dual nature is problematic if you
following the recommended practice of having "use strict" in your code.
Perl will complain when you try to use a string as a filehandle. More
seriously, it is possible for the remote user to type garbage into the
upload field, in which case what you get from param() is not a
filehandle at all, but a string.
To solve this problem the upload() method was added, which always
returns a lightweight filehandle. This generally works well, but will
have trouble interoperating with some other modules because the file
handle is not derived from IO::Handle. So that brings us to current
recommendation given above, which is to call the handle() method on the
file handle returned by upload(). That upgrades the handle to an
IO::Handle. It's a big win for compatibility for a small penalty of
loading IO::Handle the first time you call it.
CREATING A POPUP MENU
print popup_menu('menu_name',
['eenie','meenie','minie'],
'meenie');
-or-
%labels = ('eenie'=>'your first choice',
'meenie'=>'your second choice',
'minie'=>'your third choice');
%attributes = ('eenie'=>{'class'=>'class of first choice'});
print popup_menu('menu_name',
['eenie','meenie','minie'],
'meenie',\%labels,\%attributes);
-or (named parameter style)-
print popup_menu(-name=>'menu_name',
-values=>['eenie','meenie','minie'],
-default=>['meenie','minie'],
-labels=>\%labels,
-attributes=>\%attributes);
popup_menu() creates a menu.
1. The required first argument is the menu's name (-name).
2. The required second argument (-values) is an array reference
containing the list of menu items in the menu. You can pass the
method an anonymous array, as shown in the example, or a reference
to a named array, such as "\@foo".
3. The optional third parameter (-default) is the name of the default
menu choice. If not specified, the first item will be the default.
The values of the previous choice will be maintained across
queries. Pass an array reference to select multiple defaults.
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 and the value returned to your script. It's a pointer
to an hash 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).
5. The optional fifth parameter (-attributes) is provided to assign
any of the common HTML attributes to an individual menu item. It's
a pointer to a hash relating menu values to another hash with the
attribute's name as the key and the attribute's value as the value.
When the form is processed, the selected value of the popup menu can be
retrieved using:
$popup_menu_value = param('menu_name');
CREATING AN OPTION GROUP
Named parameter style
print popup_menu(-name=>'menu_name',
-values=>[qw/eenie meenie minie/,
optgroup(-name=>'optgroup_name',
-values => ['moe','catch'],
-attributes=>{'catch'=>{'class'=>'red'}})],
-labels=>{'eenie'=>'one',
'meenie'=>'two',
'minie'=>'three'},
-default=>'meenie');
Old style
print popup_menu('menu_name',
['eenie','meenie','minie',
optgroup('optgroup_name', ['moe', 'catch'],
{'catch'=>{'class'=>'red'}})],'meenie',
{'eenie'=>'one','meenie'=>'two','minie'=>'three'});
optgroup() creates an option group within a popup menu.
1. The required first argument (-name) is the label attribute of the
optgroup and is not inserted in the parameter list of the query.
2. The required second argument (-values) is an array reference
containing the list of menu items in the menu. You can pass the
method an anonymous array, as shown in the example, or a reference
to a named array, such as \@foo. If you pass a HASH reference, the
keys will be used for the menu values, and the values will be used
for the menu labels (see -labels below).
3. The optional third parameter (-labels) allows you to pass a
reference to a hash containing user-visible labels for one or more
of the menu items. You can use this when you want the user to see
one menu string, but have the browser return your program a
different one. If you don't specify this, the value string will be
used instead ("eenie", "meenie" and "minie" in this example). This
is equivalent to using a hash reference for the -values parameter.
4. An optional fourth parameter (-labeled) can be set to a true value
and indicates that the values should be used as the label attribute
for each option element within the optgroup.
5. An optional fifth parameter (-novals) can be set to a true value
and indicates to suppress the val attribute in each option element
within the optgroup.
See the discussion on optgroup at W3C
(http://www.w3.org/TR/REC-html40/interact/forms.html#edef-OPTGROUP)
for details.
6. An optional sixth parameter (-attributes) is provided to assign any
of the common HTML attributes to an individual menu item. It's a
pointer to a hash relating menu values to another hash with the
attribute's name as the key and the attribute's value as the value.
CREATING A SCROLLING LIST
print scrolling_list('list_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],5,'true',{'moe'=>{'class'=>'red'}});
-or-
print scrolling_list('list_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],5,'true',
\%labels,%attributes);
-or-
print scrolling_list(-name=>'list_name',
-values=>['eenie','meenie','minie','moe'],
-default=>['eenie','moe'],
-size=>5,
-multiple=>'true',
-labels=>\%labels,
-attributes=>\%attributes);
scrolling_list() creates a scrolling list.
Parameters:
1. The first and second arguments are the list name (-name) and values
(-values). As in the popup menu, the second argument should be an
array reference.
2. The optional third argument (-default) can be either a reference to
a list containing the values to be selected by default, or can be a
single value to select. If this argument is missing or undefined,
then nothing is selected when the list first appears. In the named
parameter version, you can use the synonym "-defaults" for this
parameter.
3. The optional fourth argument is the size of the list (-size).
4. The optional fifth argument can be set to true to allow multiple
simultaneous selections (-multiple). Otherwise only one selection
will be allowed at a time.
5. The optional sixth argument is a pointer to a hash containing long
user-visible labels for the list items (-labels). If not provided,
the values will be displayed.
6. The optional sixth parameter (-attributes) is provided to assign
any of the common HTML attributes to an individual menu item. It's
a pointer to a hash relating menu values to another hash with the
attribute's name as the key and the attribute's value as the value.
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 = param('list_name');
CREATING A GROUP OF RELATED CHECKBOXES
print checkbox_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-default=>['eenie','moe'],
-linebreak=>'true',
-disabled => ['moe'],
-labels=>\%labels,
-attributes=>\%attributes);
print checkbox_group('group_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],'true',\%labels,
{'moe'=>{'class'=>'red'}});
HTML3-COMPATIBLE BROWSERS ONLY:
print checkbox_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-rows=2,-columns=>2);
checkbox_group() creates a list of checkboxes that are related by the
same name.
Parameters:
1. The first and second arguments are the checkbox name and values,
respectively (-name and -values). As in the popup menu, the second
argument should be an array reference. These values are used for
the user-readable labels printed next to the checkboxes as well as
for the values passed to your script in the query string.
2. The optional third argument (-default) can be either a reference to
a list containing the values to be checked by default, or can be a
single value to checked. If this argument is missing or undefined,
then nothing is selected when the list first appears.
3. The optional fourth argument (-linebreak) can be set to true to
place line breaks between the checkboxes so that they appear as a
vertical list. Otherwise, they will be strung together on a
horizontal line.
The optional -labels argument is a pointer to a hash relating the
checkbox values to the user-visible labels that will be printed next to
them. If not provided, the values will be used as the default.
The optional parameters -rows, and -columns cause checkbox_group() to
return an HTML3 compatible table containing the checkbox group
formatted with the specified number of rows and columns. You can
provide just the -columns parameter if you wish; checkbox_group will
calculate the correct number of rows for you.
The option -disabled takes an array of checkbox values and disables
them by greying them out (this may not be supported by all browsers).
The optional -attributes argument is provided to assign any of the
common HTML attributes to an individual menu item. It's a pointer to a
hash relating menu values to another hash with the attribute's name as
the key and the attribute's value as the value.
The optional -tabindex argument can be used to control the order in
which radio buttons receive focus when the user presses the tab button.
If passed a scalar numeric value, the first element in the group will
receive this tab index and subsequent elements will be incremented by
one. If given a reference to an array of radio button values, then the
indexes will be jiggered so that the order specified in the array will
correspond to the tab order. You can also pass a reference to a hash
in which the hash keys are the radio button values and the values are
the tab indexes of each button. Examples:
-tabindex => 100 # this group starts at index 100 and counts up
-tabindex => ['moe','minie','eenie','meenie'] # tab in this order
-tabindex => {meenie=>100,moe=>101,minie=>102,eenie=>200} # tab in this order
The optional -labelattributes argument will contain attributes attached
to the <label> element that surrounds each button.
When the form is processed, all checked boxes will be returned as a
list under the parameter name 'group_name'. The values of the "on"
checkboxes can be retrieved with:
@turned_on = param('group_name');
The value returned by checkbox_group() is actually an array of button
elements. You can capture them and use them within tables, lists, or
in other creative ways:
@h = checkbox_group(-name=>'group_name',-values=>\@values);
&use_in_creative_way(@h);
CREATING A STANDALONE CHECKBOX
print checkbox(-name=>'checkbox_name',
-checked=>1,
-value=>'ON',
-label=>'CLICK ME');
-or-
print checkbox('checkbox_name','checked','ON','CLICK ME');
checkbox() is used to create an isolated checkbox that isn't logically
related to any others.
Parameters:
1. The first parameter is the required name for the checkbox (-name).
It will also be used for the user-readable label printed next to
the checkbox.
2. The optional second parameter (-checked) specifies that the
checkbox is turned on by default. Synonyms are -selected and -on.
3. The optional third parameter (-value) specifies the value of the
checkbox when it is checked. If not provided, the word "on" is
assumed.
4. The optional fourth parameter (-label) is the user-readable label
to be attached to the checkbox. If not provided, the checkbox name
is used.
The value of the checkbox can be retrieved using:
$turned_on = param('checkbox_name');
CREATING A RADIO BUTTON GROUP
print radio_group(-name=>'group_name',
-values=>['eenie','meenie','minie'],
-default=>'meenie',
-linebreak=>'true',
-labels=>\%labels,
-attributes=>\%attributes);
-or-
print radio_group('group_name',['eenie','meenie','minie'],
'meenie','true',\%labels,\%attributes);
HTML3-COMPATIBLE BROWSERS ONLY:
print radio_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-rows=2,-columns=>2);
radio_group() creates a set of logically-related radio buttons (turning
one member of the group on turns the others off)
Parameters:
1. The first argument is the name of the group and is required
(-name).
2. The second argument (-values) is the list of values for the radio
buttons. The values and the labels that appear on the page are
identical. Pass an array reference in the second argument, either
using an anonymous array, as shown, or by referencing a named array
as in "\@foo".
3. The optional third parameter (-default) is the name of the default
button to turn on. If not specified, the first item will be the
default. You can provide a nonexistent button name, such as "-" to
start up with no buttons selected.
4. The optional fourth parameter (-linebreak) can be set to 'true' to
put line breaks between the buttons, creating a vertical list.
5. The optional fifth parameter (-labels) is a pointer to an
associative array relating the radio button values to user-visible
labels to be used in the display. If not provided, the values
themselves are displayed.
All modern browsers can take advantage of the optional parameters
-rows, and -columns. These parameters cause radio_group() to return an
HTML3 compatible table containing the radio group formatted with the
specified number of rows and columns. You can provide just the
-columns parameter if you wish; radio_group will calculate the correct
number of rows for you.
To include row and column headings in the returned table, you can use
the -rowheaders and -colheaders parameters. Both of these accept a
pointer to an array of headings to use. The headings are just
decorative. They don't reorganize the interpretation of the radio
buttons -- they're still a single named unit.
The optional -tabindex argument can be used to control the order in
which radio buttons receive focus when the user presses the tab button.
If passed a scalar numeric value, the first element in the group will
receive this tab index and subsequent elements will be incremented by
one. If given a reference to an array of radio button values, then the
indexes will be jiggered so that the order specified in the array will
correspond to the tab order. You can also pass a reference to a hash
in which the hash keys are the radio button values and the values are
the tab indexes of each button. Examples:
-tabindex => 100 # this group starts at index 100 and counts up
-tabindex => ['moe','minie','eenie','meenie'] # tab in this order
-tabindex => {meenie=>100,moe=>101,minie=>102,eenie=>200} # tab in this order
The optional -attributes argument is provided to assign any of the
common HTML attributes to an individual menu item. It's a pointer to a
hash relating menu values to another hash with the attribute's name as
the key and the attribute's value as the value.
The optional -labelattributes argument will contain attributes attached
to the <label> element that surrounds each button.
When the form is processed, the selected radio button can be retrieved
using:
$which_radio_button = 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 = radio_group(-name=>'group_name',-values=>\@values);
&use_in_creative_way(@h);
CREATING A SUBMIT BUTTON
print submit(-name=>'button_name',
-value=>'value');
-or-
print submit('button_name','value');
submit() will create the query submission button. Every form should
have one of these.
Parameters:
1. The first argument (-name) is optional. You can give the button a
name if you have several submission buttons in your form and you
want to distinguish between them.
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. The name will also be used as the user-visible label.
3. You can use -label as an alias for -value. I always get confused
about which of -name and -value changes the user-visible label on
the button.
You can figure out which button was pressed by using different values
for each one:
$which_one = param('button_name');
CREATING A RESET BUTTON
print reset
reset() creates the "reset" button. Note that it restores the form to
its value from the last time the script was called, NOT necessarily to
the defaults.
Note that this conflicts with the Perl reset() built-in. Use
CORE::reset() to get the original reset function.
CREATING A DEFAULT BUTTON
print 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 hidden(-name=>'hidden_name',
-default=>['value1','value2'...]);
-or-
print hidden('hidden_name','value1','value2'...);
hidden() produces a text field that can't be seen by the user. It is
useful for passing state variable information from one invocation of
the script to the next.
Parameters:
1. The first argument is required and specifies the name of this field
(-name).
2. The second argument is also required and specifies its value
(-default). In the named parameter style of calling, you can
provide a single value here or a reference to a whole list
Fetch the value of a hidden field this way:
$hidden_value = param('hidden_name');
Note, that just like all the other form elements, the value of a hidden
field is "sticky". If you want to replace a hidden field with some
other values after the script has been called once you'll have to do it
manually:
param('hidden_name','new','values','here');
CREATING A CLICKABLE IMAGE BUTTON
print image_button(-name=>'button_name',
-src=>'/source/URL',
-align=>'MIDDLE');
-or-
print image_button('button_name','/source/URL','MIDDLE');
image_button() produces a clickable image. When it's clicked on the
position of the click is returned to your script as "button_name.x" and
"button_name.y", where "button_name" is the name you've assigned to it.
Parameters:
1. The first argument (-name) is required and specifies the name of
this field.
2. The second argument (-src) is also required and specifies the URL
3. The third option (-align, optional) is an alignment type, and may be
TOP, BOTTOM or MIDDLE
Fetch the value of the button this way:
$x = param('button_name.x');
$y = param('button_name.y');
CREATING A JAVASCRIPT ACTION BUTTON
print button(-name=>'button_name',
-value=>'user visible label',
-onClick=>"do_something()");
-or-
print button('button_name',"user visible value","do_something()");
button() produces an "<input>" tag with "type="button"". When it's
pressed the fragment of JavaScript code pointed to by the -onClick
parameter will be executed.
HTTP COOKIES
Browsers support a so-called "cookie" designed to help maintain state
within a browser session. CGI.pm has several methods that support
cookies.
A cookie is a name=value pair much like the named parameters in a CGI
query string. CGI scripts create one or more cookies and send them to
the browser in the HTTP header. The browser maintains a list of
cookies that belong to a particular Web server, and returns them to the
CGI script during subsequent interactions.
In addition to the required name=value pair, each cookie has several
optional attributes:
1. an expiration time
This is a time/date string (in a special GMT format) that indicates
when a cookie expires. The cookie will be saved and returned to
your script until this expiration date is reached if the user exits
the browser and restarts it. If an expiration date isn't
specified, the cookie will remain active until the user quits the
browser.
2. a domain
This is a partial or complete domain name for which the cookie is
valid. The browser will return the cookie to any host that matches
the partial domain name. For example, if you specify a domain name
of ".capricorn.com", then the browser will return the cookie to Web
servers running on any of the machines "www.capricorn.com",
"www2.capricorn.com", "feckless.capricorn.com", etc. Domain names
must contain at least two periods to prevent attempts to match on
top level domains like ".edu". If no domain is specified, then the
browser will only return the cookie to servers on the host the
cookie originated from.
3. a path
If you provide a cookie path attribute, the browser will check it
against your script's URL before returning the cookie. For
example, if you specify the path "/cgi-bin", then the cookie will
be returned to each of the scripts "/cgi-bin/tally.pl",
"/cgi-bin/order.pl", and "/cgi-bin/customer_service/complain.pl",
but not to the script "/cgi-private/site_admin.pl". By default,
path is set to "/", which causes the cookie to be sent to any CGI
script on your site.
4. a "secure" flag
If the "secure" attribute is set, the cookie will only be sent to
your script if the CGI request is occurring on a secure channel,
such as SSL.
The interface to HTTP cookies is the cookie() method:
$cookie = cookie(-name=>'sessionID',
-value=>'xyzzy',
-expires=>'+1h',
-path=>'/cgi-bin/database',
-domain=>'.capricorn.org',
-secure=>1);
print header(-cookie=>$cookie);
cookie() creates a new cookie. Its parameters include:
-name
The name of the cookie (required). This can be any string at all.
Although browsers limit their cookie names to non-whitespace
alphanumeric characters, CGI.pm removes this restriction by
escaping and unescaping cookies behind the scenes.
-value
The value of the cookie. This can be any scalar value, array
reference, or even hash reference. For example, you can store an
entire hash into a cookie this way:
$cookie=cookie(-name=>'family information',
-value=>\%childrens_ages);
-path
The optional partial path for which this cookie will be valid, as
described above.
-domain
The optional partial domain for which this cookie will be valid, as
described above.
-expires
The optional expiration date for this cookie. The format is as
described in the section on the header() method:
"+1h" one hour from now
-secure
If set to true, this cookie will only be used within a secure SSL
session.
The cookie created by cookie() must be incorporated into the HTTP
header within the string returned by the header() method:
use CGI ':standard';
print header(-cookie=>$my_cookie);
To create multiple cookies, give header() an array reference:
$cookie1 = cookie(-name=>'riddle_name',
-value=>"The Sphynx's Question");
$cookie2 = cookie(-name=>'answers',
-value=>\%answers);
print header(-cookie=>[$cookie1,$cookie2]);
To retrieve a cookie, request it by name by calling cookie() method
without the -value parameter. This example uses the object-oriented
form:
use CGI;
$query = CGI->new;
$riddle = $query->cookie('riddle_name');
%answers = $query->cookie('answers');
Cookies created with a single scalar value, such as the "riddle_name"
cookie, will be returned in that form. Cookies with array and hash
values can also be retrieved.
The cookie and CGI namespaces are separate. If you have a parameter
named 'answers' and a cookie named 'answers', the values retrieved by
param() and cookie() are independent of each other. However, it's
simple to turn a CGI parameter into a cookie, and vice-versa:
# turn a CGI parameter into a cookie
$c=cookie(-name=>'answers',-value=>[param('answers')]);
# vice-versa
param(-name=>'answers',-value=>[cookie('answers')]);
If you call cookie() without any parameters, it will return a list of
the names of all cookies passed to your script:
@cookies = cookie();
See the cookie.cgi example script for some ideas on how to use cookies
effectively.
WORKING WITH FRAMES
It's possible for CGI.pm scripts to write into several browser panels
and windows using the HTML 4 frame mechanism. There are three
techniques for defining new frames programmatically:
1. Create a <Frameset> document
After writing out the HTTP header, instead of creating a standard
HTML document using the start_html() call, create a <frameset>
document that defines the frames on the page. Specify your
script(s) (with appropriate parameters) as the SRC for each of the
frames.
There is no specific support for creating <frameset> sections in
CGI.pm, but the HTML is very simple to write.
2. Specify the destination for the document in the HTTP header
You may provide a -target parameter to the header() method:
print header(-target=>'ResultsWindow');
This will tell the browser to load the output of your script into
the frame named "ResultsWindow". If a frame of that name doesn't
already exist, the browser will pop up a new window and load your
script's document into that. There are a number of magic names
that you can use for targets. See the HTML "<frame>" documentation
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 start_form(-target=>'ResultsWindow');
When your script is reinvoked by the form, its output will be
loaded into the frame named "ResultsWindow". If one doesn't
already exist a new window will be created.
The script "frameset.cgi" in the examples directory shows one way to
create pages in which the fill-out form and the response live in side-
by-side frames.
SUPPORT FOR JAVASCRIPT
The usual way to use JavaScript is to define a set of functions in a
<SCRIPT> block inside the HTML header and then to register event
handlers in the various elements of the page. Events include such
things as the mouse passing over a form element, a button being
clicked, the contents of a text field changing, or a form being
submitted. When an event occurs that involves an element that has
registered an event handler, its associated JavaScript code gets
called.
The elements that can register event handlers include the <BODY> of an
HTML document, hypertext links, all the various elements of a fill-out
form, and the form itself. There are a large number of events, and each
applies only to the elements for which it is relevant. Here is a
partial list:
onLoad
The browser is loading the current document. Valid in:
+ The HTML <BODY> section only.
onUnload
The browser is closing the current page or frame. Valid for:
+ The HTML <BODY> section only.
onSubmit
The user has pressed the submit button of a form. This event
happens just before the form is submitted, and your function can
return a value of false in order to abort the submission. Valid
for:
+ Forms only.
onClick
The mouse has clicked on an item in a fill-out form. Valid for:
+ Buttons (including submit, reset, and image buttons)
+ Checkboxes
+ Radio buttons
onChange
The user has changed the contents of a field. Valid for:
+ Text fields
+ Text areas
+ Password fields
+ File fields
+ Popup Menus
+ Scrolling lists
onFocus
The user has selected a field to work with. Valid for:
+ Text fields
+ Text areas
+ Password fields
+ File fields
+ Popup Menus
+ Scrolling lists
onBlur
The user has deselected a field (gone to work somewhere else).
Valid for:
+ Text fields
+ Text areas
+ Password fields
+ File fields
+ Popup Menus
+ Scrolling lists
onSelect
The user has changed the part of a text field that is selected.
Valid for:
+ Text fields
+ Text areas
+ Password fields
+ File fields
onMouseOver
The mouse has moved over an element.
+ Text fields
+ Text areas
+ Password fields
+ File fields
+ Popup Menus
+ Scrolling lists
onMouseOut
The mouse has moved off an element.
+ Text fields
+ Text areas
+ Password fields
+ File fields
+ Popup Menus
+ Scrolling lists
In order to register a JavaScript event handler with an HTML element,
just use the event name as a parameter when you call the corresponding
CGI method. For example, to have your validateAge() JavaScript code
executed every time the textfield named "age" changes, generate the
field like this:
print textfield(-name=>'age',-onChange=>"validateAge(this)");
This example assumes that you've already declared the validateAge()
function by incorporating it into a <SCRIPT> block. The CGI.pm
start_html() method provides a convenient way to create this section.
Similarly, you can create a form that checks itself over for
consistency and alerts the user if some essential value is missing by
creating it this way:
print start_form(-onSubmit=>"validateMe(this)");
See the javascript.cgi script for a demonstration of how this all
works.
LIMITED SUPPORT FOR CASCADING STYLE SHEETS
CGI.pm has limited support for HTML3's cascading style sheets (css).
To incorporate a stylesheet into your document, pass the start_html()
method a -style parameter. The value of this parameter may be a
scalar, in which case it is treated as the source URL for the
stylesheet, or it may be a hash reference. In the latter case you
should provide the hash with one or more of -src or -code. -src points
to a URL where an externally-defined stylesheet can be found. -code
points to a scalar value to be incorporated into a <style> section.
Style definitions in -code override similarly-named ones in -src, hence
the name "cascading."
You may also specify the type of the stylesheet by adding the optional
-type parameter to the hash pointed to by -style. If not specified,
the style defaults to 'text/css'.
To refer to a style within the body of your document, add the -class
parameter to any HTML element:
print h1({-class=>'Fancy'},'Welcome to the Party');
Or define styles on the fly with the -style parameter:
print h1({-style=>'Color: red;'},'Welcome to Hell');
You may also use the new span() element to apply a style to a section
of text:
print span({-style=>'Color: red;'},
h1('Welcome to Hell'),
"Where did that handbasket get to?"
);
Note that you must import the ":html3" definitions to have the span()
method available. Here's a quick and dirty example of using CSS's.
See the CSS specification at http://www.w3.org/Style/CSS/ for more
information.
use CGI qw/:standard :html3/;
#here's a stylesheet incorporated directly into the page
$newStyle=<<END;
<!--
P.Tip {
margin-right: 50pt;
margin-left: 50pt;
color: red;
}
P.Alert {
font-size: 30pt;
font-family: sans-serif;
color: red;
}
-->
END
print header();
print start_html( -title=>'CGI with Style',
-style=>{-src=>'http://www.capricorn.com/style/st1.css',
-code=>$newStyle}
);
print h1('CGI with Style'),
p({-class=>'Tip'},
"Better read the cascading style sheet spec before playing with this!"),
span({-style=>'color: magenta'},
"Look Mom, no hands!",
p(),
"Whooo wee!"
);
print end_html;
Pass an array reference to -code or -src in order to incorporate
multiple stylesheets into your document.
Should you wish to incorporate a verbatim stylesheet that includes
arbitrary formatting in the header, you may pass a -verbatim tag to the
-style hash, as follows:
print start_html (-style => {-verbatim => '@import
url("/server-common/css/'.$cssFile.'");',
-src => '/server-common/css/core.css'});
This will generate an HTML header that contains this:
<link rel="stylesheet" type="text/css" href="/server-common/css/core.css">
<style type="text/css">
@import url("/server-common/css/main.css");
</style>
Any additional arguments passed in the -style value will be
incorporated into the <link> tag. For example:
start_html(-style=>{-src=>['/styles/print.css','/styles/layout.css'],
-media => 'all'});
This will give:
<link rel="stylesheet" type="text/css" href="/styles/print.css" media="all"/>
<link rel="stylesheet" type="text/css" href="/styles/layout.css" media="all"/>
<p>
To make more complicated <link> tags, use the Link() function and pass
it to start_html() in the -head argument, as in:
@h = (Link({-rel=>'stylesheet',-type=>'text/css',-src=>'/ss/ss.css',-media=>'all'}),
Link({-rel=>'stylesheet',-type=>'text/css',-src=>'/ss/fred.css',-media=>'paper'}));
print start_html({-head=>\@h})
To create primary and "alternate" stylesheet, use the -alternate
option:
start_html(-style=>{-src=>[
{-src=>'/styles/print.css'},
{-src=>'/styles/alt.css',-alternate=>1}
]
});
DEBUGGING
If you are running the script from the command line or in the perl
debugger, you can pass the script a list of keywords or parameter=value
pairs on the command line or from standard input (you don't have to
worry about tricking your script into reading from environment
variables). You can pass keywords like this:
your_script.pl keyword1 keyword2 keyword3
or this:
your_script.pl keyword1+keyword2+keyword3
or this:
your_script.pl name1=value1 name2=value2
or this:
your_script.pl name1=value1&name2=value2
To turn off this feature, use the -no_debug pragma.
To test the POST method, you may enable full debugging with the -debug
pragma. This will allow you to feed newline-delimited name=value pairs
to the script on standard input.
When debugging, you can use quotes and backslashes to escape characters
in the familiar shell manner, letting you place spaces and other funny
characters in your parameter=value pairs:
your_script.pl "name1='I am a long value'" "name2=two\ words"
Finally, you can set the path info for the script by prefixing the
first name/value parameter with the path followed by a question mark
(?):
your_script.pl /your/path/here?name1=value1&name2=value2
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 Dump
Produces something that looks like:
<ul>
<li>name1
<ul>
<li>value1
<li>value2
</ul>
<li>name2
<ul>
<li>value1
</ul>
</ul>
As a shortcut, you can interpolate the entire CGI object into a string
and it will be replaced with the a nice HTML dump shown above:
$query=CGI->new;
print "<h2>Current Values</h2> $query\n";
FETCHING ENVIRONMENT VARIABLES
Some of the more useful environment variables can be fetched through
this interface. The methods are as follows:
Accept()
Return a list of MIME types that the remote browser accepts. If you
give this method a single argument corresponding to a MIME type, as
in Accept('text/html'), it will return a floating point value
corresponding to the browser's preference for this type from 0.0
(don't want) to 1.0. Glob types (e.g. text/*) in the browser's
accept list are handled correctly.
Note that the capitalization changed between version 2.43 and 2.44
in order to avoid conflict with Perl's accept() function.
raw_cookie()
Returns the HTTP_COOKIE variable. Cookies have a special format,
and this method call just returns the raw form (?cookie dough).
See cookie() for ways of setting and retrieving cooked cookies.
Called with no parameters, raw_cookie() returns the packed cookie
structure. You can separate it into individual cookies by
splitting on the character sequence "; ". Called with the name of
a cookie, retrieves the unescaped form of the cookie. You can use
the regular cookie() method to get the names, or use the
raw_fetch() method from the CGI::Cookie module.
user_agent()
Returns the HTTP_USER_AGENT variable. If you give this method a
single argument, it will attempt to pattern match on it, allowing
you to do something like user_agent(Mozilla);
path_info()
Returns additional path information from the script URL. E.G.
fetching /cgi-bin/your_script/additional/stuff will result in
path_info() returning "/additional/stuff".
NOTE: The Microsoft Internet Information Server is broken with
respect to additional path information. If you use the Perl DLL
library, the IIS server will attempt to execute the additional path
information as a Perl script. If you use the ordinary file
associations mapping, the path information will be present in the
environment, but incorrect. The best thing to do is to avoid using
additional path information in CGI scripts destined for use with
IIS.
path_translated()
As per path_info() but returns the additional path information
translated into a physical path, e.g.
"/usr/local/etc/httpd/htdocs/additional/stuff".
The Microsoft IIS is broken with respect to the translated path as
well.
remote_host()
Returns either the remote host name or IP address. if the former
is unavailable.
remote_addr()
Returns the remote host IP address, or 127.0.0.1 if the address is
unavailable.
script_name() Return the script name as a partial URL, for self-
referring scripts.
referer()
Return the URL of the page the browser was viewing prior to
fetching your script. Not available for all browsers.
auth_type ()
Return the authorization/verification method in use for this
script, if any.
server_name ()
Returns the name of the server, usually the machine's host name.
virtual_host ()
When using virtual hosts, returns the name of the host that the
browser attempted to contact
server_port ()
Return the port that the server is listening on.
virtual_port ()
Like server_port() except that it takes virtual hosts into account.
Use this when running with virtual hosts.
server_software ()
Returns the server software and version number.
remote_user ()
Return the authorization/verification name used for user
verification, if this script is protected.
user_name ()
Attempt to obtain the remote user's name, using a variety of
different techniques. This only works with older browsers such as
Mosaic. Newer browsers do not report the user name for privacy
reasons!
request_method()
Returns the method used to access your script, usually one of
'POST', 'GET' or 'HEAD'.
content_type()
Returns the content_type of data submitted in a POST, generally
multipart/form-data or application/x-www-form-urlencoded
http()
Called with no arguments returns the list of HTTP environment
variables, including such things as HTTP_USER_AGENT,
HTTP_ACCEPT_LANGUAGE, and HTTP_ACCEPT_CHARSET, corresponding to the
like-named HTTP header fields in the request. Called with the name
of an HTTP header field, returns its value. Capitalization and the
use of hyphens versus underscores are not significant.
For example, all three of these examples are equivalent:
$requested_language = http('Accept-language');
$requested_language = http('Accept_language');
$requested_language = http('HTTP_ACCEPT_LANGUAGE');
https()
The same as http(), but operates on the HTTPS environment variables
present when the SSL protocol is in effect. Can be used to
determine whether SSL is turned on.
USING NPH SCRIPTS
NPH, or "no-parsed-header", scripts bypass the server completely by
sending the complete HTTP header directly to the browser. This has
slight performance benefits, but is of most use for taking advantage of
HTTP extensions that are not directly supported by your server, such as
server push and PICS headers.
Servers use a variety of conventions for designating CGI scripts as
NPH. Many Unix servers look at the beginning of the script's name for
the prefix "nph-". The Macintosh WebSTAR server and Microsoft's
Internet Information Server, in contrast, try to decide whether a
program is an NPH script by examining the first line of script output.
CGI.pm supports NPH scripts with a special NPH mode. When in this
mode, CGI.pm will output the necessary extra header information when
the header() and redirect() methods are called.
The Microsoft Internet Information Server requires NPH mode. As of
version 2.30, CGI.pm will automatically detect when the script is
running under IIS and put itself into this mode. You do not need to do
this manually, although it won't hurt anything if you do. However,
note that if you have applied Service Pack 6, much of the functionality
of NPH scripts, including the ability to redirect while setting a
cookie, do not work at all on IIS without a special patch from
Microsoft. See
http://web.archive.org/web/20010812012030/http://support.microsoft.com/support/kb/articles/Q280/3/41.ASP
Non-Parsed Headers Stripped From CGI Applications That Have nph- Prefix
in Name.
In the use statement
Simply add the "-nph" pragma to the list of symbols to be imported
into your script:
use CGI qw(:standard -nph)
By calling the nph() method:
Call nph() with a non-zero parameter at any point after using
CGI.pm in your program.
CGI->nph(1)
By using -nph parameters
in the header() and redirect() statements:
print header(-nph=>1);
Server Push
CGI.pm provides four simple functions for producing multipart documents
of the type needed to implement server push. These functions were
graciously provided by Ed Jordan <ed AT fidalgo.net>. To import these
into your namespace, you must import the ":push" set. You are also
advised to put the script into NPH mode and to set $| to 1 to avoid
buffering problems.
Here is a simple script that demonstrates server push:
#!/usr/local/bin/perl
use CGI qw/:push -nph/;
$| = 1;
print multipart_init(-boundary=>'----here we go!');
for (0 .. 4) {
print multipart_start(-type=>'text/plain'),
"The current time is ",scalar(localtime),"\n";
if ($_ < 4) {
print multipart_end;
} else {
print multipart_final;
}
sleep 1;
}
This script initializes server push by calling multipart_init(). It
then enters a loop in which it begins a new multipart section by
calling multipart_start(), prints the current local time, and ends a
multipart section with multipart_end(). It then sleeps a second, and
begins again. On the final iteration, it ends the multipart section
with multipart_final() rather than with multipart_end().
multipart_init()
multipart_init(-boundary=>$boundary);
Initialize the multipart system. The -boundary argument specifies
what MIME boundary string to use to separate parts of the document.
If not provided, CGI.pm chooses a reasonable boundary for you.
multipart_start()
multipart_start(-type=>$type)
Start a new part of the multipart document using the specified MIME
type. If not specified, text/html is assumed.
multipart_end()
multipart_end()
End a part. You must remember to call multipart_end() once for
each multipart_start(), except at the end of the last part of the
multipart document when multipart_final() should be called instead
of multipart_end().
multipart_final()
multipart_final()
End all parts. You should call multipart_final() rather than
multipart_end() at the end of the last part of the multipart
document.
Users interested in server push applications should also have a look at
the CGI::Push module.
Avoiding Denial of Service Attacks
A potential problem with CGI.pm is that, by default, it attempts to
process form POSTings no matter how large they are. A wily hacker
could attack your site by sending a CGI script a huge POST of many
megabytes. CGI.pm will attempt to read the entire POST into a
variable, growing hugely in size until it runs out of memory. While
the script attempts to allocate the memory the system may slow down
dramatically. This is a form of denial of service attack.
Another possible attack is for the remote user to force CGI.pm to
accept a huge file upload. CGI.pm will accept the upload and store it
in a temporary directory even if your script doesn't expect to receive
an uploaded file. CGI.pm will delete the file automatically when it
terminates, but in the meantime the remote user may have filled up the
server's disk space, causing problems for other programs.
The best way to avoid denial of service attacks is to limit the amount
of memory, CPU time and disk space that CGI scripts can use. Some Web
servers come with built-in facilities to accomplish this. In other
cases, you can use the shell limit or ulimit commands to put ceilings
on CGI resource usage.
CGI.pm also has some simple built-in protections against denial of
service attacks, but you must activate them before you can use them.
These take the form of two global variables in the CGI name space:
$CGI::POST_MAX
If set to a non-negative integer, this variable puts a ceiling on
the size of POSTings, in bytes. If CGI.pm detects a POST that is
greater than the ceiling, it will immediately exit with an error
message. This value will affect both ordinary POSTs and multipart
POSTs, meaning that it limits the maximum size of file uploads as
well. You should set this to a reasonably high value, such as 1
megabyte.
$CGI::DISABLE_UPLOADS
If set to a non-zero value, this will disable file uploads
completely. Other fill-out form values will work as usual.
You can use these variables in either of two ways.
1. On a script-by-script basis
Set the variable at the top of the script, right after the "use"
statement:
use CGI qw/:standard/;
use CGI::Carp 'fatalsToBrowser';
$CGI::POST_MAX=1024 * 100; # max 100K posts
$CGI::DISABLE_UPLOADS = 1; # no uploads
2. Globally for all scripts
Open up CGI.pm, find the definitions for $POST_MAX and
$DISABLE_UPLOADS, and set them to the desired values. You'll find
them towards the top of the file in a subroutine named
initialize_globals().
An attempt to send a POST larger than $POST_MAX bytes will cause
param() to return an empty CGI parameter list. You can test for this
event by checking cgi_error(), either after you create the CGI object
or, if you are using the function-oriented interface, call <param()>
for the first time. If the POST was intercepted, then cgi_error() will
return the message "413 POST too large".
This error message is actually defined by the HTTP protocol, and is
designed to be returned to the browser as the CGI script's status
code. For example:
$uploaded_file = param('upload');
if (!$uploaded_file && cgi_error()) {
print header(-status=>cgi_error());
exit 0;
}
However it isn't clear that any browser currently knows what to do with
this status code. It might be better just to create an HTML page that
warns the user of the problem.
COMPATIBILITY WITH CGI-LIB.PL
To make it easier to port existing programs that use cgi-lib.pl the
compatibility routine "ReadParse" is provided. Porting is simple:
OLD VERSION
require "cgi-lib.pl";
&ReadParse;
print "The value of the antique is $in{antique}.\n";
NEW VERSION
use CGI;
CGI::ReadParse();
print "The value of the antique is $in{antique}.\n";
CGI.pm's ReadParse() routine creates a tied variable named %in, which
can be accessed to obtain the query variables. Like ReadParse, you can
also provide your own variable. Infrequently used features of
ReadParse, such as the creation of @in and $in variables, are not
supported.
Once you use ReadParse, you can retrieve the query object itself this
way:
$q = $in{CGI};
print $q->textfield(-name=>'wow',
-value=>'does this really work?');
This allows you to start using the more interesting features of CGI.pm
without rewriting your old scripts from scratch.
An even simpler way to mix cgi-lib calls with CGI.pm calls is to import
both the ":cgi-lib" and ":standard" method:
use CGI qw(:cgi-lib :standard);
&ReadParse;
print "The price of your purchase is $in{price}.\n";
print textfield(-name=>'price', -default=>'$1.99');
Cgi-lib functions that are available in CGI.pm
In compatibility mode, the following cgi-lib.pl functions are available
for your use:
ReadParse()
PrintHeader()
HtmlTop()
HtmlBot()
SplitParam()
MethGet()
MethPost()
Cgi-lib functions that are not available in CGI.pm
* Extended form of ReadParse()
The extended form of ReadParse() that provides for file upload
spooling, is not available.
* MyBaseURL()
This function is not available. Use CGI.pm's url() method instead.
* MyFullURL()
This function is not available. Use CGI.pm's self_url() method
instead.
* CgiError(), CgiDie()
These functions are not supported. Look at CGI::Carp for the way I
prefer to handle error messages.
* PrintVariables()
This function is not available. To achieve the same effect,
just print out the CGI object:
use CGI qw(:standard);
$q = CGI->new;
print h1("The Variables Are"),$q;
* PrintEnv()
This function is not available. You'll have to roll your own if you really need it.
AUTHOR INFORMATION
The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is
distributed under GPL and the Artistic License 2.0. It is currently
maintained by Mark Stosberg with help from many contributors.
Address bug reports and comments to:
https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm When sending
bug reports, please provide the version of CGI.pm, the version of Perl,
the name and version of your Web server, and the name and version of
the operating system you are using. If the problem is even remotely
browser dependent, please provide information about the affected
browsers as well.
CREDITS
Thanks very much to:
Matt Heffron (heffron AT falstaff.com)
James Taylor (james.taylor AT srs.gov)
Scott Anguish <sanguish AT digifix.com>
Mike Jewell (mlj3u AT virginia.edu)
Timothy Shimmin (tes AT kbs.au)
Joergen Haegg (jh AT axis.se)
Laurent Delfosse (delfosse AT delfosse.com)
Richard Resnick (applepi1 AT aol.com)
Craig Bishop (csb AT barwonwater.au)
Tony Curtis (tc AT vcpc.at)
Tim Bunce (Tim.Bunce AT ig.uk)
Tom Christiansen (tchrist AT convex.com)
Andreas Koenig (k AT franz.DE)
Tim MacKenzie (Tim.MacKenzie AT fulcrum.au)
Kevin B. Hendricks (kbhend AT dogwood.edu)
Stephen Dahmen (joyfire AT inxpress.net)
Ed Jordan (ed AT fidalgo.net)
David Alan Pisoni (david AT cnation.com)
Doug MacEachern (dougm AT opengroup.org)
Robin Houston (robin AT oneworld.org)
...and many many more...
for suggestions and bug fixes.
A COMPLETE EXAMPLE OF A SIMPLE FORM-BASED SCRIPT
#!/usr/local/bin/perl
use CGI ':standard';
print header;
print start_html("Example CGI.pm Form");
print "<h1> Example CGI.pm Form</h1>\n";
print_prompt();
do_work();
print_tail();
print end_html;
sub print_prompt {
print start_form;
print "<em>What's your name?</em><br>";
print textfield('name');
print checkbox('Not my real name');
print "<p><em>Where can you find English Sparrows?</em><br>";
print 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>",
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 popup_menu(-name=>'Color',
-values=>['black','brown','red','yellow'],
-default=>'red');
print hidden('Reference','Monty Python and the Holy Grail');
print "<p><em>What have you got there?</em><br>";
print 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 textarea(-name=>'Comments',
-rows=>10,
-columns=>50);
print "<p>",reset;
print submit('Action','Shout');
print submit('Action','Scream');
print end_form;
print "<hr>\n";
}
sub do_work {
print "<h2>Here are the current settings in this form</h2>";
for my $key (param) {
print "<strong>$key</strong> -> ";
my @values = 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
Please report them.
SEE ALSO
CGI::Carp - provides a Carp implementation tailored to the CGI
environment.
CGI::Fast - supports running CGI applications under FastCGI
CGI::Pretty - pretty prints HTML generated by CGI.pm (with a
performance penalty)
POD ERRORS
Hey! The above document had some coding errors, which are explained
below:
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perl v5.16.3 2012-11-14 CGI(3)
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