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CGI - Simple Common Gateway Interface Class
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CGI - Simple Common Gateway Interface Class
# CGI script that creates a fill-out form
# and echoes back its values.
use CGI qw/:standard/;
print header,
start_html('A Simple Example'),
h1('A Simple Example'),
start_form,
"What's your name? ",textfield('name'),p,
"What's the combination?", p,
checkbox_group(-name=>'words',
-values=>['eenie','meenie','minie','moe'],
-defaults=>['eenie','minie']), p,
"What's your favorite color? ",
popup_menu(-name=>'color',
-values=>['red','green','blue','chartreuse']),p,
submit,
end_form,
hr;
if (param()) {
print "Your name is",em(param('name')),p,
"The keywords are: ",em(join(", ",param('words'))),p,
"Your favorite color is ",em(param('color')),
hr;
}
This perl library uses perl5 objects to make it easy to create Web
fill-out forms and parse their contents. This package defines CGI
objects, entities that contain the values of the current query string
and other state variables. Using a CGI object's methods, you can
examine keywords and parameters passed to your script, and create
forms whose initial values are taken from the current query (thereby
preserving state information). The module provides shortcut functions
that produce boilerplate HTML, reducing typing and coding errors. It
also provides functionality for some of the more advanced features of
CGI scripting, including support for file uploads, cookies, cascading
style sheets, server push, and frames.
CGI.pm also provides a simple function-oriented programming style for
those who don't need its object-oriented features.
The current version of CGI.pm is available at
http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html
ftp://ftp-genome.wi.mit.edu/pub/software/WWW/
There are two styles of programming with CGI.pm, an object-oriented
style and a function-oriented style. In the object-oriented style you
create one or more CGI objects and then use object methods to create
the various elements of the page. Each CGI object starts out with the
list of named parameters that were passed to your CGI script by the
server. You can modify the objects, save them to a file or database
and recreate them. Because each object corresponds to the ``state'' of
the CGI script, and because each object's parameter list is
independent of the others, this allows you to save the state of the
script and restore it later.
For example, using the object oriented style, here is how you create
a simple ``Hello World'' HTML page:
#!/usr/local/bin/perl -w
use CGI; # load CGI routines
$q = new CGI; # create new CGI object
print $q->header, # create the HTTP header
$q->start_html('hello world'), # start the HTML
$q->h1('hello world'), # level 1 header
$q->end_html; # end the HTML
In the function-oriented style, there is one default CGI object that
you rarely deal with directly. Instead you just call functions to
retrieve CGI parameters, create HTML tags, manage cookies, and so
on. This provides you with a cleaner programming interface, but
limits you to using one CGI object at a time. The following example
prints the same page, but uses the function-oriented interface.
The main differences are that we now need to import a set of functions
into our name space (usually the ``standard'' functions), and we don't
need to create the CGI object.
#!/usr/local/bin/perl
use CGI qw/:standard/; # load standard CGI routines
print header, # create the HTTP header
start_html('hello world'), # start the HTML
h1('hello world'), # level 1 header
end_html; # end the HTML
The examples in this document mainly use the object-oriented style.
See HOW TO IMPORT FUNCTIONS for important information on
function-oriented programming in CGI.pm
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:
-
Use another name for the argument, if one is available.
For example, -value is an alias for -values.
-
Change the capitalization, e.g. -Values
-
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''.
$query = new CGI;
This will parse the input (from both POST and GET methods) and store
it into a perl5 object called $query.
$query = new CGI(INPUTFILE);
If you provide a file handle to the new() method, it will read
parameters from the file (or STDIN, or whatever). The file can be in
any of the forms describing below under debugging (i.e. a series of
newline delimited TAG=VALUE pairs will work). Conveniently, this type
of file is created by the save() method (see below). Multiple records
can be saved and restored.
Perl purists will be pleased to know that this syntax accepts
references to file handles, or even references to filehandle globs,
which is the ``official'' way to pass a filehandle:
$query = new CGI(\*STDIN);
You can also initialize the CGI object with a FileHandle or IO::File
object.
If you are using the function-oriented interface and want to
initialize CGI state from a file handle, the way to do this is with
restore_parameters(). This will (re)initialize the
default CGI object from the indicated file handle.
open (IN,"test.in") || die;
restore_parameters(IN);
close IN;
You can also initialize the query object from an associative array
reference:
$query = new CGI( {'dinosaur'=>'barney',
'song'=>'I love you',
'friends'=>[qw/Jessica George Nancy/]}
);
or from a properly formatted, URL-escaped query string:
$query = new CGI('dinosaur=barney&color=purple');
or from a previously existing CGI object (currently this clones the
parameter list, but none of the other object-specific fields, such as
autoescaping):
$old_query = new CGI;
$new_query = new CGI($old_query);
To create an empty query, initialize it from an empty string or hash:
$empty_query = new CGI("");
-or-
$empty_query = new CGI({});
@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.
@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).
@values = $query->param('foo');
-or-
$value = $query->param('foo');
Pass the param() method a single argument to fetch the value of the
named parameter. If the parameter is multivalued (e.g. from multiple
selections in a scrolling list), you can ask to receive an array. Otherwise
the method will return a single value.
If a value is not given in the query string, as in the queries
``name1=&name2='' or ``name1&name2'', it will be returned as an empty
string. This feature is new in 2.63.
$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');
$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.
$query->import_names('R');
This creates a series of variables in the 'R' namespace. For example,
$R::foo, @R:foo. For keyword lists, a variable @R::keywords will appear.
If no namespace is given, this method will assume 'Q'.
WARNING: don't import anything into 'main'; this is a major security
risk!!!!
In older versions, this method was called import(). As of version 2.20,
this name has been removed completely to avoid conflict with the built-in
Perl module import operator.
$query->delete('foo');
This completely clears a parameter. It sometimes useful for
resetting parameters that you don't want passed down between
script invocations.
If you are using the function call interface, use ``Delete()'' instead
to avoid conflicts with Perl's built-in delete operator.
$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.
$q->param_fetch('address')->[1] = '1313 Mockingbird Lane';
unshift @{$q->param_fetch(-name=>'address')},'George Munster';
If you need access to the parameter list in a way that isn't covered
by the methods above, you can obtain a direct reference to it by
calling the param_fetch() method with the name of the . This
will return an array reference to the named parameters, which you then
can manipulate in any way you like.
You can also use a named argument style using the -name argument.
$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).
$query->save(FILEHANDLE)
This will write the current state of the form to the provided
filehandle. You can read it back in by providing a filehandle
to the new() method. Note that the filehandle can be a file, a pipe,
or whatever!
The format of the saved file is:
NAME1=VALUE1
NAME1=VALUE1'
NAME2=VALUE2
NAME3=VALUE3
=
Both name and value are URL escaped. Multi-valued CGI parameters are
represented as repeated names. A session record is delimited by a
single = symbol. You can write out multiple records and read them
back in with several calls to new. You can do this across several
sessions by opening the file in append mode, allowing you to create
primitive guest books, or to keep a history of users' queries. Here's
a short example of creating multiple session records:
use CGI;
open (OUT,">>test.out") || die;
$records = 5;
foreach (0..$records) {
my $q = new CGI;
$q->param(-name=>'counter',-value=>$_);
$q->save(OUT);
}
close OUT;
# reopen for reading
open (IN,"test.out") || die;
while (!eof(IN)) {
my $q = new CGI(IN);
print $q->param('counter'),"\n";
}
The file format used for save/restore is identical to that used by the
Whitehead Genome Center's data exchange format ``Boulderio'', and can be
manipulated and even databased using Boulderio utilities. See
http://stein.cshl.org/boulder/
for further details.
If you wish to use this method from the function-oriented (non-OO)
interface, the exported name for this method is save_parameters().
Errors can occur while processing user input, particularly when
processing uploaded files. When these errors occur, CGI will stop
processing and return an empty parameter list. You can test for
the existence and nature of errors using the cgi_error() function.
The error messages are formatted as HTTP status codes. You can either
incorporate the error text into an HTML page, or use it as the value
of the HTTP status:
my $error = $q->cgi_error;
if ($error) {
print $q->header(-status=>$error),
$q->start_html('Problems'),
$q->h2('Request not processed'),
$q->strong($error);
exit 0;
}
When using the function-oriented interface (see the next section),
errors may only occur the first time you call param(). Be ready
for this!
To use the function-oriented interface, you must specify which CGI.pm
routines or sets of routines to import into your script's namespace.
There is a small overhead 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 proposed elements (such as
<table>, <super> and <sub>).
- :netscape
-
Import all methods that generate Netscape-specific HTML extensions.
- :html
-
Import all HTML-generating shortcuts (i.e. 'html2' + 'html3' +
'netscape')...
- :standard
-
Import ``standard'' features, 'html2', 'html3', 'form' and 'cgi'.
- :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 the Exporter manpage 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;
In addition to the function sets, there are a number of pragmas that
you can import. Pragmas, which are always preceded by a hyphen,
change the way that CGI.pm functions in various ways. Pragmas,
function sets, and individual functions can all be imported in the
same use() line. For example, the following use statement imports the
standard set of functions and enables debugging mode (pragma
-debug):
use CGI qw/:standard -debug/;
The current list of pragmas is as follows:
- -any
-
When you use CGI -any, then any method that the query object
doesn't recognize will be interpreted as a new HTML tag. This allows
you to support the next ad hoc Netscape or Microsoft HTML
extension. This lets you go wild with new and unsupported tags:
use CGI qw(-any);
$q=new CGI;
print $q->gradient({speed=>'fast',start=>'red',end=>'blue'});
Since using <cite>any</cite> causes any mistyped method name
to be interpreted as an HTML tag, use it with care or not at
all.
- -compile
-
This causes the indicated autoloaded methods to be compiled up front,
rather than deferred to later. This is useful for scripts that run
for an extended period of time under FastCGI or mod_perl, and for
those destined to be crunched by Malcom Beattie's Perl compiler. Use
it in conjunction with the methods or method families you plan to use.
use CGI qw(-compile :standard :html3);
or even
use CGI qw(-compile :all);
Note that using the -compile pragma in this way will always have
the effect of importing the compiled functions into the current
namespace. If you want to compile without importing use the
compile() method instead (see below).
- -nosticky
-
This makes CGI.pm not generating the hidden fields .submit
and .cgifields. It is very useful if you don't want to
have the hidden fields appear in the querystring in a GET method.
For example, a search script generated this way will have
a very nice url with search parameters for bookmarking.
- -no_xhtml
-
By default, CGI.pm versions 2.69 and higher emit XHTML
(http://www.w3.org/TR/xhtml1/). The -no_xhtml pragma disables this
feature. Thanks to Michalis Kabrianis <kabrianis@hellug.gr> for this
feature.
- -nph
-
This makes CGI.pm produce a header appropriate for an NPH (no
parsed header) script. You may need to do other things as well
to tell the server that the script is NPH. See the discussion
of NPH scripts below.
- -newstyle_urls
-
Separate the name=value pairs in CGI parameter query strings with
semicolons rather than ampersands. For example:
?name=fred;age=24;favorite_color=3
Semicolon-delimited query strings are always accepted, but will not be
emitted by self_url() and query_string() unless the -newstyle_urls
pragma is specified.
This became the default in version 2.64.
- -oldstyle_urls
-
Separate the name=value pairs in CGI parameter query strings with
ampersands rather than semicolons. This is no longer the default.
- -autoload
-
This overrides the autoloader so that any function in your program
that is not recognized is referred to CGI.pm for possible evaluation.
This allows you to use all the CGI.pm functions without adding them to
your symbol table, which is of concern for mod_perl users who are
worried about memory consumption. Warning: when
-autoload is in effect, you cannot use ``poetry mode''
(functions without the parenthesis). Use hr() rather
than hr, or add something like use subs qw/hr p header/
to the top of your script.
- -no_debug
-
This turns off the command-line processing features. If you want to
run a CGI.pm script from the command line to produce HTML, and you
don't want it to read CGI parameters from the command line or STDIN,
then use this pragma:
use CGI qw(-no_debug :standard);
- -debug
-
This turns on full debugging. In addition to reading CGI arguments
from the command-line processing, CGI.pm will pause and try to read
arguments from STDIN, producing the message ``(offline mode: enter
name=value pairs on standard input)'' features.
See the section on debugging for more details.
- -private_tempfiles
-
CGI.pm can process uploaded file. Ordinarily it spools the uploaded
file to a temporary directory, then deletes the file when done.
However, this opens the risk of eavesdropping as described in the file
upload section. Another CGI script author could peek at this data
during the upload, even if it is confidential information. On Unix
systems, the -private_tempfiles pragma will cause the temporary file
to be unlinked as soon as it is opened and before any data is written
into it, reducing, but not eliminating the risk of eavesdropping
(there is still a potential race condition). To make life harder for
the attacker, the program chooses tempfile names by calculating a 32
bit checksum of the incoming HTTP headers.
To ensure that the temporary file cannot be read by other CGI scripts,
use suEXEC or a CGI wrapper program to run your script. The temporary
file is created with mode 0600 (neither world nor group readable).
The temporary directory is selected using the following algorithm:
1. if the current user (e.g. "nobody") has a directory named
"tmp" in its home directory, use that (Unix systems only).
2. if the environment variable TMPDIR exists, use the location
indicated.
3. Otherwise try the locations /usr/tmp, /var/tmp, C:\temp,
/tmp, /temp, ::Temporary Items, and \WWW_ROOT.
Each of these locations is checked that it is a directory and is
writable. If not, the algorithm tries the next choice.
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:
start_table() (generates a <TABLE> tag)
end_table() (generates a </TABLE> tag)
start_ul() (generates a <UL> tag)
end_ul() (generates a </UL> tag)
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.
Normally the first thing you will do in any CGI script is print out an
HTTP header. This tells the browser what type of document to expect,
and gives other optional information, such as the language, expiration
date, and whether to cache the document. The header can also be
manipulated for special purposes, such as server push and pay per view
pages.
print $query->header;
-or-
print $query->header('image/gif');
-or-
print $query->header('text/html','204 No response');
-or-
print $query->header(-type=>'image/gif',
-nph=>1,
-status=>'402 Payment required',
-expires=>'+3d',
-cookie=>$cookie,
-charset=>'utf-7',
-attachment=>'foo.gif',
-Cost=>'$2.00');
header() returns the Content-type: header. You can provide your own
MIME type if you choose, otherwise it defaults to text/html. An
optional second parameter specifies the status code and a human-readable
message. For example, you can specify 204, ``No response'' to create a
script that tells the browser to do nothing at all.
The last example shows the named argument style for passing arguments
to the CGI methods using named parameters. Recognized parameters are
-type, -status, -expires, and -cookie. Any other named
parameters will be stripped of their initial hyphens and turned into
header fields, allowing you to specify any HTTP header you desire.
Internal underscores will be turned into hyphens:
print $query->header(-Content_length=>3002);
Most browsers will not cache the output from CGI scripts. Every time
the browser reloads the page, the script is invoked anew. You can
change this behavior with the -expires parameter. When you specify
an absolute or relative expiration interval with this parameter, some
browsers and proxy servers will cache the script's output until the
indicated expiration date. The following forms are all valid for the
-expires field:
+30s 30 seconds from now
+10m ten minutes from now
+1h one hour from now
-1d yesterday (i.e. "ASAP!")
now immediately
+3M in three months
+10y in ten years time
Thursday, 25-Apr-1999 00:40:33 GMT at the indicated time & date
The -cookie parameter generates a header that tells the browser to provide
a ``magic cookie'' during all subsequent transactions with your script.
Netscape cookies have a special format that includes interesting attributes
such as expiration time. Use the cookie() method to create and retrieve
session cookies.
The -nph parameter, if set to a true value, will issue the correct
headers to work with 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''.
print $query->redirect('http://somewhere.else/in/movie/land');
Sometimes you don't want to produce a document yourself, but simply
redirect the browser elsewhere, perhaps choosing a URL based on the
time of day or the identity of the user.
The redirect() function redirects the browser to a different URL. If
you use redirection like this, you should not print out a header as
well.
One hint I can offer is that relative links may not work correctly
when you generate a redirection to another document on your site.
This is due to a well-intentioned optimization that some servers use.
The solution to this is to use the full URL (including the http: part)
of the document you are redirecting to.
You can also use named arguments:
print $query->redirect(-uri=>'http://somewhere.else/in/movie/land',
-nph=>1);
The -nph parameter, if set to a true value, will issue the correct
headers to work with a NPH (no-parse-header) script. This is important
to use with certain servers, such as Microsoft Internet Explorer, which
expect all their scripts to be NPH.
print $query->start_html(-title=>'Secrets of the Pyramids',
-author=>'fred@capricorn.org',
-base=>'true',
-target=>'_blank',
-meta=>{'keywords'=>'pharaoh secret mummy',
'copyright'=>'copyright 1996 King Tut'},
-style=>{'src'=>'/styles/style1.css'},
-BGCOLOR=>'blue');
After creating the HTTP header, most CGI scripts will start writing
out an HTML document. The start_html() routine creates the top of the
page, along with a lot of optional information that controls the
page's appearance and behavior.
This method returns a canned HTML header and the opening <BODY> tag.
All parameters are optional. In the named parameter form, recognized
parameters are -title, -author, -base, -xbase, -dtd, -lang and -target
(see below for the explanation). Any additional parameters you
provide, such as the Netscape unofficial BGCOLOR attribute, are added
to the <BODY> tag. Additional parameters must be proceeded by a
hyphen.
The argument -xbase allows you to provide an HREF for the <BASE> tag
different from the current location, as in
-xbase=>"http://home.mcom.com/";
All relative links will be interpreted relative to this tag.
The argument -target allows you to provide a default target frame
for all the links and fill-out forms on the page. This is a
non-standard HTTP feature which only works with Netscape browsers!
See the Netscape documentation on frames for details of how to
manipulate this.
-target=>"answer_window"
All relative links will be interpreted relative to this tag.
You add arbitrary meta information to the header with the -meta
argument. This argument expects a reference to an associative array
containing name/value pairs of meta information. These will be turned
into a series of header <META> tags that look something like this:
<META NAME="keywords" CONTENT="pharaoh secret mummy">
<META NAME="description" CONTENT="copyright 1996 King Tut">
To create an HTTP-EQUIV type of <META> tag, use -head, described
below.
The -style argument is used to incorporate cascading stylesheets
into your code. See the section on CASCADING STYLESHEETS for more
information.
The -lang argument is used to incorporate a language attribute into
the <HTML> tag. The default if not specified is ``en-US'' for US
English. For example:
print $q->start_html(-lang=>'fr-CA');
You can place other arbitrary HTML elements to the <HEAD> section with the
-head tag. For example, to place the rarely-used <LINK> element in the
head section, use this:
print start_html(-head=>Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}));
To incorporate multiple HTML elements into the <HEAD> section, just pass an
array reference:
print start_html(-head=>[
Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}),
Link({-rel=>'previous',
-href=>'http://www.capricorn.com/s1.html'})
]
);
And here's how to create an HTTP-EQUIV <META> tag:
print start_html(-head=>meta({-http_equiv => 'Content-Type',
-content => 'text/html'}))
JAVASCRIPTING: The -script, -noScript, -onLoad,
-onMouseOver, -onMouseOut and -onUnload parameters are used
to add Netscape JavaScript calls to your pages. -script should
point to a block of text containing JavaScript function definitions.
This block will be placed within a <SCRIPT> block inside the HTML (not
HTTP) header. The block is placed in the header in order to give your
page a fighting chance of having all its JavaScript functions in place
even if the user presses the stop button before the page has loaded
completely. CGI.pm attempts to format the script in such a way that
JavaScript-naive browsers will not choke on the code: unfortunately
there are some browsers, such as Chimera for Unix, that get confused
by it nevertheless.
The -onLoad and -onUnload parameters point to fragments of JavaScript
code to execute when the page is respectively opened and closed by the
browser. Usually these parameters are calls to functions defined in the
-script field:
$query = new CGI;
print $query->header;
$JSCRIPT=<<END;
// Ask a silly question
function riddle_me_this() {
var r = prompt("What walks on four legs in the morning, " +
"two legs in the afternoon, " +
"and three legs in the evening?");
response(r);
}
// Get a silly answer
function response(answer) {
if (answer == "man")
alert("Right you are!");
else
alert("Wrong! Guess again.");
}
END
print $query->start_html(-title=>'The Riddle of the Sphinx',
-script=>$JSCRIPT);
Use the -noScript parameter to pass some HTML text that will be displayed on
browsers that do not have JavaScript (or browsers where JavaScript is turned
off).
Netscape 3.0 recognizes several attributes of the <SCRIPT> tag,
including LANGUAGE and SRC. The latter is particularly interesting,
as it allows you to keep the JavaScript code in a file or CGI script
rather than cluttering up each page with the source. To use these
attributes pass a HASH reference in the -script parameter containing
one or more of -language, -src, or -code:
print $q->start_html(-title=>'The Riddle of the Sphinx',
-script=>{-language=>'JAVASCRIPT',
-src=>'/javascript/sphinx.js'}
);
print $q->(-title=>'The Riddle of the Sphinx',
-script=>{-language=>'PERLSCRIPT',
-code=>'print "hello world!\n;"'}
);
A final feature allows you to incorporate multiple <SCRIPT> sections into the
header. Just pass the list of script sections as an array reference.
this allows you to specify different source files for different dialects
of JavaScript. Example:
print $q->start_html(-title=>'The Riddle of the Sphinx',
-script=>[
{ -language => 'JavaScript1.0',
-src => '/javascript/utilities10.js'
},
{ -language => 'JavaScript1.1',
-src => '/javascript/utilities11.js'
},
{ -language => 'JavaScript1.2',
-src => '/javascript/utilities12.js'
},
{ -language => 'JavaScript28.2',
-src => '/javascript/utilities219.js'
}
]
);
</pre>
If this looks a bit extreme, take my advice and stick with straight CGI scripting.
See
http://home.netscape.com/eng/mozilla/2.0/handbook/javascript/
for more information about JavaScript.
The old-style positional parameters are as follows:
- Parameters:
-
-
The title
-
The author's e-mail address (will create a <LINK REV=``MADE''> tag if present
-
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!
- , 5, 6...
Any other parameters you want to include in the <BODY> tag. This is a good
place to put Netscape extensions, such as colors and wallpaper patterns.
print $query->end_html
This ends an HTML document by printing the </BODY></HTML> tags.
$myself = $query->self_url;
print q(<A HREF="$myself">I'm talking to myself.</A>);
self_url() will return a URL, that, when selected, will reinvoke
this script with all its state information intact. This is most
useful when you want to jump around within the document using
internal anchors but you don't want to disrupt the current contents
of the form(s). Something like this will do the trick.
$myself = $query->self_url;
print "<A HREF=$myself#table1>See table 1</A>";
print "<A HREF=$myself#table2>See table 2</A>";
print "<A HREF=$myself#yourself>See for yourself</A>";
If you want more control over what's returned, using the url()
method instead.
You can also retrieve the unprocessed query string with query_string():
$the_string = $query->query_string;
$full_url = $query->url();
$full_url = $query->url(-full=>1); #alternative syntax
$relative_url = $query->url(-relative=>1);
$absolute_url = $query->url(-absolute=>1);
$url_with_path = $query->url(-path_info=>1);
$url_with_path_and_query = $query->url(-path_info=>1,-query=>1);
$netloc = $query->url(-base => 1);
url() returns the script's URL in a variety of formats. Called
without any arguments, it returns the full form of the URL, including
host name and port number
http://your.host.com/path/to/script.cgi
You can modify this format with the following named arguments:
- -absolute
-
If true, produce an absolute URL, e.g.
/path/to/script.cgi
- -relative
-
Produce a relative URL. This is useful if you want to reinvoke your
script with different parameters. For example:
script.cgi
- -full
-
Produce the full URL, exactly as if called without any arguments.
This overrides the -relative and -absolute arguments.
- -path (-path_info)
-
Append the additional path information to the URL. This can be
combined with -full, -absolute or -relative. -path_info
is provided as a synonym.
- -query (-query_string)
-
Append the query string to the URL. This can be combined with
-full, -absolute or -relative. -query_string is provided
as a synonym.
- -base
-
Generate just the protocol and net location, as in http://www.foo.com:8000
$color = $query->url_param('color');
It is possible for a script to receive CGI parameters in the URL as
well as in the fill-out form by creating a form that POSTs to a URL
containing a query string (a ``?'' mark followed by arguments). The
param() method will always return the contents of the POSTed
fill-out form, ignoring the URL's query string. To retrieve URL
parameters, call the url_param() method. Use it in the same way as
param(). The main difference is that it allows you to read the
parameters, but not set them.
Under no circumstances will the contents of the URL query string
interfere with similarly-named CGI parameters in POSTed forms. If you
try to mix a URL query string with a form submitted with the GET
method, the results will not be what you expect.
CGI.pm defines general HTML shortcut methods for most, if not all of
the HTML 3 and HTML 4 tags. HTML shortcuts are named after a single
HTML element and return a fragment of HTML text that you can then
print or manipulate as you like. Each shortcut returns a fragment of
HTML code that you can append to a string, save to a file, or, most
commonly, print out so that it displays in the browser window.
This example shows how to use the HTML methods:
$q = new CGI;
print $q->blockquote(
"Many years ago on the island of",
$q->a({href=>"http://crete.org/";},"Crete"),
"there lived a Minotaur named",
$q->strong("Fred."),
),
$q->hr;
This results in the following HTML code (extra newlines have been
added for readability):
<blockquote>
Many years ago on the island of
<a HREF="http://crete.org/";>Crete</a> there lived
a minotaur named <strong>Fred.</strong>
</blockquote>
<hr>
If you find the syntax for calling the HTML shortcuts awkward, you can
import them into your namespace and dispense with the object syntax
completely (see the next section for more details):
use CGI ':standard';
print blockquote(
"Many years ago on the island of",
a({href=>"http://crete.org/";},"Crete"),
"there lived a minotaur named",
strong("Fred."),
),
hr;
The HTML methods will accept zero, one or multiple arguments. If you
provide no arguments, you get a single tag:
print hr; # <HR>
If you provide one or more string arguments, they are concatenated
together with spaces and placed between opening and closing tags:
print h1("Chapter","1"); # <H1>Chapter 1</H1>"
If the first argument is an associative array reference, then the keys
and values of the associative array become the HTML tag's attributes:
print a({-href=>'fred.html',-target=>'_new'},
"Open a new frame");
<A HREF="fred.html",TARGET="_new">Open a new frame</A>
You may dispense with the dashes in front of the attribute names if
you prefer:
print img {src=>'fred.gif',align=>'LEFT'};
<IMG ALIGN="LEFT" SRC="fred.gif">
Sometimes an HTML tag attribute has no argument. For example, ordered
lists can be marked as COMPACT. The syntax for this is an argument that
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=>''}) <IMT ALT="">
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'])
]
)
);
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.
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.
By default, all HTML that is emitted by the form-generating functions
is passed through a function called escapeHTML():
- $escaped_string = escapeHTML(``unescaped string'');
-
Escape HTML formatting characters in a string.
Provided that you have specified a character set of ISO-8859-1 (the
default), the standard HTML escaping rules will be used. The ``<''
character becomes ``<'', ``>'' becomes ``>'', ``&'' becomes ``&'', and
the quote character becomes ``"''. In addition, the hexadecimal
0x8b and 0x9b characters, which many windows-based browsers interpret
as the left and right angle-bracket characters, are replaced by their
numeric HTML entities (``‹'' and ``›''). If you manually change
the charset, either by calling the charset() method explicitly or by
passing a -charset argument to header(), then all characters will
be replaced by their numeric entities, since CGI.pm has no lookup
table for all the possible encodings.
The automatic escaping does not apply to other shortcuts, such as
h1(). You should call escapeHTML() yourself on untrusted data in
order to protect your pages against nasty tricks that people may enter
into guestbooks, etc.. To change the character set, use charset().
To turn autoescaping off completely, use autoescape():
- $charset = charset([$charset]);
-
Get or set the current character set.
- $flag = autoEscape([$flag]);
-
Get or set the value of the autoescape flag.
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 the CGI::Pretty manpage, a subclass
contributed by Brian Paulsen.
General note The various form-creating methods all return strings
to the caller, containing the tag or tags that will create the requested
form element. You are responsible for actually printing out these strings.
It's set up this way so that you can place formatting tags
around the form elements.
Another note The default values that you specify for the forms are only
used the first time the script is invoked (when there is no query
string). On subsequent invocations of the script (when there is a query
string), the former values are used even if they are blank.
If you want to change the value of a field from its previous value, you have two
choices:
(1) call the param() method to set it.
(2) use the -override (alias -force) parameter (a new feature in version 2.15).
This forces the default value to be used, regardless of the previous value:
print $query->textfield(-name=>'field_name',
-default=>'starting value',
-override=>1,
-size=>50,
-maxlength=>80);
Yet another note By default, the text and labels of form elements are
escaped according to HTML rules. This means that you can safely use
``<CLICK ME>'' as the label for a button. However, it also interferes with
your ability to incorporate special HTML character sequences, such as Á,
into your fields. If you wish to turn off automatic escaping, call the
autoEscape() method with a false value immediately after creating the CGI object:
$query = new CGI;
$query->autoEscape(undef);
print $query->isindex(-action=>$action);
-or-
print $query->isindex($action);
Prints out an <ISINDEX> tag. Not very exciting. The parameter
-action specifies the URL of the script to process the query. The
default is to process the query with the current script.
print $query->start_form(-method=>$method,
-action=>$action,
-enctype=>$encoding);
<... various form stuff ...>
print $query->endform;
-or-
print $query->start_form($method,$action,$encoding);
<... various form stuff ...>
print $query->endform;
start_form() will return a <FORM> tag with the optional method,
action and form encoding that you specify. The defaults are:
method: POST
action: this script
enctype: application/x-www-form-urlencoded
endform() returns the closing </FORM> tag.
Start_form()'s enctype argument tells the browser how to package the various
fields of the form before sending the form to the server. Two
values are possible:
Note: This method was previously named startform(), and startform()
is still recognized as an alias.
- application/x-www-form-urlencoded
-
This is the older type of encoding used by all browsers prior to
Netscape 2.0. It is compatible with many CGI scripts and is
suitable for short fields containing text data. For your
convenience, CGI.pm stores the name of this encoding
type in &CGI::URL_ENCODED.
- multipart/form-data
-
This is the newer type of encoding introduced by Netscape 2.0.
It is suitable for forms that contain very large fields or that
are intended for transferring binary data. Most importantly,
it enables the ``file upload'' feature of Netscape 2.0 forms. For
your convenience, CGI.pm stores the name of this encoding type
in &CGI::MULTIPART
Forms that use this type of encoding are not easily interpreted
by CGI scripts unless they use CGI.pm or another library designed
to handle them.
For compatibility, the start_form() method uses the older form of
encoding by default. If you want to use the newer form of encoding
by default, you can call start_multipart_form() instead of
start_form().
JAVASCRIPTING: The -name and -onSubmit parameters are provided
for use with JavaScript. The -name parameter gives the
form a name so that it can be identified and manipulated by
JavaScript functions. -onSubmit should point to a JavaScript
function that will be executed just before the form is submitted to your
server. You can use this opportunity to check the contents of the form
for consistency and completeness. If you find something wrong, you
can put up an alert box or maybe fix things up yourself. You can
abort the submission by returning false from this function.
Usually the bulk of JavaScript functions are defined in a <SCRIPT>
block in the HTML header and -onSubmit points to one of these function
call. See start_html() for details.
print $query->textfield(-name=>'field_name',
-default=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print $query->textfield('field_name','starting value',50,80);
textfield() will return a text input field.
- Parameters
-
-
The first parameter is the required name for the field (-name).
-
The optional second parameter is the default starting value for the field
contents (-default).
-
The optional third parameter is the size of the field in
characters (-size).
-
The optional fourth parameter is the maximum number of characters the
field will accept (-maxlength).
As with all these methods, the field will be initialized with its
previous contents from earlier invocations of the script.
When the form is processed, the value of the text field can be
retrieved with:
$value = $query->param('foo');
If you want to reset it from its initial value after the script has been
called once, you can do so like this:
$query->param('foo',"I'm taking over this value!");
NEW AS OF VERSION 2.15: If you don't want the field to take on its previous
value, you can force its current value by using the -override (alias -force)
parameter:
print $query->textfield(-name=>'field_name',
-default=>'starting value',
-override=>1,
-size=>50,
-maxlength=>80);
JAVASCRIPTING: You can also provide -onChange, -onFocus,
-onBlur, -onMouseOver, -onMouseOut and -onSelect
parameters to register JavaScript event handlers. The onChange
handler will be called whenever the user changes the contents of the
text field. You can do text validation if you like. onFocus and
onBlur are called respectively when the insertion point moves into and
out of the text field. onSelect is called when the user changes the
portion of the text that is selected.
print $query->textarea(-name=>'foo',
-default=>'starting value',
-rows=>10,
-columns=>50);
-or
print $query->textarea('foo','starting value',10,50);
textarea() is just like textfield, but it allows you to specify
rows and columns for a multiline text entry box. You can provide
a starting value for the field, which can be long and contain
multiple lines.
JAVASCRIPTING: The -onChange, -onFocus, -onBlur ,
-onMouseOver, -onMouseOut, and -onSelect parameters are
recognized. See textfield().
print $query->password_field(-name=>'secret',
-value=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print $query->password_field('secret','starting value',50,80);
password_field() is identical to textfield(), except that its contents
will be starred out on the web page.
JAVASCRIPTING: The -onChange, -onFocus, -onBlur,
-onMouseOver, -onMouseOut and -onSelect parameters are
recognized. See textfield().
print $query->filefield(-name=>'uploaded_file',
-default=>'starting value',
-size=>50,
-maxlength=>80);
-or-
print $query->filefield('uploaded_file','starting value',50,80);
filefield() will return a file upload field for Netscape 2.0 browsers.
In order to take full advantage of this you must use the new
multipart encoding scheme for the form. You can do this either
by calling start_form() with an encoding type of &CGI::MULTIPART,
or by calling the new method start_multipart_form() instead of
vanilla start_form().
- Parameters
-
-
The first parameter is the required name for the field (-name).
-
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.
-
The optional third parameter is the size of the field in
characters (-size).
-
The optional fourth parameter is the maximum number of characters the
field will accept (-maxlength).
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