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 now you create a simple ``Hello World'' HTML page:
#!/usr/local/bin/pelr
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/pelr
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.
You don't have to use the hyphen at allif you don't want to. After creating a CGI object, call the use_named_parameters() method with a nonzero value. This will tell CGI.pm that you intend to use named parameters exclusively:
$query = new CGI;
$query->use_named_parameters(1);
$field = $query->radio_group('name'=>'OS',
'values'=>['Unix','Windows','Macintosh'],
'default'=>'Unix');
Several routines are commonly called with just one 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:
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, there will be a single parameter named 'keywords'.
NOTE: As of version 1.5, the array of parameter names returned will be in the same order as they were submitted by the browser. Usually this order is the same as the order in which the parameters are defined in the form (however, this isn't part of the spec, and so isn't 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.
$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.
$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://www.genome.wi.mit.edu/genome_software/other/boulder.html
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().
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 gropus 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:
%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 immeidately:
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 disables debugging mode (pragma -no_debug):
use CGI qw/:standard -no_debug/;
The current list of pragmas is as follows:
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.
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).
use CGI qw(-no_debug :standard);
If you'd like to process the command-line parameters but not standard input, this should work:
use CGI qw(-no_debug :standard);
restore_parameters(join('&',@ARGV));
See the section on debugging for more details.
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,
-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, such as Microsoft Internet Explorer, which expect all their scripts to be NPH.
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. As of version 2.0, we produce both the unofficial Location: header and the official
URI: header. This should satisfy most servers and browsers.
One hint I can offer is that relative links may not work correctly when you generate a redirection to another 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 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. 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">
There is no support for the
HTTP-EQUIV type of <
META> tag. This is because you can modify the
HTTP header directly with the
header()
method. For example, if you want to send the Refresh: header, do it in the
header() method:
print $q->header(-Refresh=>'10; URL=http://www.capricorn.com');
The -style tag is used to incorporate cascading stylesheets into your code. See the section on CASCADING STYLESHEETS for more information.
You can place other arbitrary HTML elements to the < HEAD> section with the -head tag. For example, to place the rarely-used <LINK> element in the head section, use this:
print $q->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 $q->start_html(-head=>[
Link({-rel=>'next',
-href=>'http://www.capricorn.com/s2.html'}),
Link({-rel=>'previous',
-href=>'http://www.capricorn.com/s1.html'})
]
);
JAVASCRIPTING: The -script, -noScript, -onLoad, -onMouseOver, -onMouseOut and -onUnload parameters are used to add Netscape JavaScript calls to your pages. -script should point to a block of text containing JavaScript function definitions. This block will be placed within a <SCRIPT> block inside the HTML (not HTTP) header. The block is placed in the header in order to give your page a fighting chance of having all its JavaScript functions in place even if the user presses the stop button before the page has loaded completely. CGI.pm attempts to format the script in such a way that JavaScript-naive browsers will not choke on the code: unfortunately there are some browsers, such as Chimera for Unix, that get confused by it nevertheless.
The -onLoad and -onUnload parameters point to fragments of JavaScript code to execute when the page is respectively opened and closed by the browser. Usually these 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:
The title
print $query->end_html
This ends an HTML document by printing the </BODY></HTML> tags.
$myself = $query->self_url;
print "<A HREF=$myself>I'm talking to myself.</A>";
self_url() will return a
URL, that, when selected, will reinvoke this script with all its state information intact. This is most useful when you want to jump around within the document using internal anchors but you don't want to disrupt the current contents of the
form(s). Something like this will do the trick.
$myself = $query->self_url;
print "<A HREF=$myself#table1>See table 1</A>";
print "<A HREF=$myself#table2>See table 2</A>";
print "<A HREF=$myself#yourself>See for yourself</A>";
If you want more control over what's returned, using the 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);
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:
/path/to/script.cgi
script.cgi
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 accomodate 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
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.
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 $query->startform(-method=>$method,
-action=>$action,
-encoding=>$encoding);
<... various form stuff ...>
print $query->endform;
-or-
print $query->startform($method,$action,$encoding);
<... various form stuff ...>
print $query->endform;
startform() will return a
<FORM> tag with the optional method, action and form encoding that you specify. The defaults are: method:
POST action: this script encoding: application/x-www-form-urlencoded
endform() returns the closing
</FORM> tag.
Startform()'s encoding
method tells the browser how to package the various fields of the form
before sending the form to the server. Two values are possible:
Forms that use this type of encoding are not easily interpreted by CGI scripts unless they use CGI.pm or another library designed to handle them.
For compatibility, the
startform() method uses
the older form of encoding by default. If you want to use the newer form of
encoding by default, you can call start_multipart_form() instead of
startform().
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.
The first parameter is the required name for the field (-name).
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 startform() with an encoding type of $CGI::MULTIPART, or by calling the new method start_multipart_form() instead of vanilla startform().
The first parameter is the required name for the field (-name).
The beta2 version of Netscape 2.0 currently doesn'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 later versions of Netscape will honor it.
When the form is processed, you can retrieve the entered filename by calling
param().
$filename = $query->param('uploaded_file');
In Netscape Navigator 2.0, the filename that gets returned is the full local filename on the remote user's machine. If the remote user is on a Unix machine, the filename will follow Unix conventions:
/path/to/the/file
On an MS-DOS/Windows and OS/2 machines, the filename will follow DOS conventions:
C:\PATH\TO\THE\FILE.MSW
On a Macintosh machine, the filename will follow Mac conventions:
HD 40:Desktop Folder:Sort Through:Reminders
The filename returned is also a file handle. You can read the contents of the file using standard Perl file reading calls:
# Read a text file and print it out
while (<$filename>) {
print;
}
# Copy a binary file to somewhere safe
open (OUTFILE,">>/usr/local/web/users/feedback");
while ($bytesread=read($filename,$buffer,1024)) {
print OUTFILE $buffer;
}
When a file is uploaded the browser usually sends along some information along with it in the format of headers. The information usually includes the
MIME content type. Future browsers may send other information as well (such as modification date and size). To retrieve this information, call
uploadInfo(). It returns a reference to an associative array containing all the document headers.
$filename = $query->param('uploaded_file');
$type = $query->uploadInfo($filename)->{'Content-Type'};
unless ($type eq 'text/html') {
die "HTML FILES ONLY!";
}
If you are using a machine that recognizes ``text'' and ``binary'' data modes, be sure to understand when and how to use them (see the Camel book). Otherwise you may find that binary files are corrupted during file uploads.
JAVASCRIPTING: The -onChange, -onFocus, -onBlur,
-onMouseOver, -onMouseOut and -onSelect parameters are recognized. See
textfield() for details.
print $query->popup_menu('menu_name',
['eenie','meenie','minie'],
'meenie');
-or-
%labels = ('eenie'=>'your first choice',
'meenie'=>'your second choice',
'minie'=>'your third choice');
print $query->popup_menu('menu_name',
['eenie','meenie','minie'],
'meenie',\%labels);
-or (named parameter style)-
print $query->popup_menu(-name=>'menu_name',
-values=>['eenie','meenie','minie'],
-default=>'meenie',
-labels=>\%labels);
popup_menu() creates a
menu.
The required first argument is the menu's name (-name).
When the form is processed, the selected value of the popup menu can be retrieved using:
$popup_menu_value = $query->param('menu_name');
JAVASCRIPTING:
popup_menu() recognizes the following event handlers:
-onChange, -onFocus, -onMouseOver, -onMouseOut, and
-onBlur. See the
textfield() section for
details on when these handlers are called.
print $query->scrolling_list('list_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],5,'true');
-or-
print $query->scrolling_list('list_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],5,'true',
\%labels);
-or-
print $query->scrolling_list(-name=>'list_name',
-values=>['eenie','meenie','minie','moe'],
-default=>['eenie','moe'],
-size=>5,
-multiple=>'true',
-labels=>\%labels);
scrolling_list()
creates a scrolling list.
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.
When this form is processed, all selected list items will be returned as a list under the parameter name 'list_name'. The values of the selected items can be retrieved with:
@selected = $query->param('list_name');
JAVASCRIPTING:
scrolling_list() recognizes the following event handlers:
-onChange, -onFocus, -onMouseOver, -onMouseOut
and -onBlur. See
textfield() for the
description of when these handlers are called.
print $query->checkbox_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-default=>['eenie','moe'],
-linebreak=>'true',
-labels=>\%labels);
print $query->checkbox_group('group_name',
['eenie','meenie','minie','moe'],
['eenie','moe'],'true',\%labels);
HTML3-COMPATIBLE BROWSERS ONLY:
print $query->checkbox_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-rows=2,-columns=>2);
checkbox_group()
creates a list of checkboxes that are related by the same name.
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.
checkbox_group() to return an
HTML3 compatible table containing the checkbox group formatted with the specified number of rows and columns. You can provide just the -columns parameter if you wish; checkbox_group will calculate the correct number of rows for you.
To include row and column headings in the returned table, you can use the -rowheaders and -colheaders parameters. Both of these accept a pointer to an array of headings to use. The headings are just decorative. They don't reorganize the interpretation of the checkboxes -- they're still a single named unit.
When the form is processed, all checked boxes will be returned as a list under the parameter name 'group_name'. The values of the ``on'' checkboxes can be retrieved with:
@turned_on = $query->param('group_name');
The value returned by
checkbox_group() is
actually an array of button elements. You can capture them and use them
within tables, lists, or in other creative ways:
@h = $query->checkbox_group(-name=>'group_name',-values=>\@values);
&use_in_creative_way(@h);
JAVASCRIPTING:
checkbox_group() recognizes the
-onClick
parameter. This specifies a JavaScript code fragment or function call to be
executed every time the user clicks on any of the buttons in the group. You
can retrieve the identity of the particular button clicked on using the
``this'' variable.
print $query->checkbox(-name=>'checkbox_name',
-checked=>'checked',
-value=>'ON',
-label=>'CLICK ME');
-or-
print $query->checkbox('checkbox_name','checked','ON','CLICK ME');
checkbox() is used to
create an isolated checkbox that isn't logically related to any others.
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.
The value of the checkbox can be retrieved using:
$turned_on = $query->param('checkbox_name');
JAVASCRIPTING:
checkbox() recognizes the
-onClick
parameter. See
checkbox_group() for
further details.
print $query->radio_group(-name=>'group_name',
-values=>['eenie','meenie','minie'],
-default=>'meenie',
-linebreak=>'true',
-labels=>\%labels);
-or-
print $query->radio_group('group_name',['eenie','meenie','minie'],
'meenie','true',\%labels);
HTML3-COMPATIBLE BROWSERS ONLY:
print $query->radio_group(-name=>'group_name',
-values=>['eenie','meenie','minie','moe'],
-rows=2,-columns=>2);
radio_group() creates a
set of logically-related radio buttons (turning one member of the group on
turns the others off)
The first argument is the name of the group and is required (-name).
radio_group() to return an
HTML3 compatible table containing the radio group formatted with the specified number of rows and columns. You can provide just the -columns parameter if you wish; radio_group will calculate the correct number of rows for you.
To include row and column headings in the returned table, you can use the -rowheader and -colheader parameters. Both of these accept a pointer to an array of headings to use. The headings are just decorative. They don't reorganize the interpetation of the radio buttons -- they're still a single named unit.
When the form is processed, the selected radio button can be retrieved using:
$which_radio_button = $query->param('group_name');
The value returned by
radio_group() is
actually an array of button elements. You can capture them and use them
within tables, lists, or in other creative ways:
@h = $query->radio_group(-name=>'group_name',-values=>\@values);
&use_in_creative_way(@h);
print $query->submit(-name=>'button_name',
-value=>'value');
-or-
print $query->submit('button_name','value');
submit() will create the
query submission button. Every form should have one of these.
The first argument (-name) is optional. You can give the button a name if you have several submission buttons in your form and you want to distinguish between them. The name will also be used as the user-visible label. Be aware that a few older browsers don't deal with this correctly and never send back a value from a button.
You can figure out which button was pressed by using different values for each one:
$which_one = $query->param('button_name');
JAVASCRIPTING:
radio_group() recognizes the
-onClick
parameter. See
checkbox_group() for
further details.
print $query->reset
reset() creates the ``reset'' button. Note that it restores the form to its value from the last time the script was called,
NOT necessarily to the defaults.
print $query->defaults('button_label')
defaults() creates a button
that, when invoked, will cause the form to be completely reset to its
defaults, wiping out all the changes the user ever made.
print $query->hidden(-name=>'hidden_name',
-default=>['value1','value2'...]);
-or-
print $query->hidden('hidden_name','value1','value2'...);
hidden() produces a text
field that can't be seen by the user. It is useful for passing state
variable information from one invocation of the script to the next.
The first argument is required and specifies the name of this field (-name).
Fetch the value of a hidden field this way:
$hidden_value = $query->param('hidden_name');
Note, that just like all the other form elements, the value of a hidden field is ``sticky''. If you want to replace a hidden field with some other values after the script has been called once you'll have to do it manually:
$query->param('hidden_name','new','values','here');
print $query->image_button(-name=>'button_name',
-src=>'/source/URL',
-align=>'MIDDLE');
-or-
print $query->image_button('button_name','/source/URL','MIDDLE');
image_button() produces
a clickable image. When it's clicked on the position of the click is
returned to your script as ``button_name.x'' and ``button_name.y'', where
``button_name'' is the name you've assigned to it.
JAVASCRIPTING:
image_button() recognizes the
-onClick
parameter. See
checkbox_group() for
further details.
The first argument (-name) is required and specifies the name of this field.
Fetch the value of the button this way: $x =
$query->param('button_name.x'); $y =
$query->param('button_name.y');
print $query->button(-name=>'button_name',
-value=>'user visible label',
-onClick=>"do_something()");
-or-
print $query->button('button_name',"do_something()");
button() produces a button
that is compatible with Netscape 2.0's JavaScript. When it's pressed the
fragment of JavaScript code pointed to by the -onClick parameter will be executed. On non-Netscape browsers this form element will
probably not even display.
Netscape browsers versions 1.1 and higher 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:
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 Netscape and restarts it. If an expiration date isn't specified, the cookie will remain active until the user quits Netscape.
The interface to Netscape cookies is the cookie() method:
$cookie = $query->cookie(-name=>'sessionID',
-value=>'xyzzy',
-expires=>'+1h',
-path=>'/cgi-bin/database',
-domain=>'.capricorn.org',
-secure=>1);
print $query->header(-cookie=>$cookie);
cookie() creates a new cookie. Its parameters include:
$cookie=$query->cookie(-name=>'family information',
-value=>\%childrens_ages);
"+1h" one hour from now
The cookie created by
cookie() must be incorporated into the
HTTP header within the string returned by the
header() method:
print $query->header(-cookie=>$my_cookie);
To create multiple cookies, give
header() an array reference:
$cookie1 = $query->cookie(-name=>'riddle_name',
-value=>"The Sphynx's Question");
$cookie2 = $query->cookie(-name=>'answers',
-value=>\%answers);
print $query->header(-cookie=>[$cookie1,$cookie2]);
To retrieve a cookie, request it by name by calling
cookie() method without the -value parameter:
use CGI;
$query = new CGI;
%answers = $query->cookie(-name=>'answers');
# $query->cookie('answers') will work too!
The cookie and
CGI namespaces are separate. If you have a parameter named 'answers' and a cookie named 'answers', the values retrieved by
param() and
cookie() are independent of each other. However, it's simple to turn a
CGI parameter into a cookie, and vice-versa:
# turn a CGI parameter into a cookie
$c=$q->cookie(-name=>'answers',-value=>[$q->param('answers')]);
# vice-versa
$q->param(-name=>'answers',-value=>[$q->cookie('answers')]);
See the cookie.cgi example script for some ideas on how to use cookies effectively.
NOTE: There appear to be some (undocumented) restrictions on Netscape cookies. In Netscape 2.01, at least, I haven't been able to set more than three cookies at a time. There may also be limits on the length of cookies. If you need to store a lot of information, it's probably better to create a unique session ID, store it in a cookie, and use the session ID to locate an external file/database saved on the server's side of the connection.
It's possible for CGI.pm scripts to write into several browser panels and windows using Netscape's frame mechanism. There are three techniques for defining new frames programmatically:
After writing out the
HTTP header, instead of creating a standard
HTML document using the
start_html() call, create a
<FRAMESET> document that defines the frames on the page. Specify your
script(s) (with appropriate parameters) as the
SRC for each of the frames.
There is no specific support for creating <FRAMESET> sections in CGI.pm, but the HTML is very simple to write. See the frame documentation in Netscape's home pages for details
http://home.netscape.com/assist/net_sites/frames.html
You may provide a -target parameter to the
header() method: print
$q->header(-target=>'ResultsWindow');
This will tell Netscape to load the output of your script into the frame named ``ResultsWindow''. If a frame of that name doesn't already exist, Netscape will pop up a new window and load your script's document into that. There are a number of magic names that you can use for targets. See the frame documents on Netscape's home pages for details.
print $q->startform(-target=>'ResultsWindow');
When your script is reinvoked by the form, its output will be loaded into the frame named ``ResultsWindow''. If one doesn't already exist a new window will be 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.
CGI.pm has limited support for HTML3's cascading style sheets (css). To incorporate a stylesheet into your document, pass the
start_html() method a
-style parameter. The value of this parameter may be a scalar, in which case it is
incorporated directly into a <
STYLE> section, or it may be a hash reference. In
the latter case you should provide the hash with one or more of -src or
-code. -src points to a
URL where an externally-defined stylesheet can be
found. -code points to a scalar value to be incorporated into a <
STYLE> section. Style definitions in -code
override similarly-named ones in -src, hence the name ``cascading.''
You may also specify the type of the stylesheet by adding the optional -type parameter to the hash pointed to by -style. If not specified, the style defaults to 'text/css'.
To refer to a style within the body of your document, add the -class parameter to any HTML element:
print h1({-class=>'Fancy'},'Welcome to the Party');
Or define styles on the fly with the -style parameter:
print h1({-style=>'Color: red;'},'Welcome to Hell');
You may also use the new span() element to apply a style to a section of text:
print span({-style=>'Color: red;'},
h1('Welcome to Hell'),
"Where did that handbasket get to?"
);
Note that you must import the ``:html3'' definitions to have the span() method available. Here's a quick and dirty example of using CSS's. See the CSS specification at http://www.w3.org/pub/WWW/TR/Wd-css-1.html for more information.
use CGI qw/:standard :html3/;
#here's a stylesheet incorporated directly into the page
$newStyle=<<END;
<!--
P.Tip {
margin-right: 50pt;
margin-left: 50pt;
color: red;
}
P.Alert {
font-size: 30pt;
font-family: sans-serif;
color: red;
}
-->
END
print header();
print start_html( -title=>'CGI with Style',
-style=>{-src=>'http://www.capricorn.com/style/st1.css',
-code=>$newStyle}
);
print h1('CGI with Style'),
p({-class=>'Tip'},
"Better read the cascading style sheet spec before playing with this!"),
span({-style=>'color: magenta'},
"Look Mom, no hands!",
p(),
"Whooo wee!"
);
print end_html;
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
or even as newline-delimited parameters on standard input.
When debugging, you can use quotes and backslashes to escape characters in the familiar shell manner, letting you place spaces and other funny characters in your parameter=value pairs:
your_script.pl "name1='I am a long value'" "name2=two\ words"
The
dump() method produces a string
consisting of all the query's name/value pairs formatted nicely as a nested
list. This is useful for debugging purposes:
print $query->dump
Produces something that looks like:
<UL>
<LI>name1
<UL>
<LI>value1
<LI>value2
</UL>
<LI>name2
<UL>
<LI>value1
</UL>
</UL>
You can pass a value of 'true' to
dump() in order to get it to print the results out as plain text, suitable for incorporating into a
<PRE> section.
As a shortcut, as of version 1.56 you can interpolate the entire CGI object into a string and it will be replaced with the a nice HTML dump shown above:
$query=new CGI;
print "<H2>Current Values</H2> $query\n";
Some of the more useful environment variables can be fetched through this interface. The methods are as follows:
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.
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_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.
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.
There are a number of ways to put CGI.pm into NPH mode:
use CGI qw(:standard -nph)
CGI->nph(1)
print $q->header(-nph=>1);
CGI.pm provides three simple functions for producing multipart documents of the type needed to implement server push. These functions were graciously provided by Ed Jordan <ed@fidalgo.net> To import these into your namespace, you must import the ``:push'' set. You are also advised to put the script into NPH mode and to set $| to 1 to avoid buffering problems.
Here is a simple script that demonstrates server push:
#!/usr/local/bin/perl
use CGI qw/:push -nph/;
$| = 1;
print multipart_init(-boundary=>'----------------here we go!');
while (1) {
print multipart_start(-type=>'text/plain'),
"The current time is ",scalar(localtime),"\n",
multipart_end;
sleep 1;
}
This script initializes server push by calling multipart_init(). It then enters an infinite loop in which it begins a new multipart section by calling multipart_start(), prints the current local time, and ends a multipart section with multipart_end(). It then sleeps a second, and begins again.
multipart_start(-type=>$type)
Start a new part of the multipart document using the specified MIME type. If not specified, text/html is assumed.
multipart_end()
End a part. You must remember to call
multipart_end() once for each
multipart_start().
Users interested in server push applications should also have a look at the CGI::Push module.
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:
You can use these variables in either of two ways.
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
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().
Since an attempt to send a
POST larger than $POST_MAX bytes will
cause a fatal error, you might want to use CGI::Carp to echo the fatal
error message to the browser window as shown in the example above.
Otherwise the remote user will see only a generic ``Internal Server'' error
message. See the Carp manual page for more details.
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.
Copyright 1995-1997, Lincoln D. Stein. All rights reserved. It may be used and modified freely, but I do request that this copyright notice remain attached to the file. You may modify this module as you wish, but if you redistribute a modified version, please attach a note listing the modifications you have made.
Address bug reports and comments to: lstein@genome.wi.mit.edu
Thanks very much to:
#!/usr/local/bin/perl
use CGI;
$query = new CGI;
print $query->header;
print $query->start_html("Example CGI.pm Form");
print "<H1> Example CGI.pm Form</H1>\n";
&print_prompt($query);
&do_work($query);
&print_tail;
print $query->end_html;
sub print_prompt {
my($query) = @_;
print $query->startform;
print "<EM>What's your name?</EM><BR>";
print $query->textfield('name');
print $query->checkbox('Not my real name');
print "<P><EM>Where can you find English Sparrows?</EM><BR>";
print $query->checkbox_group(
-name=>'Sparrow locations',
-values=>[England,France,Spain,Asia,Hoboken],
-linebreak=>'yes',
-defaults=>[England,Asia]);
print "<P><EM>How far can they fly?</EM><BR>",
$query->radio_group(
-name=>'how far',
-values=>['10 ft','1 mile','10 miles','real far'],
-default=>'1 mile');
print "<P><EM>What's your favorite color?</EM> ";
print $query->popup_menu(-name=>'Color',
-values=>['black','brown','red','yellow'],
-default=>'red');
print $query->hidden('Reference','Monty Python and the Holy Grail');
print "<P><EM>What have you got there?</EM><BR>";
print $query->scrolling_list(
-name=>'possessions',
-values=>['A Coconut','A Grail','An Icon',
'A Sword','A Ticket'],
-size=>5,
-multiple=>'true');
print "<P><EM>Any parting comments?</EM><BR>";
print $query->textarea(-name=>'Comments',
-rows=>10,
-columns=>50);
print "<P>",$query->reset;
print $query->submit('Action','Shout');
print $query->submit('Action','Scream');
print $query->endform;
print "<HR>\n";
}
sub do_work {
my($query) = @_;
my(@values,$key);
print "<H2>Here are the current settings in this form</H2>";
foreach $key ($query->param) {
print "<STRONG>$key</STRONG> -> ";
@values = $query->param($key);
print join(", ",@values),"<BR>\n";
}
}
sub print_tail {
print <<END;
<HR>
<ADDRESS>Lincoln D. Stein</ADDRESS><BR>
<A HREF="/">Home Page</A>
END
}
This module has grown large and monolithic. Furthermore it's doing many things, such as handling URLs, parsing CGI input, writing HTML, etc., that are also done in the LWP modules. It should be discarded in favor of the CGI::* modules, but somehow I continue to work on it.
Note that the code is truly contorted in order to avoid spurious warnings when programs are run with the -w switch.
Carp, URI, Request, MiniSvr, Base, Form, Apache, Switch, Push, Fast
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.