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perlman:lib:CGI

by root (Scribe)
on Dec 23, 1999 at 00:49 UTC ( #1098=perlfunc: print w/ replies, xml ) Need Help??

lib:CGI

See the current Perl documentation for lib:CGI.

Here is our local, out-dated (pre-5.6) version:


CGI - Simple Common Gateway Interface Class



      use CGI qw/:standard/;
      print header,
            start_html('A Simple Example'),
            h1('A Simple Example'),
            start_form,
      # ...


PROGRAMMING STYLE

There are two styles of programming with CGI.pm, an object-oriented style and a function-oriented style. In the object-oriented style you create one or more CGI objects and then use object methods to create the various elements of the page. Each CGI object starts out with the list of named parameters that were passed to your CGI script by the server. You can modify the objects, save them to a file or database and recreate them. Because each object corresponds to the ``state'' of the CGI script, and because each object's parameter list is independent of the others, this allows you to save the state of the script and restore it later.

For example, using the object oriented style, here is now you create a simple ``Hello World'' HTML page:

   #!/usr/local/bin/perl
   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


CALLING CGI.PM ROUTINES

Most CGI.pm routines accept several arguments, sometimes as many as 20 optional ones! To simplify this interface, all routines use a named argument calling style that looks like this:

   print $q->header(-type=>'image/gif',-expires=>'+3d');

Each argument name is preceded by a dash. Neither case nor order matters in the argument list. -type, -Type, and -TYPE are all acceptable. In fact, only the first argument needs to begin with a dash. If a dash is present in the first argument, CGI.pm assumes dashes for the subsequent ones.

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:

  1. Use another name for the argument, if one is available. For example, -value is an alias for -values.
  2. Change the capitalization, e.g. -Values
  3. Put quotes around the argument name, e.g. '-values'

Many routines will do something useful with a named argument that it doesn't recognize. For example, you can produce non-standard HTTP header fields by providing them as named arguments:

  print $q->header(-type  =>  'text/html',
                   -cost  =>  'Three smackers',
                   -annoyance_level => 'high',
                   -complaints_to   => 'bit bucket');

This will produce the following nonstandard HTTP header:

   HTTP/1.0 200 OK
   Cost: Three smackers
   Annoyance-level: high
   Complaints-to: bit bucket
   Content-type: text/html

Notice the way that underscores are translated automatically into hyphens. HTML-generating routines perform a different type of translation.

This feature allows you to keep up with the rapidly changing HTTP and HTML ``standards''.


CREATING A NEW QUERY OBJECT (OBJECT-ORIENTED STYLE):

     $query = new CGI;

This will parse the input (from both POST and GET methods) and store it into a perl5 object called $query.


CREATING A NEW QUERY OBJECT FROM AN INPUT FILE

     $query = new CGI(INPUTFILE);

If you provide a file handle to the new() method, it will read parameters from the file (or STDIN, or whatever). The file can be in any of the forms describing below under debugging (i.e. a series of newline delimited TAG=VALUE pairs will work). Conveniently, this type of file is created by the save() method (see below). Multiple records can be saved and restored.

Perl purists will be pleased to know that this syntax accepts references to file handles, or even references to filehandle globs, which is the ``official'' way to pass a filehandle:

    $query = new CGI(\*STDIN);

You can also initialize the CGI object with a FileHandle or IO::File object.

If you are using the function-oriented interface and want to initialize CGI state from a file handle, the way to do this is with restore_parameters(). This will (re)initialize the default CGI object from the indicated file handle.

    open (IN,"test.in") || die;
    restore_parameters(IN);
    close IN;

You can also initialize the query object from an associative array reference:

    $query = new CGI( {'dinosaur'=>'barney',
                       'song'=>'I love you',
                       'friends'=>[qw/Jessica George Nancy/]}
                    );

or from a properly formatted, URL-escaped query string:

    $query = new CGI('dinosaur=barney&color=purple');

or from a previously existing CGI object (currently this clones the parameter list, but none of the other object-specific fields, such as autoescaping):

    $old_query = new CGI;
    $new_query = new CGI($old_query);

To create an empty query, initialize it from an empty string or hash:

   $empty_query = new CGI("");

       -or-

   $empty_query = new CGI({});


FETCHING A LIST OF KEYWORDS FROM THE QUERY:

     @keywords = $query->keywords

If the script was invoked as the result of an <ISINDEX> search, the parsed keywords can be obtained as an array using the keywords() method.


FETCHING THE NAMES OF ALL THE PARAMETERS PASSED TO YOUR SCRIPT:

     @names = $query->param

If the script was invoked with a parameter list (e.g. ``name1=value1&name2=value2&name3=value3''), the param() method will return the parameter names as a list. If the script was invoked as an <ISINDEX> script, 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).


FETCHING THE VALUE OR VALUES OF A SINGLE NAMED PARAMETER:

    @values = $query->param('foo');

              -or-

    $value = $query->param('foo');

Pass the param() method a single argument to fetch the value of the named parameter. If the parameter is multivalued (e.g. from multiple selections in a scrolling list), you can ask to receive an array. Otherwise the method will return a single value.


SETTING THE VALUE(S) OF A NAMED PARAMETER:

    $query->param('foo','an','array','of','values');

This sets the value for the named parameter 'foo' to an array of values. This is one way to change the value of a field AFTER the script has been invoked once before. (Another way is with the -override parameter accepted by all methods that generate form elements.)

param() also recognizes a named parameter style of calling described in more detail later:

    $query->param(-name=>'foo',-values=>['an','array','of','values']);

                              -or-

    $query->param(-name=>'foo',-value=>'the value');


APPENDING ADDITIONAL VALUES TO A NAMED PARAMETER:

   $query->append(-name=>'foo',-values=>['yet','more','values']);

This adds a value or list of values to the named parameter. The values are appended to the end of the parameter if it already exists. Otherwise the parameter is created. Note that this method only recognizes the named argument calling syntax.


IMPORTING ALL PARAMETERS INTO A NAMESPACE:

   $query->import_names('R');

This creates a series of variables in the 'R' namespace. For example, $R::foo, @R:foo. For keyword lists, a variable @R::keywords will appear. If no namespace is given, this method will assume 'Q'. WARNING: don't import anything into 'main'; this is a major security risk!!!!

In older versions, this method was called import(). As of version 2.20, this name has been removed completely to avoid conflict with the built-in Perl module import operator.


DELETING A PARAMETER COMPLETELY:

    $query->delete('foo');

This completely clears a parameter. It sometimes useful for resetting parameters that you don't want passed down between script invocations.

If you are using the function call interface, use ``Delete()'' instead to avoid conflicts with Perl's built-in delete operator.


DELETING ALL PARAMETERS:

   $query->delete_all();

This clears the CGI object completely. It might be useful to ensure that all the defaults are taken when you create a fill-out form.

Use Delete_all() instead if you are using the function call interface.


DIRECT ACCESS TO THE PARAMETER LIST:

   $q->param_fetch('address')->[1] = '1313 Mockingbird Lane';
   unshift @{$q->param_fetch(-name=>'address')},'George Munster';

If you need access to the parameter list in a way that isn't covered by the methods above, you can obtain a direct reference to it by calling the param_fetch() method with the name of the . This will return an array reference to the named parameters, which you then can manipulate in any way you like.

You can also use a named argument style using the -name argument.


SAVING THE STATE OF THE SCRIPT TO A FILE:

    $query->save(FILEHANDLE)

This will write the current state of the form to the provided filehandle. You can read it back in by providing a filehandle to the new() method. Note that the filehandle can be a file, a pipe, or whatever!

The format of the saved file is:

        NAME1=VALUE1
        NAME1=VALUE1'
        NAME2=VALUE2
        NAME3=VALUE3
        =

Both name and value are URL escaped. Multi-valued CGI parameters are represented as repeated names. A session record is delimited by a single = symbol. You can write out multiple records and read them back in with several calls to new. You can do this across several sessions by opening the file in append mode, allowing you to create primitive guest books, or to keep a history of users' queries. Here's a short example of creating multiple session records:

   use CGI;

   open (OUT,">>test.out") || die;
   $records = 5;
   foreach (0..$records) {
       my $q = new CGI;
       $q->param(-name=>'counter',-value=>$_);
       $q->save(OUT);
   }
   close OUT;

   # reopen for reading
   open (IN,"test.out") || die;
   while (!eof(IN)) {
       my $q = new CGI(IN);
       print $q->param('counter'),"\n";
   }

The file format used for save/restore is identical to that used by the Whitehead Genome Center's data exchange format ``Boulderio'', and can be manipulated and even databased using Boulderio utilities. See http://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().


USING THE FUNCTION-ORIENTED INTERFACE

To use the function-oriented interface, you must specify which CGI.pm routines or sets of routines to import into your script's namespace. There is a small overhead associated with this importation, but it isn't much.

   use CGI <list of methods>;

The listed methods will be imported into the current package; you can call them directly without creating a CGI object first. This example shows how to import the param() and header() methods, and then use them directly:

   use CGI 'param','header';
   print header('text/plain');
   $zipcode = param('zipcode');

More frequently, you'll import common sets of functions by referring to the 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:

: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 %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 Exporter syntax for specifying load symbols. This may change in the future.

If you import any of the state-maintaining CGI or form-generating methods, a default CGI object will be created and initialized automatically the first time you use any of the methods that require one to be present. This includes param(), textfield(), submit() and the like. (If you need direct access to the CGI object, you can find it in the global variable $CGI::Q). By importing CGI.pm methods, you can create visually elegant scripts:

   use CGI qw/:standard/;
   print 
       header,
       start_html('Simple Script'),
       h1('Simple Script'),
       start_form,
       "What's your name? ",textfield('name'),p,
       "What's the combination?",
       checkbox_group(-name=>'words',
                      -values=>['eenie','meenie','minie','moe'],
                      -defaults=>['eenie','moe']),p,
       "What's your favorite color?",
       popup_menu(-name=>'color',
                  -values=>['red','green','blue','chartreuse']),p,
       submit,
       end_form,
       hr,"\n";

    if (param) {
       print 
           "Your name is ",em(param('name')),p,
           "The keywords are: ",em(join(", ",param('words'))),p,
           "Your favorite color is ",em(param('color')),".\n";
    }
    print end_html;


PRAGMAS

In addition to the function sets, there are a number of pragmas that you can import. Pragmas, which are always preceded by a hyphen, change the way that CGI.pm functions in various ways. Pragmas, function sets, and individual functions can all be imported in the same use() line. For example, the following use statement imports the standard set of functions and disables debugging mode (pragma -no_debug):

   use CGI qw/:standard -no_debug/;

The current list of pragmas is as follows:

-any

When you use CGI -any, then any method that the query object doesn't recognize will be interpreted as a new HTML tag. This allows you to support the next ad hoc Netscape or Microsoft HTML extension. This lets you go wild with new and unsupported tags:

   use CGI qw(-any);
   $q=new CGI;
   print $q->gradient({speed=>'fast',start=>'red',end=>'blue'});

Since using <cite>any</cite> causes any mistyped method name to be interpreted as an HTML tag, use it with care or not at all.

-compile

This causes the indicated autoloaded methods to be compiled up front, rather than deferred to later. This is useful for scripts that run for an extended period of time under FastCGI or mod_perl, and for those destined to be crunched by Malcom Beattie's Perl compiler. Use it in conjunction with the methods or method familes 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).

-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.

-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 pausing to request CGI parameters from standard input or the command line, then use this pragma:

   use CGI qw(-no_debug :standard);

If you'd like to process the command-line parameters but not standard input, this should work:

   use CGI qw(-no_debug :standard);
   restore_parameters(join('&',@ARGV));
  
See the section on debugging for more details.
-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, eliminating the risk of eavesdropping. n =back

GENERATING DYNAMIC DOCUMENTS

Most of CGI.pm's functions deal with creating documents on the fly. Generally you will produce the HTTP header first, followed by the document itself. CGI.pm provides functions for generating HTTP headers of various types as well as for generating HTML. For creating GIF images, see the GD.pm module.

Each of these functions produces a fragment of HTML or HTTP which you can print out directly so that it displays in the browser window, append to a string, or save to a file for later use.

CREATING A STANDARD HTTP HEADER:

Normally the first thing you will do in any CGI script is print out an HTTP header. This tells the browser what type of document to expect, and gives other optional information, such as the language, expiration date, and whether to cache the document. The header can also be manipulated for special purposes, such as server push and pay per view pages.

        print $query->header;

             -or-

        print $query->header('image/gif');

             -or-

        print $query->header('text/html','204 No response');

             -or-

        print $query->header(-type=>'image/gif',
                             -nph=>1,
                             -status=>'402 Payment required',
                             -expires=>'+3d',
                             -cookie=>$cookie,
                             -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.

GENERATING A REDIRECTION HEADER

   print $query->redirect('http://somewhere.else/in/movie/land');

Sometimes you don't want to produce a document yourself, but simply redirect the browser elsewhere, perhaps choosing a URL based on the time of day or the identity of the user.

The redirect() function redirects the browser to a different URL. If you use redirection like this, you should not print out a header as well. 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.

CREATING THE HTML DOCUMENT HEADER

   print $query->start_html(-title=>'Secrets of the Pyramids',
                            -author=>'fred@capricorn.org',
                            -base=>'true',
                            -target=>'_blank',
                            -meta=>{'keywords'=>'pharaoh secret mummy',
                                    'copyright'=>'copyright 1996 King Tut'},
                            -style=>{'src'=>'/styles/style1.css'},
                            -BGCOLOR=>'blue');

After creating the HTTP header, most CGI scripts will start writing out an HTML document. The start_html() routine creates the top of the page, along with a lot of optional information that controls the page's appearance and behavior.

This method returns a canned HTML header and the opening <BODY> tag. All parameters are optional. In the named parameter form, recognized parameters are -title, -author, -base, -xbase 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=>'s2'}));

To incorporate multiple HTML elements into the <HEAD> section, just pass an array reference:

    print $q->start_html(-head=>[ 
                              Link({-rel=>'next',
                                    -href=>'s2'}),
                              Link({-rel=>'previous',
                                    -href=>'s1'})
                             ]
                     );

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-&gt;start_html(-title=&gt;'The Riddle of the Sphinx',
                          -script=&gt;[
                                    { -language =&gt; 'JavaScript1.0',
                                      -src      =&gt; '/javascript/utilities10.js'
                                    },
                                    { -language =&gt; 'JavaScript1.1',
                                      -src      =&gt; '/javascript/utilities11.js'
                                    },
                                    { -language =&gt; 'JavaScript1.2',
                                      -src      =&gt; '/javascript/utilities12.js'
                                    },
                                    { -language =&gt; 'JavaScript28.2',
                                      -src      =&gt; '/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.
  • ENDING THE HTML DOCUMENT:

            print $query->end_html
    

    This ends an HTML document by printing the </BODY></HTML> tags.

    CREATING A SELF-REFERENCING URL THAT PRESERVES STATE INFORMATION:

        $myself = $query->self_url;
        print "<A HREF=$myself>I'm talking to myself.</A>";
    

    self_url() will return a URL, that, when selected, will reinvoke this script with all its state information intact. This is most useful when you want to jump around within the document using internal anchors but you don't want to disrupt the current contents of the form(s). Something like this will do the trick.

         $myself = $query->self_url;
         print "<A HREF=$myself#table1>See table 1</A>";
         print "<A HREF=$myself#table2>See table 2</A>";
         print "<A HREF=$myself#yourself>See for yourself</A>";
    

    If you want more control over what's returned, using the url() method instead.

    You can also retrieve the unprocessed query string with query_string():

        $the_string = $query->query_string;
    

    OBTAINING THE SCRIPT'S URL

        $full_url      = $query->url();
        $full_url      = $query->url(-full=>1);  #alternative syntax
        $relative_url  = $query->url(-relative=>1);
        $absolute_url  = $query->url(-absolute=>1);
        $url_with_path = $query->url(-path_info=>1);
        $url_with_path_and_query = $query->url(-path_info=>1,-query=>1);
    

    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.

    CREATING STANDARD HTML ELEMENTS:

    CGI.pm defines general HTML shortcut methods for most, if not all of the HTML 3 and HTML 4 tags. HTML shortcuts are named after a single HTML element and return a fragment of HTML text that you can then print or manipulate as you like. Each shortcut returns a fragment of HTML code that you can append to a string, save to a file, or, most commonly, print out so that it displays in the browser window.

    This example shows how to use the HTML methods:

       $q = new CGI;
       print $q->blockquote(
                         "Many years ago on the island of",
                         $q->a({href=>"http://crete.org/";},"Crete"),
                         "there lived a minotaur named",
                         $q->strong("Fred."),
                        ),
           $q->hr;
    

    This results in the following HTML code (extra newlines have been added for readability):

       <blockquote>
       Many years ago on the island of
       <a HREF="http://crete.org/";>Crete</a> there lived
       a minotaur named <strong>Fred.</strong> 
       </blockquote>
       <hr>
    

    If you find the syntax for calling the HTML shortcuts awkward, you can import them into your namespace and dispense with the object syntax completely (see the next section for more details):

       use CGI ':standard';
       print blockquote(
          "Many years ago on the island of",
          a({href=>"http://crete.org/";},"Crete"),
          "there lived a minotaur named",
          strong("Fred."),
          ),
          hr;
    

    PROVIDING ARGUMENTS TO HTML SHORTCUTS

    The HTML methods will accept zero, one or multiple arguments. If you provide no arguments, you get a single tag:

       print hr;    #  <HR>
    

    If you provide one or more string arguments, they are concatenated together with spaces and placed between opening and closing tags:

       print h1("Chapter","1"); # <H1>Chapter 1</H1>"
    

    If the first argument is an associative array reference, then the keys and values of the associative array become the HTML tag's attributes:

       print a({-href=>'fred.html',-target=>'_new'},
          "Open a new frame");
    

                <A HREF="fred.html",TARGET="_new">Open a new frame</A>
       
    You may dispense with the dashes in front of the attribute names if
    you prefer:
    

       print img {src=>'fred.gif',align=>'LEFT'};
    

               <IMG ALIGN="LEFT" SRC="fred.gif">
    

    Sometimes an HTML tag attribute has no argument. For example, ordered lists can be marked as COMPACT. The syntax for this is an argument that 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=``''>

    THE DISTRIBUTIVE PROPERTY OF HTML SHORTCUTS

    One of the cool features of the HTML shortcuts is that they are distributive. If you give them an argument consisting of a reference to a list, the tag will be distributed across each element of the list. For example, here's one way to make an ordered list:

       print ul(
                 li({-type=>'disc'},['Sneezy','Doc','Sleepy','Happy']);
               );
    

    This example will result in HTML output that looks like this:

       <UL>
         <LI TYPE="disc">Sneezy</LI>
         <LI TYPE="disc">Doc</LI>
         <LI TYPE="disc">Sleepy</LI>
         <LI TYPE="disc">Happy</LI>
       </UL>
    

    This is extremely useful for creating tables. For example:

       print table({-border=>undef},
               caption('When Should You Eat Your Vegetables?'),
               Tr({-align=>CENTER,-valign=>TOP},
               [
                  th(['Vegetable', 'Breakfast','Lunch','Dinner']),
                  td(['Tomatoes' , 'no', 'yes', 'yes']),
                  td(['Broccoli' , 'no', 'no',  'yes']),
                  td(['Onions'   , 'yes','yes', 'yes'])
               ]
               )
            );
    

    HTML SHORTCUTS AND LIST INTERPOLATION

    Consider this bit of code:

       print blockquote(em('Hi'),'mom!'));
    

    It will ordinarily return the string that you probably expect, namely:

       <BLOCKQUOTE><EM>Hi</EM> mom!</BLOCKQUOTE>
    

    Note the space between the element ``Hi'' and the element ``mom!''. CGI.pm puts the extra space there using array interpolation, which is controlled by the magic $`` variable. Sometimes this extra space is not what you want, for example, when you are trying to align a series of images. In this case, you can simply change the value of $'' to an empty string.

       {
          local($") = '';
          print blockquote(em('Hi'),'mom!'));
        }
    

    I suggest you put the code in a block as shown here. Otherwise the change to $`` will affect all subsequent code until you explicitly reset it.

    NON-STANDARD HTML SHORTCUTS

    A few HTML tags don't follow the standard pattern for various reasons.

    comment() generates an HTML comment (<!-- comment -->). Call it like

        print comment('here is my comment');
    

    Because of conflicts with built-in Perl functions, the following functions begin with initial caps:

        Select
        Tr
        Link
        Delete
    

    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.

    CREATING FILL-OUT FORMS:

    General note The various form-creating methods all return strings to the caller, containing the tag or tags that will create the requested form element. You are responsible for actually printing out these strings. It's set up this way so that you can place formatting tags around the form elements.

    Another note The default values that you specify for the forms are only used the first time the script is invoked (when there is no query string). On subsequent invocations of the script (when there is a query string), the former values are used even if they are blank.

    If you want to change the value of a field from its previous value, you have two choices:

    (1) call the param() method to set it.

    (2) use the -override (alias -force) parameter (a new feature in version 2.15). This forces the default value to be used, regardless of the previous value:

       print $query->textfield(-name=>'field_name',
                               -default=>'starting value',
                               -override=>1,
                               -size=>50,
                               -maxlength=>80);
    

    Yet another note By default, the text and labels of form elements are escaped according to HTML rules. This means that you can safely use ``<CLICK ME>'' as the label for a button. However, it also interferes with your ability to incorporate special HTML character sequences, such as &Aacute;, into your fields. If you wish to turn off automatic escaping, call the autoEscape() method with a false value immediately after creating the CGI object:

       $query = new CGI;
       $query->autoEscape(undef);
                                 
    

    CREATING AN ISINDEX TAG

       print $query->isindex(-action=>$action);
    

             -or-
    

       print $query->isindex($action);
    

    Prints out an <ISINDEX> tag. Not very exciting. The parameter -action specifies the URL of the script to process the query. The default is to process the query with the current script.

    STARTING AND ENDING A FORM

        print $query->startform(-method=>$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:

    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 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.

    CREATING A TEXT FIELD

        print $query->textfield(-name=>'field_name',
                                -default=>'starting value',
                                -size=>50,
                                -maxlength=>80);
            -or-
    

        print $query->textfield('field_name','starting value',50,80);
    

    textfield() will return a text input field.

    Parameters
  • .

    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.

    CREATING A BIG TEXT FIELD

       print $query->textarea(-name=>'foo',
                              -default=>'starting value',
                              -rows=>10,
                              -columns=>50);
    

            -or
    

       print $query->textarea('foo','starting value',10,50);
    

    textarea() is just like textfield, but it allows you to specify rows and columns for a multiline text entry box. You can provide a starting value for the field, which can be long and contain multiple lines.

    JAVASCRIPTING: The -onChange, -onFocus, -onBlur , -onMouseOver, -onMouseOut, and -onSelect parameters are recognized. See textfield().

    CREATING A PASSWORD FIELD

       print $query->password_field(-name=>'secret',
                                    -value=>'starting value',
                                    -size=>50,
                                    -maxlength=>80);
            -or-
    

       print $query->password_field('secret','starting value',50,80);
    

    password_field() is identical to textfield(), except that its contents will be starred out on the web page.

    JAVASCRIPTING: The -onChange, -onFocus, -onBlur, -onMouseOver, -onMouseOut and -onSelect parameters are recognized. See textfield(). More

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