Porting cgi-lib.pl Scripts to CGI.pm

I heartily endorse cgi-lib.pl for people who have good reasons for sticking with Perl version 4. However, sites that use Perl 5.001 and higher should seriously consider switching to CGI.pm or to the CGI::* modules. Here are some reasons why.

Why use CGI.pm instead of cgi-lib.pl?

CGI.pm provides better support for multi-valued parameters.

Named parameters that correspond to checkboxes and selection lists are frequently multi-valued. With cgi-lib.pl, you must manually split the components with split() or (in version 2.0) with SplitParam():

      @players=split("\0",$in{'players'});
      

With CGI.pm, you retrieve single or multi-valued parameters with the same syntax:

      @players=param('players');
      

CGI.pm provides a more elegant interface to file uploads.

In cgi-lib.pl you have to anticipate in advance how large Netscape file uploads may be and select whether the file is to be read into main memory or spooled to disk. CGI.pm provides you with a variable that you can treat as a scalar to recover the original file name, or as a file handle that you can read from just as if you were reading the original file. You don't have to worry about spooling issues:

      $in_file = param('file_to_upload');
      while (<$in_file>) {
         $lineCount++;
      }
      

CGI.pm gives you lots of HTML and HTTP shortcuts.

CGI.pm includes methods that generate HTTP headers, redirection requests, and HTML tags (including the Netscape extensions). These features are not included in cgi-lib.pl

CGI.pm provides a simple way of creating "sticky" forms and maintaining state.

Among the HTML tag-generating shortcuts are methods for generating the elements of fill-out forms. By default, these methods use the current query string to initialize the form element contents. This gives you a simple mechanism for saving the state of a session, and has the nice side effect that the form doesn't revert back to its initial state every time you regenerate it. Other methods in CGI.pm allow you to save state in URLs, write the state out to a file, or even store the session state in an external database.

CGI.pm gives you access to advanced HTTP and HTML features.

Support for persistent cookies, Netscape frames and JavaScript is built into the module, along with some of the more esoteric HTTP features such as content negotiation.

Reasons not to migrate to CGI.pm

How do I migrate from cgi-lib.pl to CGI.pm?

Old Script

require "cgi-lib.pl";
&ReadParse;
print "The price of your purchase is $in{price}.\n";

New Script

use CGI qw(:cgi-lib);
&ReadParse;
print "The price of your purchase is $in{price}.\n";

use CGI qw(:cgi-lib);

ReadParse(*Query);
@partners = split("\0",$Query{'golf_partners'});

&ReadParse;
print "The price of your purchase is $in{price}.\n";
$q = $in{CGI};
print $q->textfield(-name=>'price',
                -default=>'$1.99');

use CGI qw(:cgi-lib :standard);
&ReadParse;
print "The price of your purchase is $in{price}.\n";
print textfield(-name=>'price',
                -default=>'$1.99');

Cgi-lib functions that are available in CGI.pm

1. ReadParse()
2. PrintHeader()
3. HtmlTop()
4. HtmlBot()
5. SplitParam()
6. MethGet()
7. MethPost()

Cgi-lib functions that are not available in CGI.pm

Extended form of ReadParse()

The extended form of ReadParse() that provides for file upload spooling, is not available. However you can read the contents of the file directly from %in as follows:

      print "The name of the file is $in{uploaded_file};
      while (<$in{uploaded_file}>) {
         print "Next line = $_";
      }
      

MyBaseURL()

This function is not available. Use CGI.pm's url() method instead.

MyFullURL()

This function is not available. Use CGI.pm's self_url() method instead.

CgiError(), CgiDie()

These functions are not supported. Look at CGI::Carp for the way I prefer to handle error messages.

PrintVariables()

This function is not available. To achieve the same effect, just print out the CGI object:

      use CGI qw(:standard);
      $q = new CGI;
      print h1("The Variables Are"),$q;
      

PrintEnv()

This function is not available. You'll have to roll your own if you really need it.

@in not supported

The original ReadParse() stores the individual elements of the query string in an array named @in. This rarely- used feature is not supported. To retrieve the keywords from an oldstyle <ISINDEX> search, fetch the special array key keywords:

      @keywords = SplitParam($in{'keywords'});
      

Caveats