Perl Cookbook

Creating Sticky Widgets

Problem

You want the default values for the fields in your form to be the last values submitted. For instance, you want to create a search form like AltaVista (http://altavista.digital.com/) where the keywords you’re searching with appear in the search dialog above the results.

Solution

Use CGI.pm’s HTML shortcuts to create your form, which will automatically provide previous values as defaults:

print textfield("SEARCH");          # previous SEARCH value is the default

Discussion

Example 19.8 is a simple script for querying the list of users currently logged in.

Example 19-8. who.cgi

#!/usr/bin/perl -wT
# who.cgi - run who(1) on a user and format the results nicely

$ENV{IFS}='';
$ENV{PATH}='/bin:/usr/bin';

use CGI qw(:standard);

# print search form
print header(), start_html("Query Users"), h1("Search");
print start_form(), p("Which user?", textfield("WHO")); submit(), end_form();

# print results of the query if we have someone to look for
$name = param("WHO");
if ($name) {
    print h1("Results");
    $html = '';
    
    # call who and build up text of response
    foreach (`who`) {
        next unless /^$name\s/o;            # only lines matching $name
        s/&/&/g;                        # escape HTML
        s/</&lt;/g;
        s/>/&gt;/g;
        $html .= $_;
    }
    # nice message if we didn't find anyone by that name
    $html = $html || "$name is not logged in";
    
    print pre($html);
}

print end_html();

The call to textfield generates HTML for a text entry field whose parameter name is WHO. After printing the form, we check whether we were called with a value ...