PerlHoo, Part II | 6

PerlHoo, Part II

Storing User Recommendations

Now we must deal with a few issues related to storing new site recommendations. When a user wants to recommend a new site for a particular category, he/she clicks the link labeled Suggest new link at the bottom of the directory page. This link is created dynamically in the print_footer subroutine (Lines 152-157). This calls the print_add_screen subroutine (Lines 99-122) which prints the form. The form is similar to the one below:

URL:
Title:
Description:	</td></tr><tr><td align="right"><b>Your Name:</b></td><td><input name="name" size="40" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" /></td></tr><tr><td align="right"><b>Your Email:</b></td><td><input name="email" size="40" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" /></td></tr><tr><td/><td><input type="submit" value=" Submit Resource " placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" /><input type="reset" value=" Reset " placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" /></td></tr></table></form> <p> When the user completes the form and clicks the <b>Submit Resource</b> button, the data is sent back to the script. Assuming the form method is <b>POST</b>, the <code><b>add_link</b></code> subroutine (<a href="source.html#55" target="_new">Lines 55-91</a>) appends the information to $rootdir/$reldir/$new_datafile which in our case would be /www/directory/Computers/Perl/perlhoo_new.csv if the category was Computers/Perl. </p> <p/><h2>File Permissions</h2> Because we're writing to files now, we must make sure that our Web server has proper permissions. Make sure the PerlHoo directory defined in the <code><b>$rootdir</b></code> variable on <a href="source.html#32" target="_new">Line 32</a> is writable by your Web server. <p/><h2>File Locking</h2> The <code><b>add_link</b></code> subroutine stores new site recommendations in a CSV file when the user clicks the <b>Submit Resource</b> button. This can cause a race condition where multiple users submit a new site simultaneously. In such a case, only the second set of data would be added to the file. <p> To solve this potential problem, <code><b>add_link</b></code> requests an exclusive lock on the file before it writes to it. This will ensure that data will not be lost. In <a href="source.html#60" target="_new">Line 60</a>, we open the data file in append mode. Then we request an exclusive lock in <a href="source.html#61" target="_new">Line 61</a>. We combine the form data into a CSV record in <a href="source.html#63" target="_new">Lines 63-65</a> and write it to the file. The lock is released when the file handle is closed in <a href="source.html#66" target="_new">Line 66</a>. </p> <div> <br/><table border="0" width="100%"><tr> <td align="right"> <a href="index-2.html"><img src="../../art/b_left.gif" width="18" height="18" border="0"/></a><a href="2.html"><img src="../../art/b_left.gif" width="18" height="18" border="0"/></a><a href="3.html"><img src="../../art/b_left.gif" width="18" height="18" border="0"/></a><a href="4.html"><img src="../../art/b_left.gif" width="18" height="18" border="0"/></a><a href="5.html"><img src="../../art/b_left.gif" width="18" height="18" border="0"/></a><a href="6.html"><img src="../../art/b_left.gif" width="18" height="18" border="0"/></a><img src="../../art/b_center.gif" width="18" height="18" border="0"/><a href="8.html"><img src="../../art/b_right.gif" width="18" height="18" border="0"/></a><a href="9.html"><img src="../../art/b_right.gif" width="18" height="18" border="0"/></a> </td> </tr></table><center> <p align="CENTER"><a href="https://www.internet.com/" target="_top"><img src="../../../img/URL.gif" border="0" width="161" height="18" alt="https://www.internet.com"/></a></p> <p align="CENTER"><small>Produced by <a href="../../../contact.html">Jonathan Eisenzopf</a> and <br/> Created: April 20, 1999<br/> Revised: April 21, 1999</small></p> <p align="CENTER"><small>URL: https://www.webreference.com/perl/tutorial/3/</small></p><br/></center> </div> <div id="right"><div class="image square quad" style='margin-bottom:20px;'> <!-- QS-AD: 'imu' start --> <script language="JavaScript"> var t=displayDFPTag("imu"); document.write(t); </script> <!-- QS-AD: 'imu' end --></div> <div id="ssn_widget_container"> <div id="ssn_widget_header"> <h5><img border="0" align="absbottom" alt="Justtechjobs.com" src="https://images.justtechjobs.com/images/webreference.gif"/>Find a programming school near you</h5> </div> <div id="ssn_widget_content"> <form inert id="SSN" name="populate" action="https://www.webreference.com/school-search-results.html" method="get"> <label>Zip Code:</label> <input name="pc" type="text" maxlength="5" value="" style="display:block;float:left;" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" /> <br/><br/> <label>Subject:</label> <select name="sub"> <option value="all">- Select All Subjects -</option> <optgroup label="Computers and Technology"> <option value="compapplications">Computer Applications</option> <option value="comeng">Computer Engineering</option> <option value="comscience">Computer Science</option> <option value="cnp" selected="selected">Computer Prog. - Software Dev.</option> <option value="gameprogramming">Computer Game Programming</option> <option value="webdesign">Web Design</option> <option value="webdevelopment">Web Development</option> <option value="internetsystems">Internet Systems</option> <option value="internetcertification">Internet Certification</option> <option value="databasedesign">Database Design and Development</option> <option value="infosystemsmgmt">Information Systems Management</option> <option value="itprojectmgmt">Information Technology Project Management</option> <option value="networkdesign">Network Design - Development</option> <option value="systemsanalyst">Systems Analyst</option> </select> <br/><br/> <label>Degree:</label> <select name="qual"> <option value="all" selected="selected">- Select All Degrees -</option> <option value="associate">Associate's</option> <option value="bachelor">Bachelor's</option> <option value="master">Master's</option> <option value="doctoral">Doctoral</option> <option value="certificate">Certificates</option> <option value="diploma">Diplomas</option> <option value="coursework">Coursework</option> <option value="mba">MBA</option> </select> <br style="clear:both;"/><br/> <input name="ct" type="radio" value="online" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" />Online <input name="ct" type="radio" value="campus" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" />Campus <input name="ct" type="radio" value="either" checked="checked" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" />Both <br/><br/> <input type="submit" value="Submit" placeholder="disabled" disabled="disabled" title="form boxes are disabled in cached version of the site" value="Disabled" style="opacity:0.3;" /> </form></div> </div><div class="image square quad" style='margin-bottom:20px;'> <!-- QS-AD: 'imu' start --> <script language="JavaScript"> var t=displayDFPTag("imu"); document.write(t); </script> <!-- QS-AD: 'imu' end --></div> <!-- request_uri: '/perl/tutorial/3/7.html' --> <div class="articlecategorysummary"> <iframe scrolling="no" frameborder="0" align="middle" src="https://webreference.com/sl/assetlisting/indexae18.html?wsn=www.webreference.com&wpu=/perl/tutorial/3/7.html&lurl=https://o1.qnsr.com/cgi/r?WT.qs_dlk=WkaVXwrIZ78AAHyIJ7UAAAAS%20domain=None;;n=203;c=1395323;s=9530;x=7936;f=201308291521150;u=j;z=TIMESTAMP;k=https://assetform.webreference.com/controller&wpos=AssetListing&lyt=l9&mcss=https://www.webreference.com/imageserver/b2btechleadform/webreference/styles/style_email.css&css=https://www.webreference.com/hqb2b/css/qmp/qmp_default.css&title=Top%20White%20Papers%20and%20Webcasts" name="inneriframe" id="inneriframe" height="820px" width="340px;"></iframe> </div> <script type="text/javascript"> var updateIframe = false; var t = 0; function updateQMPIframe(){ if(!updateIframe) { if($('#inneriframe').contents().find('.asset').length > 0) { if($('#inneriframe').contents().find('#widget-title').text()=='Whitepapers and More'){ $('#inneriframe').contents().find('#widget-title').html('Recommended White Papers and Resources'); //hacky way of changing the QMP widget title } var height = $('#inneriframe').contents().find('#assetsListings').height(); var iframe = document.getElementById('inneriframe'); iframe.setAttribute( 'height', height+50); clearTimeout(t); } else { updateIframe = true; t = setTimeout('updateQMPIframe()', 3000); } } } t = setTimeout('updateQMPIframe()', 5000); </script> </div> </div> <div class="clear"></div> <div id="footer"> <div id="footer_content"> <div id="quad_bottom"class="quad" align='center' style='margin-left:auto;margin-right:auto;width:720px;'> <!-- QS-AD: 'lb' start --> <script language="JavaScript"> var t=displayDFPTag("lb"); document.write(t); </script> <!-- QS-AD: 'lb' end --> </div> <div class="footer_listing"> </div> <div class="footer_listing"> <span class="list-header">WebReference</span> <ul> <li class="first"><a href="../../../js/tips/index.html">Tip Archive</a></li> <li><a href="../../../about.html">About</a></li> <li><a href="../../../sitemap.html">Sitemap</a></li> <li><a href="../../../contact.html">Contact</a></li> <li><a href="../../../accountManagement87fb.html%3FformType=registrationForm.html">Subscribe</a></li> </ul> </div> <div class="footer_listing"> <span class="list-header">Topics</span> <ul> <li class="first"><a href="https://webreference.com/authoring.html">Web Authoring</a></li> <li><a href="../../../internet/index.html">The Internet and the Web</a></li> <li><a href="../../../multimedia/index.html">Multimedia</a></li> <li><a href="https://webreference.com/programming.html">Web Programming</a></li> <li><a href="../../../promotion/index.html">Website Promotion and Marketing</a></li> <li><a href="../../../experts/index.html">Contributors</a></li> </ul> </div> <div class="footer_listing"> <span class="list-header"><a href="https://www.developer.com/"><img src="../../../img/dev.com_logo.png" alt="Developer.com"></a></span> <ul> <li class="first"><a href="../../../terms.html">Terms Of Service</a></li> <li><a href="../../../licensing.html">Licensing and Permissions</a></li> <li><a href="../../../privacy.html">Privacy Policy</a></li> <li><a href="../../../mediakit/index.html">Advertising</a></li> <li><a href="https://e-newsletters.developer.com/">Newsletters</a></li> <!--<li><a href="https://e-newsletters.developer.com/announcement_list.html">E-mail Offers</a></li> --> </ul> </div> <div class="footer_listing"> </div> <div class="clear"></div> <div id="copyright"> Copyright © 2017 QuinStreet Inc. All Rights Reserved. </div> </div> <!-- Google Analytics --> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]\|\|function(){ (i[r].q=i[r].q\|\|[]).push(arguments)},i[r].l=1new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','https://www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-48218803-1', 'auto'); ga('send', 'pageview'); </script> <!-- End Google Analytics --> </div> <!-- CREATE AJAX CONTAINERS --> <div id="ajax_alpha"></div> <div id="ajax_beta"></div> <script language="javascript" src="../../../scripts/shCore.js"> </script> <script language="javascript" src="../../../scripts/shBrushPhp.js"> </script> <script language="javascript" src="../../../scripts/shBrushXml.js"> </script> <script language="javascript" src="../../../scripts/shBrushJScript.js"> </script> <script language="javascript"> dp.SyntaxHighlighter.HighlightAll('code'); </script> <!-- FOR LIKE BUTTON --> <script src="https://connect.facebook.net/en_US/all.js#xfbml=1" type="text/javascript"> </script> <div id="fb-root"></div> <script src="https://geoip.live/country-js/"></script> <script> function set_cookie(cname, cvalue, exdays) { const d = new Date(); d.setTime(d.getTime() + (exdays246060*1000)); let expires = "expires="+ d.toUTCString(); document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/"; } set_cookie("user_country_code", user_country_code, 7); </script> <script type="text/javascript"> var sc_project=11145952; var sc_invisible=1; var sc_security="40b893f9"; </script> <script type="text/javascript" src="//www.statcounter.com/counter/counter.js" async></script> <noscript> <div class="statcounter"> <img class="statcounter" src="//c.statcounter.com/11145952/0/40b893f9/1/" alt="Web Analytics"> </div> </noscript> </body> <!-- Mirrored from www.webreference.com/perl/tutorial/3/7.html by HTTrack Website Copier/3.x [XR&CO'2014], Fri, 29 Dec 2017 21:52:40 GMT --> </html>