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File Password Protection

HTML FORM

Here is the HTML FORM for this example:

<html><body>
<center><h1>Password Protection</h1>
<hr>
<form method=POST action="cgi-bin/password2.pl">
<table>
<tr><td bgcolor="yellowgreen">Your  Name:  </td>  <td>   <INPUT NAME="name" TYPE="TEXT" SIZE="10" MAXLENGTH="20"></td>
<td> <INPUT TYPE="SUBMIT" VALUE="Submit"> </td></tr>
<tr>
<td bgcolor="yellowgreen">Your  Password:</td> <td><INPUT NAME="password" TYPE="PASSWORD" SIZE="10" MAXLENGTH="20"></td><td> <INPUT TYPE="RESET"></td>
</tr></table>
</form></center>
</body></html>

password2.pl

The following is the Perl source code:

#!/usr/local/bin/perl
########################################################################
#  password2.pl
#  11/26/97 by Zhanshou Yu
#  Any comments please send to :
#  zhanshou@hotmail.com
########################################################################

#Specify the protected file path and name
$filename="/home/CGITutorial/protectFile";

#Get the system date
$date=`/usr/bin/date`;
chop($date);         #chop the last enter character

#Define login name and password.
%PASSWD=('zyu','aaaa',
         'cwu','bbbb',
         'jeff','cccc');

#get the input data from the form. Here I use POST method
read(STDIN,$buffer,$ENV{'CONTENT_LENGTH'});

#Split the name-value pairs.
@pairs=split(/&/,$buffer);

#for each name=value pair, seperate them.
foreach $pair(@pairs){
    ($name,$value)=split(/=/,$pair);  #split name=value to name value
    $value=~tr/+/ /;                  #substitute plus sign with space sign
    $value=~s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg; #decode hexdecimal to cha
    $FORM{$name}=$value;
}

# print html header 
print" Content-type:text/html\n\n";

$flag=0;

#Check the received login name and password in our list or not, if in, open and read the file.
foreach $item(keys%PASSWD)
{ if(($item eq $FORM{'name'})&& ($FORM{'password'} eq $PASSWD{$item}))
  {
   $flag=1;
   open(FILE," $filename")||die"Cannot open $filename \n";
   while(<FILE>){
        print;
    }
   close(FILE);
   last;
  }
}

#login failed, print error message
if($flag==0)
{
   print "<title>Login failed</title>";
   print "<center><h1> Login Error </h1></center>";
   print "<hr>";
   print "<h4> Invalid login name or password!!</h4>";
}
exit;

Program Analysis

This program is very similar to the prevoius example except two different parts(shown by red color).

First we need specify the protected file name:

$filename="/home/CGITutorial/protectFile";

Now let's look at the second red parts:

{ if(($item eq $FORM{'name'})&& ($FORM{'password'} eq $PASSWD{$item}))
  {
   $flag=1;
   open(FILE," $filename")||die"Cannot open $filename \n";
   while(<FILE>){
        print;
    }
   close(FILE);
   last;
  }
}

After receiving login name and password, check whether they match any of pair in the name list:

if(($item eq $FORM{'name'})&& ($FORM{'password'} eq $PASSWD{$item}))

If found a match, open the file:

   open(FILE," $filename")||die"Cannot open $filename \n";

Then print it line by line:

while(<FILE>){
        print;
    }

Finally close the file:

close(FILE);