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Passwords

One of the interesting properties of CGI scripts is that, even though any user can execute them, there is no way to display them on the screen.

e-mail me if you know differently. This means a password script can be as simple as this:

#********BEGIN BODY**************

if ($value[0] ne "mypassword") {
print "Invalid Password";
} else {
print '

<BODY BGCOLOR="WHITE">

<H1> Welcome, you have entered the<P>
Password protected site </H1>

';
};

#*********END BODY***************

To use this script, you will need to create an HTML page with a form on it. If the password is the only box in the form, it will be passed to $value[0] when it runs this script.

Unlike JavaScript, the user cannot see this source code, so it is safe to use an IF statement at the top of the code.

if ($value[0] ne "mypassword") {

IF statement,

In Perl, the IF statement is different, depending on whether you are comparing numbers or text.
To compare numbers, you use the ==, !=, >, < signs.

If you are comparing text, you use the letters eq to test if two values are equal, and ne to test if they are not equal.

is NOT equal to

ELSE

}

Print "Invalid Password";

You have to print SOMETHING, or else you will get a "document contains no data" error. If you want to be nice, you could include a link back to the password page so they user can try again. } else {

DOES NOT

ELSE

DOES

print '

<BODY BGCOLOR="WHITE">

<H1> Welcome, you have entered the<P>
Password protected site </H1>

';

SINGLE QUOTES

$myfruit = "apples";
print "I love \nto eat $myfruit";
> I love
> to eat apples

print 'I love \nto eat $myfruit';
> I love \nto eat $myfruit

The double quotes are much smarter than the single quotes. They interpreted the \n character into a newline. The double quotes also replaced the text $myfruit with the contents of the variable. The single quotes simply displayed the text as it was typed. This is easier
for displaying an HTML page, because if the web page contains any special characters, the double quotes would try to interpret them.

You can always force the double quotes to ignore a special character by preceding it with a backslash \ character. We COULD have written the print statement this way.

print "I love \\n to eat \$myfruit";
> I love \n to eat $myfruit

IN SUMMARY: Use the single quotes when you are sure you will not want Perl to substitute any special characters. Use double quotes to allow Perl to insert variables and newlines and such.

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