here is your code fixed :) 
#!\perl\bin\perl.exe -w
use strict;
use CGI qw(:all);
my $cgi = new CGI;

#usernames and passwords
my %login = qw(antonis koukou giannis zabon);

my $user = param("user");
my $pass = param("pass");


print $cgi->header.
        $cgi-> start_html();

if ($pass eq $login{$user} && $pass && $user) {#Add && $user && $pass
    print $cgi-> p("Welcome back $user");
            
}else {
    print $cgi-> p("Sorry invalid username or password");
}
print $cgi->end_html;

[download]

In reply to Re: cgi problem by JamesNC
in thread cgi problem by atnonis

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.