Re: Using perl to teach programming

Falkkin

Your perl tutor is great, just what I needed to teach a simple Perl 101 class. I had one additional requirement though, I wanted to allow anyone to do simple Perl evals without installing Perl or having a logon to a box with Perl installed. I also wanted to be able to demo simple Perl constructs real time for people without having to log into a shell.

What I came up with, after being inspired by your post, was a simple CGI that uses evel to do just that. Because the CGI is running in a trusted environment, we don't have to worry about people running malicous code ('cos if they do, I know where they live ;-)

So without further ado, here's my own simple solution (note that the name of the textarea element on the HTML form that sits in front of this code should be "code"):

#!/bin/perl

##################################################################
#  Execute perl statements passed in via a CGI form
#
##################################################################
# This script uses the cgi-lib.pl CGI library
# available at http://cgi-lib.berkeley.edu/
require 'cgi-lib.pl';

############ MAIN ###############
# Print HTTP Header
print &PrintHeader;

# Point STDERR to STDOUT
open (STDERR, ">&STDOUT");
# Flush STDERR and STDOUT
select STDERR; $| = 1;
select STDOUT; $| = 1;

# Parse CGI arguments
&ReadParse(*in);

printTop();
evaluate($in{'code'});
printFoot();

exit 0;

############ SUBS ###############

# converts any HTML special characters in the
# code to the equivelant HTML escape characters
# also adds line numbers to the code so that you can see
# what's going on
sub HTMLize {
    my $code = shift;

    # conversion
    $code =~ s/</&lt;/g;
    $code =~ s/>/&gt;/g;
    
    # add line numbers
    # make sure we have a \r\n at the end of the code
    $code .= "\r\n";
    $code =~ s(.*\r\n)("<li>$&")ge;
    return $code;
}

# Print the top portion of the HTML page
sub printTop {
    my $code = HTMLize($in{'code'});
    print <<"END_OF_HTML"
<html>
<head>
    <title>WebQA TNT: Perl 101 - PerlRun</title>
    <style>
        OL { margin-top : 0%;
             margin-bottom : 0%;
        }
        CODE { margin-top : 0%; 
             margin-bottom : 0%;
        }
        PRE { margin-top : 0%;
             margin-bottom : 0%;
        }
    </style>
</head>

<body bgcolor=white>
<h1>WebQA TNT: Perl 101 - PerlRun</h1>
<hr>
<b>Evaluating code:</b>
<code>
<pre>
<ol>
$code
</ol>
</pre>
&lt;/code>
<hr>
<b>Results of the evaluation are:</b>
<p>
<font color=blue>
<pre>
END_OF_HTML
}

# print the bottom portion of the html code
sub printFoot {
    print <<'END_OF_HTML'
</pre>
</font>
<hr>
</body>
</html>
END_OF_HTML
}

# use an eval statement to actually execute the
# statement passed in
sub evaluate {
  package WorkSpace;
  $_ = shift;
  eval($_);
  print "<font color=red>Unrecognized command or syntax error.<br>$@</
+font><br>\n" if $@;
  print "<br>\n";
  package main;
}
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