system 'cmd.exe /c notepad.exe' || die "Cannot execute notepad.exe";
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Do you really want to launch notepad on the machine running the webserver? Why so?!?

Update: anyway, you got system's return value and ||'s precedence wrong, please read the docs.

Its just a proof of concept.

system('some_command') && die 'cannot execute some_command';
# or
system 'some_command' and die 'cannot execute some_command';
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Update: Fixed precedence and added another example with and. Thanks, kyle and blazar :-)

system 'some_command' && die 'cannot execute some_command';
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Really, both this and the OP's attempt get it wrong due to precedency issues. In fact I find myself repeating once again that as a rule of thumb, high precedence logical operators are for values and low precedence ones are for flow control. In particular, the OP's code appears to work because the die is never actually reached, while yours is the same as

system(die('cannot execute some_command'));
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So the program dies before calling system.

Even with the fix the program still dies on the system call. It works perfectly fine but run in a web browser, it dies.

system 'some_command' && die 'cannot execute some_command';

This will always die because it's interpreted as:

system( 'some_command' && die 'cannot execute some_command' );
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Since the string 'some_command' is a true value, the die always executes. To fix this, use and, which has a lower precedence:

system 'some_command' and die 'cannot execute some_command';
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The obvious DoS is to make your system open notepad.exe a hilarious number of times, simultaneously using up your webserver's MaxChildren. exec "notepad" unless fork might help with the children, but not with the hilarious number of notepads.

Just a thought, but perhaps the user that the web server is running as does not have enough permissions to affect the desktop of the user that's logged into the server?

Your call to system needs to have parentheses for the die to work (aside from the fact that system returns "false" on success).

system 'cmd.exe /c notepad.exe' || die 'no notepad';
# is the same as
system( 'cmd.exe /c notepad.exe' || die 'no notepad' );
# but you want
system( 'cmd.exe /c notepad.exe' ) && die 'no notepad';
# or you could do
system 'cmd.exe /c notepad.exe' and die 'no notepad';
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You could also get a little more explicit about what you expect from system:

0 == system 'cmd.exe /c notepad.exe'
    or die 'no notepad';
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This works for the error, it doesn't launch. However why does this not work on a server end put works alright locally executed. Is this an issue with the path? Thanks for the suggestions.

This works for the error, it doesn't launch. However why does this not work on a server end put works alright locally executed. Is this an issue with the path?

It may be. However, to quote from perldoc -f system:

You can check all the failure possibilities by inspecting $?
like this:

    if ($? == -1) {
        print "failed to execute: $!\n";
    }
    elsif ($? & 127) {
        printf "child died with signal %d, %s coredump\n",
            ($? & 127),  ($? & 128) ? 'with' : 'without';
    }
    else {
        printf "child exited with value %d\n", $? >> 8;
    }
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