find out what is idiomatic Perl and what is not

Here's my take on how to make that a bit more idiomatic/modern/whatever:

use warnings;
use strict;
use IO::Prompt;

print "RegEx Engine 1.0\n", "________________\n";
my $str     = prompt("Gimme a string: ");
my $pattern = prompt("Gimme a RegEx: ");
print $str=~$pattern ? "Yes!" : "No.", "\n";
print "kthxbye\n";
[download]

(As an alternative to IO::Prompt, you could use ExtUtils::MakeMaker 'prompt'; - ExtUtils::MakeMaker is a core module, even though it has a completely different purpose. Or, there is Term::ReadLine.)

I don't want to end up writing Python in Perl.

But why not? ;-)

use Acme::Pythonic;
use warnings
use strict
use IO::Prompt

print("RegEx Engine 1.0\n________________\n")
while 1:
    my $str = prompt("Gimme a string: ")
    unless length($str):
        last
    my $pattern = prompt("Gimme a RegEx: ")
    if $str=~$pattern:
        print("Yes!\n")
    else:
        print("No.\n")
print("kthxbye\n")
[download]