The following works without errors: 
use strict;
use warnings;

my %sym = ('x' => 4, 'y' => 7); 
while (<DATA>) {
    chomp; s/==/=/g; s/=/==/g;
    while (m/\$([a-zA-Z]\w*)/g) {
        $sym{$1} = 0 if ! exists $sym{$1};
    }
    s/\$([a-zA-Z]\w*)/\$sym{'$1'}/g;
    print "$_ evals as " . (eval() - 0) . "\n";
}

__DATA__
$x + $y = 11
$x + $y == 14
$x * ($x - $y) + 10
$x + $x1 + $x2

[download]
Note the substitutions to fix cases of = instead of ==, and to fix instances of $sym{'key'} that don't exist. 0 is also subtracted from the eval so 0 is displayed when a bool comes out false, rather than nothing.

In reply to Re: Regular expression match and substitution by TedPride
in thread Regular expression match and substitution by pip9ball

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.