It's not a good idea because it's too easy to inject code. Even if the current user of the code wouldn't do so, it might eventually make its way to where an untrusted user supplies the data. A parser is the easiest way to make sure the input is safe.

You're getting "Use of uninitialized value" error because you didn't give any value to $sym{'$b'}.

yes, eval works on strings:

$expr = '$x + 1';
print("$expr = ");
$expr =~ s/(\$\w+)/\$sym{'$1'}/g;
$sym{'$x'} = 3;
$val = eval $expr;
die("Bad equation: $@$/") if $@;
print("$val$/");

[download]

But please don't do that!

In reply to Re^3: Regular expression match and substitution by ikegami
in thread Regular expression match and substitution by pip9ball

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