Change
$ref =~ s/(\$\S)/\$sym->{'$1'}/g
to
$ref =~ s/(\$\S+)/\$sym->{'$1'}/g

Of course, that won't work too well if the person uses
$x+$y=7
instead of
$x + $y = 7
so you might want to use
$ref =~ s/(\$\w+)/\$sym->{'$1'}/g

I presume you will later eval this string? I don't think that's a very good idea. I would indeed recommend using a parser.

Thanks for the reply....

I will be using eval on the string later on. However, before executing the eval I ensure that all variables have been defined. Why isn't this a good idea?

Does eval() work on string's?

$b = "hello"

$strconcat = "$b_world"

after subs...

$strconcat = "$sym{'$b'}_world"

<code> $tmp = eval("$sym{'$b'}_world") print "\$strconcat = $tmp\n"; <\code>

I get the following error Use of uninitialized value in concatenation (.) or string at ./genParse.pl line 418, <DATA> chunk 1.

Thanks!

not "a good idea," cuz you'll be setting eval to work on what may be malicious input from user. read about untainting and generally, security.

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$/");
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But please don't do that!

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
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