Consider:

$x=1;
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One answer to your specific question is that the token '=' is recognised by Perl as an operator which demands an argument on each side. Following rules of precedence, Perl looks left for an 'lvalue' which can be assigned to, and an 'rvalue' to the right from which to draw the new value.

Your way of expressing the question suggests that you are unfamiliar with Perl syntax and spoken conventions. Perhaps The Llama or The Camel would serve you better for now, and make the excellent Black Cat more accessible.

After Compline,
Zaxo