perldoc -f say

... "say" is available only if the "say" feature is enabled or if it is prefixed with "CORE::". The "say" feature is enabled automatically with a "use v5.10" (or higher) declaration in the current scope.

So you could add

use v5.10;   # or higher
...
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or

use feature qw(say);
...
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or

$_ = 'My name is Paquito';
CORE::say if /My name is/;

s/Paquito/Paquita/;

tr/A-Z/a-z/;
CORE::say;
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Had you add use strict; the following warning would have been issued hinting that say is unknown:

Bareword "say" not allowed while "strict subs" in use at ./say.pl line
+ xyz.
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