The #include equivalent in Perl is #include. This is enabled by the -P flag.

#!/usr/bin/perl -P
#include "aa"
print $aa;
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File "aa":

$::aa = "Hi aa\n";
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Things like use and require are, generally, to be preferred. Namespace issues argue against the conceptual cleanness of simple textual replication; namespace issues usually dominate. That is why Perl's #include mechanism is so clunky. Clunky--needs the C preprocessor and enables it in its entirety, which means all your comments are subject to preprocessing.

Be well,
Rob