$ man perlvar | head
PERLVAR(1)             Perl Programmers Reference Guide             PERLVAR(1)

NAME
       perlvar - Perl predefined variables

DESCRIPTION
   The Syntax of Variable Names
       Variable names in Perl can have several formats.  Usually, they must
       begin with a letter or underscore, in which case they can be
       arbitrarily long (up to an internal limit of 251 characters) and may
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