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#! /usr/bin/perl ... 'c' => 'x', 'a' => 'z' };
my @to_keep = qw{ a c }; my %keepers; ... 'c' => 1, 'a' => 1 };
my @to_keep = qw{ a c }; my %keepers; ... $keepers1 = { 'a' => 'c' };