Exercise 1:    \$foo =~ /^[A-G]/

Exercise 2:    \$foo =~ /^[H-N]/

Exercise 3:    \$foo =~ /^\0/

Exercise 4:    \$foo =~ /IO::Handle/

Exercise 5:    \$foo =~ /IO::/ && $foo

Exercise 6:    \$foo[$[] == \$foo[$[+1]

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Exercise 7:    !eval { ($foo) = $foo }

Exercise 8:    !eval { [ @foo ] }

Exercise 9:    $foo && $foo =~ /^0\z/

Exercise 10:   $foo =~ /^0\z/ && $foo

Exercise 11:   "$|" == 2 && $| == 0

Exercise 12:   ($| = 1) == 2

Exercise 13:   undef