D:\>perl
$bar = 1; $_ = 123;  s/$bar/bar said $bar -/; print
__END__
bar said 1 -23
D:\>
D:\>
D:\>perl
$bar = 1; $_ = 123; s'$bar'bar said $bar -'; print
__END__
123
D:\>perl
$bar = 1; $_ = 123; s'1'bar said $bar -'; print
__END__
bar said $bar -23
D:\>