$_ is a global.

Beside that to get the first parameter you passed to your subs you should use

my $line = lc $_[0];
# and 
$another_line = $_[0];
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as it is the first element in the @_ array, which contains all arguments to the sub.

Beside that you should not use $ in sub names, you should not use & in function calls and you should use warnings.

Cheers, Flo