Note that tr/SEARCHLIST/REPLACEMENTLIST/ is documented with "Quote Like Operators". That document shows that it can be used with variables with a little help from eval.

Because the transliteration table is built at compile time, neither the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote interpolation. That means that if you want to use variables, you must use an eval():

eval "tr/$oldlist/$newlist/"; die $@ if $@;

eval "tr/$oldlist/$newlist/, 1"; die $@ if $@;

In your case that would be

my $count = eval "\$str =~ tr/$char//" or die $@ if $@;
[download]