The problem is most likely because you have one too many opening parenthesis somewhere, and Switch.pm only knows that when it has reached the end of the file.

But you can write your program much much easier and shorter and thus avoid the counting of parentheses by using a hash, which maps each character to the number it occurs:

#!/usr/bin/perl -w
use strict;

my $infile = $ARGV[0];
open INPUT, "<", $infile
  or die "Couldn't open '$infile' : $!";
my $input = do { local $/; <INPUT> };

my %histogram;

for my $char (split //, $input) {
  $histogram{$char}++;
};

for (keys %histogram) {
  print "$_ occurred $histogram{$_} times.\n";
};
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