You can get the size of a file with -s but that's not the same as the number of characters unless the file uses an encoding that is always one byte per character.

#!/bin/perl 
use strict;
use warnings;

my $chars = 0;
my $lines = 0; 
while (<>) {
  $chars += length;
  $lines ++;
}

print "$chars $lines\n";
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You can call this script with the files as standard input and standard output.

If you want to open the files within the Perl script instead use the open() function.