What is the minimal and maximal quality score of fastq file

fastq_min_max_qual.pl

#!/usr/bin/perl
use warnings;
use strict;
use List::Util qw(max min);

# initiate
my @characters;
my @numbers;
my $l;
my $minimum=255;
my $maximum=0;


# go thorugh the file
while(<STDIN>){
    my $sequence = <STDIN>;
    my $skipline = <STDIN>;
    my $quality =  <STDIN>; chomp $quality;
    @characters = split(//,$quality); # divide into characters
    # convert the elements of the array into their
    # equivalent ASCII codes
    @numbers = map(ord, @characters);
    if ($minimum > min(@numbers)){
    	$minimum = min(@numbers) ;
    	print $quality."\n";
    	print "minimum changed to $minimum(".chr($minimum).")\n";
    }    
    if ($maximum < max(@numbers)){
    	$maximum = max(@numbers);    
    	print $quality."\n";
    	print "maximum changed to $maximum(".chr($maximum).")\n";
    }
}
print "minimum is: $minimum(".chr($minimum).")\n";
print "maximum is: $maximum(".chr($maximum).")\n";