Try this:

use strict;
use warnings;

my $line = '48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 21';
my @cbytes = split / /, $line;
my $retString;

foreach my $byte (@cbytes)
{
    my $hex = '0x'.$byte;
    my $value = eval $hex;
    my $char = chr $value;
    $retString .= $char;
}

print $retString;
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The trick is that perl will evaluate a literal number as hex if you prefix it with '0x', you then need to use eval to force perl to re-evalute it as a number instead of a string. From there is is just a matter of using chr (see perlfunc) to turn that number into a 1 char string.