Hello, my first post here as a novice Perl user. I am attempting to form a checksum value for sections of a binary file, the checksums are a 16 bit sum of 8 bit values. I've got the 16 bit overflowing summation part working with pack and unpack but I'm struggling with accessing the bytes of the file, I've tried various combinations of packing, unpacking, using the buffer value directly etc. Could anyone point me in the right direction? Thanks. 
sub Checksum {
    my @Arguments = @_ ;
    my $Start = $Arguments[0] ;
    my $Size = $Arguments[1] ;
    my $FileHandle = $Arguments[2] ;
    
    my $BufferByte = 0 ;
    my $Checksum = 0 ;
    my $ChecksumLoopCounter = 0 ;
    my $ChecksumByteOffset = $Start ;
    while ( $ChecksumLoopCounter < $Size ) {
        unless ( sysread ( $FileHandle, $BufferByte, 1, $ChecksumByteO
+ffset ) == 1 ) {
            die "sysread size error" ;
        }
        my $Byte = pack("C",unpack("C",$BufferByte) );
        print "\nByte: ".$Byte;#." BufferByte: ".$BufferByte ;
        
        $Checksum = pack("S", unpack ("S", $CheckSum) + $Byte ) ; # Th
+is line implements the looping 16 bit sum
        $ChecksumLoopCounter += 1 ;
        $ChecksumByteOffset += 1 ;
    }
    return $Checksum;
}

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In reply to Accessing individual bytes of a binary file as numerical values by Chris01234

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