There is probably some simple, obvious thing I am missing here, but I can't seem to find the answer.

I wrote a quick & dirty script to generate test data for another program I am working on. I am trying to generate a barber pole and write it to a file. In this case byte 1 of the file should be 0x01, byte 2 should be 0x02 and so forth. A hex dump should look like this (for a 16 byte file): 

0000000: 0102 0304 0506 0708 090a 0b0c 0d0e 0f10  ................

[download]

Pretty simple stuff, right? Here's my code: 

use strict;
use warnings;

my $file = 'test.binary';
my $size = 16; #bytes to write to file;

open ( my $fh, '>', $file ) 
    or die "Unable to open $file - $!\n";
binmode $fh;

my $byte = 0;
for ( 1..$size ) {  
    $byte++; 
    $byte %= 256;
    my $char = pack 'C', $byte;

    # I tried both print and syswrite.  I get the same results with ea
+ch.
    syswrite( $fh, $char, 1); 
    #print $fh $char;         
}
close $fh;

print "\nDONE\n";

[download]

My hex dump (for a 16 byte file) looks like this: 

0000000: 0102 0304 0506 0708 090a 0b0c 0d0e 0f10  ................
0000010: 0a                                       .

[download]

Note the trailing 0x0a. If I set $bytes to 10, the hex dump is clean, no extra junk. If I set $bytes to 0, I get an empty file. If I set bytes to any other value I get a trailing 0x0a added for me. For some reason perl seems obsessed with forcing a trailing newline into the file.

I tested the script on perl 5.8.8 on win32 and 5.8.4 on a stock Debian Sarge system with the same results.

Update:

Thank you ikegami, you are absolutely correct.

I was using the handy hex editor in Vim to view my hex dumps. I had never noticed the extra 0x0A it was silently adding.


TGI says moo

In reply to Newline appearing at the end of a file by TGI

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