Binmode problem

arnk has asked for the wisdom of the Perl Monks concerning the following question:

I am writing binary files from scratch, but I cant write a byte 0x09 to a file as it gets interpreted as a tab and appears as 8 space characters 2020202020202020 instead.
This code running on Windows XP shows my problem

!/usr/bin/perl -w

use strict;
use diagnostics;

my $file = 'test.dat';
open(FILE, ">:raw", "$file") or die "Could not open $file for writing:
+ $!\n";
binmode(FILE, ":raw");

my $tmp = 9;
my $output = pack( 'C', $tmp );
print FILE $output;
close FILE;
print "...Created $file\n";
[download]

The file test.dat contains the following when viewed in hex
2020202020202020
I want it to contain
09
I am using Perl version
"This is perl, v5.8.7 built for MSWin32-x86-multi-thread"
Thanks
Al

Comment on Binmode problem Select or Download Code

Replies are listed 'Best First'.
Re: Binmode problem by grep (Monsignor) on Jul 12, 2007 at 20:12 UTC
I have a feeling you are opening the file with your editor before you check the for spaces. My bet is your editor is set to change `tab` to 8 spaces and then you're saving the change. Look at the file with hexdump before you do anything with it. grep	[reply] [d/l]
Re: Binmode problem by ikegami (Patriarch) on Jul 12, 2007 at 22:26 UTC
`:raw`/`binmode` isn't even needed, although it doesn't hurt either. `>type 626330.pl open($fh, '>', '626330.txt'); print $fh "\t"; # or "\x09" or "\011" or pack('C', 9) >perl 626330.pl >dir 626330.txt ... 2007/07/12 06:20 PM 1 626330.txt <- file len = 1 ... >debug 626330.txt -rcx CX 0001 <- file len = 1 : -d100 l1 0AFD:0100 09 <- ASCII x09 = tab -q` [download] I concur with grep. You loaded the file in an editor that converted the tab to spaces.	[reply] [d/l] [select]
Re^2: Binmode problem by arnk (Initiate) on Jul 13, 2007 at 13:58 UTC
Thanks for the wisdom. Yes Slickedit was converting tab to spaces. In my real script which was a bit more complicated (creating wav files) than this example I was also using a printf of data containing %f which was interpreted as 302E303030303030 hex or 0.000000 which confused me. ie `my @tmp = ( 0x25, 0x66 ); my $output = pack( 'C*',@tmp ); #print FILE $output; printf( FILE "$output" );` [download] Thanks again - all sorted now. Al	[reply] [d/l]