On 6/7/07, Tom Phoenix <[EMAIL PROTECTED]> wrote:
On 6/7/07, Perl WANNABE <[EMAIL PROTECTED]> wrote:
> I'm trying to copy a couple of DBM files from a disk to a RAM disk,
> one of the files is 500M the other quite small.
Some DBM implementations, if the filesystem supports doing so, will
create files with "holes" in them; that is, the file may have
arbitrarily long gaps in which there's no data. You can even have a
file that seems larger than the disk it's stored upon.
> Whether I use File::Copy or I roll my own copy by reading and writing the
> file the filesystem fills up... If I use system (cp from to) I don't have a
> problem.
It sounds as if your cp knows how to handle the holes, but File::Copy
isn't so smart. It may be worth filing a bug report over this; even if
File::Copy isn't fixed, its documentation should mention this.
Cheers!
--Tom Phoenix
Stonehenge Perl Training
#create a sparse file
perl -e '
open my $f, ">", "sparse.txt";
seek $f, 1024*1024 - 3, 0;
print $f "foo";
close $f
'
#copy it with File::Copy
perl -MFile::Copy -e 'copy("sparse.txt", "sparse.fc")'
#copy it with cp
cp sparse.txt sparse.cp
#copy it with SparseCopy*
sparsecopy.pl sparse.txt sparse.scp
#look at the sizes
du -sh sparse.*
8.0K sparse.cp
1.1M sparse.fc
8.0K sparse.scp
8.0K sparse.txt
#make sure they are all have the same contents
md5sum sparse.*
8d7e9e80e3724b84decdfc7f9b772b41 sparse.cp
8d7e9e80e3724b84decdfc7f9b772b41 sparse.fc
8d7e9e80e3724b84decdfc7f9b772b41 sparse.scp
8d7e9e80e3724b84decdfc7f9b772b41 sparse.txt
#rejoice
* Here is the program**
#!/usr/bin/perl
use strict;
use warnings;
sparsecopy(@ARGV);
sub sparsecopy {
my ($orig, $new) = @_;
open my $o, '<', $orig
or die "could not open $orig: $!";
open my $n, '>', $new
or die "could not open $new: $!";
select $o;
local $/ = \4096;
while (defined (my $block = <$o>)) {
for my $chunk (split /(\0+)/, $block) {
if ($chunk =~ /\0/) {
seek $n, length($chunk), 1;
next;
}
print $n $chunk;
}
}
}
** patents and trademark pending***
*** yeah, right
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