DIY Tie

[yosefm]

Hi, all.

I've been trying to do my own file-tying mechanism. Yes, I know that <insert_favorite_module> does that and my laundry too, but how am I ever going to learn anything by using other people's work all the time, eh?

My problem right now is this: I'd like to delete a piece of data (say, an XML entity) from the middle of a file. Is there any way of doing that without re-writing the entire file? This just seems too wasteful in disk access times.

PS Though I'm looking for a DIY answer, I'll be also hapy to know what modules you are using for this kind of job.

Thanks!

[broquaint]

You will have to re-write some of the file as the position of the data will change, so it must be reflected on the disk (unless the changed data is the same length as existing data). To do a partial re-write you can just open a file for reading+writing with something like

open( my $fh => '+<', $your_file ) or die "ack: $!";

## read up to a point
read_stuff() or last while <$fh>;

## remember where you were
my $last_pos     = tell $fh;
my $rest_of_file = do { local $/; <$fh> };

$rest_of_file =~ s<$a_regex>($replace);

## go back to where you were
seek $fh => $last_pos, 0;

print {$fh} $rest_of_file;

close $fh;

While not a marvellous example, it should give you some idea of how to partially edit a file. See. open, tell and seek for more info.
HTH

_________
broquaint

[Abigail-II]

I've been trying to do my own file-tying mechanism. Yes, I know that <insert_favorite_module> does that and my laundry too, but how am I ever going to learn anything by using other people's work all the time, eh?

You actually might learn more from studying <insert_favorite_module> than asking here.

Abigail

[BazB]

Look at Tie::File, from dominus for inspiration (or just use it!).

Tie::File has more than a few clever tricks up it's sleeve, including partial rewrites and deferred writes, which is probably what you want to do.

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