NAME

FileHandle::Rollback - FileHandle with commit and rollback

SYNOPSIS

use FileHandle::Rollback;
my ($fh);

# open file handle
$fh = FileHandle::Rollback->new("+< $path")
  or die "cannot open filehandle: $!";

# put some data at a specific address
$fh->seek(80, 0);
print $fh '1500';

# read some data, partially including data 
# that was written in this rollback segment
$fh->seek(70, 0);
$fh->read($data, 100);

# if you want to cancel the changes:
$fh->rollback;

# or, if you want save the changes:
$fh->commit;

DESCRIPTION

FileHandle::Rollback allows you to open a filehandle, write data to that handle, read the data back exactly as if it were already in the file, then cancel the whole transaction if you choose. FileHandle::Rollback works like FileHandle, with a few important differences, most notably the addition of rollback() and commit(). Those additions and differences are noted below.

$fh->rollback()

Cancels all changes since the last rollback, commit, or since you opened the file handle.

$fh->commit()

Writes changes to the file.

$fh->flock($mode)

The flock method locks the file like the built-in flock command. Use the same mode arguments: LOCK_SH, LOCK_EX, and LOCK_UN.

use Fcntl ':flock';

unless ($fh->flock(LOCK_EX))
  {die "cannot lock filehandle: $!"}

binmode

FileHandle::Rollback only works in binmode, so it will automatically put itself into binmode.

read/write

FileHandle::Rollback only works in read/write mode. Regardless of what you begin the file path with (+<, +>, >, >>, etc) FileHandle::Rollback opens the file with +< . However, if > is anywhere in the path then FileHandle::Rollback will create the file if it doesn't already exist.

TERMS AND CONDITIONS

Copyright (C) 2002 Miko O'Sullivan

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

AUTHOR

Miko O'Sullivan miko@idocs.com

A lot of the code in this module was copied from MemHandle.pm by Sheridan C. Rawlins. In fact, I started with Sheridan's module and just changed code until it worked the way I wanted, so Sheridan gets a lot of credit for FileHandle::Rollback.

VERSION

Version 1.00, June 29, 2002
First public release

Version 1.01, June 30, 2002
Minor tweaks to 1.00

Version 1.02, June 30, 2002
Small but important correction to documentation

Version 1.02, July 1, 2002
Another small but important correction to documentation.  Sheesh.