/ 
Tie-File-FixedRecLen-0.2
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/ Tie::File::FixedRecLen

NAME

Tie::File::FixedRecLen - Fixed Length Record support for Tie:File

VERSION

This document refers to version 0.2 of Tie::File::FixedRecLen.

SYNOPSIS

use Tie::File::FixedRecLen;

tie @array, 'Tie::File::FixedRecLen', $file, record_length => 20,
    or die ...;

DESCRIPTION

Use this module as a drop-in replacement to Tie::File in order to add support for fixed length records within your tied files. When tieing to a file, you must specify the length of a record in the file. This length does not include the record separator character(s).

Apart from the configuration parameters mentioned below, you should use this module in just the same way as Tie::File.

Please take just a minute to read the "CAVEATS" section, below.

CAVEATS

  • Do not try using cacheing or deferred writing, at least not yet. The current version of Tie::File is not easily overridden, and to save effort the cache and deferred writing features have not been looked at for Tie::File::FixedRecLen. Furthermore, their tests actually fail so that's a sure sign they are really broken right now in this module.

  • In Tie::File you could include the record separator character(s) within a record, and although the module might get confused, the file would still be valid.

    In Tie::File::FixedRecLen this is a really stupid thing to do, so please don't. Indeed, trailing multiple record separator character(s) on a field will be (sliently) stripped and replaced by a single record separator.

  • Anyone with multi-byte character set experience is very welcome to lend support in making this module work in those environments. Currently my best guess is that things will break if this module is used with multi-byte character set files.

CONFIGURATION

There are three configuration parameters you can pass when tieing to a file (in addition to those offered by Tie::File). This module does not support the fancy - prefix to option names that you have with Tie::File.

record_length

This parameter is required. It specifies the length (in bytes) of a record in the tied file. record_length must be an integer, and it must be greater than zero. Each time a record is read or written, it is compared to this length, and an error is raised if there is a mismatch.

When writing records to the tied file, they are padded out to record_length if necessary. Be aware that this length does not include the record separator.

pad_char

This parameter is optional.

Records will be padded with this character until they are record_length bytes in length. You should make this a single byte character, otherwise things are likely to break.

The default padding character is the space character. This allows the tied file to remain readable by a human. If you use leading or trailing space characters in your records, then select another character, and if you are not bothered about human readability, it could be a control character (e.g. ^G).

pad_dir

This parameter is optional.

Records may be padded out to the record length either before the first character or after the last character.

Set this option to "right" if you would prefer end padding; the default is to pad with the pad_char character before the first character of the record data. For example with "right" padding, a record length of 10 and pad character of '.':

data: "abc123"
written record: "abc123....\n"
returned data when read back: "abc123"

And with the same settings except we'll use the module's default "left" padding this time:

data: "abc123"
written record: "....abc123\n"
returned data when read back: "abc123"

DIAGNOSTICS

Tie::File::FixedRecLen written for Tie::File 0.97

The Tie::File programmers' API is not standardized, and may change in the future. You must have version 0.97 of Tie::File to use this version of Tie::File::FixedRecLen.

Useless use of Tie::File::FixedRecLen without a record_length

You have forgotten to provide the record_length parameter when tieing your file, or it is there but is not a positive integer.

Record '...' does not match set length (...)

When reading a record from the tied file, it is not the expected record_length in size. Are you sure the file was created and written by Tie::File::FixedRecLen?

Record '...' exceeds fixed record length (...)

When attempting to write a record to the tied file, you have passed data which exceeds record_length in size. Please don't do that.

File does not appear to be using fixed length records

Internally, Tie::File and Tie::File::FixedRecLen compute offset markers for each record in the file. This error indicates the file is not a whole multiple of record_length (+ recsep's length) in size, which probably means it is not a Tie::File::FixedRecLen file.

DEPENDENCIES

There are no dependencies other than the contents of the standard Perl distribution.

AUTHOR

Oliver Gorwits <oliver.gorwits@oucs.ox.ac.uk>

ACKNOWLEDGEMENTS

Naturally, this would not be here were it not for the brilliant Tie::File module.

COPYRIGHT & LICENSE

Copyright (c) The University of Oxford 2007. All Rights Reserved.

This program is free software; you can redistribute it and/or modify it under the terms of version 2 of the GNU General Public License as published by the Free Software Foundation.

This program 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 General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA