Provided by: libinline-files-perl_0.68-1_all 
NAME
Inline::Files::Virtual - Multiple virtual files in a single file
VERSION
This document describes version 0.53 of Inline::Files::Virtual, released May 25, 2001.
SYNOPSIS
use Inline::Files::Virtual;
# Load actual file, extracting virtual files that start with "^<VF>\n"
@virtual_filenames = vf_load($actual_file, "^<VF>\n");
# Open one of the virtual files for reading
open(FILE, $virtual_filenames[0]) or die;
print while <FILE>;
close(FILE);
# Open one of the virtual files for appending
open(FILE, ">> $virtual_filenames[1]") or die;
print FILE "extra text";
printf FILE "%6.2", $number;
close(FILE);
# Actual file will be updated at this point
WARNING
This module is still experimental. Careless use of it will almost certainly cause the
source code in files that use it to be overwritten. You are strongly advised to use the
Inline::Files module instead.
If you chose to use this module anyway, you thereby agree that the authors will b<under no
circumstances> be responsible for any loss of data, code, time, money, or limbs, or for
any other disadvantage incurred as a result of using Inline::Files.
DESCRIPTION
This module allows you to treat a single disk file as a collection of virtual files, which
may then be individually opened for reading or writing. Virtual files which have been
modified are written back to their actual disk at the end of the program's execution (or
earlier if the "vf_save" subroutine is explicitly called).
Each such virtual file is introduced by a start-of-virtual-file marker (SOVFM). This may
be any sequence (or pattern) of characters that marks the beginning of the content of a
virtual file. For example, the string "--" might be used:
--
Contents of virtual
file number 1
--
Contents of virtual
file number 2
--
Contents of virtual
file number 3
or the pattern "/##### \w+ #####/":
##### VF1 #####
Contents of virtual
file number 1
##### VF2 #####
Contents of virtual
file number 2
##### VF3 #####
Contents of virtual
file number 3
Note that the SOVFM is not considered to be part of the file contents.
Interface
The module exports the following methods:
"vf_load $file, $SOVFM_pattern"
This subroutine is called to load an actual disk file containing one or more virtual
files. The first argument specifies the name of the file to be loaded as a string. The
second argument specifies a pattern (as either a string or "qr" regex) that matches
each start-of-virtual-file marker within the file. For example, if the file
"/usr/local/details.dat" contains:
=info names
Damian
Nathan
Mephistopheles
=info numbers
555-1212
555-6874
555-3452
=info comment
Mad
Bad
Dangerous to know
then you could load it as three virtual files with:
@virtual_filenames =
vf_load("/usr/local/details.dat", qr/^=info\s+\S+\s*?\n/);
Note that, because the actual file is decomposed into virtual files using a "split",
it is vital that the pattern does not contain any capturing parentheses.
On success, "vf_load" returns a list of virtual filenames for the virtual files. Each
virtual filename consists of the actual name of the file containing the virtual file,
concatenated with the offset of the virtual file's SOVFM within the actual file. For
example, the above call to "vf_load" would return three virtual filenames:
/usr/local/details.dat(00000000000000000000)
/usr/local/details.dat(00000000000000000048)
/usr/local/details.dat(00000000000000000097)
When any of these virtual filenames is subsequently used in an "open", the
corresponding virtual file is opened.
"vf_save @actual_filenames"
"vf_save"
This subroutine causes the virtual files belonging to the nominated actual file (or
files) to be written back to disk. If "vf_save" is called without arguments, then all
currently loaded virtual files are saved to their respective actual files at that
point.
"vf_save" is automatically called in an "END" block at the termination of any program
using the module.
"vf_marker $virtual_filename"
This subroutine returns the SOVFM that preceded the nominated virtual file.
The module also modifies the "open", "close", "print", "printf", "read", "getline",
"getc", "seek", "tell", and "truncate" built-in functions so that they operate correctly
on virtual files.
As a special case, it is also possible to use the raw SOVFM as a virtual file name:
use Inline::Files::Virtual;
vf_load $filename, qr/__[A-Z]+__/;
open FILE, "__MARKER__";
# and in the file that was vf_load-ed
__MARKER__
file contents here
However, this always opens the very first virtual file with that SOVFM, no matter how
often it is called, or how many such markers appear in the file.
Handling "implicit" virtual start-of-virtual-file markers
Sometimes an SOVFM is "implicit". That is, rather thanb being a separate marker for the
start of a virtual file, it is the first part of the actual data of the virtual file. For
example, consider the following XML file:
<DATA>
<DESC>This is data set 1</DESC>
<DATUM/>datum 1
<DATUM/>datum 2
<DATUM/>datum 3
</DATA>
<DATA>
<DESC>This is data set 2</DESC>
<DATUM/>datum 4
<DATUM/>datum 5
<DATUM/>datum 6
</DATA>
Each of the "<DATA>...</DATA>" blocks could be treated as a separate virtual file by
specifying:
@datasets = vf_load("data.xml", '<DATA>');
But this would cause the individual virtual files to contain invalid XML, such as:
<DESC>This is data set 1</DESC>
<DATUM/>datum 1
<DATUM/>datum 2
<DATUM/>datum 3
</DATA>
One can indicate that the nominated SOVFMs are also part of the virtual files' contents,
by specifying the markers as a look-ahead pattern:
@datasets = vf_load("data.xml", '(?=<DATA>)');
This causes "vf_load" to identify the sequence "<DATA>" as a start-of-virtual-file marker
but not consume it, thereby leaving it as the initial sequence of the virtual file's
content.
DIAGNOSTICS
"Could not vf_load '%s'"
The module could not open the specified disk file and read it in as a set of virtual
files.
"Unable to complete vf_save"
The module could not open the specified disk file and write it out as a set of virtual
files. A preceding warning may indicate which virtual file caused the problem.
"Virtual file not open for input"
An attempt was made to "getline", "getc", or "read" a virtual file that was opened for
output only. (Warning only)
"Virtual file not open for output"
An attempt was made to "print" or "printf" a virtual file that was opened for input
only. (Warning only)
AUTHOR
Damian Conway (damian@conway.org)
EVIL GENIUS WHO MADE HIM DO IT
Brian Ingerson (INGY@cpan.org)
COPYRIGHT
Copyright (c) 2001. Damian Conway. All rights reserved.
This module is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
See http://www.perl.com/perl/misc/Artistic.html