Provided by: libinline-files-perl_0.68-1_all bug


       Inline::Files::Virtual - Multiple virtual files in a single file


       This document describes version 0.53 of Inline::Files::Virtual, released May 25, 2001.


           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>;


           # Open one of the virtual files for appending
           open(FILE, ">> $virtual_filenames[1]") or die;

           print FILE "extra text";
           printf FILE "%6.2", $number;


           # Actual file will be updated at this point


       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.


       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.

       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


                   =info numbers


                   =info comment

                   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:


           When any of these virtual filenames is subsequently used in an "open", the
           corresponding virtual file is opened.

       "vf_save @actual_filenames"
           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

           "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

           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:

                       <DESC>This is data set 1</DESC>
                       <DATUM/>datum 1
                       <DATUM/>datum 2
                       <DATUM/>datum 3
                       <DESC>This is data set 2</DESC>
                       <DATUM/>datum 4
                       <DATUM/>datum 5
                       <DATUM/>datum 6

       Each of the "<DATA>...</DATA>" blocks could be treated as a separate virtual file by

               @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

       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


       "Could not vf_load '%s'"
           The module could not open the specified disk file and read it in as a set of virtual

       "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)


       Damian Conway  (


       Brian Ingerson (


       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.