Mail::Box::File(3) User Contributed Perl Documentation Mail::Box::File(3)

Mail::Box::File - handle file-based folders

Mail::Box::File
  is a Mail::Box
  is a Mail::Reporter
Mail::Box::File is extended by
  Mail::Box::Mbox

"Mail::Box::File" is the base-class for all file-based folders: folders which bundle multiple messages into one single file. Usually, these messages are separated by a special line which indicates the start of the next one.

Extends "DESCRIPTION" in Mail::Box.

Extends "OVERLOADED" in Mail::Box.

Inherited, see "OVERLOADED" in Mail::Box
Inherited, see "OVERLOADED" in Mail::Box
Inherited, see "OVERLOADED" in Mail::Box

Extends "METHODS" in Mail::Box.

Extends "Constructors" in Mail::Box.

$class->new(%options)
Inherited, see "Constructors" in Mail::Box 
-Option           --Defined in     --Default
 access             Mail::Box        'r'
 body_delayed_type  Mail::Box        Mail::Message::Body::Delayed
 body_type                           <see description>
 coerce_options     Mail::Box        +[]
 create             Mail::Box        false
 extract            Mail::Box        10240
 field_type         Mail::Box        undef
 fix_headers        Mail::Box        false
 folder             Mail::Box        $ENV{MAIL}
 folderdir          Mail::Box        $ENV{HOME}.'/Mail'
 head_delayed_type  Mail::Box        Mail::Message::Head::Delayed
 head_type          Mail::Box        Mail::Message::Head::Complete
 keep_dups          Mail::Box        false
 lock_extension                      '.lock'
 lock_file          Mail::Box        <foldername><lock-extension>
 lock_timeout       Mail::Box        1 hour
 lock_type          Mail::Box        Mail::Box::Locker::DotLock
 lock_wait          Mail::Box        10 seconds
 locker             Mail::Box        undef
 manager            Mail::Box        undef
 message_type       Mail::Box        Mail::Box::File::Message
 multipart_type     Mail::Box        Mail::Message::Body::Multipart
 remove_when_empty  Mail::Box        true
 save_on_exit       Mail::Box        true
 trusted            Mail::Box        <depends on folder location>
 write_policy                        undef
The default "body_type" option for "File" folders, which will cause messages larger than 10kB to be stored in files and smaller files in memory, is implemented like this: 
sub determine_body_type($$)
{   my $head = shift;
    my $size = shift || 0;
    'Mail::Message::Body::' . ($size > 10000 ? 'File' : 'Lines');
}
When the dotlock locking mechanism is used, the lock is created with a hardlink to the folder file. For "Mail::Box::File" type of folders, this filename is by default named as the folder-file itself followed by ".lock". For example: the "Mail/inbox" folder file will have a hardlink made as "Mail/inbox.lock".

You may specify an absolute $file, a relative (to the folder's directory) filename, or an extension (preceded by a dot). So valid examples are:

.lock                  # appended to the folder's filename
my_own_lockfile.test   # full filename, same dir
/etc/passwd            # somewhere else

When the program runs with less privileges (as normal user), often the default inbox folder can not be locked with the lockfile name which is produced by default.

Sets the default write policy, as default for a later call to write(policy). With "undef", the best policy is autodetected.

Extends "Attributes" in Mail::Box.

$obj->filename()
Returns the filename for this folder, which may be an absolute or relative path to the file.

» example:

print $folder->filename;
$obj->fixHeaders()
Inherited, see "Attributes" in Mail::Box
$obj->folderdir( [$directory] )
Inherited, see "Attributes" in Mail::Box
$obj->isTrusted()
Inherited, see "Attributes" in Mail::Box
$obj->name()
Inherited, see "Attributes" in Mail::Box
$obj->removeEmpty()
Inherited, see "Attributes" in Mail::Box
$obj->type()
Inherited, see "Attributes" in Mail::Box

Extends "The folder" in Mail::Box.

$obj->addMessage($message, %options)
Inherited, see "The folder" in Mail::Box
$obj->addMessages(@messages)
Inherited, see "The folder" in Mail::Box
$class->appendMessages(%options)
Appending messages to a file based folder which is not opened is a little risky. In practice, this is often done without locking the folder. So, another application may write to the folder at the same time... :( Hopefully, all goes fast enough that the chance on collision is small.

All %options of Mail::Box::Mbox::new() can be supplied. Improves base, see "The folder" in Mail::Box

-Option   --Defined in     --Default
 folder     Mail::Box        <required>
 lock_type                   NONE
 message    Mail::Box        undef
 messages   Mail::Box        undef
 share      Mail::Box        false
See Mail::Box::new(lock_type) for possible values.
$obj->close(%options)
Inherited, see "The folder" in Mail::Box
$obj->copyTo($folder, %options)
Inherited, see "The folder" in Mail::Box
$obj->delete(%options)
Inherited, see "The folder" in Mail::Box
$obj->organization()
Inherited, see "The folder" in Mail::Box
$obj->size()
Inherited, see "The folder" in Mail::Box
$obj->update(%options)
Inherited, see "The folder" in Mail::Box
$obj->url()
Inherited, see "The folder" in Mail::Box

Extends "Folder flags" in Mail::Box.

$obj->access()
Inherited, see "Folder flags" in Mail::Box
$obj->isModified()
Inherited, see "Folder flags" in Mail::Box
$obj->modified( [BOOLEAN] )
Inherited, see "Folder flags" in Mail::Box
$obj->writable()
Inherited, see "Folder flags" in Mail::Box

Extends "The messages" in Mail::Box.

$obj->current( [$number|$message|$message_id] )
Inherited, see "The messages" in Mail::Box
$obj->find($message_id)
Inherited, see "The messages" in Mail::Box
$obj->findFirstLabeled( $label, [BOOLEAN, [\@msgs]] )
Inherited, see "The messages" in Mail::Box
$obj->message( $index, [$message] )
Inherited, see "The messages" in Mail::Box
$obj->messageId( $message_id, [$message] )
Inherited, see "The messages" in Mail::Box
$obj->messageIds()
Inherited, see "The messages" in Mail::Box
$obj->messages( <'ALL'|$range|'ACTIVE'|'DELETED'|$label| !$label|$filter> )
Inherited, see "The messages" in Mail::Box
$obj->nrMessages(%options)
Inherited, see "The messages" in Mail::Box
$obj->scanForMessages($message, $message_ids, $timespan, $window)
Inherited, see "The messages" in Mail::Box

Extends "Sub-folders" in Mail::Box.

$any->listSubFolders(%options)
Inherited, see "Sub-folders" in Mail::Box
$any->nameOfSubFolder( $subname, [$parentname] )
Inherited, see "Sub-folders" in Mail::Box
$obj->openRelatedFolder(%options)
Inherited, see "Sub-folders" in Mail::Box
$obj->openSubFolder($subname, %options)
Inherited, see "Sub-folders" in Mail::Box
$any->topFolderWithMessages()
Inherited, see "Sub-folders" in Mail::Box

Extends "Internals" in Mail::Box.

$obj->coerce($message, %options)
Inherited, see "Internals" in Mail::Box
$any->create($foldername, %options)
Inherited, see "Internals" in Mail::Box 
-Option   --Defined in--Default
 folderdir  Mail::Box   undef
$obj->determineBodyType($message, $head)
Inherited, see "Internals" in Mail::Box
$any->folderToFilename( $foldername, $folderdir, [$subext] )
Translate a $foldername into a filename, using the $folderdir value to replace a leading "=". The optional $subext is only used for MBOX folders.
$class->foundIn( [$foldername], %options )
Inherited, see "Internals" in Mail::Box
$obj->lineSeparator( [<STRING|'CR'|'LF'|'CRLF'>] )
Inherited, see "Internals" in Mail::Box
$obj->locker()
Inherited, see "Internals" in Mail::Box
$obj->messageCreateOptions( [$type, $config] )
Returns a key-value list of options to be used each time a new message is read from a file. The list is preceded by the $type of message which has to be created.

This data is used by readMessages() and updateMessages(). With $type and $config, a new configuration is set.

$obj->moveAwaySubFolder($directory, $extension)
The $directory is renamed by appending the $extension, which defaults to ".d", to make place for a folder file on that specific location. "false" is returned if this failed.
$obj->parser()
Create a parser for this mailbox. The parser stays alive as long as the folder is open.
$obj->read(%options)
Inherited, see "Internals" in Mail::Box
$obj->readMessages(%options)
Inherited, see "Internals" in Mail::Box
$obj->storeMessage($message)
Inherited, see "Internals" in Mail::Box
$obj->toBeThreaded($messages)
Inherited, see "Internals" in Mail::Box
$obj->toBeUnthreaded($messages)
Inherited, see "Internals" in Mail::Box
$obj->updateMessages(%options)
For file based folders, the file handle stays open until the folder is closed. Update is therefore rather simple: move to the end of the last known message, and continue reading... Improves base, see "Internals" in Mail::Box
$obj->write(%options)
Inherited, see "Internals" in Mail::Box 
-Option      --Defined in     --Default
 force         Mail::Box        false
 policy                         undef
 save_deleted  Mail::Box        false
In what way will the mail folder be updated. If not specified during the write, the value of the new(write_policy) at folder creation is taken.

Valid values:

  • "REPLACE"

    First a new folder is written in the same directory as the folder which has to be updated, and then a call to move will throw away the old immediately replacing it by the new.

    Writing in "REPLACE" module is slightly optimized: messages which are not modified are copied from file to file, byte by byte. This is much faster than printing the data which is will be done for modified messages.

  • "INPLACE"

    The original folder file will be opened read/write. All message which where not changed will be left untouched, until the first deleted or modified message is detected. All further messages are printed again.

  • "undef"

    As default, or when "undef" is explicitly specified, first "REPLACE" mode is tried. Only when that fails, an "INPLACE" update is performed.

"INPLACE" will be much faster than "REPLACE" when applied on large folders, however requires the "truncate" function to be implemented on your operating system (at least available for recent versions of Linux, Solaris, Tru64, HPUX). It is also dangerous: when the program is interrupted during the update process, the folder is corrupted. Data may be lost.

However, in some cases it is not possible to write the folder with "REPLACE". For instance, the usual incoming mail folder on UNIX is stored in a directory where a user can not write. Of course, the "root" and "mail" users can, but if you want to use this Perl module with permission of a normal user, you can only get it to work in "INPLACE" mode. Be warned that in this case folder locking via a lockfile is not possible as well.

$obj->writeMessages(%options)
Inherited, see "Internals" in Mail::Box

Extends "Other methods" in Mail::Box.

$any->timespan2seconds($time)
Inherited, see "Other methods" in Mail::Box

Extends "Error handling" in Mail::Box.

$obj->AUTOLOAD()
Inherited, see "Error handling" in Mail::Reporter
$obj->notImplemented()
Inherited, see "Error handling" in Mail::Reporter

Extends "Cleanup" in Mail::Box.

$obj->DESTROY()
Inherited, see "Cleanup" in Mail::Box

File based folders

File based folders maintain a folder (a set of messages) in one single file. The advantage is that your folder has only one single name, which speeds-up access to all messages at once.

The disadvantage over directory based folder (see Mail::Box::Dir) is that you have to construct some means to keep all message apart, for instance by adding a message separator, and this will cause problems. Where access to all messages at once is faster in file based folders, access to a single message is (much) slower, because the whole folder must be read.

Extends "DETAILS" in Mail::Box.

Appending messages to a not-opened file-organized folder may fail when the operating system does not allow write access to the file at hand. Cast by appendMessages()
While creating a file-organized folder, at most one level of directories is created above it. Apparently, more levels of directories are needed, or the operating system does not allow you to create the directory. Cast by create()
The file-organized folder file cannot be created for the indicated reason. In common cases, the operating system does not grant you write access to the directory where the folder file should be stored. Cast by create()
Cast by new()
Cast by moveAwaySubFolder()
Writing an empty folder will usually cause that folder to be removed, which fails for the indicated reason. new(remove_when_empty) controls whether the empty folder will removed; setting it to "false" (0) may be needed to avoid this message. Cast by write()
The replace policy wrote a new folder file to update the existing, but was unable to give the final touch: replacing the old version of the folder file for the indicated reason. Cast by write()
You have opened the folder read-only --which is the default set by new(access)--, made modifications, and now want to close it. Set close(force) if you want to overrule the access mode, or close the folder with close(write) set to "NEVER". Cast by close()
Fatal error: the specific $package (or one of its superclasses) does not implement this method where it should. This message means that some other related classes do implement this method however the class at hand does not. Probably you should investigate this and probably inform the author of the package. Cast by notImplemented()
For some reason, for instance disk full, removed by external process, or read-protection, it is impossible to copy one of the messages. Copying will proceed for the other messages. Cast by copyTo()
The folder where the messages are copied to is not opened with write access (see new(access)). This has no relation with write permission to the folder which is controlled by your operating system. Cast by copyTo()
The message id is discovered more than once within the same folder, but the content of the message seems to be different. This should not be possible: each message must be unique. Cast by messageId()
Mail::Box is lazy: it tries to leave messages in the folders until they are used, which saves time and memory usage. When this message appears, something is terribly wrong: some lazy message are needed for updating the folder, but they cannot be retrieved from the original file anymore. In this case, messages can be lost.

This message does appear regularly on Windows systems when using the 'replace' write policy. Please help to find the cause, probably something to do with Windows incorrectly handling multiple filehandles open in the same file. Cast by write()

The folder is opened writable or for appending via new(access), but the operating system does not permit writing to the $file. The folder will be opened read-only. Cast by new()
The folder must be opened with write access via new(access), otherwise removing it will be refused. So, you may have write-access according to the operating system, but that will not automatically mean that this "delete" method permits you to. The reverse remark is valid as well. Cast by delete()
Cast by new()
The string does not follow the strict rules of the time span syntax which is permitted as parameter. Cast by timespan2seconds()
According to the RFCs, message-ids need to contain a unique random part, then an "@", and then a domain name. This is made to avoid the creation of two messages with the same id. The warning emerges when the "@" is missing from the string. Cast by messageId()
When a folder is to be written, both replace and inplace write policies are tried, If both fail, the whole update fails. You may see other, related, error messages to indicate the real problem. Cast by write()
Cast by close()
Cast by addMessage()

This module is part of Mail-Box version 4.01, built on December 13, 2025. Website: http://perl.overmeer.net/CPAN/

For contributors see file ChangeLog.

This software is copyright (c) 2001-2025 by Mark Overmeer.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

2025-12-14 perl v5.42.0