Provided by: libfile-save-home-perl_0.11-1_all bug

NAME

       File::Save::Home - Place file safely under user home directory

VERSION

       This document refers to version 0.11, released October 26 2017.

SYNOPSIS

           use File::Save::Home qw(
               get_home_directory
               get_subhome_directory_status
               make_subhome_directory
               restore_subhome_directory_status
               conceal_target_file
               reveal_target_file
               make_subhome_temp_directory
           );

           $home_dir = get_home_directory();

           $desired_dir_ref = get_subhome_directory_status("desired/directory");

           $desired_dir_ref = get_subhome_directory_status(
               "desired/directory",
               "pseudohome/directory",    # two-argument version
           );

           $desired_dir = make_subhome_directory($desired_dir_ref);

           restore_subhome_directory_status($desired_dir_ref);

           $target_ref = conceal_target_file( {
               dir     => $desired_dir,
               file    => 'file_to_be_checked',
               test    => 0,
           } );

           reveal_target_file($target_ref);

           $tmpdir = make_subhome_temp_directory();

           $tmpdir = make_subhome_temp_directory(
               "pseudohome/directory",    # optional argument version
           );

DESCRIPTION

       In the course of deploying an application on another user's system, you sometimes need to
       place a file in or underneath that user's home directory.  Can you do so safely?

       This Perl extension provides several functions which try to determine whether you can,
       indeed, safely create directories and files underneath a user's home directory.  Among
       other things, if you are placing a file in such a location only temporarily -- say, for
       testing purposes -- you can temporarily hide any already existing file with the same name
       and restore it to its original name and timestamps when you are done.

   Limitations
       The preceding description was written in 2005.  Experience has shown that any claim that
       one can make about the safety of the creation or deletion of directories and files
       underneath a user's home directory must be qualified.  File::Save::Home is satisfactory
       for the use case for which it was originally designed, but there are other situations
       where it falls short.

       The original use case for which File::Save::Home was designed was to support the placement
       of personal preference files in a user's home directory.  Such personal preference files
       are often referred to as dot-rc files because their names typically start with a "."
       character to render them hidden from commands like "ls" and end in "rc" much like
       ".bashrc" or <.shrc>.  A developer using CPAN::Mini, for example, often makes use of
       ".minicpanrc" to store the developer's preferred CPAN mirror.  File::Save::Home was
       created specifically to support the creation of a ".modulemakerrc" file by users of
       ExtUtils::ModuleMaker and a ".podmultirc" file by users of Pod::Multi.
       (ExtUtils::ModuleMaker and Pod::Multi are maintained by the author of File::Save::Home.)
       These libraries are developer's tools, i.e., they are intended to assist individual humans
       in software development rather than being used "in production."  As such, their use of
       dot-rc files implicitly assumes:

       ·   Only one user is concerned with the status of the directories and files, including
           dot-rc files, underneath the user's home directory.

       ·   Only one user has permissions to create, modify or remove directories and files
           underneath the user's home directory -- an assumption that is easily violated by a
           superuser such as "root".

       ·   The user is running processes to create, modify or remove directories and files
           underneath the user's home directory one-at-a-time, "i.e.," the user is not running
           such processes in parallel.  Running such processes in parallel would raise the
           possibility, for example, of process trying to rename a dot-rc file that a second,
           parallel process had already deleted.

       When either the second or third assumption above is violated, we have the possibility of
       race conditions (<https://en.wikipedia.org/wiki/Race_condition>) and time of check to time
       of use (TOCTTOU) errors (<https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use>).
       Such conditions may lead to either spurious testing failures (e.g., when CPANtesteers run
       tests in parallel on libraries using File::Save::Home) or to security violations.

USAGE

   "get_home_directory()"
       Analyzes environmental information to determine whether there exists on the system a
       'HOME' or 'home-equivalent' directory.  Takes no arguments.  Returns that directory if it
       exists; "croak"s otherwise.

       On Win32, this directory is the one returned by the following function from the
       Win32module:

           Win32->import( qw(CSIDL_LOCAL_APPDATA) );
           $realhome =  Win32::GetFolderPath( CSIDL_LOCAL_APPDATA() );

       ... which translates to something like C:\Documents and Settings\localuser\Local
       Settings\Application Data.  (For a further discussion of Win32, see below "SEE ALSO".)

       On Unix-like systems, things are much simpler.  We simply check the value of $ENV{HOME}.
       We cannot do that on Win32 because $ENV{HOME} is not defined there.

   "get_subhome_directory_status()"
       Single argument version

       Takes as argument a string holding the name of a directory, either single-level ("mydir")
       or multi-level ("path/to/mydir").  Determines whether that directory already exists
       underneath the user's home or home-equivalent directory. Calls "get_home_directory()"
       internally, then tacks on the path passed as argument.

       Two-argument version

       Suppose you want to determine the name of a user's home directory by some other route than
       "get_home_directory()".  Suppose, for example, that you're on Win32 and want to use the
       "my_home()" method supplied by CPAN distribution File::HomeDir -- a method which returns a
       different result from that of our "get_home_directory()" -- but you still want to use
       those File::Save::Home functions which normally call "get_home_directory()" internally.
       Or, suppose you want to supply an arbitrary path.

       You can now do so by supplying an optional second argument to
       "get_subhome_directory_status".  This argument should be a valid path name for a directory
       to which you have write privileges.  "get_subhome_directory_status" will determine if the
       directory exists and, if so, determine whether the first argument is a subdirectory of the
       second argument.

       Both versions

       Whether you use the single argument version or the two-argument version,
       "get_subhome_directory_status" returns a reference to a four-element hash whose keys are:

       home
           The absolute path of the home directory.

       abs The absolute path of the directory specified as first argument to the function.

       flag
           A Boolean value indicating whether the desired directory already exists (a true value)
           or not ("undef").

       top The uppermost subdirectory passed as the argument to this function.

   "make_subhome_directory()"
       Takes as argument the hash reference returned by "get_subhome_directory_status()".
       Examines the first element in that array -- the directory name -- and creates the
       directory if it doesn't already exist.  The function "croak"s if the directory cannot be
       created.

   "restore_subhome_directory_status()"
       Undoes "make_subhome_directory()", i.e., if there was no specified directory under the
       user's home directory on the user's system before testing, any such directory created
       during testing is removed.  On the other hand, if there was such a directory present
       before testing, it is left unchanged.

   "make_subhome_temp_directory()"
       Regular version:  no arguments

       Creates a randomly named temporary directory underneath the home or home-equivalent
       directory returned by "get_home_directory()".

       Optional argument version

       Creates a randomly named temporary directory underneath the directory supplied as the
       single argument.  This version is analogous to the two-argument version of
       "get_subhome_directory_status()" above.  You could use it if, for example, you wanted to
       use "File::HomeDir-"my_home()> to supply a value for the user's home directory instead of
       our "get_home_directory()".

       Both versions

       In both versions, the temporary subdirectory is created by calling "File::Temp::tempdir
       (DIR =" $home, CLEANUP => 1)>.  The function returns the directory path if successful;
       "croak"s otherwise.

       Note:  Any temporary directory so created remains in existence for the duration of the
       program, but is deleted (along with all its contents) when the program exits.

   "conceal_target_file()"
       Determines whether file with specified name already exists in specified directory and, if
       so, temporarily hides it by renaming it with a .hidden suffix and storing away its last
       access and modification times.  Takes as argument a reference to a hash with these keys:

       dir The directory in which the file is presumed to exist.

       file
           The targeted file, i.e., the file to be temporarily hidden if it already exists.

       test
           Boolean value which, if turned on (1), will cause the function, when called, to run
           two "Test::More::ok()" tests.  Defaults to off (0).

       Returns a reference to a hash with these keys:

       full
           The absolute path to the target file.

       hidden
           The absolute path to the now-hidden file.

       atime
           The last access time to the target file ("(stat($file{full}))[8]").

       modtime
           The last modification time to the target file ("(stat($file{full}))[9]").

       test
           The value of the key "test" in the hash passed by reference as an argument to this
           function.

   "reveal_target_file()"
       Used in conjunction with "conceal_target_file()" to restore the original status of the
       file targeted by "conceal_target_file()", i.e., renames the hidden file to its original
       name by removing the .hidden suffix, thereby deleting any other file with the original
       name created between the calls tothe two functions.  "croak"s if the hidden file cannot be
       renamed.  Takes as argument the hash reference returned by "conceal_target_file()".  If
       the value for the "test" key in the hash passed as an argument to "conceal_target_file()"
       was true, then a call to "reveal_target_file" will run three "Test::More::ok()" tests.

BUGS AND TODO

       So far tested only on Unix-like systems and Win32.

SEE ALSO

       perl(1).  ExtUtils::ModuleMaker::Auxiliary.  ExtUtils::ModuleMaker::Utility.  The latter
       two packages are part of the ExtUtils::ModuleMaker distribution available from the same
       author on CPAN.  They and the ExtUtils::ModuleMaker test suite provide examples of the use
       of File::Save::Home.

       Two other distributions located on CPAN, File::HomeDir and File::HomeDir::Win32, may also
       be used to locate a suitable value for a user's home directory.  It should be noted,
       however, that those modules and File::Save::Home each take a different approach to
       defining a home directory on Win32 systems.  Hence, each may deliver a different result on
       a given system.  I cannot say that one distribution's approach is any more or less correct
       than the other two's approaches.  The following comments should be viewed as my subjective
       impressions; YMMV.

       File::HomeDir was originally written by Sean M Burke and is now maintained by Adam
       Kennedy.  As of version 0.52 its interface provides three methods for the ''current
       user'':

           $home = File::HomeDir->my_home;
           $docs = File::HomeDir->my_documents;
           $data = File::HomeDir->my_data;

       When I ran these three methods on a Win2K Pro system running ActivePerl 8, I got these
       results:

           C:\WINNT\system32>perl -MFile::HomeDir -e "print File::HomeDir->my_home"
           C:\Documents and Settings\localuser

           C:\WINNT\system32>perl -MFile::HomeDir -e "print File::HomeDir->my_documents"
           C:\Documents and Settings\localuser\My Documents

           C:\WINNT\system32>perl -MFile::HomeDir -e "print File::HomeDir->my_data"
           C:\Documents and Settings\localuser\Local Settings\Application Data

       In contrast, when I ran the closest equivalent method in File::Save::Home,
       "get_home_directory", I got this result:

           C:\WINNT\system32>perl -MFile::Save::Home -e "print File::Save::Home->get_home_directory"
           C:\Documents and Settings\localuser\Local Settings\Application Data

       In other words, "File::Save::Home->get_home_directory" gave the same result as
       "File::HomeDir->my_data", not, as I might have expected, the same result as
       "File::HomeDir->my_home".

       These results can be explained by peeking behind the curtains and looking at the source
       code for each module.

   File::HomeDir
       File::HomeDir's objective is to provide a value for a user's home directory on a wide
       variety of operating systems.  When invoked, it detects the operating system you're on and
       calls a subclassed module.  When used on a Win32 system, that subclass is called
       File::HomeDir::Windows (not to be confused with the separate CPAN distribution
       File::HomeDir::Win32).  "File::HomeDir::Windows->my_home()" looks like this:

           sub my_home {
               my $class = shift;
               if ( $ENV{USERPROFILE} ) { return $ENV{USERPROFILE}; }
               if ( $ENV{HOMEDRIVE} and $ENV{HOMEPATH} ) {
                       return File::Spec->catpath( $ENV{HOMEDRIVE}, $ENV{HOMEPATH}, '',);
               }
               Carp::croak("Could not locate current user's home directory");
           }

       In other words, determine the current user's home directory simply by checking
       environmental variables analogous to the $ENV{HOME} on Unix-like systems.  A very
       straightforward approach!

       As mentioned above, File::Save::Home takes a different approach.  It uses the Win32 module
       to, in effect, check a particular key in the registry.

           Win32->import( qw(CSIDL_LOCAL_APPDATA) );
           $realhome =  Win32::GetFolderPath( CSIDL_LOCAL_APPDATA() );

       This approach was suggested to me in August 2005 by several members of Perlmonks.  (See
       threads Installing a config file during module operation
       (<http://perlmonks.org/?node_id=481690>) and Win32 CSIDL_LOCAL_APPDATA
       (<http://perlmonks.org/?node_id=485902>).)  I adopted this approach in part because the
       people recommending it knew more about Windows than I did, and in part because
       File::HomeDir was not quite as mature as it has since become.

       But don't trust me; trust Microsoft!  Here's their explanation for the use of CSIDL values
       in general and CSIDL_LOCAL_APPDATA() in particular:

       ·   CSIDL values provide a unique system-independent way to identify special folders used
           frequently by applications, but which may not have the same name or location on any
           given system. For example, the system folder may be ''C:\Windows'' on one system and
           ''C:\Winnt'' on another. These constants are defined in Shlobj.h and Shfolder.h.

       ·   CSIDL_LOCAL_APPDATA (0x001c) Version 5.0. The file system directory that serves as a
           data repository for local (nonroaming) applications.  A typical path is C:\Documents
           and Settings\username\Local Settings\Application Data.

       (Source:
       <http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/shell/reference/enums/csidl.asp>.
       Link valid as of Feb 18 2006.  Thanks to Soren Andersen for reminding me of this
       citation.)

       It is interesting that the other two File::HomeDir methods listed above, "my_documents()"
       and "my_data()" both rely on using a Win32 module to peer into the registry, albeit in a
       slightly different manner from "File::Save::Home->get_home_directory".  TIMTOWTDI.

       In an event, File::Save::Home has a number of useful methods besides
       "get_home_directory()" which merit your consideration.  And, as noted above, you can
       supply any valid directory as an optional additional argument to the two File::Save::Home
       functions which normally default to calling "get_home_directory" internally.

   File::HomeDir::Win32
       File::HomeDir::Win32 was originally written by Rob Rothenberg and is now maintained by
       Randy Kobes.  According to Adam Kennedy
       (<http://annocpan.org/~JKEENAN/File-Save-Home-0.07/lib/File/Save/Home.pm#note_636>), ''The
       functionality in File::HomeDir::Win32 is gradually being merged into File::HomeDir over
       time and will eventually be deprecated (although left in place for compatibility
       purposes).''  Because I have not yet fully installed File::HomeDir::Win32, I will defer
       further comparison between it and File::Save::Home to a later date.

AUTHOR

               James E Keenan
               CPAN ID: JKEENAN
               jkeenan@cpan.org
               http://search.cpan.org/~jkeenan

ACKNOWLEDGMENTS

       File::Save::Home has its origins in the maintenance revisions I was doing on CPAN
       distribution ExtUtils::ModuleMaker in the summer of 2005.  After I made a presentation
       about that distribution to the Toronto Perlmongers on October 27, 2005, Michael Graham
       suggested that certain utility functions could be extracted to a separate Perl extension
       for more general applicability.  This module is the implementation of Michael's
       suggestion.

       While I was developing those utility functions for ExtUtils::ModuleMaker, I turned to the
       Perlmonks for assistance with the problem of determining a suitable value for the user's
       home directory on Win32 systems.  In the Perlmonks discussion threads referred to above I
       received helpful suggestions from monks CountZero, Tanktalus, xdg and holli, among others.

       Thanks to Rob Rothenberg for prodding me to expand the SEE ALSO section and to Adam
       Kennedy for responding to questions about File::HomeDir.

       Thanks to Damyan Ivanov, Xavier Guimard and Gregor Herrman of Debian Perl Group for
       patches.

COPYRIGHT

       Copyright (c) 2005-2017 James E. Keenan.  United States.  All rights reserved.

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

       The full text of the license can be found in the LICENSE file included with this module.

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