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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       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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       IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY
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