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Id: 130464
Status: new
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Queue: perl6

Owner: cpan [at] zoffix.com
Requestors: comdog <brian.d.foy [at] gmail.com>
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From: brian d foy <brian.d.foy [...] gmail.com>
To: rakudobug [...] perl.org
Date: Sat, 31 Dec 2016 04:12:45 -0500
Subject: Should the way to set tmpdir from the environment be known to the user?
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I was looking at how tmpdir does its work so I can explain what people need to do in order for it to do its work. All of the current IO::Spec modules currently inherit from IO::Spec::Unix, and it looks like these three have the same tmpdir code that differs only by the list of directories to try: IO::Spec::Unix %*ENV<TMPDIR>, '/tmp', IO::Spec::Win32 (is IO::Spec::Unix) $ENV<TMPDIR>, $ENV<TEMP>, $ENV<TMP>, 'SYS:/temp', 'C:\system\temp', 'C:/temp', '/tmp', '/', IO::Spec::Cygwin (is IO::Spec::Unix) %ENV<TMPDIR>, "/tmp", %ENV<TMP>, %ENV<TEMP>, 'C:/temp', I have a couple of questions about that. 0. I mostly want to be able to say "Set FOO to set the temporary directory" and have that be a solid commitment from Perl 6. The docs for $*TMPDIR and tmpdir do not document how they decide what value to have. 1. Aside for platform specific expectations, should tmpdir look at environment variables in the same order? Notice that in Cygwin, '/tmp' shows up in the middle (right after TMPDIR, like in Unix), but it would also look in other environment variables. I tend to think that if an environment variable is set, it should come before a hard-coded solution. Notice also that Win32 and Cygwin check TMP and TEMP in different orders. I saw on MSDN (from Raymond Chen, no less) that Windows's GetTempFileName looks at TMP first and then TEMP, but I don't think that matters much and most systems seem to set both to the same value. (https://blogs.msdn.microsoft.com/oldnewthing/20150417-00/?p=44213) 2. As a matter of code duplication, is there some issue or future work that precludes having the derived classes define a directory order while leaving tmpdir in the base class (IO::Spec::Unix)? The thing that I would think might kill that is platform-specific filesystem checks (ACLs? whatever NTFS does? etc) that are not be handled by the unixy file test methods. method temp-dirs-to-try { ... } # in each base class method tmpdir { # only in the base class my $ENV := %*ENV; my $io; first( { if .defined { $io = .IO; $io.d && $io.r && $io.w && $io.x; } }, self.temp-dirs-to-try ) ?? $io !! IO::Path.new("."); } 3. Whatever those answers are, do we guarantee to a Perl 6 user a particular way to set the value. For instance, someone writes a portable program and tells their users to set TMP because that is what works for them and they don't know about other options. But, someone runs it on a Unixy place and they use TMP because the instructions say to use that. I suppose this comes down to how much of the underlying system and practice do you let leak through and your tolerance for "On Unix set FOO, on Windows set BAR". That answer might be to tell everyone that TMPDIR will always be checked first. But, also possibly let users set all the same variables in each environment. 4. Or, it just doesn't matter because you should care where the temporary files are. 5. Except, if none of the locations work, the temp files end up in the current working directory (and is it odd to get that by IO::Path.new(".") instead of $*CWD?), which might not have the attributes required of the other candidates (that is, is writeable)? That blows up potentially far away from the place that set it.


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