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bc34412328
This is scary:
#use sort 'stable';
require re; re->import('/x');
eval '
print "a b" =~ /a b/ ? "ok\n" : "nokay\n";
use re "/m";
print "a b" =~ /a b/ ? "ok\n" : "nokay\n";
';
It prints:
ok
nokay
The re->import statement is supposed to apply to the caller that
is currently being compiled, but it makes ‘use re "/m"’ enable
/x as well.
Uncomment the ‘use sort’ line, and you get:
ok
ok
which is even scarier.
eval"" is supposed to compile its argument with the hints under which
the eval itself was compiled.
Whenever %^H is modified, a flag (HINT_LOCALIZE_HH; LHH hereinafter)
is set in $^H.
When eval is called, it checks the LHH flag in the hints from the time
it was compiled, to determine whether to reset %^H. If LHH is set,
it creates a new %^H based on the hints under which it was compiled.
Otherwise, it just leaves %^H alone.
The problem is that %^H and LHH may be set some time later
(re->import), so when the eval runs there is junk in %^H that
does not apply to the contents of the eval.
There are two layers at which the hints hash is stored. There is the
Perl-level hash, %^H, and then there is a faster cop-hints-hash struc-
ture underneath. It’s the latter that is actually used during compi-
lation. %^H is just a Perl front-end to it.
When eval does not reset %^H and %^H has junk in it, the two get
out of sync, because eval always sets the cop-hints-hash correctly.
Hence the first print in the first example above compiles without
‘use re "/x"’. The ‘use re’ statement after it modifies the %^H-with-
junk-in-it, which then gets synchronised with the cop-hints-hash,
turning on /x for the next print statement.
Adding ‘use sort’ to the top of the program makes the problem go
away, because, since sort.pm uses %^H, LHH is set when eval() itself
is compiled.
This commit fixes this by having pp_entereval check not only the LHH
flag from the hints under which it was compiled, but also the hints of
the currently compiling code ($^H / PL_hints).
Perl is Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 by Larry Wall and others. All rights reserved. ABOUT PERL ========== Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including system administration, web development, network programming, GUI development, and more. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). Its major features are that it's easy to use, supports both procedural and object-oriented (OO) programming, has powerful built-in support for text processing, and has one of the world's most impressive collections of third-party modules. For an introduction to the language's features, see pod/perlintro.pod. For a discussion of the important changes in this release, see pod/perldelta.pod. There are also many Perl books available, covering a wide variety of topics, from various publishers. See pod/perlbook.pod for more information. INSTALLATION ============ If you're using a relatively modern operating system and want to install this version of Perl locally, run the following commands: ./Configure -des -Dprefix=$HOME/localperl make test make install This will configure and compile perl for your platform, run the regression tests, and install perl in a subdirectory "localperl" of your home directory. If you run into any trouble whatsoever or you need to install a customized version of Perl, you should read the detailed instructions in the "INSTALL" file that came with this distribution. Additionally, there are a number of "README" files with hints and tips about building and using Perl on a wide variety of platforms, some more common than others. Once you have Perl installed, a wealth of documentation is available to you through the 'perldoc' tool. To get started, run this command: perldoc perl IF YOU RUN INTO TROUBLE ======================= Perl is a large and complex system that's used for everything from knitting to rocket science. If you run into trouble, it's quite likely that someone else has already solved the problem you're facing. Once you've exhausted the documentation, please report bugs to us using the 'perlbug' tool. For more information about perlbug, either type 'perldoc perlbug' or just 'perlbug' on a line by itself. While it was current when we made it available, Perl is constantly evolving and there may be a more recent version that fixes bugs you've run into or adds new features that you might find useful. You can always find the latest version of perl on a CPAN (Comprehensive Perl Archive Network) site near you at http://www.cpan.org/src/ Just a personal note: I want you to know that I create nice things like this because it pleases the Author of my story. If this bothers you, then your notion of Authorship needs some revision. But you can use perl anyway. :-) The author. LICENSING ========= This program is free software; you can redistribute it and/or modify it under the terms of either: a) the GNU General Public License as published by the Free Software Foundation; either version 1, or (at your option) any later version, or b) the "Artistic License" which comes with this Kit. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See either the GNU General Public License or the Artistic License for more details. You should have received a copy of the Artistic License with this Kit, in the file named "Artistic". If not, I'll be glad to provide one. You should also have received a copy of the GNU General Public License along with this program in the file named "Copying". If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA or visit their web page on the internet at http://www.gnu.org/copyleft/gpl.html. For those of you that choose to use the GNU General Public License, my interpretation of the GNU General Public License is that no Perl script falls under the terms of the GPL unless you explicitly put said script under the terms of the GPL yourself. Furthermore, any object code linked with perl does not automatically fall under the terms of the GPL, provided such object code only adds definitions of subroutines and variables, and does not otherwise impair the resulting interpreter from executing any standard Perl script. I consider linking in C subroutines in this manner to be the moral equivalent of defining subroutines in the Perl language itself. You may sell such an object file as proprietary provided that you provide or offer to provide the Perl source, as specified by the GNU General Public License. (This is merely an alternate way of specifying input to the program.) You may also sell a binary produced by the dumping of a running Perl script that belongs to you, provided that you provide or offer to provide the Perl source as specified by the GPL. (The fact that a Perl interpreter and your code are in the same binary file is, in this case, a form of mere aggregation.) This is my interpretation of the GPL. If you still have concerns or difficulties understanding my intent, feel free to contact me. Of course, the Artistic License spells all this out for your protection, so you may prefer to use that.