perl571delta - what's new for perl v5.7.1


perl571delta - what's new for perl v5.7.1


This document describes differences between the 5.7.0 release and the 5.7.1 release.

(To view the differences between the 5.6.0 release and the 5.7.0 release, see the perl570delta manpage.)

Security Vulnerability Closed

(This change was already made in 5.7.0 but bears repeating here.)

A potential security vulnerability in the optional suidperl component of Perl was identified in August 2000. suidperl is neither built nor installed by default. As of April 2001 the only known vulnerable platform is Linux, most likely all Linux distributions. CERT and various vendors and distributors have been alerted about the vulnerability. See for more information.

The problem was caused by Perl trying to report a suspected security exploit attempt using an external program, /bin/mail. On Linux platforms the /bin/mail program had an undocumented feature which when combined with suidperl gave access to a root shell, resulting in a serious compromise instead of reporting the exploit attempt. If you don't have /bin/mail, or if you have 'safe setuid scripts', or if suidperl is not installed, you are safe.

The exploit attempt reporting feature has been completely removed from all the Perl 5.7 releases (and will be gone also from the maintenance release 5.6.1), so that particular vulnerability isn't there anymore. However, further security vulnerabilities are, unfortunately, always possible. The suidperl code is being reviewed and if deemed too risky to continue to be supported, it may be completely removed from future releases. In any case, suidperl should only be used by security experts who know exactly what they are doing and why they are using suidperl instead of some other solution such as sudo ( see ).

Incompatible Changes

Core Enhancements

AUTOLOAD Is Now Lvaluable

AUTOLOAD is now lvaluable, meaning that you can add the :lvalue attribute to AUTOLOAD subroutines and you can assign to the AUTOLOAD return value.

PerlIO is Now The Default

Signals Are Now Safe

Perl used to be fragile in that signals arriving at inopportune moments could corrupt Perl's internal state.

Modules and Pragmata

New Modules

Updated And Improved Modules and Pragmata

The following modules have been upgraded from the versions at CPAN: CPAN, CGI, DB_File, File::Temp, Getopt::Long, Pod::Man, Pod::Text, Storable, Text-Tabs+Wrap.

Performance Enhancements

Utility Changes

New Documentation


Internal replacements for standard C library functions. (Interesting only for extension writers and Perl core hackers.)


Internals of PerlIO with layers.


Documentation on compiling Perl on AIX has been added. AIX has several different C compilers and getting the right patch level is essential. On install README.aix will be installed as perlaix.


Documentation on compiling Perl on the POSIX-BC platform (an EBCDIC mainframe environment) has been added.

This was formerly known as README.posix-bc but the name was considered to be too confusing (it has nothing to do with the POSIX module or the POSIX standard). On install README.bs2000 will be installed as perlbs2000.


In perl 5.7.1 (and in the 5.6.1) the MacPerl sources have been synchronised with the standard Perl sources. To compile MacPerl some additional steps are required, and this file documents those steps. On install README.macos will be installed as perlmacos.


The README.mpeix has been podified, which means that this information about compiling and using Perl on the MPE/iX miniframe platform will be installed as perlmpeix.


README.solaris has been created and Solaris wisdom from elsewhere in the Perl documentation has been collected there. On install README.solaris will be installed as perlsolaris.


The README.vos has been podified, which means that this information about compiling and using Perl on the Stratus VOS miniframe platform will be installed as perlvos.


Documentation on how to use the Perl source repository has been added.

Installation and Configuration Improvements

New Or Improved Platforms

For the list of platforms known to support Perl, see Supported Platforms in the perlport manpage.

Generic Improvements

Selected Bug Fixes

Numerous memory leaks and uninitialized memory accesses have been hunted down. Most importantly anonymous subs used to leak quite a bit.

Platform Specific Changes and Fixes

New or Changed Diagnostics

Two new debugging options have been added: if you have compiled your Perl with debugging, you can use the -DT and -DR options to trace tokenising and to add reference counts to displaying variables, respectively.

Changed Internals

New Tests

Many new tests have been added. The most notable is probably the lib/1_compile: it is very notable because running it takes quite a long time -- it test compiles all the Perl modules in the distribution. Please be patient.

Known Problems

Note that unlike other sections in this document (which describe changes since 5.7.0) this section is cumulative containing known problems for all the 5.7 releases.

AIX vac May Produce Buggy Code For Perl

The AIX C compiler vac version may produce buggy code, resulting in few random tests failing, but when the failing tests are run by hand, they succeed. We suggest upgrading to at least vac version, that has been known to compile Perl correctly. ``lslpp -L|grep vac.C'' will tell you the vac version.

lib/ftmp-security tests warn 'system possibly insecure'

Don't panic. Read INSTALL 'make test' section instead.

lib/io_multihomed Fails In LP64-Configured HP-UX

The lib/io_multihomed test may hang in HP-UX if Perl has been configured to be 64-bit. Because other 64-bit platforms do not hang in this test, HP-UX is suspect. All other tests pass in 64-bit HP-UX. The test attempts to create and connect to ``multihomed'' sockets (sockets which have multiple IP addresses).

Test lib/posix Subtest 9 Fails In LP64-Configured HP-UX

If perl is configured with -Duse64bitall, the successful result of the subtest 10 of lib/posix may arrive before the successful result of the subtest 9, which confuses the test harness so much that it thinks the subtest 9 failed.

lib/b test 19

The test fails on various platforms (PA64 and IA64 are known), but the exact cause is still being investigated.

Linux With Sfio Fails op/misc Test 48

No known fix.

sigaction test 13 in VMS

The test is known to fail; whether it's because of VMS of because of faulty test is not known.

sprintf tests 129 and 130

The op/sprintf tests 129 and 130 are known to fail on some platforms. Examples include any platform using sfio, and Compaq/Tandem's NonStop-UX. The failing platforms do not comply with the ANSI C Standard, line 19ff on page 134 of ANSI X3.159 1989 to be exact. (They produce something else than ``1'' and ``-1'' when formatting 0.6 and -0.6 using the printf format ``%.0f'', most often they produce ``0'' and ``-0''.)

Failure of Thread tests

The subtests 19 and 20 of lib/thr5005.t test are known to fail due to fundamental problems in the 5.005 threading implementation. These are not new failures--Perl 5.005_0x has the same bugs, but didn't have these tests. (Note that support for 5.005-style threading remains experimental.)

Localising a Tied Variable Leaks Memory

    use Tie::Hash;
    tie my %tie_hash => 'Tie::StdHash';
    local($tie_hash{Foo}) = 1; # leaks

Code like the above is known to leak memory every time the local() is executed.

Self-tying of Arrays and Hashes Is Forbidden

Self-tying of arrays and hashes is broken in rather deep and hard-to-fix ways. As a stop-gap measure to avoid people from getting frustrated at the mysterious results (core dumps, most often) it is for now forbidden (you will get a fatal error even from an attempt).

Building Extensions Can Fail Because Of Largefiles

Some extensions like mod_perl are known to have issues with `largefiles', a change brought by Perl 5.6.0 in which file offsets default to 64 bits wide, where supported. Modules may fail to compile at all or compile and work incorrectly. Currently there is no good solution for the problem, but Configure now provides appropriate non-largefile ccflags, ldflags, libswanted, and libs in the %Config hash (e.g., $Config{ccflags_nolargefiles}) so the extensions that are having problems can try configuring themselves without the largefileness. This is admittedly not a clean solution, and the solution may not even work at all. One potential failure is whether one can (or, if one can, whether it's a good idea) link together at all binaries with different ideas about file offsets, all this is platform-dependent.

The Compiler Suite Is Still Experimental

The compiler suite is slowly getting better but is nowhere near working order yet.

Reporting Bugs

If you find what you think is a bug, you might check the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at There may also be information at , the Perl Home Page.

If you believe you have an unreported bug, please run the perlbug program included with your release. Be sure to trim your bug down to a tiny but sufficient test case. Your bug report, along with the output of perl -V, will be sent off to to be analysed by the Perl porting team.


The Changes file for exhaustive details on what changed.

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.


Written by Jarkko Hietaniemi <>, with many contributions from The Perl Porters and Perl Users submitting feedback and patches.

Send omissions or corrections to <>.

 perl571delta - what's new for perl v5.7.1