• TUX



Perl 5 version 12.5 documentation
Recently read



perl572delta - what's new for perl v5.7.2


This document describes differences between the 5.7.1 release and the 5.7.2 release.

(To view the differences between the 5.6.0 release and the 5.7.0 release, see perl570delta. To view the differences between the 5.7.0 release and the 5.7.1 release, see perl571delta.)

Security Vulnerability Closed

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

A security vulnerability affecting all Perl versions prior to 5.6.1 was found in August 2000. The vulnerability does not affect default installations and as far as is known affects only the Linux platform.

You should upgrade your Perl to 5.6.1 as soon as possible. Patches for earlier releases exist but using the patches require full recompilation from the source code anyway, so 5.6.1 is your best choice.

See for more information.

Incompatible Changes

64-bit platforms and malloc

If your pointers are 64 bits wide, the Perl malloc is no more being used because it simply does not work with 8-byte pointers. Also, usually the system malloc on such platforms are much better optimized for such large memory models than the Perl malloc.

AIX Dynaloading

The AIX dynaloading now uses in AIX releases 4.3 and newer the native dlopen interface of AIX instead of the old emulated interface. This change will probably break backward compatibility with compiled modules. The change was made to make Perl more compliant with other applications like modperl which are using the AIX native interface.

Socket Extension Dynamic in VMS

The Socket extension is now dynamically loaded instead of being statically built in. This may or may not be a problem with ancient TCP/IP stacks of VMS: we do not know since we weren't able to test Perl in such configurations.

Different Definition of the Unicode Character Classes \p{In...}

As suggested by the Unicode consortium, the Unicode character classes now prefer scripts as opposed to blocks (as defined by Unicode); in Perl, when the \p{In....} and the \p{In....} regular expression constructs are used. This has changed the definition of some of those character classes.

The difference between scripts and blocks is that scripts are the glyphs used by a language or a group of languages, while the blocks are more artificial groupings of 256 characters based on the Unicode numbering.

In general this change results in more inclusive Unicode character classes, but changes to the other direction also do take place: for example while the script Latin includes all the Latin characters and their various diacritic-adorned versions, it does not include the various punctuation or digits (since they are not solely Latin ).

Changes in the character class semantics may have happened if a script and a block happen to have the same name, for example Hebrew . In such cases the script wins and \p{InHebrew} now means the script definition of Hebrew. The block definition in still available, though, by appending Block to the name: \p{InHebrewBlock} means what \p{InHebrew} meant in perl 5.6.0. For the full list of affected character classes, see Blocks in perlunicode.


The current user-visible implementation of pseudo-hashes (the weird use of the first array element) is deprecated starting from Perl 5.8.0 and will be removed in Perl 5.10.0, and the feature will be implemented differently. Not only is the current interface rather ugly, but the current implementation slows down normal array and hash use quite noticeably. The fields pragma interface will remain available.

The syntaxes @a->[...] and @h->{...} have now been deprecated.

The suidperl is also considered to be too much a risk to continue maintaining and the suidperl code is likely to be removed in a future release.

The package; syntax (package without an argument has been deprecated. Its semantics were never that clear and its implementation even less so. If you have used that feature to disallow all but fully qualified variables, use strict; instead.

The chdir(undef) and chdir('') behaviors to match chdir() has been deprecated. In future versions, chdir(undef) and chdir('') will simply fail.

Core Enhancements

In general a lot of fixing has happened in the area of Perl's understanding of numbers, both integer and floating point. Since in many systems the standard number parsing functions like strtoul() and atof() seem to have bugs, Perl tries to work around their deficiencies. This results hopefully in more accurate numbers.

  • The rules for allowing underscores (underbars) in numeric constants have been relaxed and simplified: now you can have an underscore between digits.

  • GMAGIC (right-hand side magic) could in many cases such as string concatenation be invoked too many times.

  • Lexicals I: lexicals outside an eval "" weren't resolved correctly inside a subroutine definition inside the eval "" if they were not already referenced in the top level of the eval""ed code.

  • Lexicals II: lexicals leaked at file scope into subroutines that were declared before the lexicals.

  • Lvalue subroutines can now return undef in list context.

  • The op_clear and op_null are now exported.

  • A new special regular expression variable has been introduced: $^N , which contains the most-recently closed group (submatch).

  • utime now supports utime undef, undef, @files to change the file timestamps to the current time.

  • The Perl parser has been stress tested using both random input and Markov chain input.

  • eval "v200" now works.

  • VMS now works under PerlIO.

  • END blocks are now run even if you exit/die in a BEGIN block. The execution of END blocks is now controlled by PL_exit_flags & PERL_EXIT_DESTRUCT_END. This enables the new behaviour for perl embedders. This will default in 5.10. See perlembed.

Modules and Pragmata

New Modules and Distributions

  • Attribute::Handlers - Simpler definition of attribute handlers

  • ExtUtils::Constant - generate XS code to import C header constants

  • I18N::Langinfo - query locale information

  • I18N::LangTags - functions for dealing with RFC3066-style language tags

  • libnet - a collection of perl5 modules related to network programming

    Perl installation leaves libnet unconfigured, use libnetcfg to configure.

  • List::Util - selection of general-utility list subroutines

  • Locale::Maketext - framework for localization

  • Memoize - Make your functions faster by trading space for time

  • NEXT - pseudo-class for method redispatch

  • Scalar::Util - selection of general-utility scalar subroutines

  • Test::More - yet another framework for writing test scripts

  • Test::Simple - Basic utilities for writing tests

  • Time::HiRes - high resolution ualarm, usleep, and gettimeofday

  • Time::Piece - Object Oriented time objects

    (Previously known as Time::Object.)

  • Time::Seconds - a simple API to convert seconds to other date values

  • UnicodeCD - Unicode Character Database

Updated And Improved Modules and Pragmata

  • B::Deparse module has been significantly enhanced. It now can deparse almost all of the standard test suite (so that the tests still succeed). There is a make target "test.deparse" for trying this out.

  • Class::Struct now assigns the array/hash element if the accessor is called with an array/hash element as the sole argument.

  • Cwd extension is now (even) faster.

  • DB_File extension has been updated to version 1.77.

  • Fcntl, Socket, and Sys::Syslog have been rewritten to use the new-style constant dispatch section (see ExtUtils::Constant).

  • File::Find is now (again) reentrant. It also has been made more portable.

  • File::Glob now supports GLOB_LIMIT constant to limit the size of the returned list of filenames.

  • IO::Socket::INET now supports LocalPort of zero (usually meaning that the operating system will make one up.)

  • The vars pragma now supports declaring fully qualified variables. (Something that our() does not and will not support.)

Utility Changes

  • The emacs/ is now much faster.

  • h2ph now supports C trigraphs.

  • h2xs uses the new ExtUtils::Constant module which will affect newly created extensions that define constants. Since the new code is more correct (if you have two constants where the first one is a prefix of the second one, the first constant never gets defined), less lossy (it uses integers for integer constant, as opposed to the old code that used floating point numbers even for integer constants), and slightly faster, you might want to consider regenerating your extension code (the new scheme makes regenerating easy). h2xs now also supports C trigraphs.

  • libnetcfg has been added to configure the libnet.

  • The Pod::Html (and thusly pod2html) now allows specifying a cache directory.

New Documentation

  • Locale::Maketext::TPJ13 is an article about software localization, originally published in The Perl Journal #13, republished here with kind permission.

  • More README.$PLATFORM files have been converted into pod, which also means that they also be installed as perl$PLATFORM documentation files. The new files are perlapollo, perlbeos, perldgux, perlhurd, perlmint, perlnetware, perlplan9, perlqnx, and perltru64.

  • The Todo and Todo-5.6 files have been merged into perltodo.

  • Use of the gprof tool to profile Perl has been documented in perlhack. There is a make target "perl.gprof" for generating a gprofiled Perl executable.

Installation and Configuration Improvements

New Or Improved Platforms

  • AIX should now work better with gcc, threads, and 64-bitness. Also the long doubles support in AIX should be better now. See perlaix.

  • AtheOS ( ) is a new platform.

  • DG/UX platform now supports the 5.005-style threads. See perldgux.

  • DYNIX/ptx platform (a.k.a. dynixptx) is supported at or near osvers 4.5.2.

  • Several Mac OS (Classic) portability patches have been applied. We hope to get a fully working port by 5.8.0. (The remaining problems relate to the changed IO model of Perl.) See perlmacos.

  • Mac OS X (or Darwin) should now be able to build Perl even on HFS+ filesystems. (The case-insensitivity confused the Perl build process.)

  • NetWare from Novell is now supported. See perlnetware.

  • The Amdahl UTS Unix mainframe platform is now supported.

Generic Improvements

  • In AFS installations one can configure the root of the AFS to be somewhere else than the default /afs by using the Configure parameter -Dafsroot=/some/where/else.

  • The version of Berkeley DB used when the Perl (and, presumably, the DB_File extension) was built is now available as @Config{qw(db_version_major db_version_minor db_version_patch)} from Perl and as DB_VERSION_MAJOR_CFG DB_VERSION_MINOR_CFG DB_VERSION_PATCH_CFG from C.

  • The Thread extension is now not built at all under ithreads (Configure -Duseithreads ) because it wouldn't work anyway (the Thread extension requires being Configured with -Duse5005threads ).

  • The B::Deparse compiler backend has been so significantly improved that almost the whole Perl test suite passes after being deparsed. A make target has been added to help in further testing: make test.deparse .

Selected Bug Fixes

  • The autouse pragma didn't work for Multi::Part::Function::Names.

  • The behaviour of non-decimal but numeric string constants such as "0x23" was platform-dependent: in some platforms that was seen as 35, in some as 0, in some as a floating point number (don't ask). This was caused by Perl using the operating system libraries in a situation where the result of the string to number conversion is undefined: now Perl consistently handles such strings as zero in numeric contexts.

  • dprofpp -R didn't work.

  • PERL5OPT with embedded spaces didn't work.

  • Sys::Syslog ignored the LOG_AUTH constant.

Platform Specific Changes and Fixes

  • Some versions of glibc have a broken modfl(). This affects builds with -Duselongdouble . This version of Perl detects this brokenness and has a workaround for it. The glibc release 2.2.2 is known to have fixed the modfl() bug.

New or Changed Diagnostics

  • In the regular expression diagnostics the << HERE marker introduced in 5.7.0 has been changed to be <-- HERE since too many people found the << to be too similar to here-document starters.

  • If you try to pack a number less than 0 or larger than 255 using the "C" format you will get an optional warning. Similarly for the "c" format and a number less than -128 or more than 127.

  • Certain regex modifiers such as (?o) make sense only if applied to the entire regex. You will an optional warning if you try to do otherwise.

  • Using arrays or hashes as references (e.g. %foo->{bar} has been deprecated for a while. Now you will get an optional warning.

Source Code Enhancements

MAGIC constants

The MAGIC constants (e.g. 'P' ) have been macrofied (e.g. PERL_MAGIC_TIED ) for better source code readability and maintainability.

Better commented code

perly.c, sv.c, and sv.h have now been extensively commented.

Regex pre-/post-compilation items matched up

The regex compiler now maintains a structure that identifies nodes in the compiled bytecode with the corresponding syntactic features of the original regex expression. The information is attached to the new offsets member of the struct regexp . See perldebguts for more complete information.

gcc -Wall

The C code has been made much more gcc -Wall clean. Some warning messages still remain, though, so if you are compiling with gcc you will see some warnings about dubious practices. The warnings are being worked on.

New Tests

Several new tests have been added, especially for the lib subsection.

The tests are now reported in a different order than in earlier Perls. (This happens because the test scripts from under t/lib have been moved to be closer to the library/extension they are testing.)

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.


  • In AIX 4.2 Perl extensions that use C++ functions that use statics may have problems in that the statics are not getting initialized. In newer AIX releases this has been solved by linking Perl with the libC_r library, but unfortunately in AIX 4.2 the said library has an obscure bug where the various functions related to time (such as time() and gettimeofday()) return broken values, and therefore in AIX 4.2 Perl is not linked against the libC_r.

  • 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.

Amiga Perl Invoking Mystery

One cannot call Perl using the volume: syntax, that is, perl -v works, but for example bin:perl -v doesn't. The exact reason is known but the current suspect is the ixemul library.

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

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

Cygwin intermittent failures of lib/Memoize/t/expire_file 11 and 12

The subtests 11 and 12 sometimes fail and sometimes work.

HP-UX lib/io_multihomed Fails When LP64-Configured

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).

HP-UX lib/posix Subtest 9 Fails When LP64-Configured

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.

Linux With Sfio Fails op/misc Test 48

No known fix.


OS/390 has rather many test failures but the situation is actually better than it was in 5.6.0, it's just that so many new modules and tests have been added.

  1. Failed Test Stat Wstat Total Fail Failed List of Failed
  2. -----------------------------------------------------------------------------
  3. ../ext/B/Deparse.t 14 1 7.14% 14
  4. ../ext/B/Showlex.t 1 1 100.00% 1
  5. ../ext/Encode/Encode/Tcl.t 610 13 2.13% 592 594 596 598
  6. 600 602 604-610
  7. ../ext/IO/lib/IO/t/io_unix.t 113 28928 5 3 60.00% 3-5
  8. ../ext/POSIX/POSIX.t 29 1 3.45% 14
  9. ../ext/Storable/t/lock.t 255 65280 5 3 60.00% 3-5
  10. ../lib/locale.t 129 33024 117 19 16.24% 99-117
  11. ../lib/warnings.t 434 1 0.23% 75
  12. ../lib/ExtUtils.t 27 1 3.70% 25
  13. ../lib/Math/BigInt/t/bigintpm.t 1190 1 0.08% 1145
  14. ../lib/Unicode/UCD.t 81 48 59.26% 1-16 49-64 66-81
  15. ../lib/User/pwent.t 9 1 11.11% 4
  16. op/pat.t 660 6 0.91% 242-243 424-425
  17. 626-627
  18. op/split.t 0 9 ?? ?? % ??
  19. op/taint.t 174 3 1.72% 156 162 168
  20. op/tr.t 70 3 4.29% 50 58-59
  21. Failed 16/422 test scripts, 96.21% okay. 105/23251 subtests failed, 99.55% okay.

op/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 other 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

Note that support for 5.005-style threading remains experimental.

The following tests 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.

  1. lib/autouse.t 4
  2. t/lib/thr5005.t 19-20


  • ext/POSIX/sigaction subtests 6 and 13 may fail.

  • lib/ExtUtils may spuriously claim that subtest 28 failed, which is interesting since the test only has 27 tests.

  • Numerous numerical test failures

    1. op/numconvert 209,210,217,218
    2. op/override 7
    3. ext/Time/HiRes/HiRes 9
    4. lib/Math/BigInt/t/bigintpm 1145
    5. lib/Math/Trig 25

    These tests fail because of yet unresolved floating point inaccuracies.


There are a few known test failures, see perluts.


Rather many tests are failing in VMS but that actually more tests succeed in VMS than they used to, it's just that there are many, many more tests than there used to be.

Here are the known failures from some compiler/platform combinations.

DEC C V5.3-006 on OpenVMS VAX V6.2

  1. [-.ext.list.util.t]tainted..............FAILED on test 3
  2. [-.ext.posix]sigaction..................FAILED on test 7
  3. [-.ext.time.hires]hires.................FAILED on test 14
  4. [-.lib.file.find]taint..................FAILED on test 17
  5. [-.lib.math.bigint.t]bigintpm...........FAILED on test 1183
  6. [-.lib.test.simple.t]exit...............FAILED on test 1
  7. [.lib]vmsish............................FAILED on test 13
  8. [.op]sprintf............................FAILED on test 12
  9. Failed 8/399 tests, 91.23% okay.

DEC C V6.0-001 on OpenVMS Alpha V7.2-1 and Compaq C V6.2-008 on OpenVMS Alpha V7.1

  1. [-.ext.list.util.t]tainted..............FAILED on test 3
  2. [-.lib.file.find]taint..................FAILED on test 17
  3. [-.lib.test.simple.t]exit...............FAILED on test 1
  4. [.lib]vmsish............................FAILED on test 13
  5. Failed 4/399 tests, 92.48% okay.

Compaq C V6.4-005 on OpenVMS Alpha 7.2.1

  1. [-.ext.b]showlex........................FAILED on test 1
  2. [-.ext.list.util.t]tainted..............FAILED on test 3
  3. [-.lib.file.find]taint..................FAILED on test 17
  4. [-.lib.test.simple.t]exit...............FAILED on test 1
  5. [.lib]vmsish............................FAILED on test 13
  6. [.op]misc...............................FAILED on test 49
  7. Failed 6/401 tests, 92.77% okay.


In multi-CPU boxes there are some problems with the I/O buffering: some output may appear twice.

Localising a Tied Variable Leaks Memory

  1. use Tie::Hash;
  2. tie my %tie_hash => 'Tie::StdHash';
  3. ...
  4. 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).

Variable Attributes are not Currently Usable for Tieing

This limitation will hopefully be fixed in future. (Subroutine attributes work fine for tieing, see Attribute::Handlers).

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.

The Long Double Support is Still Experimental

The ability to configure Perl's numbers to use "long doubles", floating point numbers of hopefully better accuracy, is still experimental. The implementations of long doubles are not yet widespread and the existing implementations are not quite mature or standardised, therefore trying to support them is a rare and moving target. The gain of more precision may also be offset by slowdown in computations (more bits to move around, and the operations are more likely to be executed by less optimised libraries).

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 <>.