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   1  =head1 NAME
   2  
   3  perl561delta - what's new for perl v5.6.x
   4  
   5  =head1 DESCRIPTION
   6  
   7  This document describes differences between the 5.005 release and the 5.6.1
   8  release.
   9  
  10  =head1 Summary of changes between 5.6.0 and 5.6.1
  11  
  12  This section contains a summary of the changes between the 5.6.0 release
  13  and the 5.6.1 release.  More details about the changes mentioned here
  14  may be found in the F<Changes> files that accompany the Perl source
  15  distribution.  See L<perlhack> for pointers to online resources where you
  16  can inspect the individual patches described by these changes.
  17  
  18  =head2 Security Issues
  19  
  20  suidperl will not run /bin/mail anymore, because some platforms have
  21  a /bin/mail that is vulnerable to buffer overflow attacks.
  22  
  23  Note that suidperl is neither built nor installed by default in
  24  any recent version of perl.  Use of suidperl is highly discouraged.
  25  If you think you need it, try alternatives such as sudo first.
  26  See http://www.courtesan.com/sudo/ .
  27  
  28  =head2 Core bug fixes
  29  
  30  This is not an exhaustive list.  It is intended to cover only the
  31  significant user-visible changes.
  32  
  33  =over
  34  
  35  =item C<UNIVERSAL::isa()>
  36  
  37  A bug in the caching mechanism used by C<UNIVERSAL::isa()> that affected
  38  base.pm has been fixed.  The bug has existed since the 5.005 releases,
  39  but wasn't tickled by base.pm in those releases.
  40  
  41  =item Memory leaks
  42  
  43  Various cases of memory leaks and attempts to access uninitialized memory
  44  have been cured.  See L</"Known Problems"> below for further issues.
  45  
  46  =item Numeric conversions
  47  
  48  Numeric conversions did not recognize changes in the string value
  49  properly in certain circumstances.
  50  
  51  In other situations, large unsigned numbers (those above 2**31) could
  52  sometimes lose their unsignedness, causing bogus results in arithmetic
  53  operations.
  54  
  55  Integer modulus on large unsigned integers sometimes returned
  56  incorrect values.
  57  
  58  Perl 5.6.0 generated "not a number" warnings on certain conversions where
  59  previous versions didn't.
  60  
  61  These problems have all been rectified.
  62  
  63  Infinity is now recognized as a number.
  64  
  65  =item qw(a\\b)
  66  
  67  In Perl 5.6.0, qw(a\\b) produced a string with two backslashes instead
  68  of one, in a departure from the behavior in previous versions.  The
  69  older behavior has been reinstated.  
  70  
  71  =item caller()
  72  
  73  caller() could cause core dumps in certain situations.  Carp was sometimes
  74  affected by this problem.
  75  
  76  =item Bugs in regular expressions
  77  
  78  Pattern matches on overloaded values are now handled correctly.
  79  
  80  Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious warnings.
  81  This has been corrected.
  82  
  83  The RE engine found in Perl 5.6.0 accidentally pessimised certain kinds
  84  of simple pattern matches.  These are now handled better.
  85  
  86  Regular expression debug output (whether through C<use re 'debug'>
  87  or via C<-Dr>) now looks better.
  88  
  89  Multi-line matches like C<"a\nxb\n" =~ /(?!\A)x/m> were flawed.  The
  90  bug has been fixed.
  91  
  92  Use of $& could trigger a core dump under some situations.  This
  93  is now avoided.
  94  
  95  Match variables $1 et al., weren't being unset when a pattern match
  96  was backtracking, and the anomaly showed up inside C</...(?{ ... }).../>
  97  etc.  These variables are now tracked correctly.
  98  
  99  pos() did not return the correct value within s///ge in earlier
 100  versions.  This is now handled correctly.
 101  
 102  =item "slurp" mode
 103  
 104  readline() on files opened in "slurp" mode could return an extra "" at
 105  the end in certain situations.  This has been corrected.
 106  
 107  =item Autovivification of symbolic references to special variables
 108  
 109  Autovivification of symbolic references of special variables described
 110  in L<perlvar> (as in C<${$num}>) was accidentally disabled.  This works
 111  again now.
 112  
 113  =item Lexical warnings 
 114  
 115  Lexical warnings now propagate correctly into C<eval "...">.
 116  
 117  C<use warnings qw(FATAL all)> did not work as intended.  This has been
 118  corrected.
 119  
 120  Lexical warnings could leak into other scopes in some situations.
 121  This is now fixed.
 122  
 123  warnings::enabled() now reports the state of $^W correctly if the caller
 124  isn't using lexical warnings.
 125  
 126  =item Spurious warnings and errors
 127  
 128  Perl 5.6.0 could emit spurious warnings about redefinition of dl_error()
 129  when statically building extensions into perl.  This has been corrected.
 130  
 131  "our" variables could result in bogus "Variable will not stay shared"
 132  warnings.  This is now fixed.
 133  
 134  "our" variables of the same name declared in two sibling blocks
 135  resulted in bogus warnings about "redeclaration" of the variables.
 136  The problem has been corrected.
 137  
 138  =item glob()
 139  
 140  Compatibility of the builtin glob() with old csh-based glob has been
 141  improved with the addition of GLOB_ALPHASORT option.  See C<File::Glob>.
 142  
 143  File::Glob::glob() has been renamed to File::Glob::bsd_glob()
 144  because the name clashes with the builtin glob().  The older
 145  name is still available for compatibility, but is deprecated.
 146  
 147  Spurious syntax errors generated in certain situations, when glob()
 148  caused File::Glob to be loaded for the first time, have been fixed.
 149  
 150  =item Tainting
 151  
 152  Some cases of inconsistent taint propagation (such as within hash
 153  values) have been fixed.
 154  
 155  The tainting behavior of sprintf() has been rationalized.  It does
 156  not taint the result of floating point formats anymore, making the
 157  behavior consistent with that of string interpolation.
 158  
 159  =item sort()
 160  
 161  Arguments to sort() weren't being provided the right wantarray() context.
 162  The comparison block is now run in scalar context, and the arguments to
 163  be sorted are always provided list context.
 164  
 165  sort() is also fully reentrant, in the sense that the sort function
 166  can itself call sort().  This did not work reliably in previous releases.
 167  
 168  =item #line directives
 169  
 170  #line directives now work correctly when they appear at the very
 171  beginning of C<eval "...">.
 172  
 173  =item Subroutine prototypes
 174  
 175  The (\&) prototype now works properly.
 176  
 177  =item map()
 178  
 179  map() could get pathologically slow when the result list it generates
 180  is larger than the source list.  The performance has been improved for
 181  common scenarios.
 182  
 183  =item Debugger
 184  
 185  Debugger exit code now reflects the script exit code.
 186  
 187  Condition C<"0"> in breakpoints is now treated correctly.
 188  
 189  The C<d> command now checks the line number.
 190  
 191  C<$.> is no longer corrupted by the debugger.
 192  
 193  All debugger output now correctly goes to the socket if RemotePort
 194  is set.
 195  
 196  =item PERL5OPT
 197  
 198  PERL5OPT can be set to more than one switch group.  Previously,
 199  it used to be limited to one group of options only.
 200  
 201  =item chop()
 202  
 203  chop(@list) in list context returned the characters chopped in reverse
 204  order.  This has been reversed to be in the right order.
 205  
 206  =item Unicode support
 207  
 208  Unicode support has seen a large number of incremental improvements,
 209  but continues to be highly experimental.  It is not expected to be
 210  fully supported in the 5.6.x maintenance releases.
 211  
 212  substr(), join(), repeat(), reverse(), quotemeta() and string
 213  concatenation were all handling Unicode strings incorrectly in
 214  Perl 5.6.0.  This has been corrected.
 215  
 216  Support for C<tr///CU> and C<tr///UC> etc., have been removed since
 217  we realized the interface is broken.  For similar functionality,
 218  see L<perlfunc/pack>.
 219  
 220  The Unicode Character Database has been updated to version 3.0.1
 221  with additions made available to the public as of August 30, 2000.
 222  
 223  The Unicode character classes \p{Blank} and \p{SpacePerl} have been
 224  added.  "Blank" is like C isblank(), that is, it contains only
 225  "horizontal whitespace" (the space character is, the newline isn't),
 226  and the "SpacePerl" is the Unicode equivalent of C<\s> (\p{Space}
 227  isn't, since that includes the vertical tabulator character, whereas
 228  C<\s> doesn't.)
 229  
 230  If you are experimenting with Unicode support in perl, the development
 231  versions of Perl may have more to offer.  In particular, I/O layers
 232  are now available in the development track, but not in the maintenance
 233  track, primarily to do backward compatibility issues.  Unicode support
 234  is also evolving rapidly on a daily basis in the development track--the
 235  maintenance track only reflects the most conservative of these changes.
 236  
 237  =item 64-bit support
 238  
 239  Support for 64-bit platforms has been improved, but continues to be
 240  experimental.  The level of support varies greatly among platforms.
 241  
 242  =item Compiler
 243  
 244  The B Compiler and its various backends have had many incremental
 245  improvements, but they continue to remain highly experimental.  Use in
 246  production environments is discouraged.
 247  
 248  The perlcc tool has been rewritten so that the user interface is much
 249  more like that of a C compiler.
 250  
 251  The perlbc tools has been removed.  Use C<perlcc -B> instead.
 252  
 253  =item Lvalue subroutines
 254  
 255  There have been various bugfixes to support lvalue subroutines better.
 256  However, the feature still remains experimental.
 257  
 258  =item IO::Socket
 259  
 260  IO::Socket::INET failed to open the specified port if the service
 261  name was not known.  It now correctly uses the supplied port number
 262  as is.
 263  
 264  =item File::Find
 265  
 266  File::Find now chdir()s correctly when chasing symbolic links.
 267  
 268  =item xsubpp
 269  
 270  xsubpp now tolerates embedded POD sections.
 271  
 272  =item C<no Module;>
 273  
 274  C<no Module;> does not produce an error even if Module does not have an
 275  unimport() method.  This parallels the behavior of C<use> vis-a-vis
 276  C<import>.
 277  
 278  =item Tests
 279  
 280  A large number of tests have been added.
 281  
 282  =back
 283  
 284  =head2 Core features
 285  
 286  untie() will now call an UNTIE() hook if it exists.  See L<perltie>
 287  for details.
 288  
 289  The C<-DT> command line switch outputs copious tokenizing information.
 290  See L<perlrun>.
 291  
 292  Arrays are now always interpolated in double-quotish strings.  Previously,
 293  C<"foo@bar.com"> used to be a fatal error at compile time, if an array
 294  C<@bar> was not used or declared.  This transitional behavior was
 295  intended to help migrate perl4 code, and is deemed to be no longer useful.
 296  See L</"Arrays now always interpolate into double-quoted strings">.
 297  
 298  keys(), each(), pop(), push(), shift(), splice() and unshift()
 299  can all be overridden now.
 300  
 301  C<my __PACKAGE__ $obj> now does the expected thing.
 302  
 303  =head2 Configuration issues
 304  
 305  On some systems (IRIX and Solaris among them) the system malloc is demonstrably
 306  better.  While the defaults haven't been changed in order to retain binary
 307  compatibility with earlier releases, you may be better off building perl
 308  with C<Configure -Uusemymalloc ...> as discussed in the F<INSTALL> file.
 309  
 310  C<Configure> has been enhanced in various ways:
 311  
 312  =over
 313  
 314  =item *
 315  
 316  Minimizes use of temporary files.
 317  
 318  =item *
 319  
 320  By default, does not link perl with libraries not used by it, such as
 321  the various dbm libraries.  SunOS 4.x hints preserve behavior on that
 322  platform.
 323  
 324  =item *
 325  
 326  Support for pdp11-style memory models has been removed due to obsolescence.
 327  
 328  =item *
 329  
 330  Building outside the source tree is supported on systems that have
 331  symbolic links. This is done by running
 332  
 333      sh /path/to/source/Configure -Dmksymlinks ...
 334      make all test install
 335  
 336  in a directory other than the perl source directory.  See F<INSTALL>.
 337  
 338  =item *
 339  
 340  C<Configure -S> can be run non-interactively.
 341  
 342  =back
 343  
 344  =head2 Documentation
 345  
 346  README.aix, README.solaris and README.macos have been added.
 347  README.posix-bc has been renamed to README.bs2000.  These are
 348  installed as L<perlaix>, L<perlsolaris>, L<perlmacos>, and
 349  L<perlbs2000> respectively.
 350  
 351  The following pod documents are brand new:
 352  
 353      perlclib    Internal replacements for standard C library functions
 354      perldebtut    Perl debugging tutorial
 355      perlebcdic    Considerations for running Perl on EBCDIC platforms
 356      perlnewmod    Perl modules: preparing a new module for distribution
 357      perlrequick    Perl regular expressions quick start
 358      perlretut    Perl regular expressions tutorial
 359      perlutil    utilities packaged with the Perl distribution
 360  
 361  The F<INSTALL> file has been expanded to cover various issues, such as
 362  64-bit support.
 363  
 364  A longer list of contributors has been added to the source distribution.
 365  See the file C<AUTHORS>.
 366  
 367  Numerous other changes have been made to the included documentation and FAQs.
 368  
 369  =head2 Bundled modules
 370  
 371  The following modules have been added.
 372  
 373  =over
 374  
 375  =item B::Concise
 376  
 377  Walks Perl syntax tree, printing concise info about ops.  See L<B::Concise>.
 378  
 379  =item File::Temp
 380  
 381  Returns name and handle of a temporary file safely.  See L<File::Temp>.
 382  
 383  =item Pod::LaTeX
 384  
 385  Converts Pod data to formatted LaTeX.  See L<Pod::LaTeX>.
 386  
 387  =item Pod::Text::Overstrike
 388  
 389  Converts POD data to formatted overstrike text.  See L<Pod::Text::Overstrike>.
 390  
 391  =back
 392  
 393  The following modules have been upgraded.
 394  
 395  =over
 396  
 397  =item CGI
 398  
 399  CGI v2.752 is now included.
 400  
 401  =item CPAN
 402  
 403  CPAN v1.59_54 is now included.
 404  
 405  =item Class::Struct
 406  
 407  Various bugfixes have been added.
 408  
 409  =item DB_File
 410  
 411  DB_File v1.75 supports newer Berkeley DB versions, among other
 412  improvements.
 413  
 414  =item Devel::Peek
 415  
 416  Devel::Peek has been enhanced to support dumping of memory statistics,
 417  when perl is built with the included malloc().
 418  
 419  =item File::Find
 420  
 421  File::Find now supports pre and post-processing of the files in order
 422  to sort() them, etc.
 423  
 424  =item Getopt::Long
 425  
 426  Getopt::Long v2.25 is included.
 427  
 428  =item IO::Poll
 429  
 430  Various bug fixes have been included.
 431  
 432  =item IPC::Open3
 433  
 434  IPC::Open3 allows use of numeric file descriptors.
 435  
 436  =item Math::BigFloat
 437  
 438  The fmod() function supports modulus operations.  Various bug fixes
 439  have also been included.
 440  
 441  =item Math::Complex
 442  
 443  Math::Complex handles inf, NaN etc., better.
 444  
 445  =item Net::Ping
 446  
 447  ping() could fail on odd number of data bytes, and when the echo service
 448  isn't running.  This has been corrected.
 449  
 450  =item Opcode
 451  
 452  A memory leak has been fixed.
 453  
 454  =item Pod::Parser
 455  
 456  Version 1.13 of the Pod::Parser suite is included.
 457  
 458  =item Pod::Text
 459  
 460  Pod::Text and related modules have been upgraded to the versions
 461  in podlators suite v2.08.
 462  
 463  =item SDBM_File
 464  
 465  On dosish platforms, some keys went missing because of lack of support for
 466  files with "holes".  A workaround for the problem has been added.
 467  
 468  =item Sys::Syslog
 469  
 470  Various bug fixes have been included.
 471  
 472  =item Tie::RefHash
 473  
 474  Now supports Tie::RefHash::Nestable to automagically tie hashref values.
 475  
 476  =item Tie::SubstrHash
 477  
 478  Various bug fixes have been included.
 479  
 480  =back
 481  
 482  =head2 Platform-specific improvements
 483  
 484  The following new ports are now available.
 485  
 486  =over
 487  
 488  =item NCR MP-RAS
 489  
 490  =item NonStop-UX
 491  
 492  =back
 493  
 494  Perl now builds under Amdahl UTS.
 495  
 496  Perl has also been verified to build under Amiga OS.
 497  
 498  Support for EPOC has been much improved.  See README.epoc.
 499  
 500  Building perl with -Duseithreads or -Duse5005threads now works
 501  under HP-UX 10.20 (previously it only worked under 10.30 or later).
 502  You will need a thread library package installed.  See README.hpux.
 503  
 504  Long doubles should now work under Linux.
 505  
 506  Mac OS Classic is now supported in the mainstream source package.
 507  See README.macos.
 508  
 509  Support for MPE/iX has been updated.  See README.mpeix.
 510  
 511  Support for OS/2 has been improved.  See C<os2/Changes> and README.os2.
 512  
 513  Dynamic loading on z/OS (formerly OS/390) has been improved.  See
 514  README.os390.
 515  
 516  Support for VMS has seen many incremental improvements, including
 517  better support for operators like backticks and system(), and better
 518  %ENV handling.  See C<README.vms> and L<perlvms>.
 519  
 520  Support for Stratus VOS has been improved.  See C<vos/Changes> and README.vos.
 521  
 522  Support for Windows has been improved.
 523  
 524  =over
 525  
 526  =item *
 527  
 528  fork() emulation has been improved in various ways, but still continues
 529  to be experimental.  See L<perlfork> for known bugs and caveats.
 530  
 531  =item *
 532  
 533  %SIG has been enabled under USE_ITHREADS, but its use is completely
 534  unsupported under all configurations.
 535  
 536  =item *
 537  
 538  Borland C++ v5.5 is now a supported compiler that can build Perl.
 539  However, the generated binaries continue to be incompatible with those
 540  generated by the other supported compilers (GCC and Visual C++).
 541  
 542  =item *
 543  
 544  Non-blocking waits for child processes (or pseudo-processes) are
 545  supported via C<waitpid($pid, &POSIX::WNOHANG)>.
 546  
 547  =item *
 548  
 549  A memory leak in accept() has been fixed.
 550  
 551  =item *
 552  
 553  wait(), waitpid() and backticks now return the correct exit status under
 554  Windows 9x.
 555  
 556  =item *
 557  
 558  Trailing new %ENV entries weren't propagated to child processes.  This
 559  is now fixed.
 560  
 561  =item *
 562  
 563  Current directory entries in %ENV are now correctly propagated to child
 564  processes.
 565  
 566  =item *
 567  
 568  Duping socket handles with open(F, ">&MYSOCK") now works under Windows 9x.
 569  
 570  =item *
 571  
 572  The makefiles now provide a single switch to bulk-enable all the features
 573  enabled in ActiveState ActivePerl (a popular binary distribution).
 574  
 575  =item *
 576  
 577  Win32::GetCwd() correctly returns C:\ instead of C: when at the drive root.
 578  Other bugs in chdir() and Cwd::cwd() have also been fixed.
 579  
 580  =item *
 581  
 582  fork() correctly returns undef and sets EAGAIN when it runs out of
 583  pseudo-process handles.
 584  
 585  =item *
 586  
 587  ExtUtils::MakeMaker now uses $ENV{LIB} to search for libraries.
 588  
 589  =item *
 590  
 591  UNC path handling is better when perl is built to support fork().
 592  
 593  =item *
 594  
 595  A handle leak in socket handling has been fixed.
 596  
 597  =item *
 598  
 599  send() works from within a pseudo-process.
 600  
 601  =back
 602  
 603  Unless specifically qualified otherwise, the remainder of this document
 604  covers changes between the 5.005 and 5.6.0 releases.
 605  
 606  =head1 Core Enhancements
 607  
 608  =head2 Interpreter cloning, threads, and concurrency
 609  
 610  Perl 5.6.0 introduces the beginnings of support for running multiple
 611  interpreters concurrently in different threads.  In conjunction with
 612  the perl_clone() API call, which can be used to selectively duplicate
 613  the state of any given interpreter, it is possible to compile a
 614  piece of code once in an interpreter, clone that interpreter
 615  one or more times, and run all the resulting interpreters in distinct
 616  threads.
 617  
 618  On the Windows platform, this feature is used to emulate fork() at the
 619  interpreter level.  See L<perlfork> for details about that.
 620  
 621  This feature is still in evolution.  It is eventually meant to be used
 622  to selectively clone a subroutine and data reachable from that
 623  subroutine in a separate interpreter and run the cloned subroutine
 624  in a separate thread.  Since there is no shared data between the
 625  interpreters, little or no locking will be needed (unless parts of
 626  the symbol table are explicitly shared).  This is obviously intended
 627  to be an easy-to-use replacement for the existing threads support.
 628  
 629  Support for cloning interpreters and interpreter concurrency can be
 630  enabled using the -Dusethreads Configure option (see win32/Makefile for
 631  how to enable it on Windows.)  The resulting perl executable will be
 632  functionally identical to one that was built with -Dmultiplicity, but
 633  the perl_clone() API call will only be available in the former.
 634  
 635  -Dusethreads enables the cpp macro USE_ITHREADS by default, which in turn
 636  enables Perl source code changes that provide a clear separation between
 637  the op tree and the data it operates with.  The former is immutable, and
 638  can therefore be shared between an interpreter and all of its clones,
 639  while the latter is considered local to each interpreter, and is therefore
 640  copied for each clone.
 641  
 642  Note that building Perl with the -Dusemultiplicity Configure option
 643  is adequate if you wish to run multiple B<independent> interpreters
 644  concurrently in different threads.  -Dusethreads only provides the
 645  additional functionality of the perl_clone() API call and other
 646  support for running B<cloned> interpreters concurrently.
 647  
 648      NOTE: This is an experimental feature.  Implementation details are
 649      subject to change.
 650  
 651  =head2 Lexically scoped warning categories
 652  
 653  You can now control the granularity of warnings emitted by perl at a finer
 654  level using the C<use warnings> pragma.  L<warnings> and L<perllexwarn>
 655  have copious documentation on this feature.
 656  
 657  =head2 Unicode and UTF-8 support
 658  
 659  Perl now uses UTF-8 as its internal representation for character
 660  strings.  The C<utf8> and C<bytes> pragmas are used to control this support
 661  in the current lexical scope.  See L<perlunicode>, L<utf8> and L<bytes> for
 662  more information.
 663  
 664  This feature is expected to evolve quickly to support some form of I/O
 665  disciplines that can be used to specify the kind of input and output data
 666  (bytes or characters).  Until that happens, additional modules from CPAN
 667  will be needed to complete the toolkit for dealing with Unicode.
 668  
 669      NOTE: This should be considered an experimental feature.  Implementation
 670      details are subject to change.
 671  
 672  =head2 Support for interpolating named characters
 673  
 674  The new C<\N> escape interpolates named characters within strings.
 675  For example, C<"Hi! \N{WHITE SMILING FACE}"> evaluates to a string
 676  with a Unicode smiley face at the end.
 677  
 678  =head2 "our" declarations
 679  
 680  An "our" declaration introduces a value that can be best understood
 681  as a lexically scoped symbolic alias to a global variable in the
 682  package that was current where the variable was declared.  This is
 683  mostly useful as an alternative to the C<vars> pragma, but also provides
 684  the opportunity to introduce typing and other attributes for such
 685  variables.  See L<perlfunc/our>.
 686  
 687  =head2 Support for strings represented as a vector of ordinals
 688  
 689  Literals of the form C<v1.2.3.4> are now parsed as a string composed
 690  of characters with the specified ordinals.  This is an alternative, more
 691  readable way to construct (possibly Unicode) strings instead of
 692  interpolating characters, as in C<"\x{1}\x{2}\x{3}\x{4}">.  The leading
 693  C<v> may be omitted if there are more than two ordinals, so C<1.2.3> is
 694  parsed the same as C<v1.2.3>.
 695  
 696  Strings written in this form are also useful to represent version "numbers".
 697  It is easy to compare such version "numbers" (which are really just plain
 698  strings) using any of the usual string comparison operators C<eq>, C<ne>,
 699  C<lt>, C<gt>, etc., or perform bitwise string operations on them using C<|>,
 700  C<&>, etc.
 701  
 702  In conjunction with the new C<$^V> magic variable (which contains
 703  the perl version as a string), such literals can be used as a readable way
 704  to check if you're running a particular version of Perl:
 705  
 706      # this will parse in older versions of Perl also
 707      if ($^V and $^V gt v5.6.0) {
 708          # new features supported
 709      }
 710  
 711  C<require> and C<use> also have some special magic to support such literals.
 712  They will be interpreted as a version rather than as a module name:
 713  
 714      require v5.6.0;        # croak if $^V lt v5.6.0
 715      use v5.6.0;            # same, but croaks at compile-time
 716  
 717  Alternatively, the C<v> may be omitted if there is more than one dot:
 718  
 719      require 5.6.0;
 720      use 5.6.0;
 721  
 722  Also, C<sprintf> and C<printf> support the Perl-specific format flag C<%v>
 723  to print ordinals of characters in arbitrary strings:
 724  
 725      printf "v%vd", $^V;        # prints current version, such as "v5.5.650"
 726      printf "%*vX", ":", $addr;    # formats IPv6 address
 727      printf "%*vb", " ", $bits;    # displays bitstring
 728  
 729  See L<perldata/"Scalar value constructors"> for additional information.
 730  
 731  =head2 Improved Perl version numbering system
 732  
 733  Beginning with Perl version 5.6.0, the version number convention has been
 734  changed to a "dotted integer" scheme that is more commonly found in open
 735  source projects.
 736  
 737  Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
 738  The next development series following v5.6.0 will be numbered v5.7.x,
 739  beginning with v5.7.0, and the next major production release following
 740  v5.6.0 will be v5.8.0.
 741  
 742  The English module now sets $PERL_VERSION to $^V (a string value) rather
 743  than C<$]> (a numeric value).  (This is a potential incompatibility.
 744  Send us a report via perlbug if you are affected by this.)
 745  
 746  The v1.2.3 syntax is also now legal in Perl.
 747  See L<Support for strings represented as a vector of ordinals> for more on that.
 748  
 749  To cope with the new versioning system's use of at least three significant
 750  digits for each version component, the method used for incrementing the
 751  subversion number has also changed slightly.  We assume that versions older
 752  than v5.6.0 have been incrementing the subversion component in multiples of
 753  10.  Versions after v5.6.0 will increment them by 1.  Thus, using the new
 754  notation, 5.005_03 is the "same" as v5.5.30, and the first maintenance
 755  version following v5.6.0 will be v5.6.1 (which should be read as being
 756  equivalent to a floating point value of 5.006_001 in the older format,
 757  stored in C<$]>).
 758  
 759  =head2 New syntax for declaring subroutine attributes
 760  
 761  Formerly, if you wanted to mark a subroutine as being a method call or
 762  as requiring an automatic lock() when it is entered, you had to declare
 763  that with a C<use attrs> pragma in the body of the subroutine.
 764  That can now be accomplished with declaration syntax, like this:
 765  
 766      sub mymethod : locked method;
 767      ...
 768      sub mymethod : locked method {
 769      ...
 770      }
 771  
 772      sub othermethod :locked :method;
 773      ...
 774      sub othermethod :locked :method {
 775      ...
 776      }
 777  
 778  
 779  (Note how only the first C<:> is mandatory, and whitespace surrounding
 780  the C<:> is optional.)
 781  
 782  F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
 783  with the stubs they provide.  See L<attributes>.
 784  
 785  =head2 File and directory handles can be autovivified
 786  
 787  Similar to how constructs such as C<< $x->[0] >> autovivify a reference,
 788  handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(),
 789  socket(), and accept()) now autovivify a file or directory handle
 790  if the handle passed to them is an uninitialized scalar variable.  This
 791  allows the constructs such as C<open(my $fh, ...)> and C<open(local $fh,...)>
 792  to be used to create filehandles that will conveniently be closed
 793  automatically when the scope ends, provided there are no other references
 794  to them.  This largely eliminates the need for typeglobs when opening
 795  filehandles that must be passed around, as in the following example:
 796  
 797      sub myopen {
 798          open my $fh, "@_"
 799           or die "Can't open '@_': $!";
 800      return $fh;
 801      }
 802  
 803      {
 804          my $f = myopen("</etc/motd");
 805      print <$f>;
 806      # $f implicitly closed here
 807      }
 808  
 809  =head2 open() with more than two arguments
 810  
 811  If open() is passed three arguments instead of two, the second argument
 812  is used as the mode and the third argument is taken to be the file name.
 813  This is primarily useful for protecting against unintended magic behavior
 814  of the traditional two-argument form.  See L<perlfunc/open>.
 815  
 816  =head2 64-bit support
 817  
 818  Any platform that has 64-bit integers either
 819  
 820      (1) natively as longs or ints
 821      (2) via special compiler flags
 822      (3) using long long or int64_t
 823  
 824  is able to use "quads" (64-bit integers) as follows:
 825  
 826  =over 4
 827  
 828  =item *
 829  
 830  constants (decimal, hexadecimal, octal, binary) in the code 
 831  
 832  =item *
 833  
 834  arguments to oct() and hex()
 835  
 836  =item *
 837  
 838  arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
 839  
 840  =item *
 841  
 842  printed as such
 843  
 844  =item *
 845  
 846  pack() and unpack() "q" and "Q" formats
 847  
 848  =item *
 849  
 850  in basic arithmetics: + - * / % (NOTE: operating close to the limits
 851  of the integer values may produce surprising results)
 852  
 853  =item *
 854  
 855  in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced 
 856  to be 32 bits wide but now operate on the full native width.)
 857  
 858  =item *
 859  
 860  vec()
 861  
 862  =back
 863  
 864  Note that unless you have the case (a) you will have to configure
 865  and compile Perl using the -Duse64bitint Configure flag.
 866  
 867      NOTE: The Configure flags -Duselonglong and -Duse64bits have been
 868      deprecated.  Use -Duse64bitint instead.
 869  
 870  There are actually two modes of 64-bitness: the first one is achieved
 871  using Configure -Duse64bitint and the second one using Configure
 872  -Duse64bitall.  The difference is that the first one is minimal and
 873  the second one maximal.  The first works in more places than the second.
 874  
 875  The C<use64bitint> does only as much as is required to get 64-bit
 876  integers into Perl (this may mean, for example, using "long longs")
 877  while your memory may still be limited to 2 gigabytes (because your
 878  pointers could still be 32-bit).  Note that the name C<64bitint> does
 879  not imply that your C compiler will be using 64-bit C<int>s (it might,
 880  but it doesn't have to): the C<use64bitint> means that you will be
 881  able to have 64 bits wide scalar values.
 882  
 883  The C<use64bitall> goes all the way by attempting to switch also
 884  integers (if it can), longs (and pointers) to being 64-bit.  This may
 885  create an even more binary incompatible Perl than -Duse64bitint: the
 886  resulting executable may not run at all in a 32-bit box, or you may
 887  have to reboot/reconfigure/rebuild your operating system to be 64-bit
 888  aware.
 889  
 890  Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint
 891  nor -Duse64bitall.
 892  
 893  Last but not least: note that due to Perl's habit of always using
 894  floating point numbers, the quads are still not true integers.
 895  When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
 896  -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
 897  are silently promoted to floating point numbers, after which they will
 898  start losing precision (in their lower digits).
 899  
 900      NOTE: 64-bit support is still experimental on most platforms.
 901      Existing support only covers the LP64 data model.  In particular, the
 902      LLP64 data model is not yet supported.  64-bit libraries and system
 903      APIs on many platforms have not stabilized--your mileage may vary.
 904  
 905  =head2 Large file support
 906  
 907  If you have filesystems that support "large files" (files larger than
 908  2 gigabytes), you may now also be able to create and access them from
 909  Perl.
 910  
 911      NOTE: The default action is to enable large file support, if
 912      available on the platform.
 913  
 914  If the large file support is on, and you have a Fcntl constant
 915  O_LARGEFILE, the O_LARGEFILE is automatically added to the flags
 916  of sysopen().
 917  
 918  Beware that unless your filesystem also supports "sparse files" seeking
 919  to umpteen petabytes may be inadvisable.
 920  
 921  Note that in addition to requiring a proper file system to do large
 922  files you may also need to adjust your per-process (or your
 923  per-system, or per-process-group, or per-user-group) maximum filesize
 924  limits before running Perl scripts that try to handle large files,
 925  especially if you intend to write such files.
 926  
 927  Finally, in addition to your process/process group maximum filesize
 928  limits, you may have quota limits on your filesystems that stop you
 929  (your user id or your user group id) from using large files.
 930  
 931  Adjusting your process/user/group/file system/operating system limits
 932  is outside the scope of Perl core language.  For process limits, you
 933  may try increasing the limits using your shell's limits/limit/ulimit
 934  command before running Perl.  The BSD::Resource extension (not
 935  included with the standard Perl distribution) may also be of use, it
 936  offers the getrlimit/setrlimit interface that can be used to adjust
 937  process resource usage limits, including the maximum filesize limit.
 938  
 939  =head2 Long doubles
 940  
 941  In some systems you may be able to use long doubles to enhance the
 942  range and precision of your double precision floating point numbers
 943  (that is, Perl's numbers).  Use Configure -Duselongdouble to enable
 944  this support (if it is available).
 945  
 946  =head2 "more bits"
 947  
 948  You can "Configure -Dusemorebits" to turn on both the 64-bit support
 949  and the long double support.
 950  
 951  =head2 Enhanced support for sort() subroutines
 952  
 953  Perl subroutines with a prototype of C<($$)>, and XSUBs in general, can
 954  now be used as sort subroutines.  In either case, the two elements to
 955  be compared are passed as normal parameters in @_.  See L<perlfunc/sort>.
 956  
 957  For unprototyped sort subroutines, the historical behavior of passing 
 958  the elements to be compared as the global variables $a and $b remains
 959  unchanged.
 960  
 961  =head2 C<sort $coderef @foo> allowed
 962  
 963  sort() did not accept a subroutine reference as the comparison
 964  function in earlier versions.  This is now permitted.
 965  
 966  =head2 File globbing implemented internally
 967  
 968  Perl now uses the File::Glob implementation of the glob() operator
 969  automatically.  This avoids using an external csh process and the
 970  problems associated with it.
 971  
 972      NOTE: This is currently an experimental feature.  Interfaces and
 973      implementation are subject to change.
 974  
 975  =head2 Support for CHECK blocks
 976  
 977  In addition to C<BEGIN>, C<INIT>, C<END>, C<DESTROY> and C<AUTOLOAD>,
 978  subroutines named C<CHECK> are now special.  These are queued up during
 979  compilation and behave similar to END blocks, except they are called at
 980  the end of compilation rather than at the end of execution.  They cannot
 981  be called directly.
 982  
 983  =head2 POSIX character class syntax [: :] supported
 984  
 985  For example to match alphabetic characters use /[[:alpha:]]/.
 986  See L<perlre> for details.
 987  
 988  =head2 Better pseudo-random number generator
 989  
 990  In 5.005_0x and earlier, perl's rand() function used the C library
 991  rand(3) function.  As of 5.005_52, Configure tests for drand48(),
 992  random(), and rand() (in that order) and picks the first one it finds.
 993  
 994  These changes should result in better random numbers from rand().
 995  
 996  =head2 Improved C<qw//> operator
 997  
 998  The C<qw//> operator is now evaluated at compile time into a true list
 999  instead of being replaced with a run time call to C<split()>.  This
1000  removes the confusing misbehaviour of C<qw//> in scalar context, which
1001  had inherited that behaviour from split().
1002  
1003  Thus:
1004  
1005      $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
1006  
1007  now correctly prints "3|a", instead of "2|a".
1008  
1009  =head2 Better worst-case behavior of hashes
1010  
1011  Small changes in the hashing algorithm have been implemented in
1012  order to improve the distribution of lower order bits in the
1013  hashed value.  This is expected to yield better performance on
1014  keys that are repeated sequences.
1015  
1016  =head2 pack() format 'Z' supported
1017  
1018  The new format type 'Z' is useful for packing and unpacking null-terminated
1019  strings.  See L<perlfunc/"pack">.
1020  
1021  =head2 pack() format modifier '!' supported
1022  
1023  The new format type modifier '!' is useful for packing and unpacking
1024  native shorts, ints, and longs.  See L<perlfunc/"pack">.
1025  
1026  =head2 pack() and unpack() support counted strings
1027  
1028  The template character '/' can be used to specify a counted string
1029  type to be packed or unpacked.  See L<perlfunc/"pack">.
1030  
1031  =head2 Comments in pack() templates
1032  
1033  The '#' character in a template introduces a comment up to
1034  end of the line.  This facilitates documentation of pack()
1035  templates.
1036  
1037  =head2 Weak references
1038  
1039  In previous versions of Perl, you couldn't cache objects so as
1040  to allow them to be deleted if the last reference from outside 
1041  the cache is deleted.  The reference in the cache would hold a
1042  reference count on the object and the objects would never be
1043  destroyed.
1044  
1045  Another familiar problem is with circular references.  When an
1046  object references itself, its reference count would never go
1047  down to zero, and it would not get destroyed until the program
1048  is about to exit.
1049  
1050  Weak references solve this by allowing you to "weaken" any
1051  reference, that is, make it not count towards the reference count.
1052  When the last non-weak reference to an object is deleted, the object
1053  is destroyed and all the weak references to the object are
1054  automatically undef-ed.
1055  
1056  To use this feature, you need the Devel::WeakRef package from CPAN, which
1057  contains additional documentation.
1058  
1059      NOTE: This is an experimental feature.  Details are subject to change.  
1060  
1061  =head2 Binary numbers supported
1062  
1063  Binary numbers are now supported as literals, in s?printf formats, and
1064  C<oct()>:
1065  
1066      $answer = 0b101010;
1067      printf "The answer is: %b\n", oct("0b101010");
1068  
1069  =head2 Lvalue subroutines
1070  
1071  Subroutines can now return modifiable lvalues.
1072  See L<perlsub/"Lvalue subroutines">.
1073  
1074      NOTE: This is an experimental feature.  Details are subject to change.
1075  
1076  =head2 Some arrows may be omitted in calls through references
1077  
1078  Perl now allows the arrow to be omitted in many constructs
1079  involving subroutine calls through references.  For example,
1080  C<< $foo[10]->('foo') >> may now be written C<$foo[10]('foo')>.
1081  This is rather similar to how the arrow may be omitted from
1082  C<< $foo[10]->{'foo'} >>.  Note however, that the arrow is still
1083  required for C<< foo(10)->('bar') >>.
1084  
1085  =head2 Boolean assignment operators are legal lvalues
1086  
1087  Constructs such as C<($a ||= 2) += 1> are now allowed.
1088  
1089  =head2 exists() is supported on subroutine names
1090  
1091  The exists() builtin now works on subroutine names.  A subroutine
1092  is considered to exist if it has been declared (even if implicitly).
1093  See L<perlfunc/exists> for examples.
1094  
1095  =head2 exists() and delete() are supported on array elements
1096  
1097  The exists() and delete() builtins now work on simple arrays as well.
1098  The behavior is similar to that on hash elements.
1099  
1100  exists() can be used to check whether an array element has been
1101  initialized.  This avoids autovivifying array elements that don't exist.
1102  If the array is tied, the EXISTS() method in the corresponding tied
1103  package will be invoked.
1104  
1105  delete() may be used to remove an element from the array and return
1106  it.  The array element at that position returns to its uninitialized
1107  state, so that testing for the same element with exists() will return
1108  false.  If the element happens to be the one at the end, the size of
1109  the array also shrinks up to the highest element that tests true for
1110  exists(), or 0 if none such is found.  If the array is tied, the DELETE() 
1111  method in the corresponding tied package will be invoked.
1112  
1113  See L<perlfunc/exists> and L<perlfunc/delete> for examples.
1114  
1115  =head2 Pseudo-hashes work better
1116  
1117  Dereferencing some types of reference values in a pseudo-hash,
1118  such as C<< $ph->{foo}[1] >>, was accidentally disallowed.  This has
1119  been corrected.
1120  
1121  When applied to a pseudo-hash element, exists() now reports whether
1122  the specified value exists, not merely if the key is valid.
1123  
1124  delete() now works on pseudo-hashes.  When given a pseudo-hash element
1125  or slice it deletes the values corresponding to the keys (but not the keys
1126  themselves).  See L<perlref/"Pseudo-hashes: Using an array as a hash">.
1127  
1128  Pseudo-hash slices with constant keys are now optimized to array lookups
1129  at compile-time.
1130  
1131  List assignments to pseudo-hash slices are now supported.
1132  
1133  The C<fields> pragma now provides ways to create pseudo-hashes, via
1134  fields::new() and fields::phash().  See L<fields>.
1135  
1136      NOTE: The pseudo-hash data type continues to be experimental.
1137      Limiting oneself to the interface elements provided by the
1138      fields pragma will provide protection from any future changes.
1139  
1140  =head2 Automatic flushing of output buffers
1141  
1142  fork(), exec(), system(), qx//, and pipe open()s now flush buffers
1143  of all files opened for output when the operation was attempted.  This
1144  mostly eliminates confusing buffering mishaps suffered by users unaware
1145  of how Perl internally handles I/O.
1146  
1147  This is not supported on some platforms like Solaris where a suitably
1148  correct implementation of fflush(NULL) isn't available.
1149  
1150  =head2 Better diagnostics on meaningless filehandle operations
1151  
1152  Constructs such as C<< open(<FH>) >> and C<< close(<FH>) >>
1153  are compile time errors.  Attempting to read from filehandles that
1154  were opened only for writing will now produce warnings (just as
1155  writing to read-only filehandles does).
1156  
1157  =head2 Where possible, buffered data discarded from duped input filehandle
1158  
1159  C<< open(NEW, "<&OLD") >> now attempts to discard any data that
1160  was previously read and buffered in C<OLD> before duping the handle.
1161  On platforms where doing this is allowed, the next read operation
1162  on C<NEW> will return the same data as the corresponding operation
1163  on C<OLD>.  Formerly, it would have returned the data from the start
1164  of the following disk block instead.
1165  
1166  =head2 eof() has the same old magic as <>
1167  
1168  C<eof()> would return true if no attempt to read from C<< <> >> had
1169  yet been made.  C<eof()> has been changed to have a little magic of its
1170  own, it now opens the C<< <> >> files.
1171  
1172  =head2 binmode() can be used to set :crlf and :raw modes
1173  
1174  binmode() now accepts a second argument that specifies a discipline
1175  for the handle in question.  The two pseudo-disciplines ":raw" and
1176  ":crlf" are currently supported on DOS-derivative platforms.
1177  See L<perlfunc/"binmode"> and L<open>.
1178  
1179  =head2 C<-T> filetest recognizes UTF-8 encoded files as "text"
1180  
1181  The algorithm used for the C<-T> filetest has been enhanced to
1182  correctly identify UTF-8 content as "text".
1183  
1184  =head2 system(), backticks and pipe open now reflect exec() failure
1185  
1186  On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
1187  etc., are implemented via fork() and exec().  When the underlying
1188  exec() fails, earlier versions did not report the error properly,
1189  since the exec() happened to be in a different process.
1190  
1191  The child process now communicates with the parent about the
1192  error in launching the external command, which allows these
1193  constructs to return with their usual error value and set $!.
1194  
1195  =head2 Improved diagnostics
1196  
1197  Line numbers are no longer suppressed (under most likely circumstances)
1198  during the global destruction phase.
1199  
1200  Diagnostics emitted from code running in threads other than the main
1201  thread are now accompanied by the thread ID.
1202  
1203  Embedded null characters in diagnostics now actually show up.  They
1204  used to truncate the message in prior versions.
1205  
1206  $foo::a and $foo::b are now exempt from "possible typo" warnings only
1207  if sort() is encountered in package C<foo>.
1208  
1209  Unrecognized alphabetic escapes encountered when parsing quote
1210  constructs now generate a warning, since they may take on new
1211  semantics in later versions of Perl.
1212  
1213  Many diagnostics now report the internal operation in which the warning
1214  was provoked, like so:
1215  
1216      Use of uninitialized value in concatenation (.) at (eval 1) line 1.
1217      Use of uninitialized value in print at (eval 1) line 1.
1218  
1219  Diagnostics  that occur within eval may also report the file and line
1220  number where the eval is located, in addition to the eval sequence
1221  number and the line number within the evaluated text itself.  For
1222  example:
1223  
1224      Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF
1225  
1226  =head2 Diagnostics follow STDERR
1227  
1228  Diagnostic output now goes to whichever file the C<STDERR> handle
1229  is pointing at, instead of always going to the underlying C runtime
1230  library's C<stderr>.
1231  
1232  =head2 More consistent close-on-exec behavior
1233  
1234  On systems that support a close-on-exec flag on filehandles, the
1235  flag is now set for any handles created by pipe(), socketpair(),
1236  socket(), and accept(), if that is warranted by the value of $^F
1237  that may be in effect.  Earlier versions neglected to set the flag
1238  for handles created with these operators.  See L<perlfunc/pipe>,
1239  L<perlfunc/socketpair>, L<perlfunc/socket>, L<perlfunc/accept>,
1240  and L<perlvar/$^F>.
1241  
1242  =head2 syswrite() ease-of-use
1243  
1244  The length argument of C<syswrite()> has become optional.
1245  
1246  =head2 Better syntax checks on parenthesized unary operators
1247  
1248  Expressions such as:
1249  
1250      print defined(&foo,&bar,&baz);
1251      print uc("foo","bar","baz");
1252      undef($foo,&bar);
1253  
1254  used to be accidentally allowed in earlier versions, and produced
1255  unpredictable behaviour.  Some produced ancillary warnings
1256  when used in this way; others silently did the wrong thing.
1257  
1258  The parenthesized forms of most unary operators that expect a single
1259  argument now ensure that they are not called with more than one
1260  argument, making the cases shown above syntax errors.  The usual
1261  behaviour of:
1262  
1263      print defined &foo, &bar, &baz;
1264      print uc "foo", "bar", "baz";
1265      undef $foo, &bar;
1266  
1267  remains unchanged.  See L<perlop>.
1268  
1269  =head2 Bit operators support full native integer width
1270  
1271  The bit operators (& | ^ ~ << >>) now operate on the full native
1272  integral width (the exact size of which is available in $Config{ivsize}).
1273  For example, if your platform is either natively 64-bit or if Perl
1274  has been configured to use 64-bit integers, these operations apply
1275  to 8 bytes (as opposed to 4 bytes on 32-bit platforms).
1276  For portability, be sure to mask off the excess bits in the result of
1277  unary C<~>, e.g., C<~$x & 0xffffffff>.
1278  
1279  =head2 Improved security features
1280  
1281  More potentially unsafe operations taint their results for improved
1282  security.
1283  
1284  The C<passwd> and C<shell> fields returned by the getpwent(), getpwnam(),
1285  and getpwuid() are now tainted, because the user can affect their own
1286  encrypted password and login shell.
1287  
1288  The variable modified by shmread(), and messages returned by msgrcv()
1289  (and its object-oriented interface IPC::SysV::Msg::rcv) are also tainted,
1290  because other untrusted processes can modify messages and shared memory
1291  segments for their own nefarious purposes.
1292  
1293  =head2 More functional bareword prototype (*)
1294  
1295  Bareword prototypes have been rationalized to enable them to be used
1296  to override builtins that accept barewords and interpret them in
1297  a special way, such as C<require> or C<do>.
1298  
1299  Arguments prototyped as C<*> will now be visible within the subroutine
1300  as either a simple scalar or as a reference to a typeglob.
1301  See L<perlsub/Prototypes>.
1302  
1303  =head2 C<require> and C<do> may be overridden
1304  
1305  C<require> and C<do 'file'> operations may be overridden locally
1306  by importing subroutines of the same name into the current package 
1307  (or globally by importing them into the CORE::GLOBAL:: namespace).
1308  Overriding C<require> will also affect C<use>, provided the override
1309  is visible at compile-time.
1310  See L<perlsub/"Overriding Built-in Functions">.
1311  
1312  =head2 $^X variables may now have names longer than one character
1313  
1314  Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
1315  error.  Now variable names that begin with a control character may be
1316  arbitrarily long.  However, for compatibility reasons, these variables
1317  I<must> be written with explicit braces, as C<${^XY}> for example.
1318  C<${^XYZ}> is synonymous with ${"\cXYZ"}.  Variable names with more
1319  than one control character, such as C<${^XY^Z}>, are illegal.
1320  
1321  The old syntax has not changed.  As before, `^X' may be either a
1322  literal control-X character or the two-character sequence `caret' plus
1323  `X'.  When braces are omitted, the variable name stops after the
1324  control character.  Thus C<"$^XYZ"> continues to be synonymous with
1325  C<$^X . "YZ"> as before.
1326  
1327  As before, lexical variables may not have names beginning with control
1328  characters.  As before, variables whose names begin with a control
1329  character are always forced to be in package `main'.  All such variables
1330  are reserved for future extensions, except those that begin with
1331  C<^_>, which may be used by user programs and are guaranteed not to
1332  acquire special meaning in any future version of Perl.
1333  
1334  =head2 New variable $^C reflects C<-c> switch
1335  
1336  C<$^C> has a boolean value that reflects whether perl is being run
1337  in compile-only mode (i.e. via the C<-c> switch).  Since
1338  BEGIN blocks are executed under such conditions, this variable
1339  enables perl code to determine whether actions that make sense
1340  only during normal running are warranted.  See L<perlvar>.
1341  
1342  =head2 New variable $^V contains Perl version as a string
1343  
1344  C<$^V> contains the Perl version number as a string composed of
1345  characters whose ordinals match the version numbers, i.e. v5.6.0.
1346  This may be used in string comparisons.
1347  
1348  See C<Support for strings represented as a vector of ordinals> for an
1349  example.
1350  
1351  =head2 Optional Y2K warnings
1352  
1353  If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
1354  it emits optional warnings when concatenating the number 19
1355  with another number.
1356  
1357  This behavior must be specifically enabled when running Configure.
1358  See F<INSTALL> and F<README.Y2K>.
1359  
1360  =head2 Arrays now always interpolate into double-quoted strings
1361  
1362  In double-quoted strings, arrays now interpolate, no matter what.  The
1363  behavior in earlier versions of perl 5 was that arrays would interpolate
1364  into strings if the array had been mentioned before the string was
1365  compiled, and otherwise Perl would raise a fatal compile-time error.
1366  In versions 5.000 through 5.003, the error was
1367  
1368          Literal @example now requires backslash
1369  
1370  In versions 5.004_01 through 5.6.0, the error was
1371  
1372          In string, @example now must be written as \@example
1373  
1374  The idea here was to get people into the habit of writing
1375  C<"fred\@example.com"> when they wanted a literal C<@> sign, just as
1376  they have always written C<"Give me back my \$5"> when they wanted a
1377  literal C<$> sign.
1378  
1379  Starting with 5.6.1, when Perl now sees an C<@> sign in a
1380  double-quoted string, it I<always> attempts to interpolate an array,
1381  regardless of whether or not the array has been used or declared
1382  already.  The fatal error has been downgraded to an optional warning:
1383  
1384          Possible unintended interpolation of @example in string
1385  
1386  This warns you that C<"fred@example.com"> is going to turn into
1387  C<fred.com> if you don't backslash the C<@>.
1388  See http://www.plover.com/~mjd/perl/at-error.html for more details
1389  about the history here.
1390  
1391  =head2 @- and @+ provide starting/ending offsets of regex submatches
1392  
1393  The new magic variables @- and @+ provide the starting and ending
1394  offsets, respectively, of $&, $1, $2, etc.  See L<perlvar> for
1395  details.
1396  
1397  =head1 Modules and Pragmata
1398  
1399  =head2 Modules
1400  
1401  =over 4
1402  
1403  =item attributes
1404  
1405  While used internally by Perl as a pragma, this module also
1406  provides a way to fetch subroutine and variable attributes.
1407  See L<attributes>.
1408  
1409  =item B
1410  
1411  The Perl Compiler suite has been extensively reworked for this
1412  release.  More of the standard Perl test suite passes when run
1413  under the Compiler, but there is still a significant way to
1414  go to achieve production quality compiled executables.
1415  
1416      NOTE: The Compiler suite remains highly experimental.  The
1417      generated code may not be correct, even when it manages to execute
1418      without errors.
1419  
1420  =item Benchmark
1421  
1422  Overall, Benchmark results exhibit lower average error and better timing
1423  accuracy.  
1424  
1425  You can now run tests for I<n> seconds instead of guessing the right
1426  number of tests to run: e.g., timethese(-5, ...) will run each 
1427  code for at least 5 CPU seconds.  Zero as the "number of repetitions"
1428  means "for at least 3 CPU seconds".  The output format has also
1429  changed.  For example:
1430  
1431     use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1432  
1433  will now output something like this:
1434  
1435     Benchmark: running a, b, each for at least 5 CPU seconds...
1436              a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
1437              b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)
1438  
1439  New features: "each for at least N CPU seconds...", "wallclock secs",
1440  and the "@ operations/CPU second (n=operations)".
1441  
1442  timethese() now returns a reference to a hash of Benchmark objects containing
1443  the test results, keyed on the names of the tests.
1444  
1445  timethis() now returns the iterations field in the Benchmark result object
1446  instead of 0.
1447  
1448  timethese(), timethis(), and the new cmpthese() (see below) can also take
1449  a format specifier of 'none' to suppress output.
1450  
1451  A new function countit() is just like timeit() except that it takes a
1452  TIME instead of a COUNT.
1453  
1454  A new function cmpthese() prints a chart comparing the results of each test
1455  returned from a timethese() call.  For each possible pair of tests, the
1456  percentage speed difference (iters/sec or seconds/iter) is shown.
1457  
1458  For other details, see L<Benchmark>.
1459  
1460  =item ByteLoader
1461  
1462  The ByteLoader is a dedicated extension to generate and run
1463  Perl bytecode.  See L<ByteLoader>.
1464  
1465  =item constant
1466  
1467  References can now be used.
1468  
1469  The new version also allows a leading underscore in constant names, but
1470  disallows a double leading underscore (as in "__LINE__").  Some other names
1471  are disallowed or warned against, including BEGIN, END, etc.  Some names
1472  which were forced into main:: used to fail silently in some cases; now they're
1473  fatal (outside of main::) and an optional warning (inside of main::).
1474  The ability to detect whether a constant had been set with a given name has
1475  been added.
1476  
1477  See L<constant>.
1478  
1479  =item charnames
1480  
1481  This pragma implements the C<\N> string escape.  See L<charnames>.
1482  
1483  =item Data::Dumper
1484  
1485  A C<Maxdepth> setting can be specified to avoid venturing
1486  too deeply into deep data structures.  See L<Data::Dumper>.
1487  
1488  The XSUB implementation of Dump() is now automatically called if the
1489  C<Useqq> setting is not in use.
1490  
1491  Dumping C<qr//> objects works correctly.
1492  
1493  =item DB
1494  
1495  C<DB> is an experimental module that exposes a clean abstraction
1496  to Perl's debugging API.
1497  
1498  =item DB_File
1499  
1500  DB_File can now be built with Berkeley DB versions 1, 2 or 3.
1501  See C<ext/DB_File/Changes>.
1502  
1503  =item Devel::DProf
1504  
1505  Devel::DProf, a Perl source code profiler has been added.  See
1506  L<Devel::DProf> and L<dprofpp>.
1507  
1508  =item Devel::Peek
1509  
1510  The Devel::Peek module provides access to the internal representation
1511  of Perl variables and data.  It is a data debugging tool for the XS programmer.
1512  
1513  =item Dumpvalue
1514  
1515  The Dumpvalue module provides screen dumps of Perl data.
1516  
1517  =item DynaLoader
1518  
1519  DynaLoader now supports a dl_unload_file() function on platforms that
1520  support unloading shared objects using dlclose().
1521  
1522  Perl can also optionally arrange to unload all extension shared objects
1523  loaded by Perl.  To enable this, build Perl with the Configure option
1524  C<-Accflags=-DDL_UNLOAD_ALL_AT_EXIT>.  (This maybe useful if you are
1525  using Apache with mod_perl.)
1526  
1527  =item English
1528  
1529  $PERL_VERSION now stands for C<$^V> (a string value) rather than for C<$]>
1530  (a numeric value).
1531  
1532  =item Env
1533  
1534  Env now supports accessing environment variables like PATH as array
1535  variables.
1536  
1537  =item Fcntl
1538  
1539  More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1540  large file (more than 4GB) access (NOTE: the O_LARGEFILE is
1541  automatically added to sysopen() flags if large file support has been
1542  configured, as is the default), Free/Net/OpenBSD locking behaviour
1543  flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined
1544  mask of O_RDONLY, O_WRONLY, and O_RDWR.  The seek()/sysseek()
1545  constants SEEK_SET, SEEK_CUR, and SEEK_END are available via the
1546  C<:seek> tag.  The chmod()/stat() S_IF* constants and S_IS* functions
1547  are available via the C<:mode> tag.
1548  
1549  =item File::Compare
1550  
1551  A compare_text() function has been added, which allows custom
1552  comparison functions.  See L<File::Compare>.
1553  
1554  =item File::Find
1555  
1556  File::Find now works correctly when the wanted() function is either
1557  autoloaded or is a symbolic reference.
1558  
1559  A bug that caused File::Find to lose track of the working directory
1560  when pruning top-level directories has been fixed.
1561  
1562  File::Find now also supports several other options to control its
1563  behavior.  It can follow symbolic links if the C<follow> option is
1564  specified.  Enabling the C<no_chdir> option will make File::Find skip
1565  changing the current directory when walking directories.  The C<untaint>
1566  flag can be useful when running with taint checks enabled.
1567  
1568  See L<File::Find>.
1569  
1570  =item File::Glob
1571  
1572  This extension implements BSD-style file globbing.  By default,
1573  it will also be used for the internal implementation of the glob()
1574  operator.  See L<File::Glob>.
1575  
1576  =item File::Spec
1577  
1578  New methods have been added to the File::Spec module: devnull() returns
1579  the name of the null device (/dev/null on Unix) and tmpdir() the name of
1580  the temp directory (normally /tmp on Unix).  There are now also methods
1581  to convert between absolute and relative filenames: abs2rel() and
1582  rel2abs().  For compatibility with operating systems that specify volume
1583  names in file paths, the splitpath(), splitdir(), and catdir() methods
1584  have been added.
1585  
1586  =item File::Spec::Functions
1587  
1588  The new File::Spec::Functions modules provides a function interface
1589  to the File::Spec module.  Allows shorthand
1590  
1591      $fullname = catfile($dir1, $dir2, $file);
1592  
1593  instead of
1594  
1595      $fullname = File::Spec->catfile($dir1, $dir2, $file);
1596  
1597  =item Getopt::Long
1598  
1599  Getopt::Long licensing has changed to allow the Perl Artistic License
1600  as well as the GPL. It used to be GPL only, which got in the way of
1601  non-GPL applications that wanted to use Getopt::Long.
1602  
1603  Getopt::Long encourages the use of Pod::Usage to produce help
1604  messages. For example:
1605  
1606      use Getopt::Long;
1607      use Pod::Usage;
1608      my $man = 0;
1609      my $help = 0;
1610      GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1611      pod2usage(1) if $help;
1612      pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1613  
1614      __END__
1615  
1616      =head1 NAME
1617  
1618      sample - Using Getopt::Long and Pod::Usage
1619  
1620      =head1 SYNOPSIS
1621  
1622      sample [options] [file ...]
1623  
1624       Options:
1625         -help            brief help message
1626         -man             full documentation
1627  
1628      =head1 OPTIONS
1629  
1630      =over 8
1631  
1632      =item B<-help>
1633  
1634      Print a brief help message and exits.
1635  
1636      =item B<-man>
1637  
1638      Prints the manual page and exits.
1639  
1640      =back
1641  
1642      =head1 DESCRIPTION
1643  
1644      B<This program> will read the given input file(s) and do something
1645      useful with the contents thereof.
1646  
1647      =cut
1648  
1649  See L<Pod::Usage> for details.
1650  
1651  A bug that prevented the non-option call-back <> from being
1652  specified as the first argument has been fixed.
1653  
1654  To specify the characters < and > as option starters, use ><. Note,
1655  however, that changing option starters is strongly deprecated. 
1656  
1657  =item IO
1658  
1659  write() and syswrite() will now accept a single-argument
1660  form of the call, for consistency with Perl's syswrite().
1661  
1662  You can now create a TCP-based IO::Socket::INET without forcing
1663  a connect attempt.  This allows you to configure its options
1664  (like making it non-blocking) and then call connect() manually.
1665  
1666  A bug that prevented the IO::Socket::protocol() accessor
1667  from ever returning the correct value has been corrected.
1668  
1669  IO::Socket::connect now uses non-blocking IO instead of alarm()
1670  to do connect timeouts.
1671  
1672  IO::Socket::accept now uses select() instead of alarm() for doing
1673  timeouts.
1674  
1675  IO::Socket::INET->new now sets $! correctly on failure. $@ is
1676  still set for backwards compatibility.
1677  
1678  =item JPL
1679  
1680  Java Perl Lingo is now distributed with Perl.  See jpl/README
1681  for more information.
1682  
1683  =item lib
1684  
1685  C<use lib> now weeds out any trailing duplicate entries.
1686  C<no lib> removes all named entries.
1687  
1688  =item Math::BigInt
1689  
1690  The bitwise operations C<<< << >>>, C<<< >> >>>, C<&>, C<|>,
1691  and C<~> are now supported on bigints.
1692  
1693  =item Math::Complex
1694  
1695  The accessor methods Re, Im, arg, abs, rho, and theta can now also
1696  act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1697  
1698  The class method C<display_format> and the corresponding object method
1699  C<display_format>, in addition to accepting just one argument, now can
1700  also accept a parameter hash.  Recognized keys of a parameter hash are
1701  C<"style">, which corresponds to the old one parameter case, and two
1702  new parameters: C<"format">, which is a printf()-style format string
1703  (defaults usually to C<"%.15g">, you can revert to the default by
1704  setting the format string to C<undef>) used for both parts of a
1705  complex number, and C<"polar_pretty_print"> (defaults to true),
1706  which controls whether an attempt is made to try to recognize small
1707  multiples and rationals of pi (2pi, pi/2) at the argument (angle) of a
1708  polar complex number.
1709  
1710  The potentially disruptive change is that in list context both methods
1711  now I<return the parameter hash>, instead of only the value of the
1712  C<"style"> parameter.
1713  
1714  =item Math::Trig
1715  
1716  A little bit of radial trigonometry (cylindrical and spherical),
1717  radial coordinate conversions, and the great circle distance were added.
1718  
1719  =item Pod::Parser, Pod::InputObjects
1720  
1721  Pod::Parser is a base class for parsing and selecting sections of
1722  pod documentation from an input stream.  This module takes care of
1723  identifying pod paragraphs and commands in the input and hands off the
1724  parsed paragraphs and commands to user-defined methods which are free
1725  to interpret or translate them as they see fit.
1726  
1727  Pod::InputObjects defines some input objects needed by Pod::Parser, and
1728  for advanced users of Pod::Parser that need more about a command besides
1729  its name and text.
1730  
1731  As of release 5.6.0 of Perl, Pod::Parser is now the officially sanctioned
1732  "base parser code" recommended for use by all pod2xxx translators.
1733  Pod::Text (pod2text) and Pod::Man (pod2man) have already been converted
1734  to use Pod::Parser and efforts to convert Pod::HTML (pod2html) are already
1735  underway.  For any questions or comments about pod parsing and translating
1736  issues and utilities, please use the pod-people@perl.org mailing list.
1737  
1738  For further information, please see L<Pod::Parser> and L<Pod::InputObjects>.
1739  
1740  =item Pod::Checker, podchecker
1741  
1742  This utility checks pod files for correct syntax, according to
1743  L<perlpod>.  Obvious errors are flagged as such, while warnings are
1744  printed for mistakes that can be handled gracefully.  The checklist is
1745  not complete yet.  See L<Pod::Checker>.
1746  
1747  =item Pod::ParseUtils, Pod::Find
1748  
1749  These modules provide a set of gizmos that are useful mainly for pod
1750  translators.  L<Pod::Find|Pod::Find> traverses directory structures and
1751  returns found pod files, along with their canonical names (like
1752  C<File::Spec::Unix>).  L<Pod::ParseUtils|Pod::ParseUtils> contains
1753  B<Pod::List> (useful for storing pod list information), B<Pod::Hyperlink>
1754  (for parsing the contents of C<LE<lt>E<gt>> sequences) and B<Pod::Cache>
1755  (for caching information about pod files, e.g., link nodes).
1756  
1757  =item Pod::Select, podselect
1758  
1759  Pod::Select is a subclass of Pod::Parser which provides a function
1760  named "podselect()" to filter out user-specified sections of raw pod
1761  documentation from an input stream. podselect is a script that provides
1762  access to Pod::Select from other scripts to be used as a filter.
1763  See L<Pod::Select>.
1764  
1765  =item Pod::Usage, pod2usage
1766  
1767  Pod::Usage provides the function "pod2usage()" to print usage messages for
1768  a Perl script based on its embedded pod documentation.  The pod2usage()
1769  function is generally useful to all script authors since it lets them
1770  write and maintain a single source (the pods) for documentation, thus
1771  removing the need to create and maintain redundant usage message text
1772  consisting of information already in the pods.
1773  
1774  There is also a pod2usage script which can be used from other kinds of
1775  scripts to print usage messages from pods (even for non-Perl scripts
1776  with pods embedded in comments).
1777  
1778  For details and examples, please see L<Pod::Usage>.
1779  
1780  =item Pod::Text and Pod::Man
1781  
1782  Pod::Text has been rewritten to use Pod::Parser.  While pod2text() is
1783  still available for backwards compatibility, the module now has a new
1784  preferred interface.  See L<Pod::Text> for the details.  The new Pod::Text
1785  module is easily subclassed for tweaks to the output, and two such
1786  subclasses (Pod::Text::Termcap for man-page-style bold and underlining
1787  using termcap information, and Pod::Text::Color for markup with ANSI color
1788  sequences) are now standard.
1789  
1790  pod2man has been turned into a module, Pod::Man, which also uses
1791  Pod::Parser.  In the process, several outstanding bugs related to quotes
1792  in section headers, quoting of code escapes, and nested lists have been
1793  fixed.  pod2man is now a wrapper script around this module.
1794  
1795  =item SDBM_File
1796  
1797  An EXISTS method has been added to this module (and sdbm_exists() has
1798  been added to the underlying sdbm library), so one can now call exists
1799  on an SDBM_File tied hash and get the correct result, rather than a
1800  runtime error.
1801  
1802  A bug that may have caused data loss when more than one disk block
1803  happens to be read from the database in a single FETCH() has been
1804  fixed.
1805  
1806  =item Sys::Syslog
1807  
1808  Sys::Syslog now uses XSUBs to access facilities from syslog.h so it
1809  no longer requires syslog.ph to exist. 
1810  
1811  =item Sys::Hostname
1812  
1813  Sys::Hostname now uses XSUBs to call the C library's gethostname() or
1814  uname() if they exist.
1815  
1816  =item Term::ANSIColor
1817  
1818  Term::ANSIColor is a very simple module to provide easy and readable
1819  access to the ANSI color and highlighting escape sequences, supported by
1820  most ANSI terminal emulators.  It is now included standard.
1821  
1822  =item Time::Local
1823  
1824  The timelocal() and timegm() functions used to silently return bogus
1825  results when the date fell outside the machine's integer range.  They
1826  now consistently croak() if the date falls in an unsupported range.
1827  
1828  =item Win32
1829  
1830  The error return value in list context has been changed for all functions
1831  that return a list of values.  Previously these functions returned a list
1832  with a single element C<undef> if an error occurred.  Now these functions
1833  return the empty list in these situations.  This applies to the following
1834  functions:
1835  
1836      Win32::FsType
1837      Win32::GetOSVersion
1838  
1839  The remaining functions are unchanged and continue to return C<undef> on
1840  error even in list context.
1841  
1842  The Win32::SetLastError(ERROR) function has been added as a complement
1843  to the Win32::GetLastError() function.
1844  
1845  The new Win32::GetFullPathName(FILENAME) returns the full absolute
1846  pathname for FILENAME in scalar context.  In list context it returns
1847  a two-element list containing the fully qualified directory name and
1848  the filename.  See L<Win32>.
1849  
1850  =item XSLoader
1851  
1852  The XSLoader extension is a simpler alternative to DynaLoader.
1853  See L<XSLoader>.
1854  
1855  =item DBM Filters
1856  
1857  A new feature called "DBM Filters" has been added to all the
1858  DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1859  DBM Filters add four new methods to each DBM module:
1860  
1861      filter_store_key
1862      filter_store_value
1863      filter_fetch_key
1864      filter_fetch_value
1865  
1866  These can be used to filter key-value pairs before the pairs are
1867  written to the database or just after they are read from the database.
1868  See L<perldbmfilter> for further information.
1869  
1870  =back
1871  
1872  =head2 Pragmata
1873  
1874  C<use attrs> is now obsolete, and is only provided for
1875  backward-compatibility.  It's been replaced by the C<sub : attributes>
1876  syntax.  See L<perlsub/"Subroutine Attributes"> and L<attributes>.
1877  
1878  Lexical warnings pragma, C<use warnings;>, to control optional warnings.
1879  See L<perllexwarn>.
1880  
1881  C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
1882  ...).  Currently only one subpragma implemented, "use filetest
1883  'access';", that uses access(2) or equivalent to check permissions
1884  instead of using stat(2) as usual.  This matters in filesystems
1885  where there are ACLs (access control lists): the stat(2) might lie,
1886  but access(2) knows better.
1887  
1888  The C<open> pragma can be used to specify default disciplines for
1889  handle constructors (e.g. open()) and for qx//.  The two
1890  pseudo-disciplines C<:raw> and C<:crlf> are currently supported on
1891  DOS-derivative platforms (i.e. where binmode is not a no-op).
1892  See also L</"binmode() can be used to set :crlf and :raw modes">.
1893  
1894  =head1 Utility Changes
1895  
1896  =head2 dprofpp
1897  
1898  C<dprofpp> is used to display profile data generated using C<Devel::DProf>.
1899  See L<dprofpp>.
1900  
1901  =head2 find2perl
1902  
1903  The C<find2perl> utility now uses the enhanced features of the File::Find
1904  module.  The -depth and -follow options are supported.  Pod documentation
1905  is also included in the script.
1906  
1907  =head2 h2xs
1908  
1909  The C<h2xs> tool can now work in conjunction with C<C::Scan> (available
1910  from CPAN) to automatically parse real-life header files.  The C<-M>,
1911  C<-a>, C<-k>, and C<-o> options are new.
1912  
1913  =head2 perlcc
1914  
1915  C<perlcc> now supports the C and Bytecode backends.  By default,
1916  it generates output from the simple C backend rather than the
1917  optimized C backend.
1918  
1919  Support for non-Unix platforms has been improved.
1920  
1921  =head2 perldoc
1922  
1923  C<perldoc> has been reworked to avoid possible security holes.
1924  It will not by default let itself be run as the superuser, but you
1925  may still use the B<-U> switch to try to make it drop privileges
1926  first.
1927  
1928  =head2 The Perl Debugger
1929  
1930  Many bug fixes and enhancements were added to F<perl5db.pl>, the
1931  Perl debugger.  The help documentation was rearranged.  New commands
1932  include C<< < ? >>, C<< > ? >>, and C<< { ? >> to list out current
1933  actions, C<man I<docpage>> to run your doc viewer on some perl
1934  docset, and support for quoted options.  The help information was
1935  rearranged, and should be viewable once again if you're using B<less>
1936  as your pager.  A serious security hole was plugged--you should
1937  immediately remove all older versions of the Perl debugger as
1938  installed in previous releases, all the way back to perl3, from
1939  your system to avoid being bitten by this.
1940  
1941  =head1 Improved Documentation
1942  
1943  Many of the platform-specific README files are now part of the perl
1944  installation.  See L<perl> for the complete list.
1945  
1946  =over 4
1947  
1948  =item perlapi.pod
1949  
1950  The official list of public Perl API functions.
1951  
1952  =item perlboot.pod
1953  
1954  A tutorial for beginners on object-oriented Perl.
1955  
1956  =item perlcompile.pod
1957  
1958  An introduction to using the Perl Compiler suite.
1959  
1960  =item perldbmfilter.pod
1961  
1962  A howto document on using the DBM filter facility.
1963  
1964  =item perldebug.pod
1965  
1966  All material unrelated to running the Perl debugger, plus all
1967  low-level guts-like details that risked crushing the casual user
1968  of the debugger, have been relocated from the old manpage to the
1969  next entry below.
1970  
1971  =item perldebguts.pod
1972  
1973  This new manpage contains excessively low-level material not related
1974  to the Perl debugger, but slightly related to debugging Perl itself.
1975  It also contains some arcane internal details of how the debugging
1976  process works that may only be of interest to developers of Perl
1977  debuggers.
1978  
1979  =item perlfork.pod
1980  
1981  Notes on the fork() emulation currently available for the Windows platform.
1982  
1983  =item perlfilter.pod
1984  
1985  An introduction to writing Perl source filters.
1986  
1987  =item perlhack.pod
1988  
1989  Some guidelines for hacking the Perl source code.
1990  
1991  =item perlintern.pod
1992  
1993  A list of internal functions in the Perl source code.
1994  (List is currently empty.)
1995  
1996  =item perllexwarn.pod
1997  
1998  Introduction and reference information about lexically scoped
1999  warning categories.
2000  
2001  =item perlnumber.pod
2002  
2003  Detailed information about numbers as they are represented in Perl.
2004  
2005  =item perlopentut.pod
2006  
2007  A tutorial on using open() effectively.
2008  
2009  =item perlreftut.pod
2010  
2011  A tutorial that introduces the essentials of references.
2012  
2013  =item perltootc.pod
2014  
2015  A tutorial on managing class data for object modules.
2016  
2017  =item perltodo.pod
2018  
2019  Discussion of the most often wanted features that may someday be
2020  supported in Perl.
2021  
2022  =item perlunicode.pod
2023  
2024  An introduction to Unicode support features in Perl.
2025  
2026  =back
2027  
2028  =head1 Performance enhancements
2029  
2030  =head2 Simple sort() using { $a <=> $b } and the like are optimized
2031  
2032  Many common sort() operations using a simple inlined block are now
2033  optimized for faster performance.
2034  
2035  =head2 Optimized assignments to lexical variables
2036  
2037  Certain operations in the RHS of assignment statements have been
2038  optimized to directly set the lexical variable on the LHS,
2039  eliminating redundant copying overheads.
2040  
2041  =head2 Faster subroutine calls
2042  
2043  Minor changes in how subroutine calls are handled internally
2044  provide marginal improvements in performance.
2045  
2046  =head2 delete(), each(), values() and hash iteration are faster
2047  
2048  The hash values returned by delete(), each(), values() and hashes in a
2049  list context are the actual values in the hash, instead of copies.
2050  This results in significantly better performance, because it eliminates
2051  needless copying in most situations.
2052  
2053  =head1 Installation and Configuration Improvements
2054  
2055  =head2 -Dusethreads means something different
2056  
2057  The -Dusethreads flag now enables the experimental interpreter-based thread
2058  support by default.  To get the flavor of experimental threads that was in
2059  5.005 instead, you need to run Configure with "-Dusethreads -Duse5005threads".
2060  
2061  As of v5.6.0, interpreter-threads support is still lacking a way to
2062  create new threads from Perl (i.e., C<use Thread;> will not work with
2063  interpreter threads).  C<use Thread;> continues to be available when you
2064  specify the -Duse5005threads option to Configure, bugs and all.
2065  
2066      NOTE: Support for threads continues to be an experimental feature.
2067      Interfaces and implementation are subject to sudden and drastic changes.
2068  
2069  =head2 New Configure flags
2070  
2071  The following new flags may be enabled on the Configure command line
2072  by running Configure with C<-Dflag>.
2073  
2074      usemultiplicity
2075      usethreads useithreads    (new interpreter threads: no Perl API yet)
2076      usethreads use5005threads    (threads as they were in 5.005)
2077  
2078      use64bitint            (equal to now deprecated 'use64bits')
2079      use64bitall
2080  
2081      uselongdouble
2082      usemorebits
2083      uselargefiles
2084      usesocks            (only SOCKS v5 supported)
2085  
2086  =head2 Threadedness and 64-bitness now more daring
2087  
2088  The Configure options enabling the use of threads and the use of
2089  64-bitness are now more daring in the sense that they no more have an
2090  explicit list of operating systems of known threads/64-bit
2091  capabilities.  In other words: if your operating system has the
2092  necessary APIs and datatypes, you should be able just to go ahead and
2093  use them, for threads by Configure -Dusethreads, and for 64 bits
2094  either explicitly by Configure -Duse64bitint or implicitly if your
2095  system has 64-bit wide datatypes.  See also L<"64-bit support">.
2096  
2097  =head2 Long Doubles
2098  
2099  Some platforms have "long doubles", floating point numbers of even
2100  larger range than ordinary "doubles".  To enable using long doubles for
2101  Perl's scalars, use -Duselongdouble.
2102  
2103  =head2 -Dusemorebits
2104  
2105  You can enable both -Duse64bitint and -Duselongdouble with -Dusemorebits.
2106  See also L<"64-bit support">.
2107  
2108  =head2 -Duselargefiles
2109  
2110  Some platforms support system APIs that are capable of handling large files
2111  (typically, files larger than two gigabytes).  Perl will try to use these
2112  APIs if you ask for -Duselargefiles.
2113  
2114  See L<"Large file support"> for more information. 
2115  
2116  =head2 installusrbinperl
2117  
2118  You can use "Configure -Uinstallusrbinperl" which causes installperl
2119  to skip installing perl also as /usr/bin/perl.  This is useful if you
2120  prefer not to modify /usr/bin for some reason or another but harmful
2121  because many scripts assume to find Perl in /usr/bin/perl.
2122  
2123  =head2 SOCKS support
2124  
2125  You can use "Configure -Dusesocks" which causes Perl to probe
2126  for the SOCKS proxy protocol library (v5, not v4).  For more information
2127  on SOCKS, see:
2128  
2129      http://www.socks.nec.com/
2130  
2131  =head2 C<-A> flag
2132  
2133  You can "post-edit" the Configure variables using the Configure C<-A>
2134  switch.  The editing happens immediately after the platform specific
2135  hints files have been processed but before the actual configuration
2136  process starts.  Run C<Configure -h> to find out the full C<-A> syntax.
2137  
2138  =head2 Enhanced Installation Directories
2139  
2140  The installation structure has been enriched to improve the support
2141  for maintaining multiple versions of perl, to provide locations for
2142  vendor-supplied modules, scripts, and manpages, and to ease maintenance
2143  of locally-added modules, scripts, and manpages.  See the section on
2144  Installation Directories in the INSTALL file for complete details.
2145  For most users building and installing from source, the defaults should
2146  be fine.
2147  
2148  If you previously used C<Configure -Dsitelib> or C<-Dsitearch> to set
2149  special values for library directories, you might wish to consider using
2150  the new C<-Dsiteprefix> setting instead.  Also, if you wish to re-use a
2151  config.sh file from an earlier version of perl, you should be sure to
2152  check that Configure makes sensible choices for the new directories.
2153  See INSTALL for complete details.
2154  
2155  =head2 gcc automatically tried if 'cc' does not seem to be working
2156  
2157  In many platforms the vendor-supplied 'cc' is too stripped-down to
2158  build Perl (basically, the 'cc' doesn't do ANSI C).  If this seems
2159  to be the case and the 'cc' does not seem to be the GNU C compiler
2160  'gcc', an automatic attempt is made to find and use 'gcc' instead.
2161  
2162  =head1 Platform specific changes
2163  
2164  =head2 Supported platforms
2165  
2166  =over 4
2167  
2168  =item *
2169  
2170  The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
2171  extension.
2172  
2173  =item *
2174  
2175  GNU/Hurd is now supported.
2176  
2177  =item *
2178  
2179  Rhapsody/Darwin is now supported.
2180  
2181  =item *
2182  
2183  EPOC is now supported (on Psion 5).
2184  
2185  =item *
2186  
2187  The cygwin port (formerly cygwin32) has been greatly improved.
2188  
2189  =back
2190  
2191  =head2 DOS
2192  
2193  =over 4
2194  
2195  =item *
2196  
2197  Perl now works with djgpp 2.02 (and 2.03 alpha).
2198  
2199  =item *
2200  
2201  Environment variable names are not converted to uppercase any more.
2202  
2203  =item *
2204  
2205  Incorrect exit codes from backticks have been fixed.
2206  
2207  =item *
2208  
2209  This port continues to use its own builtin globbing (not File::Glob).
2210  
2211  =back
2212  
2213  =head2 OS390 (OpenEdition MVS)
2214  
2215  Support for this EBCDIC platform has not been renewed in this release.
2216  There are difficulties in reconciling Perl's standardization on UTF-8
2217  as its internal representation for characters with the EBCDIC character
2218  set, because the two are incompatible.
2219  
2220  It is unclear whether future versions will renew support for this
2221  platform, but the possibility exists.
2222  
2223  =head2 VMS
2224  
2225  Numerous revisions and extensions to configuration, build, testing, and
2226  installation process to accommodate core changes and VMS-specific options.
2227  
2228  Expand %ENV-handling code to allow runtime mapping to logical names,
2229  CLI symbols, and CRTL environ array.
2230  
2231  Extension of subprocess invocation code to accept filespecs as command
2232  "verbs".
2233  
2234  Add to Perl command line processing the ability to use default file types and
2235  to recognize Unix-style C<2E<gt>&1>.
2236  
2237  Expansion of File::Spec::VMS routines, and integration into ExtUtils::MM_VMS.
2238  
2239  Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly.
2240  
2241  Barewords at start of Unix-syntax paths may be treated as text rather than
2242  only as logical names.
2243  
2244  Optional secure translation of several logical names used internally by Perl.
2245  
2246  Miscellaneous bugfixing and porting of new core code to VMS.
2247  
2248  Thanks are gladly extended to the many people who have contributed VMS
2249  patches, testing, and ideas.
2250  
2251  =head2 Win32
2252  
2253  Perl can now emulate fork() internally, using multiple interpreters running
2254  in different concurrent threads.  This support must be enabled at build
2255  time.  See L<perlfork> for detailed information.
2256  
2257  When given a pathname that consists only of a drivename, such as C<A:>,
2258  opendir() and stat() now use the current working directory for the drive
2259  rather than the drive root.
2260  
2261  The builtin XSUB functions in the Win32:: namespace are documented.  See
2262  L<Win32>.
2263  
2264  $^X now contains the full path name of the running executable.
2265  
2266  A Win32::GetLongPathName() function is provided to complement
2267  Win32::GetFullPathName() and Win32::GetShortPathName().  See L<Win32>.
2268  
2269  POSIX::uname() is supported.
2270  
2271  system(1,...) now returns true process IDs rather than process
2272  handles.  kill() accepts any real process id, rather than strictly
2273  return values from system(1,...).
2274  
2275  For better compatibility with Unix, C<kill(0, $pid)> can now be used to
2276  test whether a process exists.
2277  
2278  The C<Shell> module is supported.
2279  
2280  Better support for building Perl under command.com in Windows 95
2281  has been added.
2282  
2283  Scripts are read in binary mode by default to allow ByteLoader (and
2284  the filter mechanism in general) to work properly.  For compatibility,
2285  the DATA filehandle will be set to text mode if a carriage return is
2286  detected at the end of the line containing the __END__ or __DATA__
2287  token; if not, the DATA filehandle will be left open in binary mode.
2288  Earlier versions always opened the DATA filehandle in text mode.
2289  
2290  The glob() operator is implemented via the C<File::Glob> extension,
2291  which supports glob syntax of the C shell.  This increases the flexibility
2292  of the glob() operator, but there may be compatibility issues for
2293  programs that relied on the older globbing syntax.  If you want to
2294  preserve compatibility with the older syntax, you might want to run
2295  perl with C<-MFile::DosGlob>.  For details and compatibility information,
2296  see L<File::Glob>.
2297  
2298  =head1 Significant bug fixes
2299  
2300  =head2 <HANDLE> on empty files
2301  
2302  With C<$/> set to C<undef>, "slurping" an empty file returns a string of
2303  zero length (instead of C<undef>, as it used to) the first time the
2304  HANDLE is read after C<$/> is set to C<undef>.  Further reads yield
2305  C<undef>.
2306  
2307  This means that the following will append "foo" to an empty file (it used
2308  to do nothing):
2309  
2310      perl -0777 -pi -e 's/^/foo/' empty_file
2311  
2312  The behaviour of:
2313  
2314      perl -pi -e 's/^/foo/' empty_file
2315  
2316  is unchanged (it continues to leave the file empty).
2317  
2318  =head2 C<eval '...'> improvements
2319  
2320  Line numbers (as reflected by caller() and most diagnostics) within
2321  C<eval '...'> were often incorrect where here documents were involved.
2322  This has been corrected.
2323  
2324  Lexical lookups for variables appearing in C<eval '...'> within
2325  functions that were themselves called within an C<eval '...'> were
2326  searching the wrong place for lexicals.  The lexical search now
2327  correctly ends at the subroutine's block boundary.
2328  
2329  The use of C<return> within C<eval {...}> caused $@ not to be reset
2330  correctly when no exception occurred within the eval.  This has
2331  been fixed.
2332  
2333  Parsing of here documents used to be flawed when they appeared as
2334  the replacement expression in C<eval 's/.../.../e'>.  This has
2335  been fixed.
2336  
2337  =head2 All compilation errors are true errors
2338  
2339  Some "errors" encountered at compile time were by necessity 
2340  generated as warnings followed by eventual termination of the
2341  program.  This enabled more such errors to be reported in a
2342  single run, rather than causing a hard stop at the first error
2343  that was encountered.
2344  
2345  The mechanism for reporting such errors has been reimplemented
2346  to queue compile-time errors and report them at the end of the
2347  compilation as true errors rather than as warnings.  This fixes
2348  cases where error messages leaked through in the form of warnings
2349  when code was compiled at run time using C<eval STRING>, and
2350  also allows such errors to be reliably trapped using C<eval "...">.
2351  
2352  =head2 Implicitly closed filehandles are safer
2353  
2354  Sometimes implicitly closed filehandles (as when they are localized,
2355  and Perl automatically closes them on exiting the scope) could
2356  inadvertently set $? or $!.  This has been corrected.
2357  
2358  
2359  =head2 Behavior of list slices is more consistent
2360  
2361  When taking a slice of a literal list (as opposed to a slice of
2362  an array or hash), Perl used to return an empty list if the
2363  result happened to be composed of all undef values.
2364  
2365  The new behavior is to produce an empty list if (and only if)
2366  the original list was empty.  Consider the following example:
2367  
2368      @a = (1,undef,undef,2)[2,1,2];
2369  
2370  The old behavior would have resulted in @a having no elements.
2371  The new behavior ensures it has three undefined elements.
2372  
2373  Note in particular that the behavior of slices of the following
2374  cases remains unchanged:
2375  
2376      @a = ()[1,2];
2377      @a = (getpwent)[7,0];
2378      @a = (anything_returning_empty_list())[2,1,2];
2379      @a = @b[2,1,2];
2380      @a = @c{'a','b','c'};
2381  
2382  See L<perldata>.
2383  
2384  =head2 C<(\$)> prototype and C<$foo{a}>
2385  
2386  A scalar reference prototype now correctly allows a hash or
2387  array element in that slot.
2388  
2389  =head2 C<goto &sub> and AUTOLOAD
2390  
2391  The C<goto &sub> construct works correctly when C<&sub> happens
2392  to be autoloaded.
2393  
2394  =head2 C<-bareword> allowed under C<use integer>
2395  
2396  The autoquoting of barewords preceded by C<-> did not work
2397  in prior versions when the C<integer> pragma was enabled.
2398  This has been fixed.
2399  
2400  =head2 Failures in DESTROY()
2401  
2402  When code in a destructor threw an exception, it went unnoticed
2403  in earlier versions of Perl, unless someone happened to be
2404  looking in $@ just after the point the destructor happened to
2405  run.  Such failures are now visible as warnings when warnings are
2406  enabled.
2407  
2408  =head2 Locale bugs fixed
2409  
2410  printf() and sprintf() previously reset the numeric locale
2411  back to the default "C" locale.  This has been fixed.
2412  
2413  Numbers formatted according to the local numeric locale
2414  (such as using a decimal comma instead of a decimal dot) caused
2415  "isn't numeric" warnings, even while the operations accessing
2416  those numbers produced correct results.  These warnings have been
2417  discontinued.
2418  
2419  =head2 Memory leaks
2420  
2421  The C<eval 'return sub {...}'> construct could sometimes leak
2422  memory.  This has been fixed.
2423  
2424  Operations that aren't filehandle constructors used to leak memory
2425  when used on invalid filehandles.  This has been fixed.
2426  
2427  Constructs that modified C<@_> could fail to deallocate values
2428  in C<@_> and thus leak memory.  This has been corrected.
2429  
2430  =head2 Spurious subroutine stubs after failed subroutine calls
2431  
2432  Perl could sometimes create empty subroutine stubs when a
2433  subroutine was not found in the package.  Such cases stopped
2434  later method lookups from progressing into base packages.
2435  This has been corrected.
2436  
2437  =head2 Taint failures under C<-U>
2438  
2439  When running in unsafe mode, taint violations could sometimes
2440  cause silent failures.  This has been fixed.
2441  
2442  =head2 END blocks and the C<-c> switch
2443  
2444  Prior versions used to run BEGIN B<and> END blocks when Perl was
2445  run in compile-only mode.  Since this is typically not the expected
2446  behavior, END blocks are not executed anymore when the C<-c> switch
2447  is used, or if compilation fails.
2448  
2449  See L</"Support for CHECK blocks"> for how to run things when the compile 
2450  phase ends.
2451  
2452  =head2 Potential to leak DATA filehandles
2453  
2454  Using the C<__DATA__> token creates an implicit filehandle to
2455  the file that contains the token.  It is the program's
2456  responsibility to close it when it is done reading from it.
2457  
2458  This caveat is now better explained in the documentation.
2459  See L<perldata>.
2460  
2461  =head1 New or Changed Diagnostics
2462  
2463  =over 4
2464  
2465  =item "%s" variable %s masks earlier declaration in same %s
2466  
2467  (W misc) A "my" or "our" variable has been redeclared in the current scope or statement,
2468  effectively eliminating all access to the previous instance.  This is almost
2469  always a typographical error.  Note that the earlier variable will still exist
2470  until the end of the scope or until all closure referents to it are
2471  destroyed.
2472  
2473  =item "my sub" not yet implemented
2474  
2475  (F) Lexically scoped subroutines are not yet implemented.  Don't try that
2476  yet.
2477  
2478  =item "our" variable %s redeclared
2479  
2480  (W misc) You seem to have already declared the same global once before in the
2481  current lexical scope.
2482  
2483  =item '!' allowed only after types %s
2484  
2485  (F) The '!' is allowed in pack() and unpack() only after certain types.
2486  See L<perlfunc/pack>.
2487  
2488  =item / cannot take a count
2489  
2490  (F) You had an unpack template indicating a counted-length string,
2491  but you have also specified an explicit size for the string.
2492  See L<perlfunc/pack>.
2493  
2494  =item / must be followed by a, A or Z
2495  
2496  (F) You had an unpack template indicating a counted-length string,
2497  which must be followed by one of the letters a, A or Z
2498  to indicate what sort of string is to be unpacked.
2499  See L<perlfunc/pack>.
2500  
2501  =item / must be followed by a*, A* or Z*
2502  
2503  (F) You had a pack template indicating a counted-length string,
2504  Currently the only things that can have their length counted are a*, A* or Z*.
2505  See L<perlfunc/pack>.
2506  
2507  =item / must follow a numeric type
2508  
2509  (F) You had an unpack template that contained a '#',
2510  but this did not follow some numeric unpack specification.
2511  See L<perlfunc/pack>.
2512  
2513  =item /%s/: Unrecognized escape \\%c passed through
2514  
2515  (W regexp) You used a backslash-character combination which is not recognized
2516  by Perl.  This combination appears in an interpolated variable or a
2517  C<'>-delimited regular expression.  The character was understood literally.
2518  
2519  =item /%s/: Unrecognized escape \\%c in character class passed through
2520  
2521  (W regexp) You used a backslash-character combination which is not recognized
2522  by Perl inside character classes.  The character was understood literally.
2523  
2524  =item /%s/ should probably be written as "%s"
2525  
2526  (W syntax) You have used a pattern where Perl expected to find a string,
2527  as in the first argument to C<join>.  Perl will treat the true
2528  or false result of matching the pattern against $_ as the string,
2529  which is probably not what you had in mind.
2530  
2531  =item %s() called too early to check prototype
2532  
2533  (W prototype) You've called a function that has a prototype before the parser saw a
2534  definition or declaration for it, and Perl could not check that the call
2535  conforms to the prototype.  You need to either add an early prototype
2536  declaration for the subroutine in question, or move the subroutine
2537  definition ahead of the call to get proper prototype checking.  Alternatively,
2538  if you are certain that you're calling the function correctly, you may put
2539  an ampersand before the name to avoid the warning.  See L<perlsub>.
2540  
2541  =item %s argument is not a HASH or ARRAY element
2542  
2543  (F) The argument to exists() must be a hash or array element, such as:
2544  
2545      $foo{$bar}
2546      $ref->{"susie"}[12]
2547  
2548  =item %s argument is not a HASH or ARRAY element or slice
2549  
2550  (F) The argument to delete() must be either a hash or array element, such as:
2551  
2552      $foo{$bar}
2553      $ref->{"susie"}[12]
2554  
2555  or a hash or array slice, such as:
2556  
2557      @foo[$bar, $baz, $xyzzy]
2558      @{$ref->[12]}{"susie", "queue"}
2559  
2560  =item %s argument is not a subroutine name
2561  
2562  (F) The argument to exists() for C<exists &sub> must be a subroutine
2563  name, and not a subroutine call.  C<exists &sub()> will generate this error.
2564  
2565  =item %s package attribute may clash with future reserved word: %s
2566  
2567  (W reserved) A lowercase attribute name was used that had a package-specific handler.
2568  That name might have a meaning to Perl itself some day, even though it
2569  doesn't yet.  Perhaps you should use a mixed-case attribute name, instead.
2570  See L<attributes>.
2571  
2572  =item (in cleanup) %s
2573  
2574  (W misc) This prefix usually indicates that a DESTROY() method raised
2575  the indicated exception.  Since destructors are usually called by
2576  the system at arbitrary points during execution, and often a vast
2577  number of times, the warning is issued only once for any number
2578  of failures that would otherwise result in the same message being
2579  repeated.
2580  
2581  Failure of user callbacks dispatched using the C<G_KEEPERR> flag
2582  could also result in this warning.  See L<perlcall/G_KEEPERR>.
2583  
2584  =item <> should be quotes
2585  
2586  (F) You wrote C<< require <file> >> when you should have written
2587  C<require 'file'>.
2588  
2589  =item Attempt to join self
2590  
2591  (F) You tried to join a thread from within itself, which is an
2592  impossible task.  You may be joining the wrong thread, or you may
2593  need to move the join() to some other thread.
2594  
2595  =item Bad evalled substitution pattern
2596  
2597  (F) You've used the /e switch to evaluate the replacement for a
2598  substitution, but perl found a syntax error in the code to evaluate,
2599  most likely an unexpected right brace '}'.
2600  
2601  =item Bad realloc() ignored
2602  
2603  (S) An internal routine called realloc() on something that had never been
2604  malloc()ed in the first place. Mandatory, but can be disabled by
2605  setting environment variable C<PERL_BADFREE> to 1.
2606  
2607  =item Bareword found in conditional
2608  
2609  (W bareword) The compiler found a bareword where it expected a conditional,
2610  which often indicates that an || or && was parsed as part of the
2611  last argument of the previous construct, for example:
2612  
2613      open FOO || die;
2614  
2615  It may also indicate a misspelled constant that has been interpreted
2616  as a bareword:
2617  
2618      use constant TYPO => 1;
2619      if (TYOP) { print "foo" }
2620  
2621  The C<strict> pragma is useful in avoiding such errors.
2622  
2623  =item Binary number > 0b11111111111111111111111111111111 non-portable
2624  
2625  (W portable) The binary number you specified is larger than 2**32-1
2626  (4294967295) and therefore non-portable between systems.  See
2627  L<perlport> for more on portability concerns.
2628  
2629  =item Bit vector size > 32 non-portable
2630  
2631  (W portable) Using bit vector sizes larger than 32 is non-portable.
2632  
2633  =item Buffer overflow in prime_env_iter: %s
2634  
2635  (W internal) A warning peculiar to VMS.  While Perl was preparing to iterate over
2636  %ENV, it encountered a logical name or symbol definition which was too long,
2637  so it was truncated to the string shown.
2638  
2639  =item Can't check filesystem of script "%s"
2640  
2641  (P) For some reason you can't check the filesystem of the script for nosuid.
2642  
2643  =item Can't declare class for non-scalar %s in "%s"
2644  
2645  (S) Currently, only scalar variables can declared with a specific class
2646  qualifier in a "my" or "our" declaration.  The semantics may be extended
2647  for other types of variables in future.
2648  
2649  =item Can't declare %s in "%s"
2650  
2651  (F) Only scalar, array, and hash variables may be declared as "my" or
2652  "our" variables.  They must have ordinary identifiers as names.
2653  
2654  =item Can't ignore signal CHLD, forcing to default
2655  
2656  (W signal) Perl has detected that it is being run with the SIGCHLD signal
2657  (sometimes known as SIGCLD) disabled.  Since disabling this signal
2658  will interfere with proper determination of exit status of child
2659  processes, Perl has reset the signal to its default value.
2660  This situation typically indicates that the parent program under
2661  which Perl may be running (e.g., cron) is being very careless.
2662  
2663  =item Can't modify non-lvalue subroutine call
2664  
2665  (F) Subroutines meant to be used in lvalue context should be declared as
2666  such, see L<perlsub/"Lvalue subroutines">.
2667  
2668  =item Can't read CRTL environ
2669  
2670  (S) A warning peculiar to VMS.  Perl tried to read an element of %ENV
2671  from the CRTL's internal environment array and discovered the array was
2672  missing.  You need to figure out where your CRTL misplaced its environ
2673  or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched.
2674  
2675  =item Can't remove %s: %s, skipping file 
2676  
2677  (S) You requested an inplace edit without creating a backup file.  Perl
2678  was unable to remove the original file to replace it with the modified
2679  file.  The file was left unmodified.
2680  
2681  =item Can't return %s from lvalue subroutine
2682  
2683  (F) Perl detected an attempt to return illegal lvalues (such
2684  as temporary or readonly values) from a subroutine used as an lvalue.
2685  This is not allowed.
2686  
2687  =item Can't weaken a nonreference
2688  
2689  (F) You attempted to weaken something that was not a reference.  Only
2690  references can be weakened.
2691  
2692  =item Character class [:%s:] unknown
2693  
2694  (F) The class in the character class [: :] syntax is unknown.
2695  See L<perlre>.
2696  
2697  =item Character class syntax [%s] belongs inside character classes
2698  
2699  (W unsafe) The character class constructs [: :], [= =], and [. .]  go
2700  I<inside> character classes, the [] are part of the construct,
2701  for example: /[012[:alpha:]345]/.  Note that [= =] and [. .]
2702  are not currently implemented; they are simply placeholders for
2703  future extensions.
2704  
2705  =item Constant is not %s reference
2706  
2707  (F) A constant value (perhaps declared using the C<use constant> pragma)
2708  is being dereferenced, but it amounts to the wrong type of reference.  The
2709  message indicates the type of reference that was expected. This usually
2710  indicates a syntax error in dereferencing the constant value.
2711  See L<perlsub/"Constant Functions"> and L<constant>.
2712  
2713  =item constant(%s): %s
2714  
2715  (F) The parser found inconsistencies either while attempting to define an
2716  overloaded constant, or when trying to find the character name specified
2717  in the C<\N{...}> escape.  Perhaps you forgot to load the corresponding
2718  C<overload> or C<charnames> pragma?  See L<charnames> and L<overload>.
2719  
2720  =item CORE::%s is not a keyword
2721  
2722  (F) The CORE:: namespace is reserved for Perl keywords.
2723  
2724  =item defined(@array) is deprecated
2725  
2726  (D) defined() is not usually useful on arrays because it checks for an
2727  undefined I<scalar> value.  If you want to see if the array is empty,
2728  just use C<if (@array) { # not empty }> for example.  
2729  
2730  =item defined(%hash) is deprecated
2731  
2732  (D) defined() is not usually useful on hashes because it checks for an
2733  undefined I<scalar> value.  If you want to see if the hash is empty,
2734  just use C<if (%hash) { # not empty }> for example.  
2735  
2736  =item Did not produce a valid header
2737  
2738  See Server error.
2739  
2740  =item (Did you mean "local" instead of "our"?)
2741  
2742  (W misc) Remember that "our" does not localize the declared global variable.
2743  You have declared it again in the same lexical scope, which seems superfluous.
2744  
2745  =item Document contains no data
2746  
2747  See Server error.
2748  
2749  =item entering effective %s failed
2750  
2751  (F) While under the C<use filetest> pragma, switching the real and
2752  effective uids or gids failed.
2753  
2754  =item false [] range "%s" in regexp
2755  
2756  (W regexp) A character class range must start and end at a literal character, not
2757  another character class like C<\d> or C<[:alpha:]>.  The "-" in your false
2758  range is interpreted as a literal "-".  Consider quoting the "-",  "\-".
2759  See L<perlre>.
2760  
2761  =item Filehandle %s opened only for output
2762  
2763  (W io) You tried to read from a filehandle opened only for writing.  If you
2764  intended it to be a read/write filehandle, you needed to open it with
2765  "+<" or "+>" or "+>>" instead of with "<" or nothing.  If
2766  you intended only to read from the file, use "<".  See
2767  L<perlfunc/open>.
2768  
2769  =item flock() on closed filehandle %s
2770  
2771  (W closed) The filehandle you're attempting to flock() got itself closed some
2772  time before now.  Check your logic flow.  flock() operates on filehandles.
2773  Are you attempting to call flock() on a dirhandle by the same name?
2774  
2775  =item Global symbol "%s" requires explicit package name
2776  
2777  (F) You've said "use strict vars", which indicates that all variables
2778  must either be lexically scoped (using "my"), declared beforehand using
2779  "our", or explicitly qualified to say which package the global variable
2780  is in (using "::").
2781  
2782  =item Hexadecimal number > 0xffffffff non-portable
2783  
2784  (W portable) The hexadecimal number you specified is larger than 2**32-1
2785  (4294967295) and therefore non-portable between systems.  See
2786  L<perlport> for more on portability concerns.
2787  
2788  =item Ill-formed CRTL environ value "%s"
2789  
2790  (W internal) A warning peculiar to VMS.  Perl tried to read the CRTL's internal
2791  environ array, and encountered an element without the C<=> delimiter
2792  used to separate keys from values.  The element is ignored.
2793  
2794  =item Ill-formed message in prime_env_iter: |%s|
2795  
2796  (W internal) A warning peculiar to VMS.  Perl tried to read a logical name
2797  or CLI symbol definition when preparing to iterate over %ENV, and
2798  didn't see the expected delimiter between key and value, so the
2799  line was ignored.
2800  
2801  =item Illegal binary digit %s
2802  
2803  (F) You used a digit other than 0 or 1 in a binary number.
2804  
2805  =item Illegal binary digit %s ignored
2806  
2807  (W digit) You may have tried to use a digit other than 0 or 1 in a binary number.
2808  Interpretation of the binary number stopped before the offending digit.
2809  
2810  =item Illegal number of bits in vec
2811  
2812  (F) The number of bits in vec() (the third argument) must be a power of
2813  two from 1 to 32 (or 64, if your platform supports that).
2814  
2815  =item Integer overflow in %s number
2816  
2817  (W overflow) The hexadecimal, octal or binary number you have specified either
2818  as a literal or as an argument to hex() or oct() is too big for your
2819  architecture, and has been converted to a floating point number.  On a
2820  32-bit architecture the largest hexadecimal, octal or binary number
2821  representable without overflow is 0xFFFFFFFF, 037777777777, or
2822  0b11111111111111111111111111111111 respectively.  Note that Perl
2823  transparently promotes all numbers to a floating point representation
2824  internally--subject to loss of precision errors in subsequent
2825  operations.
2826  
2827  =item Invalid %s attribute: %s
2828  
2829  The indicated attribute for a subroutine or variable was not recognized
2830  by Perl or by a user-supplied handler.  See L<attributes>.
2831  
2832  =item Invalid %s attributes: %s
2833  
2834  The indicated attributes for a subroutine or variable were not recognized
2835  by Perl or by a user-supplied handler.  See L<attributes>.
2836  
2837  =item invalid [] range "%s" in regexp
2838  
2839  The offending range is now explicitly displayed.
2840  
2841  =item Invalid separator character %s in attribute list
2842  
2843  (F) Something other than a colon or whitespace was seen between the
2844  elements of an attribute list.  If the previous attribute
2845  had a parenthesised parameter list, perhaps that list was terminated
2846  too soon.  See L<attributes>.
2847  
2848  =item Invalid separator character %s in subroutine attribute list
2849  
2850  (F) Something other than a colon or whitespace was seen between the
2851  elements of a subroutine attribute list.  If the previous attribute
2852  had a parenthesised parameter list, perhaps that list was terminated
2853  too soon.
2854  
2855  =item leaving effective %s failed
2856  
2857  (F) While under the C<use filetest> pragma, switching the real and
2858  effective uids or gids failed.
2859  
2860  =item Lvalue subs returning %s not implemented yet
2861  
2862  (F) Due to limitations in the current implementation, array and hash
2863  values cannot be returned in subroutines used in lvalue context.
2864  See L<perlsub/"Lvalue subroutines">.
2865  
2866  =item Method %s not permitted
2867  
2868  See Server error.
2869  
2870  =item Missing %sbrace%s on \N{}
2871  
2872  (F) Wrong syntax of character name literal C<\N{charname}> within
2873  double-quotish context.
2874  
2875  =item Missing command in piped open
2876  
2877  (W pipe) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
2878  construction, but the command was missing or blank.
2879  
2880  =item Missing name in "my sub"
2881  
2882  (F) The reserved syntax for lexically scoped subroutines requires that they
2883  have a name with which they can be found.
2884  
2885  =item No %s specified for -%c
2886  
2887  (F) The indicated command line switch needs a mandatory argument, but
2888  you haven't specified one.
2889  
2890  =item No package name allowed for variable %s in "our"
2891  
2892  (F) Fully qualified variable names are not allowed in "our" declarations,
2893  because that doesn't make much sense under existing semantics.  Such
2894  syntax is reserved for future extensions.
2895  
2896  =item No space allowed after -%c
2897  
2898  (F) The argument to the indicated command line switch must follow immediately
2899  after the switch, without intervening spaces.
2900  
2901  =item no UTC offset information; assuming local time is UTC
2902  
2903  (S) A warning peculiar to VMS.  Perl was unable to find the local
2904  timezone offset, so it's assuming that local system time is equivalent
2905  to UTC.  If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL>
2906  to translate to the number of seconds which need to be added to UTC to
2907  get local time.
2908  
2909  =item Octal number > 037777777777 non-portable
2910  
2911  (W portable) The octal number you specified is larger than 2**32-1 (4294967295)
2912  and therefore non-portable between systems.  See L<perlport> for more
2913  on portability concerns.
2914  
2915  See also L<perlport> for writing portable code.
2916  
2917  =item panic: del_backref
2918  
2919  (P) Failed an internal consistency check while trying to reset a weak
2920  reference.
2921  
2922  =item panic: kid popen errno read
2923  
2924  (F) forked child returned an incomprehensible message about its errno.
2925  
2926  =item panic: magic_killbackrefs
2927  
2928  (P) Failed an internal consistency check while trying to reset all weak
2929  references to an object.
2930  
2931  =item Parentheses missing around "%s" list
2932  
2933  (W parenthesis) You said something like
2934  
2935      my $foo, $bar = @_;
2936  
2937  when you meant
2938  
2939      my ($foo, $bar) = @_;
2940  
2941  Remember that "my", "our", and "local" bind tighter than comma.
2942  
2943  =item Possible unintended interpolation of %s in string
2944  
2945  (W ambiguous) It used to be that Perl would try to guess whether you
2946  wanted an array interpolated or a literal @.  It no longer does this;
2947  arrays are now I<always> interpolated into strings.  This means that 
2948  if you try something like:
2949  
2950          print "fred@example.com";
2951  
2952  and the array C<@example> doesn't exist, Perl is going to print
2953  C<fred.com>, which is probably not what you wanted.  To get a literal
2954  C<@> sign in a string, put a backslash before it, just as you would
2955  to get a literal C<$> sign.
2956  
2957  =item Possible Y2K bug: %s
2958  
2959  (W y2k) You are concatenating the number 19 with another number, which
2960  could be a potential Year 2000 problem.
2961  
2962  =item pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
2963  
2964  (W deprecated) You have written something like this:
2965  
2966      sub doit
2967      {
2968          use attrs qw(locked);
2969      }
2970  
2971  You should use the new declaration syntax instead.
2972  
2973      sub doit : locked
2974      {
2975          ...
2976  
2977  The C<use attrs> pragma is now obsolete, and is only provided for
2978  backward-compatibility. See L<perlsub/"Subroutine Attributes">.
2979  
2980  
2981  =item Premature end of script headers
2982  
2983  See Server error.
2984  
2985  =item Repeat count in pack overflows
2986  
2987  (F) You can't specify a repeat count so large that it overflows
2988  your signed integers.  See L<perlfunc/pack>.
2989  
2990  =item Repeat count in unpack overflows
2991  
2992  (F) You can't specify a repeat count so large that it overflows
2993  your signed integers.  See L<perlfunc/unpack>.
2994  
2995  =item realloc() of freed memory ignored
2996  
2997  (S) An internal routine called realloc() on something that had already
2998  been freed.
2999  
3000  =item Reference is already weak
3001  
3002  (W misc) You have attempted to weaken a reference that is already weak.
3003  Doing so has no effect.
3004  
3005  =item setpgrp can't take arguments
3006  
3007  (F) Your system has the setpgrp() from BSD 4.2, which takes no arguments,
3008  unlike POSIX setpgid(), which takes a process ID and process group ID.
3009  
3010  =item Strange *+?{} on zero-length expression
3011  
3012  (W regexp) You applied a regular expression quantifier in a place where it
3013  makes no sense, such as on a zero-width assertion.
3014  Try putting the quantifier inside the assertion instead.  For example,
3015  the way to match "abc" provided that it is followed by three
3016  repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.
3017  
3018  =item switching effective %s is not implemented
3019  
3020  (F) While under the C<use filetest> pragma, we cannot switch the
3021  real and effective uids or gids.
3022  
3023  =item This Perl can't reset CRTL environ elements (%s)
3024  
3025  =item This Perl can't set CRTL environ elements (%s=%s)
3026  
3027  (W internal) Warnings peculiar to VMS.  You tried to change or delete an element
3028  of the CRTL's internal environ array, but your copy of Perl wasn't
3029  built with a CRTL that contained the setenv() function.  You'll need to
3030  rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see
3031  L<perlvms>) so that the environ array isn't the target of the change to
3032  %ENV which produced the warning.
3033  
3034  =item Too late to run %s block
3035  
3036  (W void) A CHECK or INIT block is being defined during run time proper,
3037  when the opportunity to run them has already passed.  Perhaps you are
3038  loading a file with C<require> or C<do> when you should be using
3039  C<use> instead.  Or perhaps you should put the C<require> or C<do>
3040  inside a BEGIN block.
3041  
3042  =item Unknown open() mode '%s'
3043  
3044  (F) The second argument of 3-argument open() is not among the list
3045  of valid modes: C<< < >>, C<< > >>, C<<< >> >>>, C<< +< >>,
3046  C<< +> >>, C<<< +>> >>>, C<-|>, C<|->.
3047  
3048  =item Unknown process %x sent message to prime_env_iter: %s
3049  
3050  (P) An error peculiar to VMS.  Perl was reading values for %ENV before
3051  iterating over it, and someone else stuck a message in the stream of
3052  data Perl expected.  Someone's very confused, or perhaps trying to
3053  subvert Perl's population of %ENV for nefarious purposes.
3054  
3055  =item Unrecognized escape \\%c passed through
3056  
3057  (W misc) You used a backslash-character combination which is not recognized
3058  by Perl.  The character was understood literally.
3059  
3060  =item Unterminated attribute parameter in attribute list
3061  
3062  (F) The lexer saw an opening (left) parenthesis character while parsing an
3063  attribute list, but the matching closing (right) parenthesis
3064  character was not found.  You may need to add (or remove) a backslash
3065  character to get your parentheses to balance.  See L<attributes>.
3066  
3067  =item Unterminated attribute list
3068  
3069  (F) The lexer found something other than a simple identifier at the start
3070  of an attribute, and it wasn't a semicolon or the start of a
3071  block.  Perhaps you terminated the parameter list of the previous attribute
3072  too soon.  See L<attributes>.
3073  
3074  =item Unterminated attribute parameter in subroutine attribute list
3075  
3076  (F) The lexer saw an opening (left) parenthesis character while parsing a
3077  subroutine attribute list, but the matching closing (right) parenthesis
3078  character was not found.  You may need to add (or remove) a backslash
3079  character to get your parentheses to balance.
3080  
3081  =item Unterminated subroutine attribute list
3082  
3083  (F) The lexer found something other than a simple identifier at the start
3084  of a subroutine attribute, and it wasn't a semicolon or the start of a
3085  block.  Perhaps you terminated the parameter list of the previous attribute
3086  too soon.
3087  
3088  =item Value of CLI symbol "%s" too long
3089  
3090  (W misc) A warning peculiar to VMS.  Perl tried to read the value of an %ENV
3091  element from a CLI symbol table, and found a resultant string longer
3092  than 1024 characters.  The return value has been truncated to 1024
3093  characters.
3094  
3095  =item Version number must be a constant number
3096  
3097  (P) The attempt to translate a C<use Module n.n LIST> statement into
3098  its equivalent C<BEGIN> block found an internal inconsistency with
3099  the version number.
3100  
3101  =back
3102  
3103  =head1 New tests
3104  
3105  =over 4
3106  
3107  =item    lib/attrs
3108  
3109  Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
3110  
3111  =item    lib/env
3112  
3113  Tests for new environment scalar capability (e.g., C<use Env qw($BAR);>).
3114  
3115  =item    lib/env-array
3116  
3117  Tests for new environment array capability (e.g., C<use Env qw(@PATH);>).
3118  
3119  =item    lib/io_const
3120  
3121  IO constants (SEEK_*, _IO*).
3122  
3123  =item    lib/io_dir
3124  
3125  Directory-related IO methods (new, read, close, rewind, tied delete).
3126  
3127  =item    lib/io_multihomed
3128  
3129  INET sockets with multi-homed hosts.
3130  
3131  =item    lib/io_poll
3132  
3133  IO poll().
3134  
3135  =item    lib/io_unix
3136  
3137  UNIX sockets.
3138  
3139  =item    op/attrs
3140  
3141  Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
3142  
3143  =item    op/filetest
3144  
3145  File test operators.
3146  
3147  =item    op/lex_assign
3148  
3149  Verify operations that access pad objects (lexicals and temporaries).
3150  
3151  =item    op/exists_sub
3152  
3153  Verify C<exists &sub> operations.
3154  
3155  =back
3156  
3157  =head1 Incompatible Changes
3158  
3159  =head2 Perl Source Incompatibilities
3160  
3161  Beware that any new warnings that have been added or old ones
3162  that have been enhanced are B<not> considered incompatible changes.
3163  
3164  Since all new warnings must be explicitly requested via the C<-w>
3165  switch or the C<warnings> pragma, it is ultimately the programmer's
3166  responsibility to ensure that warnings are enabled judiciously.
3167  
3168  =over 4
3169  
3170  =item CHECK is a new keyword
3171  
3172  All subroutine definitions named CHECK are now special.  See
3173  C</"Support for CHECK blocks"> for more information.
3174  
3175  =item Treatment of list slices of undef has changed
3176  
3177  There is a potential incompatibility in the behavior of list slices
3178  that are comprised entirely of undefined values.
3179  See L</"Behavior of list slices is more consistent">.
3180  
3181  =item Format of $English::PERL_VERSION is different
3182  
3183  The English module now sets $PERL_VERSION to $^V (a string value) rather
3184  than C<$]> (a numeric value).  This is a potential incompatibility.
3185  Send us a report via perlbug if you are affected by this.
3186  
3187  See L</"Improved Perl version numbering system"> for the reasons for
3188  this change.
3189  
3190  =item Literals of the form C<1.2.3> parse differently
3191  
3192  Previously, numeric literals with more than one dot in them were
3193  interpreted as a floating point number concatenated with one or more
3194  numbers.  Such "numbers" are now parsed as strings composed of the
3195  specified ordinals.
3196  
3197  For example, C<print 97.98.99> used to output C<97.9899> in earlier
3198  versions, but now prints C<abc>.
3199  
3200  See L</"Support for strings represented as a vector of ordinals">.
3201  
3202  =item Possibly changed pseudo-random number generator
3203  
3204  Perl programs that depend on reproducing a specific set of pseudo-random
3205  numbers may now produce different output due to improvements made to the
3206  rand() builtin.  You can use C<sh Configure -Drandfunc=rand> to obtain
3207  the old behavior.
3208  
3209  See L</"Better pseudo-random number generator">.
3210  
3211  =item Hashing function for hash keys has changed
3212  
3213  Even though Perl hashes are not order preserving, the apparently
3214  random order encountered when iterating on the contents of a hash
3215  is actually determined by the hashing algorithm used.  Improvements
3216  in the algorithm may yield a random order that is B<different> from
3217  that of previous versions, especially when iterating on hashes.
3218  
3219  See L</"Better worst-case behavior of hashes"> for additional
3220  information.
3221  
3222  =item C<undef> fails on read only values
3223  
3224  Using the C<undef> operator on a readonly value (such as $1) has
3225  the same effect as assigning C<undef> to the readonly value--it
3226  throws an exception.
3227  
3228  =item Close-on-exec bit may be set on pipe and socket handles
3229  
3230  Pipe and socket handles are also now subject to the close-on-exec
3231  behavior determined by the special variable $^F.
3232  
3233  See L</"More consistent close-on-exec behavior">.
3234  
3235  =item Writing C<"$$1"> to mean C<"${$}1"> is unsupported
3236  
3237  Perl 5.004 deprecated the interpretation of C<$$1> and
3238  similar within interpolated strings to mean C<$$ . "1">,
3239  but still allowed it.
3240  
3241  In Perl 5.6.0 and later, C<"$$1"> always means C<"${$1}">.
3242  
3243  =item delete(), each(), values() and C<\(%h)>
3244  
3245  operate on aliases to values, not copies
3246  
3247  delete(), each(), values() and hashes (e.g. C<\(%h)>)
3248  in a list context return the actual
3249  values in the hash, instead of copies (as they used to in earlier
3250  versions).  Typical idioms for using these constructs copy the
3251  returned values, but this can make a significant difference when
3252  creating references to the returned values.  Keys in the hash are still
3253  returned as copies when iterating on a hash.
3254  
3255  See also L</"delete(), each(), values() and hash iteration are faster">.
3256  
3257  =item vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
3258  
3259  vec() generates a run-time error if the BITS argument is not
3260  a valid power-of-two integer.
3261  
3262  =item Text of some diagnostic output has changed
3263  
3264  Most references to internal Perl operations in diagnostics
3265  have been changed to be more descriptive.  This may be an
3266  issue for programs that may incorrectly rely on the exact
3267  text of diagnostics for proper functioning.
3268  
3269  =item C<%@> has been removed
3270  
3271  The undocumented special variable C<%@> that used to accumulate
3272  "background" errors (such as those that happen in DESTROY())
3273  has been removed, because it could potentially result in memory
3274  leaks.
3275  
3276  =item Parenthesized not() behaves like a list operator
3277  
3278  The C<not> operator now falls under the "if it looks like a function,
3279  it behaves like a function" rule.
3280  
3281  As a result, the parenthesized form can be used with C<grep> and C<map>.
3282  The following construct used to be a syntax error before, but it works
3283  as expected now:
3284  
3285      grep not($_), @things;
3286  
3287  On the other hand, using C<not> with a literal list slice may not
3288  work.  The following previously allowed construct:
3289  
3290      print not (1,2,3)[0];
3291  
3292  needs to be written with additional parentheses now:
3293  
3294      print not((1,2,3)[0]);
3295  
3296  The behavior remains unaffected when C<not> is not followed by parentheses.
3297  
3298  =item Semantics of bareword prototype C<(*)> have changed
3299  
3300  The semantics of the bareword prototype C<*> have changed.  Perl 5.005
3301  always coerced simple scalar arguments to a typeglob, which wasn't useful
3302  in situations where the subroutine must distinguish between a simple
3303  scalar and a typeglob.  The new behavior is to not coerce bareword
3304  arguments to a typeglob.  The value will always be visible as either
3305  a simple scalar or as a reference to a typeglob.
3306  
3307  See L</"More functional bareword prototype (*)">.
3308  
3309  =item Semantics of bit operators may have changed on 64-bit platforms
3310  
3311  If your platform is either natively 64-bit or if Perl has been
3312  configured to used 64-bit integers, i.e., $Config{ivsize} is 8, 
3313  there may be a potential incompatibility in the behavior of bitwise
3314  numeric operators (& | ^ ~ << >>).  These operators used to strictly
3315  operate on the lower 32 bits of integers in previous versions, but now
3316  operate over the entire native integral width.  In particular, note
3317  that unary C<~> will produce different results on platforms that have
3318  different $Config{ivsize}.  For portability, be sure to mask off
3319  the excess bits in the result of unary C<~>, e.g., C<~$x & 0xffffffff>.
3320  
3321  See L</"Bit operators support full native integer width">.
3322  
3323  =item More builtins taint their results
3324  
3325  As described in L</"Improved security features">, there may be more
3326  sources of taint in a Perl program.
3327  
3328  To avoid these new tainting behaviors, you can build Perl with the
3329  Configure option C<-Accflags=-DINCOMPLETE_TAINTS>.  Beware that the
3330  ensuing perl binary may be insecure.
3331  
3332  =back
3333  
3334  =head2 C Source Incompatibilities
3335  
3336  =over 4
3337  
3338  =item C<PERL_POLLUTE>
3339  
3340  Release 5.005 grandfathered old global symbol names by providing preprocessor
3341  macros for extension source compatibility.  As of release 5.6.0, these
3342  preprocessor definitions are not available by default.  You need to explicitly
3343  compile perl with C<-DPERL_POLLUTE> to get these definitions.  For
3344  extensions still using the old symbols, this option can be
3345  specified via MakeMaker:
3346  
3347      perl Makefile.PL POLLUTE=1
3348  
3349  =item C<PERL_IMPLICIT_CONTEXT>
3350  
3351  This new build option provides a set of macros for all API functions
3352  such that an implicit interpreter/thread context argument is passed to
3353  every API function.  As a result of this, something like C<sv_setsv(foo,bar)>
3354  amounts to a macro invocation that actually translates to something like
3355  C<Perl_sv_setsv(my_perl,foo,bar)>.  While this is generally expected
3356  to not have any significant source compatibility issues, the difference
3357  between a macro and a real function call will need to be considered.
3358  
3359  This means that there B<is> a source compatibility issue as a result of
3360  this if your extensions attempt to use pointers to any of the Perl API
3361  functions.
3362  
3363  Note that the above issue is not relevant to the default build of
3364  Perl, whose interfaces continue to match those of prior versions
3365  (but subject to the other options described here).
3366  
3367  See L<perlguts/"The Perl API"> for detailed information on the
3368  ramifications of building Perl with this option.
3369  
3370      NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
3371      with one of -Dusethreads, -Dusemultiplicity, or both.  It is not
3372      intended to be enabled by users at this time.
3373  
3374  =item C<PERL_POLLUTE_MALLOC>
3375  
3376  Enabling Perl's malloc in release 5.005 and earlier caused the namespace of
3377  the system's malloc family of functions to be usurped by the Perl versions,
3378  since by default they used the same names.  Besides causing problems on
3379  platforms that do not allow these functions to be cleanly replaced, this
3380  also meant that the system versions could not be called in programs that
3381  used Perl's malloc.  Previous versions of Perl have allowed this behaviour
3382  to be suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor
3383  definitions.
3384  
3385  As of release 5.6.0, Perl's malloc family of functions have default names
3386  distinct from the system versions.  You need to explicitly compile perl with
3387  C<-DPERL_POLLUTE_MALLOC> to get the older behaviour.  HIDEMYMALLOC
3388  and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
3389  the default.
3390  
3391  Note that these functions do B<not> constitute Perl's memory allocation API.
3392  See L<perlguts/"Memory Allocation"> for further information about that.
3393  
3394  =back
3395  
3396  =head2 Compatible C Source API Changes
3397  
3398  =over 4
3399  
3400  =item C<PATCHLEVEL> is now C<PERL_VERSION>
3401  
3402  The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
3403  are now available by default from perl.h, and reflect the base revision,
3404  patchlevel, and subversion respectively.  C<PERL_REVISION> had no
3405  prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
3406  previously available as C<PATCHLEVEL> and C<SUBVERSION>.
3407  
3408  The new names cause less pollution of the B<cpp> namespace and reflect what
3409  the numbers have come to stand for in common practice.  For compatibility,
3410  the old names are still supported when F<patchlevel.h> is explicitly
3411  included (as required before), so there is no source incompatibility
3412  from the change.
3413  
3414  =back
3415  
3416  =head2 Binary Incompatibilities
3417  
3418  In general, the default build of this release is expected to be binary
3419  compatible for extensions built with the 5.005 release or its maintenance
3420  versions.  However, specific platforms may have broken binary compatibility
3421  due to changes in the defaults used in hints files.  Therefore, please be
3422  sure to always check the platform-specific README files for any notes to
3423  the contrary.
3424  
3425  The usethreads or usemultiplicity builds are B<not> binary compatible
3426  with the corresponding builds in 5.005.
3427  
3428  On platforms that require an explicit list of exports (AIX, OS/2 and Windows,
3429  among others), purely internal symbols such as parser functions and the
3430  run time opcodes are not exported by default.  Perl 5.005 used to export
3431  all functions irrespective of whether they were considered part of the
3432  public API or not.
3433  
3434  For the full list of public API functions, see L<perlapi>.
3435  
3436  =head1 Known Problems
3437  
3438  =head2 Localizing a tied hash element may leak memory
3439  
3440  As of the 5.6.1 release, there is a known leak when code such as this
3441  is executed:
3442  
3443      use Tie::Hash;
3444      tie my %tie_hash => 'Tie::StdHash';
3445  
3446      ...
3447  
3448      local($tie_hash{Foo}) = 1; # leaks
3449  
3450  =head2 Known test failures
3451  
3452  =over
3453  
3454  =item *
3455  
3456  64-bit builds
3457  
3458  Subtest #15 of lib/b.t may fail under 64-bit builds on platforms such
3459  as HP-UX PA64 and Linux IA64.  The issue is still being investigated.
3460  
3461  The lib/io_multihomed test may hang in HP-UX if Perl has been
3462  configured to be 64-bit.  Because other 64-bit platforms do not
3463  hang in this test, HP-UX is suspect.  All other tests pass
3464  in 64-bit HP-UX.  The test attempts to create and connect to
3465  "multihomed" sockets (sockets which have multiple IP addresses).
3466  
3467  Note that 64-bit support is still experimental.
3468  
3469  =item *
3470  
3471  Failure of Thread tests
3472  
3473  The subtests 19 and 20 of lib/thr5005.t test are known to fail due to
3474  fundamental problems in the 5.005 threading implementation.  These are
3475  not new failures--Perl 5.005_0x has the same bugs, but didn't have these
3476  tests.  (Note that support for 5.005-style threading remains experimental.)
3477  
3478  =item *
3479  
3480  NEXTSTEP 3.3 POSIX test failure
3481  
3482  In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the
3483  operating system libraries is buggy: the %j format numbers the days of
3484  a month starting from zero, which, while being logical to programmers,
3485  will cause the subtests 19 to 27 of the lib/posix test may fail.
3486  
3487  =item *
3488  
3489  Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc
3490  
3491  If compiled with gcc 2.95 the lib/sdbm test will fail (dump core).
3492  The cure is to use the vendor cc, it comes with the operating system
3493  and produces good code.
3494  
3495  =back
3496  
3497  =head2 EBCDIC platforms not fully supported
3498  
3499  In earlier releases of Perl, EBCDIC environments like OS390 (also
3500  known as Open Edition MVS) and VM-ESA were supported.  Due to changes
3501  required by the UTF-8 (Unicode) support, the EBCDIC platforms are not
3502  supported in Perl 5.6.0.
3503  
3504  The 5.6.1 release improves support for EBCDIC platforms, but they
3505  are not fully supported yet.
3506  
3507  =head2 UNICOS/mk CC failures during Configure run
3508  
3509  In UNICOS/mk the following errors may appear during the Configure run:
3510  
3511      Guessing which symbols your C compiler and preprocessor define...
3512      CC-20 cc: ERROR File = try.c, Line = 3
3513      ...
3514        bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
3515      ...
3516      4 errors detected in the compilation of "try.c".
3517  
3518  The culprit is the broken awk of UNICOS/mk.  The effect is fortunately
3519  rather mild: Perl itself is not adversely affected by the error, only
3520  the h2ph utility coming with Perl, and that is rather rarely needed
3521  these days.
3522  
3523  =head2 Arrow operator and arrays
3524  
3525  When the left argument to the arrow operator C<< -> >> is an array, or
3526  the C<scalar> operator operating on an array, the result of the
3527  operation must be considered erroneous. For example:
3528  
3529      @x->[2]
3530      scalar(@x)->[2]
3531  
3532  These expressions will get run-time errors in some future release of
3533  Perl.
3534  
3535  =head2 Experimental features
3536  
3537  As discussed above, many features are still experimental.  Interfaces and
3538  implementation of these features are subject to change, and in extreme cases,
3539  even subject to removal in some future release of Perl.  These features
3540  include the following:
3541  
3542  =over 4
3543  
3544  =item Threads
3545  
3546  =item Unicode
3547  
3548  =item 64-bit support
3549  
3550  =item Lvalue subroutines
3551  
3552  =item Weak references
3553  
3554  =item The pseudo-hash data type
3555  
3556  =item The Compiler suite
3557  
3558  =item Internal implementation of file globbing
3559  
3560  =item The DB module
3561  
3562  =item The regular expression code constructs: 
3563  
3564  C<(?{ code })> and C<(??{ code })>
3565  
3566  =back
3567  
3568  =head1 Obsolete Diagnostics
3569  
3570  =over 4
3571  
3572  =item Character class syntax [: :] is reserved for future extensions
3573  
3574  (W) Within regular expression character classes ([]) the syntax beginning
3575  with "[:" and ending with ":]" is reserved for future extensions.
3576  If you need to represent those character sequences inside a regular
3577  expression character class, just quote the square brackets with the
3578  backslash: "\[:" and ":\]".
3579  
3580  =item Ill-formed logical name |%s| in prime_env_iter
3581  
3582  (W) A warning peculiar to VMS.  A logical name was encountered when preparing
3583  to iterate over %ENV which violates the syntactic rules governing logical
3584  names.  Because it cannot be translated normally, it is skipped, and will not
3585  appear in %ENV.  This may be a benign occurrence, as some software packages
3586  might directly modify logical name tables and introduce nonstandard names,
3587  or it may indicate that a logical name table has been corrupted.
3588  
3589  =item In string, @%s now must be written as \@%s
3590  
3591  The description of this error used to say:
3592  
3593          (Someday it will simply assume that an unbackslashed @
3594           interpolates an array.)
3595  
3596  That day has come, and this fatal error has been removed.  It has been
3597  replaced by a non-fatal warning instead.
3598  See L</Arrays now always interpolate into double-quoted strings> for
3599  details.
3600  
3601  =item Probable precedence problem on %s
3602  
3603  (W) The compiler found a bareword where it expected a conditional,
3604  which often indicates that an || or && was parsed as part of the
3605  last argument of the previous construct, for example:
3606  
3607      open FOO || die;
3608  
3609  =item regexp too big
3610  
3611  (F) The current implementation of regular expressions uses shorts as
3612  address offsets within a string.  Unfortunately this means that if
3613  the regular expression compiles to longer than 32767, it'll blow up.
3614  Usually when you want a regular expression this big, there is a better
3615  way to do it with multiple statements.  See L<perlre>.
3616  
3617  =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
3618  
3619  (D) Perl versions before 5.004 misinterpreted any type marker followed
3620  by "$" and a digit.  For example, "$$0" was incorrectly taken to mean
3621  "${$}0" instead of "${$0}".  This bug is (mostly) fixed in Perl 5.004.
3622  
3623  However, the developers of Perl 5.004 could not fix this bug completely,
3624  because at least two widely-used modules depend on the old meaning of
3625  "$$0" in a string.  So Perl 5.004 still interprets "$$<digit>" in the
3626  old (broken) way inside strings; but it generates this message as a
3627  warning.  And in Perl 5.005, this special treatment will cease.
3628  
3629  =back
3630  
3631  =head1 Reporting Bugs
3632  
3633  If you find what you think is a bug, you might check the
3634  articles recently posted to the comp.lang.perl.misc newsgroup.
3635  There may also be information at http://www.perl.com/ , the Perl
3636  Home Page.
3637  
3638  If you believe you have an unreported bug, please run the B<perlbug>
3639  program included with your release.  Be sure to trim your bug down
3640  to a tiny but sufficient test case.  Your bug report, along with the
3641  output of C<perl -V>, will be sent off to perlbug@perl.org to be
3642  analysed by the Perl porting team.
3643  
3644  =head1 SEE ALSO
3645  
3646  The F<Changes> file for exhaustive details on what changed.
3647  
3648  The F<INSTALL> file for how to build Perl.
3649  
3650  The F<README> file for general stuff.
3651  
3652  The F<Artistic> and F<Copying> files for copyright information.
3653  
3654  =head1 HISTORY
3655  
3656  Written by Gurusamy Sarathy <F<gsar@ActiveState.com>>, with many
3657  contributions from The Perl Porters.
3658  
3659  Send omissions or corrections to <F<perlbug@perl.org>>.
3660  
3661  =cut