1=head1 NAME 2 3perl56delta - what's new for perl v5.6.0 4 5=head1 DESCRIPTION 6 7This document describes differences between the 5.005 release and the 5.6.0 8release. 9 10=head1 Core Enhancements 11 12=head2 Interpreter cloning, threads, and concurrency 13 14Perl 5.6.0 introduces the beginnings of support for running multiple 15interpreters concurrently in different threads. In conjunction with 16the perl_clone() API call, which can be used to selectively duplicate 17the state of any given interpreter, it is possible to compile a 18piece of code once in an interpreter, clone that interpreter 19one or more times, and run all the resulting interpreters in distinct 20threads. 21 22On the Windows platform, this feature is used to emulate fork() at the 23interpreter level. See L<perlfork> for details about that. 24 25This feature is still in evolution. It is eventually meant to be used 26to selectively clone a subroutine and data reachable from that 27subroutine in a separate interpreter and run the cloned subroutine 28in a separate thread. Since there is no shared data between the 29interpreters, little or no locking will be needed (unless parts of 30the symbol table are explicitly shared). This is obviously intended 31to be an easy-to-use replacement for the existing threads support. 32 33Support for cloning interpreters and interpreter concurrency can be 34enabled using the -Dusethreads Configure option (see win32/Makefile for 35how to enable it on Windows.) The resulting perl executable will be 36functionally identical to one that was built with -Dmultiplicity, but 37the perl_clone() API call will only be available in the former. 38 39-Dusethreads enables the cpp macro USE_ITHREADS by default, which in turn 40enables Perl source code changes that provide a clear separation between 41the op tree and the data it operates with. The former is immutable, and 42can therefore be shared between an interpreter and all of its clones, 43while the latter is considered local to each interpreter, and is therefore 44copied for each clone. 45 46Note that building Perl with the -Dusemultiplicity Configure option 47is adequate if you wish to run multiple B<independent> interpreters 48concurrently in different threads. -Dusethreads only provides the 49additional functionality of the perl_clone() API call and other 50support for running B<cloned> interpreters concurrently. 51 52 NOTE: This is an experimental feature. Implementation details are 53 subject to change. 54 55=head2 Lexically scoped warning categories 56 57You can now control the granularity of warnings emitted by perl at a finer 58level using the C<use warnings> pragma. L<warnings> and L<perllexwarn> 59have copious documentation on this feature. 60 61=head2 Unicode and UTF-8 support 62 63Perl now uses UTF-8 as its internal representation for character 64strings. The C<utf8> and C<bytes> pragmas are used to control this support 65in the current lexical scope. See L<perlunicode>, L<utf8> and L<bytes> for 66more information. 67 68This feature is expected to evolve quickly to support some form of I/O 69disciplines that can be used to specify the kind of input and output data 70(bytes or characters). Until that happens, additional modules from CPAN 71will be needed to complete the toolkit for dealing with Unicode. 72 73 NOTE: This should be considered an experimental feature. Implementation 74 details are subject to change. 75 76=head2 Support for interpolating named characters 77 78The new C<\N> escape interpolates named characters within strings. 79For example, C<"Hi! \N{WHITE SMILING FACE}"> evaluates to a string 80with a unicode smiley face at the end. 81 82=head2 "our" declarations 83 84An "our" declaration introduces a value that can be best understood 85as a lexically scoped symbolic alias to a global variable in the 86package that was current where the variable was declared. This is 87mostly useful as an alternative to the C<vars> pragma, but also provides 88the opportunity to introduce typing and other attributes for such 89variables. See L<perlfunc/our>. 90 91=head2 Support for strings represented as a vector of ordinals 92 93Literals of the form C<v1.2.3.4> are now parsed as a string composed 94of characters with the specified ordinals. This is an alternative, more 95readable way to construct (possibly unicode) strings instead of 96interpolating characters, as in C<"\x{1}\x{2}\x{3}\x{4}">. The leading 97C<v> may be omitted if there are more than two ordinals, so C<1.2.3> is 98parsed the same as C<v1.2.3>. 99 100Strings written in this form are also useful to represent version "numbers". 101It is easy to compare such version "numbers" (which are really just plain 102strings) using any of the usual string comparison operators C<eq>, C<ne>, 103C<lt>, C<gt>, etc., or perform bitwise string operations on them using C<|>, 104C<&>, etc. 105 106In conjunction with the new C<$^V> magic variable (which contains 107the perl version as a string), such literals can be used as a readable way 108to check if you're running a particular version of Perl: 109 110 # this will parse in older versions of Perl also 111 if ($^V and $^V gt v5.6.0) { 112 # new features supported 113 } 114 115C<require> and C<use> also have some special magic to support such 116literals, but this particular usage should be avoided because it leads to 117misleading error messages under versions of Perl which don't support vector 118strings. Using a true version number will ensure correct behavior in all 119versions of Perl: 120 121 require 5.006; # run time check for v5.6 122 use 5.006_001; # compile time check for v5.6.1 123 124Also, C<sprintf> and C<printf> support the Perl-specific format flag C<%v> 125to print ordinals of characters in arbitrary strings: 126 127 printf "v%vd", $^V; # prints current version, such as "v5.5.650" 128 printf "%*vX", ":", $addr; # formats IPv6 address 129 printf "%*vb", " ", $bits; # displays bitstring 130 131See L<perldata/"Scalar value constructors"> for additional information. 132 133=head2 Improved Perl version numbering system 134 135Beginning with Perl version 5.6.0, the version number convention has been 136changed to a "dotted integer" scheme that is more commonly found in open 137source projects. 138 139Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc. 140The next development series following v5.6.0 will be numbered v5.7.x, 141beginning with v5.7.0, and the next major production release following 142v5.6.0 will be v5.8.0. 143 144The English module now sets $PERL_VERSION to $^V (a string value) rather 145than C<$]> (a numeric value). (This is a potential incompatibility. 146Send us a report via perlbug if you are affected by this.) 147 148The v1.2.3 syntax is also now legal in Perl. 149See L<Support for strings represented as a vector of ordinals> for more on that. 150 151To cope with the new versioning system's use of at least three significant 152digits for each version component, the method used for incrementing the 153subversion number has also changed slightly. We assume that versions older 154than v5.6.0 have been incrementing the subversion component in multiples of 15510. Versions after v5.6.0 will increment them by 1. Thus, using the new 156notation, 5.005_03 is the "same" as v5.5.30, and the first maintenance 157version following v5.6.0 will be v5.6.1 (which should be read as being 158equivalent to a floating point value of 5.006_001 in the older format, 159stored in C<$]>). 160 161=head2 New syntax for declaring subroutine attributes 162 163Formerly, if you wanted to mark a subroutine as being a method call or 164as requiring an automatic lock() when it is entered, you had to declare 165that with a C<use attrs> pragma in the body of the subroutine. 166That can now be accomplished with declaration syntax, like this: 167 168 sub mymethod : locked method ; 169 ... 170 sub mymethod : locked method { 171 ... 172 } 173 174 sub othermethod :locked :method ; 175 ... 176 sub othermethod :locked :method { 177 ... 178 } 179 180 181(Note how only the first C<:> is mandatory, and whitespace surrounding 182the C<:> is optional.) 183 184F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes 185with the stubs they provide. See L<attributes>. 186 187=head2 File and directory handles can be autovivified 188 189Similar to how constructs such as C<< $x->[0] >> autovivify a reference, 190handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(), 191socket(), and accept()) now autovivify a file or directory handle 192if the handle passed to them is an uninitialized scalar variable. This 193allows the constructs such as C<open(my $fh, ...)> and C<open(local $fh,...)> 194to be used to create filehandles that will conveniently be closed 195automatically when the scope ends, provided there are no other references 196to them. This largely eliminates the need for typeglobs when opening 197filehandles that must be passed around, as in the following example: 198 199 sub myopen { 200 open my $fh, "@_" 201 or die "Can't open '@_': $!"; 202 return $fh; 203 } 204 205 { 206 my $f = myopen("</etc/motd"); 207 print <$f>; 208 # $f implicitly closed here 209 } 210 211=head2 open() with more than two arguments 212 213If open() is passed three arguments instead of two, the second argument 214is used as the mode and the third argument is taken to be the file name. 215This is primarily useful for protecting against unintended magic behavior 216of the traditional two-argument form. See L<perlfunc/open>. 217 218=head2 64-bit support 219 220Any platform that has 64-bit integers either 221 222 (1) natively as longs or ints 223 (2) via special compiler flags 224 (3) using long long or int64_t 225 226is able to use "quads" (64-bit integers) as follows: 227 228=over 4 229 230=item * 231 232constants (decimal, hexadecimal, octal, binary) in the code 233 234=item * 235 236arguments to oct() and hex() 237 238=item * 239 240arguments to print(), printf() and sprintf() (flag prefixes ll, L, q) 241 242=item * 243 244printed as such 245 246=item * 247 248pack() and unpack() "q" and "Q" formats 249 250=item * 251 252in basic arithmetics: + - * / % (NOTE: operating close to the limits 253of the integer values may produce surprising results) 254 255=item * 256 257in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced 258to be 32 bits wide but now operate on the full native width.) 259 260=item * 261 262vec() 263 264=back 265 266Note that unless you have the case (a) you will have to configure 267and compile Perl using the -Duse64bitint Configure flag. 268 269 NOTE: The Configure flags -Duselonglong and -Duse64bits have been 270 deprecated. Use -Duse64bitint instead. 271 272There are actually two modes of 64-bitness: the first one is achieved 273using Configure -Duse64bitint and the second one using Configure 274-Duse64bitall. The difference is that the first one is minimal and 275the second one maximal. The first works in more places than the second. 276 277The C<use64bitint> does only as much as is required to get 64-bit 278integers into Perl (this may mean, for example, using "long longs") 279while your memory may still be limited to 2 gigabytes (because your 280pointers could still be 32-bit). Note that the name C<64bitint> does 281not imply that your C compiler will be using 64-bit C<int>s (it might, 282but it doesn't have to): the C<use64bitint> means that you will be 283able to have 64 bits wide scalar values. 284 285The C<use64bitall> goes all the way by attempting to switch also 286integers (if it can), longs (and pointers) to being 64-bit. This may 287create an even more binary incompatible Perl than -Duse64bitint: the 288resulting executable may not run at all in a 32-bit box, or you may 289have to reboot/reconfigure/rebuild your operating system to be 64-bit 290aware. 291 292Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint 293nor -Duse64bitall. 294 295Last but not least: note that due to Perl's habit of always using 296floating point numbers, the quads are still not true integers. 297When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned, 298-9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they 299are silently promoted to floating point numbers, after which they will 300start losing precision (in their lower digits). 301 302 NOTE: 64-bit support is still experimental on most platforms. 303 Existing support only covers the LP64 data model. In particular, the 304 LLP64 data model is not yet supported. 64-bit libraries and system 305 APIs on many platforms have not stabilized--your mileage may vary. 306 307=head2 Large file support 308 309If you have filesystems that support "large files" (files larger than 3102 gigabytes), you may now also be able to create and access them from 311Perl. 312 313 NOTE: The default action is to enable large file support, if 314 available on the platform. 315 316If the large file support is on, and you have a Fcntl constant 317O_LARGEFILE, the O_LARGEFILE is automatically added to the flags 318of sysopen(). 319 320Beware that unless your filesystem also supports "sparse files" seeking 321to umpteen petabytes may be inadvisable. 322 323Note that in addition to requiring a proper file system to do large 324files you may also need to adjust your per-process (or your 325per-system, or per-process-group, or per-user-group) maximum filesize 326limits before running Perl scripts that try to handle large files, 327especially if you intend to write such files. 328 329Finally, in addition to your process/process group maximum filesize 330limits, you may have quota limits on your filesystems that stop you 331(your user id or your user group id) from using large files. 332 333Adjusting your process/user/group/file system/operating system limits 334is outside the scope of Perl core language. For process limits, you 335may try increasing the limits using your shell's limits/limit/ulimit 336command before running Perl. The BSD::Resource extension (not 337included with the standard Perl distribution) may also be of use, it 338offers the getrlimit/setrlimit interface that can be used to adjust 339process resource usage limits, including the maximum filesize limit. 340 341=head2 Long doubles 342 343In some systems you may be able to use long doubles to enhance the 344range and precision of your double precision floating point numbers 345(that is, Perl's numbers). Use Configure -Duselongdouble to enable 346this support (if it is available). 347 348=head2 "more bits" 349 350You can "Configure -Dusemorebits" to turn on both the 64-bit support 351and the long double support. 352 353=head2 Enhanced support for sort() subroutines 354 355Perl subroutines with a prototype of C<($$)>, and XSUBs in general, can 356now be used as sort subroutines. In either case, the two elements to 357be compared are passed as normal parameters in @_. See L<perlfunc/sort>. 358 359For unprototyped sort subroutines, the historical behavior of passing 360the elements to be compared as the global variables $a and $b remains 361unchanged. 362 363=head2 C<sort $coderef @foo> allowed 364 365sort() did not accept a subroutine reference as the comparison 366function in earlier versions. This is now permitted. 367 368=head2 File globbing implemented internally 369 370Perl now uses the File::Glob implementation of the glob() operator 371automatically. This avoids using an external csh process and the 372problems associated with it. 373 374 NOTE: This is currently an experimental feature. Interfaces and 375 implementation are subject to change. 376 377=head2 Support for CHECK blocks 378 379In addition to C<BEGIN>, C<INIT>, C<END>, C<DESTROY> and C<AUTOLOAD>, 380subroutines named C<CHECK> are now special. These are queued up during 381compilation and behave similar to END blocks, except they are called at 382the end of compilation rather than at the end of execution. They cannot 383be called directly. 384 385=head2 POSIX character class syntax [: :] supported 386 387For example to match alphabetic characters use /[[:alpha:]]/. 388See L<perlre> for details. 389 390=head2 Better pseudo-random number generator 391 392In 5.005_0x and earlier, perl's rand() function used the C library 393rand(3) function. As of 5.005_52, Configure tests for drand48(), 394random(), and rand() (in that order) and picks the first one it finds. 395 396These changes should result in better random numbers from rand(). 397 398=head2 Improved C<qw//> operator 399 400The C<qw//> operator is now evaluated at compile time into a true list 401instead of being replaced with a run time call to C<split()>. This 402removes the confusing misbehaviour of C<qw//> in scalar context, which 403had inherited that behaviour from split(). 404 405Thus: 406 407 $foo = ($bar) = qw(a b c); print "$foo|$bar\n"; 408 409now correctly prints "3|a", instead of "2|a". 410 411=head2 Better worst-case behavior of hashes 412 413Small changes in the hashing algorithm have been implemented in 414order to improve the distribution of lower order bits in the 415hashed value. This is expected to yield better performance on 416keys that are repeated sequences. 417 418=head2 pack() format 'Z' supported 419 420The new format type 'Z' is useful for packing and unpacking null-terminated 421strings. See L<perlfunc/"pack">. 422 423=head2 pack() format modifier '!' supported 424 425The new format type modifier '!' is useful for packing and unpacking 426native shorts, ints, and longs. See L<perlfunc/"pack">. 427 428=head2 pack() and unpack() support counted strings 429 430The template character '/' can be used to specify a counted string 431type to be packed or unpacked. See L<perlfunc/"pack">. 432 433=head2 Comments in pack() templates 434 435The '#' character in a template introduces a comment up to 436end of the line. This facilitates documentation of pack() 437templates. 438 439=head2 Weak references 440 441In previous versions of Perl, you couldn't cache objects so as 442to allow them to be deleted if the last reference from outside 443the cache is deleted. The reference in the cache would hold a 444reference count on the object and the objects would never be 445destroyed. 446 447Another familiar problem is with circular references. When an 448object references itself, its reference count would never go 449down to zero, and it would not get destroyed until the program 450is about to exit. 451 452Weak references solve this by allowing you to "weaken" any 453reference, that is, make it not count towards the reference count. 454When the last non-weak reference to an object is deleted, the object 455is destroyed and all the weak references to the object are 456automatically undef-ed. 457 458To use this feature, you need the Devel::WeakRef package from CPAN, which 459contains additional documentation. 460 461 NOTE: This is an experimental feature. Details are subject to change. 462 463=head2 Binary numbers supported 464 465Binary numbers are now supported as literals, in s?printf formats, and 466C<oct()>: 467 468 $answer = 0b101010; 469 printf "The answer is: %b\n", oct("0b101010"); 470 471=head2 Lvalue subroutines 472 473Subroutines can now return modifiable lvalues. 474See L<perlsub/"Lvalue subroutines">. 475 476 NOTE: This is an experimental feature. Details are subject to change. 477 478=head2 Some arrows may be omitted in calls through references 479 480Perl now allows the arrow to be omitted in many constructs 481involving subroutine calls through references. For example, 482C<< $foo[10]->('foo') >> may now be written C<$foo[10]('foo')>. 483This is rather similar to how the arrow may be omitted from 484C<< $foo[10]->{'foo'} >>. Note however, that the arrow is still 485required for C<< foo(10)->('bar') >>. 486 487=head2 Boolean assignment operators are legal lvalues 488 489Constructs such as C<($a ||= 2) += 1> are now allowed. 490 491=head2 exists() is supported on subroutine names 492 493The exists() builtin now works on subroutine names. A subroutine 494is considered to exist if it has been declared (even if implicitly). 495See L<perlfunc/exists> for examples. 496 497=head2 exists() and delete() are supported on array elements 498 499The exists() and delete() builtins now work on simple arrays as well. 500The behavior is similar to that on hash elements. 501 502exists() can be used to check whether an array element has been 503initialized. This avoids autovivifying array elements that don't exist. 504If the array is tied, the EXISTS() method in the corresponding tied 505package will be invoked. 506 507delete() may be used to remove an element from the array and return 508it. The array element at that position returns to its uninitialized 509state, so that testing for the same element with exists() will return 510false. If the element happens to be the one at the end, the size of 511the array also shrinks up to the highest element that tests true for 512exists(), or 0 if none such is found. If the array is tied, the DELETE() 513method in the corresponding tied package will be invoked. 514 515See L<perlfunc/exists> and L<perlfunc/delete> for examples. 516 517=head2 Pseudo-hashes work better 518 519Dereferencing some types of reference values in a pseudo-hash, 520such as C<< $ph->{foo}[1] >>, was accidentally disallowed. This has 521been corrected. 522 523When applied to a pseudo-hash element, exists() now reports whether 524the specified value exists, not merely if the key is valid. 525 526delete() now works on pseudo-hashes. When given a pseudo-hash element 527or slice it deletes the values corresponding to the keys (but not the keys 528themselves). See L<perlref/"Pseudo-hashes: Using an array as a hash">. 529 530Pseudo-hash slices with constant keys are now optimized to array lookups 531at compile-time. 532 533List assignments to pseudo-hash slices are now supported. 534 535The C<fields> pragma now provides ways to create pseudo-hashes, via 536fields::new() and fields::phash(). See L<fields>. 537 538 NOTE: The pseudo-hash data type continues to be experimental. 539 Limiting oneself to the interface elements provided by the 540 fields pragma will provide protection from any future changes. 541 542=head2 Automatic flushing of output buffers 543 544fork(), exec(), system(), qx//, and pipe open()s now flush buffers 545of all files opened for output when the operation was attempted. This 546mostly eliminates confusing buffering mishaps suffered by users unaware 547of how Perl internally handles I/O. 548 549This is not supported on some platforms like Solaris where a suitably 550correct implementation of fflush(NULL) isn't available. 551 552=head2 Better diagnostics on meaningless filehandle operations 553 554Constructs such as C<< open(<FH>) >> and C<< close(<FH>) >> 555are compile time errors. Attempting to read from filehandles that 556were opened only for writing will now produce warnings (just as 557writing to read-only filehandles does). 558 559=head2 Where possible, buffered data discarded from duped input filehandle 560 561C<< open(NEW, "<&OLD") >> now attempts to discard any data that 562was previously read and buffered in C<OLD> before duping the handle. 563On platforms where doing this is allowed, the next read operation 564on C<NEW> will return the same data as the corresponding operation 565on C<OLD>. Formerly, it would have returned the data from the start 566of the following disk block instead. 567 568=head2 eof() has the same old magic as <> 569 570C<eof()> would return true if no attempt to read from C<< <> >> had 571yet been made. C<eof()> has been changed to have a little magic of its 572own, it now opens the C<< <> >> files. 573 574=head2 binmode() can be used to set :crlf and :raw modes 575 576binmode() now accepts a second argument that specifies a discipline 577for the handle in question. The two pseudo-disciplines ":raw" and 578":crlf" are currently supported on DOS-derivative platforms. 579See L<perlfunc/"binmode"> and L<open>. 580 581=head2 C<-T> filetest recognizes UTF-8 encoded files as "text" 582 583The algorithm used for the C<-T> filetest has been enhanced to 584correctly identify UTF-8 content as "text". 585 586=head2 system(), backticks and pipe open now reflect exec() failure 587 588On Unix and similar platforms, system(), qx() and open(FOO, "cmd |") 589etc., are implemented via fork() and exec(). When the underlying 590exec() fails, earlier versions did not report the error properly, 591since the exec() happened to be in a different process. 592 593The child process now communicates with the parent about the 594error in launching the external command, which allows these 595constructs to return with their usual error value and set $!. 596 597=head2 Improved diagnostics 598 599Line numbers are no longer suppressed (under most likely circumstances) 600during the global destruction phase. 601 602Diagnostics emitted from code running in threads other than the main 603thread are now accompanied by the thread ID. 604 605Embedded null characters in diagnostics now actually show up. They 606used to truncate the message in prior versions. 607 608$foo::a and $foo::b are now exempt from "possible typo" warnings only 609if sort() is encountered in package C<foo>. 610 611Unrecognized alphabetic escapes encountered when parsing quote 612constructs now generate a warning, since they may take on new 613semantics in later versions of Perl. 614 615Many diagnostics now report the internal operation in which the warning 616was provoked, like so: 617 618 Use of uninitialized value in concatenation (.) at (eval 1) line 1. 619 Use of uninitialized value in print at (eval 1) line 1. 620 621Diagnostics that occur within eval may also report the file and line 622number where the eval is located, in addition to the eval sequence 623number and the line number within the evaluated text itself. For 624example: 625 626 Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF 627 628=head2 Diagnostics follow STDERR 629 630Diagnostic output now goes to whichever file the C<STDERR> handle 631is pointing at, instead of always going to the underlying C runtime 632library's C<stderr>. 633 634=head2 More consistent close-on-exec behavior 635 636On systems that support a close-on-exec flag on filehandles, the 637flag is now set for any handles created by pipe(), socketpair(), 638socket(), and accept(), if that is warranted by the value of $^F 639that may be in effect. Earlier versions neglected to set the flag 640for handles created with these operators. See L<perlfunc/pipe>, 641L<perlfunc/socketpair>, L<perlfunc/socket>, L<perlfunc/accept>, 642and L<perlvar/$^F>. 643 644=head2 syswrite() ease-of-use 645 646The length argument of C<syswrite()> has become optional. 647 648=head2 Better syntax checks on parenthesized unary operators 649 650Expressions such as: 651 652 print defined(&foo,&bar,&baz); 653 print uc("foo","bar","baz"); 654 undef($foo,&bar); 655 656used to be accidentally allowed in earlier versions, and produced 657unpredictable behaviour. Some produced ancillary warnings 658when used in this way; others silently did the wrong thing. 659 660The parenthesized forms of most unary operators that expect a single 661argument now ensure that they are not called with more than one 662argument, making the cases shown above syntax errors. The usual 663behaviour of: 664 665 print defined &foo, &bar, &baz; 666 print uc "foo", "bar", "baz"; 667 undef $foo, &bar; 668 669remains unchanged. See L<perlop>. 670 671=head2 Bit operators support full native integer width 672 673The bit operators (& | ^ ~ << >>) now operate on the full native 674integral width (the exact size of which is available in $Config{ivsize}). 675For example, if your platform is either natively 64-bit or if Perl 676has been configured to use 64-bit integers, these operations apply 677to 8 bytes (as opposed to 4 bytes on 32-bit platforms). 678For portability, be sure to mask off the excess bits in the result of 679unary C<~>, e.g., C<~$x & 0xffffffff>. 680 681=head2 Improved security features 682 683More potentially unsafe operations taint their results for improved 684security. 685 686The C<passwd> and C<shell> fields returned by the getpwent(), getpwnam(), 687and getpwuid() are now tainted, because the user can affect their own 688encrypted password and login shell. 689 690The variable modified by shmread(), and messages returned by msgrcv() 691(and its object-oriented interface IPC::SysV::Msg::rcv) are also tainted, 692because other untrusted processes can modify messages and shared memory 693segments for their own nefarious purposes. 694 695=head2 More functional bareword prototype (*) 696 697Bareword prototypes have been rationalized to enable them to be used 698to override builtins that accept barewords and interpret them in 699a special way, such as C<require> or C<do>. 700 701Arguments prototyped as C<*> will now be visible within the subroutine 702as either a simple scalar or as a reference to a typeglob. 703See L<perlsub/Prototypes>. 704 705=head2 C<require> and C<do> may be overridden 706 707C<require> and C<do 'file'> operations may be overridden locally 708by importing subroutines of the same name into the current package 709(or globally by importing them into the CORE::GLOBAL:: namespace). 710Overriding C<require> will also affect C<use>, provided the override 711is visible at compile-time. 712See L<perlsub/"Overriding Built-in Functions">. 713 714=head2 $^X variables may now have names longer than one character 715 716Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax 717error. Now variable names that begin with a control character may be 718arbitrarily long. However, for compatibility reasons, these variables 719I<must> be written with explicit braces, as C<${^XY}> for example. 720C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more 721than one control character, such as C<${^XY^Z}>, are illegal. 722 723The old syntax has not changed. As before, `^X' may be either a 724literal control-X character or the two-character sequence `caret' plus 725`X'. When braces are omitted, the variable name stops after the 726control character. Thus C<"$^XYZ"> continues to be synonymous with 727C<$^X . "YZ"> as before. 728 729As before, lexical variables may not have names beginning with control 730characters. As before, variables whose names begin with a control 731character are always forced to be in package `main'. All such variables 732are reserved for future extensions, except those that begin with 733C<^_>, which may be used by user programs and are guaranteed not to 734acquire special meaning in any future version of Perl. 735 736=head2 New variable $^C reflects C<-c> switch 737 738C<$^C> has a boolean value that reflects whether perl is being run 739in compile-only mode (i.e. via the C<-c> switch). Since 740BEGIN blocks are executed under such conditions, this variable 741enables perl code to determine whether actions that make sense 742only during normal running are warranted. See L<perlvar>. 743 744=head2 New variable $^V contains Perl version as a string 745 746C<$^V> contains the Perl version number as a string composed of 747characters whose ordinals match the version numbers, i.e. v5.6.0. 748This may be used in string comparisons. 749 750See C<Support for strings represented as a vector of ordinals> for an 751example. 752 753=head2 Optional Y2K warnings 754 755If Perl is built with the cpp macro C<PERL_Y2KWARN> defined, 756it emits optional warnings when concatenating the number 19 757with another number. 758 759This behavior must be specifically enabled when running Configure. 760See F<INSTALL> and F<README.Y2K>. 761 762=head2 Arrays now always interpolate into double-quoted strings 763 764In double-quoted strings, arrays now interpolate, no matter what. The 765behavior in earlier versions of perl 5 was that arrays would interpolate 766into strings if the array had been mentioned before the string was 767compiled, and otherwise Perl would raise a fatal compile-time error. 768In versions 5.000 through 5.003, the error was 769 770 Literal @example now requires backslash 771 772In versions 5.004_01 through 5.6.0, the error was 773 774 In string, @example now must be written as \@example 775 776The idea here was to get people into the habit of writing 777C<"fred\@example.com"> when they wanted a literal C<@> sign, just as 778they have always written C<"Give me back my \$5"> when they wanted a 779literal C<$> sign. 780 781Starting with 5.6.1, when Perl now sees an C<@> sign in a 782double-quoted string, it I<always> attempts to interpolate an array, 783regardless of whether or not the array has been used or declared 784already. The fatal error has been downgraded to an optional warning: 785 786 Possible unintended interpolation of @example in string 787 788This warns you that C<"fred@example.com"> is going to turn into 789C<fred.com> if you don't backslash the C<@>. 790See http://www.plover.com/~mjd/perl/at-error.html for more details 791about the history here. 792 793=head1 Modules and Pragmata 794 795=head2 Modules 796 797=over 4 798 799=item attributes 800 801While used internally by Perl as a pragma, this module also 802provides a way to fetch subroutine and variable attributes. 803See L<attributes>. 804 805=item B 806 807The Perl Compiler suite has been extensively reworked for this 808release. More of the standard Perl testsuite passes when run 809under the Compiler, but there is still a significant way to 810go to achieve production quality compiled executables. 811 812 NOTE: The Compiler suite remains highly experimental. The 813 generated code may not be correct, even when it manages to execute 814 without errors. 815 816=item Benchmark 817 818Overall, Benchmark results exhibit lower average error and better timing 819accuracy. 820 821You can now run tests for I<n> seconds instead of guessing the right 822number of tests to run: e.g., timethese(-5, ...) will run each 823code for at least 5 CPU seconds. Zero as the "number of repetitions" 824means "for at least 3 CPU seconds". The output format has also 825changed. For example: 826 827 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}}) 828 829will now output something like this: 830 831 Benchmark: running a, b, each for at least 5 CPU seconds... 832 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516) 833 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686) 834 835New features: "each for at least N CPU seconds...", "wallclock secs", 836and the "@ operations/CPU second (n=operations)". 837 838timethese() now returns a reference to a hash of Benchmark objects containing 839the test results, keyed on the names of the tests. 840 841timethis() now returns the iterations field in the Benchmark result object 842instead of 0. 843 844timethese(), timethis(), and the new cmpthese() (see below) can also take 845a format specifier of 'none' to suppress output. 846 847A new function countit() is just like timeit() except that it takes a 848TIME instead of a COUNT. 849 850A new function cmpthese() prints a chart comparing the results of each test 851returned from a timethese() call. For each possible pair of tests, the 852percentage speed difference (iters/sec or seconds/iter) is shown. 853 854For other details, see L<Benchmark>. 855 856=item ByteLoader 857 858The ByteLoader is a dedicated extension to generate and run 859Perl bytecode. See L<ByteLoader>. 860 861=item constant 862 863References can now be used. 864 865The new version also allows a leading underscore in constant names, but 866disallows a double leading underscore (as in "__LINE__"). Some other names 867are disallowed or warned against, including BEGIN, END, etc. Some names 868which were forced into main:: used to fail silently in some cases; now they're 869fatal (outside of main::) and an optional warning (inside of main::). 870The ability to detect whether a constant had been set with a given name has 871been added. 872 873See L<constant>. 874 875=item charnames 876 877This pragma implements the C<\N> string escape. See L<charnames>. 878 879=item Data::Dumper 880 881A C<Maxdepth> setting can be specified to avoid venturing 882too deeply into deep data structures. See L<Data::Dumper>. 883 884The XSUB implementation of Dump() is now automatically called if the 885C<Useqq> setting is not in use. 886 887Dumping C<qr//> objects works correctly. 888 889=item DB 890 891C<DB> is an experimental module that exposes a clean abstraction 892to Perl's debugging API. 893 894=item DB_File 895 896DB_File can now be built with Berkeley DB versions 1, 2 or 3. 897See C<ext/DB_File/Changes>. 898 899=item Devel::DProf 900 901Devel::DProf, a Perl source code profiler has been added. See 902L<Devel::DProf> and L<dprofpp>. 903 904=item Devel::Peek 905 906The Devel::Peek module provides access to the internal representation 907of Perl variables and data. It is a data debugging tool for the XS programmer. 908 909=item Dumpvalue 910 911The Dumpvalue module provides screen dumps of Perl data. 912 913=item DynaLoader 914 915DynaLoader now supports a dl_unload_file() function on platforms that 916support unloading shared objects using dlclose(). 917 918Perl can also optionally arrange to unload all extension shared objects 919loaded by Perl. To enable this, build Perl with the Configure option 920C<-Accflags=-DDL_UNLOAD_ALL_AT_EXIT>. (This maybe useful if you are 921using Apache with mod_perl.) 922 923=item English 924 925$PERL_VERSION now stands for C<$^V> (a string value) rather than for C<$]> 926(a numeric value). 927 928=item Env 929 930Env now supports accessing environment variables like PATH as array 931variables. 932 933=item Fcntl 934 935More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for 936large file (more than 4GB) access (NOTE: the O_LARGEFILE is 937automatically added to sysopen() flags if large file support has been 938configured, as is the default), Free/Net/OpenBSD locking behaviour 939flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined 940mask of O_RDONLY, O_WRONLY, and O_RDWR. The seek()/sysseek() 941constants SEEK_SET, SEEK_CUR, and SEEK_END are available via the 942C<:seek> tag. The chmod()/stat() S_IF* constants and S_IS* functions 943are available via the C<:mode> tag. 944 945=item File::Compare 946 947A compare_text() function has been added, which allows custom 948comparison functions. See L<File::Compare>. 949 950=item File::Find 951 952File::Find now works correctly when the wanted() function is either 953autoloaded or is a symbolic reference. 954 955A bug that caused File::Find to lose track of the working directory 956when pruning top-level directories has been fixed. 957 958File::Find now also supports several other options to control its 959behavior. It can follow symbolic links if the C<follow> option is 960specified. Enabling the C<no_chdir> option will make File::Find skip 961changing the current directory when walking directories. The C<untaint> 962flag can be useful when running with taint checks enabled. 963 964See L<File::Find>. 965 966=item File::Glob 967 968This extension implements BSD-style file globbing. By default, 969it will also be used for the internal implementation of the glob() 970operator. See L<File::Glob>. 971 972=item File::Spec 973 974New methods have been added to the File::Spec module: devnull() returns 975the name of the null device (/dev/null on Unix) and tmpdir() the name of 976the temp directory (normally /tmp on Unix). There are now also methods 977to convert between absolute and relative filenames: abs2rel() and 978rel2abs(). For compatibility with operating systems that specify volume 979names in file paths, the splitpath(), splitdir(), and catdir() methods 980have been added. 981 982=item File::Spec::Functions 983 984The new File::Spec::Functions modules provides a function interface 985to the File::Spec module. Allows shorthand 986 987 $fullname = catfile($dir1, $dir2, $file); 988 989instead of 990 991 $fullname = File::Spec->catfile($dir1, $dir2, $file); 992 993=item Getopt::Long 994 995Getopt::Long licensing has changed to allow the Perl Artistic License 996as well as the GPL. It used to be GPL only, which got in the way of 997non-GPL applications that wanted to use Getopt::Long. 998 999Getopt::Long encourages the use of Pod::Usage to produce help 1000messages. For example: 1001 1002 use Getopt::Long; 1003 use Pod::Usage; 1004 my $man = 0; 1005 my $help = 0; 1006 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2); 1007 pod2usage(1) if $help; 1008 pod2usage(-exitstatus => 0, -verbose => 2) if $man; 1009 1010 __END__ 1011 1012 =head1 NAME 1013 1014 sample - Using Getopt::Long and Pod::Usage 1015 1016 =head1 SYNOPSIS 1017 1018 sample [options] [file ...] 1019 1020 Options: 1021 -help brief help message 1022 -man full documentation 1023 1024 =head1 OPTIONS 1025 1026 =over 8 1027 1028 =item B<-help> 1029 1030 Print a brief help message and exits. 1031 1032 =item B<-man> 1033 1034 Prints the manual page and exits. 1035 1036 =back 1037 1038 =head1 DESCRIPTION 1039 1040 B<This program> will read the given input file(s) and do something 1041 useful with the contents thereof. 1042 1043 =cut 1044 1045See L<Pod::Usage> for details. 1046 1047A bug that prevented the non-option call-back <> from being 1048specified as the first argument has been fixed. 1049 1050To specify the characters < and > as option starters, use ><. Note, 1051however, that changing option starters is strongly deprecated. 1052 1053=item IO 1054 1055write() and syswrite() will now accept a single-argument 1056form of the call, for consistency with Perl's syswrite(). 1057 1058You can now create a TCP-based IO::Socket::INET without forcing 1059a connect attempt. This allows you to configure its options 1060(like making it non-blocking) and then call connect() manually. 1061 1062A bug that prevented the IO::Socket::protocol() accessor 1063from ever returning the correct value has been corrected. 1064 1065IO::Socket::connect now uses non-blocking IO instead of alarm() 1066to do connect timeouts. 1067 1068IO::Socket::accept now uses select() instead of alarm() for doing 1069timeouts. 1070 1071IO::Socket::INET->new now sets $! correctly on failure. $@ is 1072still set for backwards compatibility. 1073 1074=item JPL 1075 1076Java Perl Lingo is now distributed with Perl. See jpl/README 1077for more information. 1078 1079=item lib 1080 1081C<use lib> now weeds out any trailing duplicate entries. 1082C<no lib> removes all named entries. 1083 1084=item Math::BigInt 1085 1086The bitwise operations C<<< << >>>, C<<< >> >>>, C<&>, C<|>, 1087and C<~> are now supported on bigints. 1088 1089=item Math::Complex 1090 1091The accessor methods Re, Im, arg, abs, rho, and theta can now also 1092act as mutators (accessor $z->Re(), mutator $z->Re(3)). 1093 1094The class method C<display_format> and the corresponding object method 1095C<display_format>, in addition to accepting just one argument, now can 1096also accept a parameter hash. Recognized keys of a parameter hash are 1097C<"style">, which corresponds to the old one parameter case, and two 1098new parameters: C<"format">, which is a printf()-style format string 1099(defaults usually to C<"%.15g">, you can revert to the default by 1100setting the format string to C<undef>) used for both parts of a 1101complex number, and C<"polar_pretty_print"> (defaults to true), 1102which controls whether an attempt is made to try to recognize small 1103multiples and rationals of pi (2pi, pi/2) at the argument (angle) of a 1104polar complex number. 1105 1106The potentially disruptive change is that in list context both methods 1107now I<return the parameter hash>, instead of only the value of the 1108C<"style"> parameter. 1109 1110=item Math::Trig 1111 1112A little bit of radial trigonometry (cylindrical and spherical), 1113radial coordinate conversions, and the great circle distance were added. 1114 1115=item Pod::Parser, Pod::InputObjects 1116 1117Pod::Parser is a base class for parsing and selecting sections of 1118pod documentation from an input stream. This module takes care of 1119identifying pod paragraphs and commands in the input and hands off the 1120parsed paragraphs and commands to user-defined methods which are free 1121to interpret or translate them as they see fit. 1122 1123Pod::InputObjects defines some input objects needed by Pod::Parser, and 1124for advanced users of Pod::Parser that need more about a command besides 1125its name and text. 1126 1127As of release 5.6.0 of Perl, Pod::Parser is now the officially sanctioned 1128"base parser code" recommended for use by all pod2xxx translators. 1129Pod::Text (pod2text) and Pod::Man (pod2man) have already been converted 1130to use Pod::Parser and efforts to convert Pod::HTML (pod2html) are already 1131underway. For any questions or comments about pod parsing and translating 1132issues and utilities, please use the pod-people@perl.org mailing list. 1133 1134For further information, please see L<Pod::Parser> and L<Pod::InputObjects>. 1135 1136=item Pod::Checker, podchecker 1137 1138This utility checks pod files for correct syntax, according to 1139L<perlpod>. Obvious errors are flagged as such, while warnings are 1140printed for mistakes that can be handled gracefully. The checklist is 1141not complete yet. See L<Pod::Checker>. 1142 1143=item Pod::ParseUtils, Pod::Find 1144 1145These modules provide a set of gizmos that are useful mainly for pod 1146translators. L<Pod::Find|Pod::Find> traverses directory structures and 1147returns found pod files, along with their canonical names (like 1148C<File::Spec::Unix>). L<Pod::ParseUtils|Pod::ParseUtils> contains 1149B<Pod::List> (useful for storing pod list information), B<Pod::Hyperlink> 1150(for parsing the contents of C<LE<lt>E<gt>> sequences) and B<Pod::Cache> 1151(for caching information about pod files, e.g., link nodes). 1152 1153=item Pod::Select, podselect 1154 1155Pod::Select is a subclass of Pod::Parser which provides a function 1156named "podselect()" to filter out user-specified sections of raw pod 1157documentation from an input stream. podselect is a script that provides 1158access to Pod::Select from other scripts to be used as a filter. 1159See L<Pod::Select>. 1160 1161=item Pod::Usage, pod2usage 1162 1163Pod::Usage provides the function "pod2usage()" to print usage messages for 1164a Perl script based on its embedded pod documentation. The pod2usage() 1165function is generally useful to all script authors since it lets them 1166write and maintain a single source (the pods) for documentation, thus 1167removing the need to create and maintain redundant usage message text 1168consisting of information already in the pods. 1169 1170There is also a pod2usage script which can be used from other kinds of 1171scripts to print usage messages from pods (even for non-Perl scripts 1172with pods embedded in comments). 1173 1174For details and examples, please see L<Pod::Usage>. 1175 1176=item Pod::Text and Pod::Man 1177 1178Pod::Text has been rewritten to use Pod::Parser. While pod2text() is 1179still available for backwards compatibility, the module now has a new 1180preferred interface. See L<Pod::Text> for the details. The new Pod::Text 1181module is easily subclassed for tweaks to the output, and two such 1182subclasses (Pod::Text::Termcap for man-page-style bold and underlining 1183using termcap information, and Pod::Text::Color for markup with ANSI color 1184sequences) are now standard. 1185 1186pod2man has been turned into a module, Pod::Man, which also uses 1187Pod::Parser. In the process, several outstanding bugs related to quotes 1188in section headers, quoting of code escapes, and nested lists have been 1189fixed. pod2man is now a wrapper script around this module. 1190 1191=item SDBM_File 1192 1193An EXISTS method has been added to this module (and sdbm_exists() has 1194been added to the underlying sdbm library), so one can now call exists 1195on an SDBM_File tied hash and get the correct result, rather than a 1196runtime error. 1197 1198A bug that may have caused data loss when more than one disk block 1199happens to be read from the database in a single FETCH() has been 1200fixed. 1201 1202=item Sys::Syslog 1203 1204Sys::Syslog now uses XSUBs to access facilities from syslog.h so it 1205no longer requires syslog.ph to exist. 1206 1207=item Sys::Hostname 1208 1209Sys::Hostname now uses XSUBs to call the C library's gethostname() or 1210uname() if they exist. 1211 1212=item Term::ANSIColor 1213 1214Term::ANSIColor is a very simple module to provide easy and readable 1215access to the ANSI color and highlighting escape sequences, supported by 1216most ANSI terminal emulators. It is now included standard. 1217 1218=item Time::Local 1219 1220The timelocal() and timegm() functions used to silently return bogus 1221results when the date fell outside the machine's integer range. They 1222now consistently croak() if the date falls in an unsupported range. 1223 1224=item Win32 1225 1226The error return value in list context has been changed for all functions 1227that return a list of values. Previously these functions returned a list 1228with a single element C<undef> if an error occurred. Now these functions 1229return the empty list in these situations. This applies to the following 1230functions: 1231 1232 Win32::FsType 1233 Win32::GetOSVersion 1234 1235The remaining functions are unchanged and continue to return C<undef> on 1236error even in list context. 1237 1238The Win32::SetLastError(ERROR) function has been added as a complement 1239to the Win32::GetLastError() function. 1240 1241The new Win32::GetFullPathName(FILENAME) returns the full absolute 1242pathname for FILENAME in scalar context. In list context it returns 1243a two-element list containing the fully qualified directory name and 1244the filename. See L<Win32>. 1245 1246=item XSLoader 1247 1248The XSLoader extension is a simpler alternative to DynaLoader. 1249See L<XSLoader>. 1250 1251=item DBM Filters 1252 1253A new feature called "DBM Filters" has been added to all the 1254DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File. 1255DBM Filters add four new methods to each DBM module: 1256 1257 filter_store_key 1258 filter_store_value 1259 filter_fetch_key 1260 filter_fetch_value 1261 1262These can be used to filter key-value pairs before the pairs are 1263written to the database or just after they are read from the database. 1264See L<perldbmfilter> for further information. 1265 1266=back 1267 1268=head2 Pragmata 1269 1270C<use attrs> is now obsolete, and is only provided for 1271backward-compatibility. It's been replaced by the C<sub : attributes> 1272syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>. 1273 1274Lexical warnings pragma, C<use warnings;>, to control optional warnings. 1275See L<perllexwarn>. 1276 1277C<use filetest> to control the behaviour of filetests (C<-r> C<-w> 1278...). Currently only one subpragma implemented, "use filetest 1279'access';", that uses access(2) or equivalent to check permissions 1280instead of using stat(2) as usual. This matters in filesystems 1281where there are ACLs (access control lists): the stat(2) might lie, 1282but access(2) knows better. 1283 1284The C<open> pragma can be used to specify default disciplines for 1285handle constructors (e.g. open()) and for qx//. The two 1286pseudo-disciplines C<:raw> and C<:crlf> are currently supported on 1287DOS-derivative platforms (i.e. where binmode is not a no-op). 1288See also L</"binmode() can be used to set :crlf and :raw modes">. 1289 1290=head1 Utility Changes 1291 1292=head2 dprofpp 1293 1294C<dprofpp> is used to display profile data generated using C<Devel::DProf>. 1295See L<dprofpp>. 1296 1297=head2 find2perl 1298 1299The C<find2perl> utility now uses the enhanced features of the File::Find 1300module. The -depth and -follow options are supported. Pod documentation 1301is also included in the script. 1302 1303=head2 h2xs 1304 1305The C<h2xs> tool can now work in conjunction with C<C::Scan> (available 1306from CPAN) to automatically parse real-life header files. The C<-M>, 1307C<-a>, C<-k>, and C<-o> options are new. 1308 1309=head2 perlcc 1310 1311C<perlcc> now supports the C and Bytecode backends. By default, 1312it generates output from the simple C backend rather than the 1313optimized C backend. 1314 1315Support for non-Unix platforms has been improved. 1316 1317=head2 perldoc 1318 1319C<perldoc> has been reworked to avoid possible security holes. 1320It will not by default let itself be run as the superuser, but you 1321may still use the B<-U> switch to try to make it drop privileges 1322first. 1323 1324=head2 The Perl Debugger 1325 1326Many bug fixes and enhancements were added to F<perl5db.pl>, the 1327Perl debugger. The help documentation was rearranged. New commands 1328include C<< < ? >>, C<< > ? >>, and C<< { ? >> to list out current 1329actions, C<man I<docpage>> to run your doc viewer on some perl 1330docset, and support for quoted options. The help information was 1331rearranged, and should be viewable once again if you're using B<less> 1332as your pager. A serious security hole was plugged--you should 1333immediately remove all older versions of the Perl debugger as 1334installed in previous releases, all the way back to perl3, from 1335your system to avoid being bitten by this. 1336 1337=head1 Improved Documentation 1338 1339Many of the platform-specific README files are now part of the perl 1340installation. See L<perl> for the complete list. 1341 1342=over 4 1343 1344=item perlapi.pod 1345 1346The official list of public Perl API functions. 1347 1348=item perlboot.pod 1349 1350A tutorial for beginners on object-oriented Perl. 1351 1352=item perlcompile.pod 1353 1354An introduction to using the Perl Compiler suite. 1355 1356=item perldbmfilter.pod 1357 1358A howto document on using the DBM filter facility. 1359 1360=item perldebug.pod 1361 1362All material unrelated to running the Perl debugger, plus all 1363low-level guts-like details that risked crushing the casual user 1364of the debugger, have been relocated from the old manpage to the 1365next entry below. 1366 1367=item perldebguts.pod 1368 1369This new manpage contains excessively low-level material not related 1370to the Perl debugger, but slightly related to debugging Perl itself. 1371It also contains some arcane internal details of how the debugging 1372process works that may only be of interest to developers of Perl 1373debuggers. 1374 1375=item perlfork.pod 1376 1377Notes on the fork() emulation currently available for the Windows platform. 1378 1379=item perlfilter.pod 1380 1381An introduction to writing Perl source filters. 1382 1383=item perlhack.pod 1384 1385Some guidelines for hacking the Perl source code. 1386 1387=item perlintern.pod 1388 1389A list of internal functions in the Perl source code. 1390(List is currently empty.) 1391 1392=item perllexwarn.pod 1393 1394Introduction and reference information about lexically scoped 1395warning categories. 1396 1397=item perlnumber.pod 1398 1399Detailed information about numbers as they are represented in Perl. 1400 1401=item perlopentut.pod 1402 1403A tutorial on using open() effectively. 1404 1405=item perlreftut.pod 1406 1407A tutorial that introduces the essentials of references. 1408 1409=item perltootc.pod 1410 1411A tutorial on managing class data for object modules. 1412 1413=item perltodo.pod 1414 1415Discussion of the most often wanted features that may someday be 1416supported in Perl. 1417 1418=item perlunicode.pod 1419 1420An introduction to Unicode support features in Perl. 1421 1422=back 1423 1424=head1 Performance enhancements 1425 1426=head2 Simple sort() using { $a <=> $b } and the like are optimized 1427 1428Many common sort() operations using a simple inlined block are now 1429optimized for faster performance. 1430 1431=head2 Optimized assignments to lexical variables 1432 1433Certain operations in the RHS of assignment statements have been 1434optimized to directly set the lexical variable on the LHS, 1435eliminating redundant copying overheads. 1436 1437=head2 Faster subroutine calls 1438 1439Minor changes in how subroutine calls are handled internally 1440provide marginal improvements in performance. 1441 1442=head2 delete(), each(), values() and hash iteration are faster 1443 1444The hash values returned by delete(), each(), values() and hashes in a 1445list context are the actual values in the hash, instead of copies. 1446This results in significantly better performance, because it eliminates 1447needless copying in most situations. 1448 1449=head1 Installation and Configuration Improvements 1450 1451=head2 -Dusethreads means something different 1452 1453The -Dusethreads flag now enables the experimental interpreter-based thread 1454support by default. To get the flavor of experimental threads that was in 14555.005 instead, you need to run Configure with "-Dusethreads -Duse5005threads". 1456 1457As of v5.6.0, interpreter-threads support is still lacking a way to 1458create new threads from Perl (i.e., C<use Thread;> will not work with 1459interpreter threads). C<use Thread;> continues to be available when you 1460specify the -Duse5005threads option to Configure, bugs and all. 1461 1462 NOTE: Support for threads continues to be an experimental feature. 1463 Interfaces and implementation are subject to sudden and drastic changes. 1464 1465=head2 New Configure flags 1466 1467The following new flags may be enabled on the Configure command line 1468by running Configure with C<-Dflag>. 1469 1470 usemultiplicity 1471 usethreads useithreads (new interpreter threads: no Perl API yet) 1472 usethreads use5005threads (threads as they were in 5.005) 1473 1474 use64bitint (equal to now deprecated 'use64bits') 1475 use64bitall 1476 1477 uselongdouble 1478 usemorebits 1479 uselargefiles 1480 usesocks (only SOCKS v5 supported) 1481 1482=head2 Threadedness and 64-bitness now more daring 1483 1484The Configure options enabling the use of threads and the use of 148564-bitness are now more daring in the sense that they no more have an 1486explicit list of operating systems of known threads/64-bit 1487capabilities. In other words: if your operating system has the 1488necessary APIs and datatypes, you should be able just to go ahead and 1489use them, for threads by Configure -Dusethreads, and for 64 bits 1490either explicitly by Configure -Duse64bitint or implicitly if your 1491system has 64-bit wide datatypes. See also L<"64-bit support">. 1492 1493=head2 Long Doubles 1494 1495Some platforms have "long doubles", floating point numbers of even 1496larger range than ordinary "doubles". To enable using long doubles for 1497Perl's scalars, use -Duselongdouble. 1498 1499=head2 -Dusemorebits 1500 1501You can enable both -Duse64bitint and -Duselongdouble with -Dusemorebits. 1502See also L<"64-bit support">. 1503 1504=head2 -Duselargefiles 1505 1506Some platforms support system APIs that are capable of handling large files 1507(typically, files larger than two gigabytes). Perl will try to use these 1508APIs if you ask for -Duselargefiles. 1509 1510See L<"Large file support"> for more information. 1511 1512=head2 installusrbinperl 1513 1514You can use "Configure -Uinstallusrbinperl" which causes installperl 1515to skip installing perl also as /usr/bin/perl. This is useful if you 1516prefer not to modify /usr/bin for some reason or another but harmful 1517because many scripts assume to find Perl in /usr/bin/perl. 1518 1519=head2 SOCKS support 1520 1521You can use "Configure -Dusesocks" which causes Perl to probe 1522for the SOCKS proxy protocol library (v5, not v4). For more information 1523on SOCKS, see: 1524 1525 http://www.socks.nec.com/ 1526 1527=head2 C<-A> flag 1528 1529You can "post-edit" the Configure variables using the Configure C<-A> 1530switch. The editing happens immediately after the platform specific 1531hints files have been processed but before the actual configuration 1532process starts. Run C<Configure -h> to find out the full C<-A> syntax. 1533 1534=head2 Enhanced Installation Directories 1535 1536The installation structure has been enriched to improve the support 1537for maintaining multiple versions of perl, to provide locations for 1538vendor-supplied modules, scripts, and manpages, and to ease maintenance 1539of locally-added modules, scripts, and manpages. See the section on 1540Installation Directories in the INSTALL file for complete details. 1541For most users building and installing from source, the defaults should 1542be fine. 1543 1544If you previously used C<Configure -Dsitelib> or C<-Dsitearch> to set 1545special values for library directories, you might wish to consider using 1546the new C<-Dsiteprefix> setting instead. Also, if you wish to re-use a 1547config.sh file from an earlier version of perl, you should be sure to 1548check that Configure makes sensible choices for the new directories. 1549See INSTALL for complete details. 1550 1551=head1 Platform specific changes 1552 1553=head2 Supported platforms 1554 1555=over 4 1556 1557=item * 1558 1559The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread 1560extension. 1561 1562=item * 1563 1564GNU/Hurd is now supported. 1565 1566=item * 1567 1568Rhapsody/Darwin is now supported. 1569 1570=item * 1571 1572EPOC is now supported (on Psion 5). 1573 1574=item * 1575 1576The cygwin port (formerly cygwin32) has been greatly improved. 1577 1578=back 1579 1580=head2 DOS 1581 1582=over 4 1583 1584=item * 1585 1586Perl now works with djgpp 2.02 (and 2.03 alpha). 1587 1588=item * 1589 1590Environment variable names are not converted to uppercase any more. 1591 1592=item * 1593 1594Incorrect exit codes from backticks have been fixed. 1595 1596=item * 1597 1598This port continues to use its own builtin globbing (not File::Glob). 1599 1600=back 1601 1602=head2 OS390 (OpenEdition MVS) 1603 1604Support for this EBCDIC platform has not been renewed in this release. 1605There are difficulties in reconciling Perl's standardization on UTF-8 1606as its internal representation for characters with the EBCDIC character 1607set, because the two are incompatible. 1608 1609It is unclear whether future versions will renew support for this 1610platform, but the possibility exists. 1611 1612=head2 VMS 1613 1614Numerous revisions and extensions to configuration, build, testing, and 1615installation process to accommodate core changes and VMS-specific options. 1616 1617Expand %ENV-handling code to allow runtime mapping to logical names, 1618CLI symbols, and CRTL environ array. 1619 1620Extension of subprocess invocation code to accept filespecs as command 1621"verbs". 1622 1623Add to Perl command line processing the ability to use default file types and 1624to recognize Unix-style C<2E<gt>&1>. 1625 1626Expansion of File::Spec::VMS routines, and integration into ExtUtils::MM_VMS. 1627 1628Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly. 1629 1630Barewords at start of Unix-syntax paths may be treated as text rather than 1631only as logical names. 1632 1633Optional secure translation of several logical names used internally by Perl. 1634 1635Miscellaneous bugfixing and porting of new core code to VMS. 1636 1637Thanks are gladly extended to the many people who have contributed VMS 1638patches, testing, and ideas. 1639 1640=head2 Win32 1641 1642Perl can now emulate fork() internally, using multiple interpreters running 1643in different concurrent threads. This support must be enabled at build 1644time. See L<perlfork> for detailed information. 1645 1646When given a pathname that consists only of a drivename, such as C<A:>, 1647opendir() and stat() now use the current working directory for the drive 1648rather than the drive root. 1649 1650The builtin XSUB functions in the Win32:: namespace are documented. See 1651L<Win32>. 1652 1653$^X now contains the full path name of the running executable. 1654 1655A Win32::GetLongPathName() function is provided to complement 1656Win32::GetFullPathName() and Win32::GetShortPathName(). See L<Win32>. 1657 1658POSIX::uname() is supported. 1659 1660system(1,...) now returns true process IDs rather than process 1661handles. kill() accepts any real process id, rather than strictly 1662return values from system(1,...). 1663 1664For better compatibility with Unix, C<kill(0, $pid)> can now be used to 1665test whether a process exists. 1666 1667The C<Shell> module is supported. 1668 1669Better support for building Perl under command.com in Windows 95 1670has been added. 1671 1672Scripts are read in binary mode by default to allow ByteLoader (and 1673the filter mechanism in general) to work properly. For compatibility, 1674the DATA filehandle will be set to text mode if a carriage return is 1675detected at the end of the line containing the __END__ or __DATA__ 1676token; if not, the DATA filehandle will be left open in binary mode. 1677Earlier versions always opened the DATA filehandle in text mode. 1678 1679The glob() operator is implemented via the C<File::Glob> extension, 1680which supports glob syntax of the C shell. This increases the flexibility 1681of the glob() operator, but there may be compatibility issues for 1682programs that relied on the older globbing syntax. If you want to 1683preserve compatibility with the older syntax, you might want to run 1684perl with C<-MFile::DosGlob>. For details and compatibility information, 1685see L<File::Glob>. 1686 1687=head1 Significant bug fixes 1688 1689=head2 <HANDLE> on empty files 1690 1691With C<$/> set to C<undef>, "slurping" an empty file returns a string of 1692zero length (instead of C<undef>, as it used to) the first time the 1693HANDLE is read after C<$/> is set to C<undef>. Further reads yield 1694C<undef>. 1695 1696This means that the following will append "foo" to an empty file (it used 1697to do nothing): 1698 1699 perl -0777 -pi -e 's/^/foo/' empty_file 1700 1701The behaviour of: 1702 1703 perl -pi -e 's/^/foo/' empty_file 1704 1705is unchanged (it continues to leave the file empty). 1706 1707=head2 C<eval '...'> improvements 1708 1709Line numbers (as reflected by caller() and most diagnostics) within 1710C<eval '...'> were often incorrect where here documents were involved. 1711This has been corrected. 1712 1713Lexical lookups for variables appearing in C<eval '...'> within 1714functions that were themselves called within an C<eval '...'> were 1715searching the wrong place for lexicals. The lexical search now 1716correctly ends at the subroutine's block boundary. 1717 1718The use of C<return> within C<eval {...}> caused $@ not to be reset 1719correctly when no exception occurred within the eval. This has 1720been fixed. 1721 1722Parsing of here documents used to be flawed when they appeared as 1723the replacement expression in C<eval 's/.../.../e'>. This has 1724been fixed. 1725 1726=head2 All compilation errors are true errors 1727 1728Some "errors" encountered at compile time were by necessity 1729generated as warnings followed by eventual termination of the 1730program. This enabled more such errors to be reported in a 1731single run, rather than causing a hard stop at the first error 1732that was encountered. 1733 1734The mechanism for reporting such errors has been reimplemented 1735to queue compile-time errors and report them at the end of the 1736compilation as true errors rather than as warnings. This fixes 1737cases where error messages leaked through in the form of warnings 1738when code was compiled at run time using C<eval STRING>, and 1739also allows such errors to be reliably trapped using C<eval "...">. 1740 1741=head2 Implicitly closed filehandles are safer 1742 1743Sometimes implicitly closed filehandles (as when they are localized, 1744and Perl automatically closes them on exiting the scope) could 1745inadvertently set $? or $!. This has been corrected. 1746 1747 1748=head2 Behavior of list slices is more consistent 1749 1750When taking a slice of a literal list (as opposed to a slice of 1751an array or hash), Perl used to return an empty list if the 1752result happened to be composed of all undef values. 1753 1754The new behavior is to produce an empty list if (and only if) 1755the original list was empty. Consider the following example: 1756 1757 @a = (1,undef,undef,2)[2,1,2]; 1758 1759The old behavior would have resulted in @a having no elements. 1760The new behavior ensures it has three undefined elements. 1761 1762Note in particular that the behavior of slices of the following 1763cases remains unchanged: 1764 1765 @a = ()[1,2]; 1766 @a = (getpwent)[7,0]; 1767 @a = (anything_returning_empty_list())[2,1,2]; 1768 @a = @b[2,1,2]; 1769 @a = @c{'a','b','c'}; 1770 1771See L<perldata>. 1772 1773=head2 C<(\$)> prototype and C<$foo{a}> 1774 1775A scalar reference prototype now correctly allows a hash or 1776array element in that slot. 1777 1778=head2 C<goto &sub> and AUTOLOAD 1779 1780The C<goto &sub> construct works correctly when C<&sub> happens 1781to be autoloaded. 1782 1783=head2 C<-bareword> allowed under C<use integer> 1784 1785The autoquoting of barewords preceded by C<-> did not work 1786in prior versions when the C<integer> pragma was enabled. 1787This has been fixed. 1788 1789=head2 Failures in DESTROY() 1790 1791When code in a destructor threw an exception, it went unnoticed 1792in earlier versions of Perl, unless someone happened to be 1793looking in $@ just after the point the destructor happened to 1794run. Such failures are now visible as warnings when warnings are 1795enabled. 1796 1797=head2 Locale bugs fixed 1798 1799printf() and sprintf() previously reset the numeric locale 1800back to the default "C" locale. This has been fixed. 1801 1802Numbers formatted according to the local numeric locale 1803(such as using a decimal comma instead of a decimal dot) caused 1804"isn't numeric" warnings, even while the operations accessing 1805those numbers produced correct results. These warnings have been 1806discontinued. 1807 1808=head2 Memory leaks 1809 1810The C<eval 'return sub {...}'> construct could sometimes leak 1811memory. This has been fixed. 1812 1813Operations that aren't filehandle constructors used to leak memory 1814when used on invalid filehandles. This has been fixed. 1815 1816Constructs that modified C<@_> could fail to deallocate values 1817in C<@_> and thus leak memory. This has been corrected. 1818 1819=head2 Spurious subroutine stubs after failed subroutine calls 1820 1821Perl could sometimes create empty subroutine stubs when a 1822subroutine was not found in the package. Such cases stopped 1823later method lookups from progressing into base packages. 1824This has been corrected. 1825 1826=head2 Taint failures under C<-U> 1827 1828When running in unsafe mode, taint violations could sometimes 1829cause silent failures. This has been fixed. 1830 1831=head2 END blocks and the C<-c> switch 1832 1833Prior versions used to run BEGIN B<and> END blocks when Perl was 1834run in compile-only mode. Since this is typically not the expected 1835behavior, END blocks are not executed anymore when the C<-c> switch 1836is used, or if compilation fails. 1837 1838See L</"Support for CHECK blocks"> for how to run things when the compile 1839phase ends. 1840 1841=head2 Potential to leak DATA filehandles 1842 1843Using the C<__DATA__> token creates an implicit filehandle to 1844the file that contains the token. It is the program's 1845responsibility to close it when it is done reading from it. 1846 1847This caveat is now better explained in the documentation. 1848See L<perldata>. 1849 1850=head1 New or Changed Diagnostics 1851 1852=over 4 1853 1854=item "%s" variable %s masks earlier declaration in same %s 1855 1856(W misc) A "my" or "our" variable has been redeclared in the current scope or statement, 1857effectively eliminating all access to the previous instance. This is almost 1858always a typographical error. Note that the earlier variable will still exist 1859until the end of the scope or until all closure referents to it are 1860destroyed. 1861 1862=item "my sub" not yet implemented 1863 1864(F) Lexically scoped subroutines are not yet implemented. Don't try that 1865yet. 1866 1867=item "our" variable %s redeclared 1868 1869(W misc) You seem to have already declared the same global once before in the 1870current lexical scope. 1871 1872=item '!' allowed only after types %s 1873 1874(F) The '!' is allowed in pack() and unpack() only after certain types. 1875See L<perlfunc/pack>. 1876 1877=item / cannot take a count 1878 1879(F) You had an unpack template indicating a counted-length string, 1880but you have also specified an explicit size for the string. 1881See L<perlfunc/pack>. 1882 1883=item / must be followed by a, A or Z 1884 1885(F) You had an unpack template indicating a counted-length string, 1886which must be followed by one of the letters a, A or Z 1887to indicate what sort of string is to be unpacked. 1888See L<perlfunc/pack>. 1889 1890=item / must be followed by a*, A* or Z* 1891 1892(F) You had a pack template indicating a counted-length string, 1893Currently the only things that can have their length counted are a*, A* or Z*. 1894See L<perlfunc/pack>. 1895 1896=item / must follow a numeric type 1897 1898(F) You had an unpack template that contained a '#', 1899but this did not follow some numeric unpack specification. 1900See L<perlfunc/pack>. 1901 1902=item /%s/: Unrecognized escape \\%c passed through 1903 1904(W regexp) You used a backslash-character combination which is not recognized 1905by Perl. This combination appears in an interpolated variable or a 1906C<'>-delimited regular expression. The character was understood literally. 1907 1908=item /%s/: Unrecognized escape \\%c in character class passed through 1909 1910(W regexp) You used a backslash-character combination which is not recognized 1911by Perl inside character classes. The character was understood literally. 1912 1913=item /%s/ should probably be written as "%s" 1914 1915(W syntax) You have used a pattern where Perl expected to find a string, 1916as in the first argument to C<join>. Perl will treat the true 1917or false result of matching the pattern against $_ as the string, 1918which is probably not what you had in mind. 1919 1920=item %s() called too early to check prototype 1921 1922(W prototype) You've called a function that has a prototype before the parser saw a 1923definition or declaration for it, and Perl could not check that the call 1924conforms to the prototype. You need to either add an early prototype 1925declaration for the subroutine in question, or move the subroutine 1926definition ahead of the call to get proper prototype checking. Alternatively, 1927if you are certain that you're calling the function correctly, you may put 1928an ampersand before the name to avoid the warning. See L<perlsub>. 1929 1930=item %s argument is not a HASH or ARRAY element 1931 1932(F) The argument to exists() must be a hash or array element, such as: 1933 1934 $foo{$bar} 1935 $ref->{"susie"}[12] 1936 1937=item %s argument is not a HASH or ARRAY element or slice 1938 1939(F) The argument to delete() must be either a hash or array element, such as: 1940 1941 $foo{$bar} 1942 $ref->{"susie"}[12] 1943 1944or a hash or array slice, such as: 1945 1946 @foo[$bar, $baz, $xyzzy] 1947 @{$ref->[12]}{"susie", "queue"} 1948 1949=item %s argument is not a subroutine name 1950 1951(F) The argument to exists() for C<exists &sub> must be a subroutine 1952name, and not a subroutine call. C<exists &sub()> will generate this error. 1953 1954=item %s package attribute may clash with future reserved word: %s 1955 1956(W reserved) A lowercase attribute name was used that had a package-specific handler. 1957That name might have a meaning to Perl itself some day, even though it 1958doesn't yet. Perhaps you should use a mixed-case attribute name, instead. 1959See L<attributes>. 1960 1961=item (in cleanup) %s 1962 1963(W misc) This prefix usually indicates that a DESTROY() method raised 1964the indicated exception. Since destructors are usually called by 1965the system at arbitrary points during execution, and often a vast 1966number of times, the warning is issued only once for any number 1967of failures that would otherwise result in the same message being 1968repeated. 1969 1970Failure of user callbacks dispatched using the C<G_KEEPERR> flag 1971could also result in this warning. See L<perlcall/G_KEEPERR>. 1972 1973=item <> should be quotes 1974 1975(F) You wrote C<< require <file> >> when you should have written 1976C<require 'file'>. 1977 1978=item Attempt to join self 1979 1980(F) You tried to join a thread from within itself, which is an 1981impossible task. You may be joining the wrong thread, or you may 1982need to move the join() to some other thread. 1983 1984=item Bad evalled substitution pattern 1985 1986(F) You've used the /e switch to evaluate the replacement for a 1987substitution, but perl found a syntax error in the code to evaluate, 1988most likely an unexpected right brace '}'. 1989 1990=item Bad realloc() ignored 1991 1992(S) An internal routine called realloc() on something that had never been 1993malloc()ed in the first place. Mandatory, but can be disabled by 1994setting environment variable C<PERL_BADFREE> to 1. 1995 1996=item Bareword found in conditional 1997 1998(W bareword) The compiler found a bareword where it expected a conditional, 1999which often indicates that an || or && was parsed as part of the 2000last argument of the previous construct, for example: 2001 2002 open FOO || die; 2003 2004It may also indicate a misspelled constant that has been interpreted 2005as a bareword: 2006 2007 use constant TYPO => 1; 2008 if (TYOP) { print "foo" } 2009 2010The C<strict> pragma is useful in avoiding such errors. 2011 2012=item Binary number > 0b11111111111111111111111111111111 non-portable 2013 2014(W portable) The binary number you specified is larger than 2**32-1 2015(4294967295) and therefore non-portable between systems. See 2016L<perlport> for more on portability concerns. 2017 2018=item Bit vector size > 32 non-portable 2019 2020(W portable) Using bit vector sizes larger than 32 is non-portable. 2021 2022=item Buffer overflow in prime_env_iter: %s 2023 2024(W internal) A warning peculiar to VMS. While Perl was preparing to iterate over 2025%ENV, it encountered a logical name or symbol definition which was too long, 2026so it was truncated to the string shown. 2027 2028=item Can't check filesystem of script "%s" 2029 2030(P) For some reason you can't check the filesystem of the script for nosuid. 2031 2032=item Can't declare class for non-scalar %s in "%s" 2033 2034(S) Currently, only scalar variables can declared with a specific class 2035qualifier in a "my" or "our" declaration. The semantics may be extended 2036for other types of variables in future. 2037 2038=item Can't declare %s in "%s" 2039 2040(F) Only scalar, array, and hash variables may be declared as "my" or 2041"our" variables. They must have ordinary identifiers as names. 2042 2043=item Can't ignore signal CHLD, forcing to default 2044 2045(W signal) Perl has detected that it is being run with the SIGCHLD signal 2046(sometimes known as SIGCLD) disabled. Since disabling this signal 2047will interfere with proper determination of exit status of child 2048processes, Perl has reset the signal to its default value. 2049This situation typically indicates that the parent program under 2050which Perl may be running (e.g., cron) is being very careless. 2051 2052=item Can't modify non-lvalue subroutine call 2053 2054(F) Subroutines meant to be used in lvalue context should be declared as 2055such, see L<perlsub/"Lvalue subroutines">. 2056 2057=item Can't read CRTL environ 2058 2059(S) A warning peculiar to VMS. Perl tried to read an element of %ENV 2060from the CRTL's internal environment array and discovered the array was 2061missing. You need to figure out where your CRTL misplaced its environ 2062or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched. 2063 2064=item Can't remove %s: %s, skipping file 2065 2066(S) You requested an inplace edit without creating a backup file. Perl 2067was unable to remove the original file to replace it with the modified 2068file. The file was left unmodified. 2069 2070=item Can't return %s from lvalue subroutine 2071 2072(F) Perl detected an attempt to return illegal lvalues (such 2073as temporary or readonly values) from a subroutine used as an lvalue. 2074This is not allowed. 2075 2076=item Can't weaken a nonreference 2077 2078(F) You attempted to weaken something that was not a reference. Only 2079references can be weakened. 2080 2081=item Character class [:%s:] unknown 2082 2083(F) The class in the character class [: :] syntax is unknown. 2084See L<perlre>. 2085 2086=item Character class syntax [%s] belongs inside character classes 2087 2088(W unsafe) The character class constructs [: :], [= =], and [. .] go 2089I<inside> character classes, the [] are part of the construct, 2090for example: /[012[:alpha:]345]/. Note that [= =] and [. .] 2091are not currently implemented; they are simply placeholders for 2092future extensions. 2093 2094=item Constant is not %s reference 2095 2096(F) A constant value (perhaps declared using the C<use constant> pragma) 2097is being dereferenced, but it amounts to the wrong type of reference. The 2098message indicates the type of reference that was expected. This usually 2099indicates a syntax error in dereferencing the constant value. 2100See L<perlsub/"Constant Functions"> and L<constant>. 2101 2102=item constant(%s): %s 2103 2104(F) The parser found inconsistencies either while attempting to define an 2105overloaded constant, or when trying to find the character name specified 2106in the C<\N{...}> escape. Perhaps you forgot to load the corresponding 2107C<overload> or C<charnames> pragma? See L<charnames> and L<overload>. 2108 2109=item CORE::%s is not a keyword 2110 2111(F) The CORE:: namespace is reserved for Perl keywords. 2112 2113=item defined(@array) is deprecated 2114 2115(D) defined() is not usually useful on arrays because it checks for an 2116undefined I<scalar> value. If you want to see if the array is empty, 2117just use C<if (@array) { # not empty }> for example. 2118 2119=item defined(%hash) is deprecated 2120 2121(D) defined() is not usually useful on hashes because it checks for an 2122undefined I<scalar> value. If you want to see if the hash is empty, 2123just use C<if (%hash) { # not empty }> for example. 2124 2125=item Did not produce a valid header 2126 2127See Server error. 2128 2129=item (Did you mean "local" instead of "our"?) 2130 2131(W misc) Remember that "our" does not localize the declared global variable. 2132You have declared it again in the same lexical scope, which seems superfluous. 2133 2134=item Document contains no data 2135 2136See Server error. 2137 2138=item entering effective %s failed 2139 2140(F) While under the C<use filetest> pragma, switching the real and 2141effective uids or gids failed. 2142 2143=item false [] range "%s" in regexp 2144 2145(W regexp) A character class range must start and end at a literal character, not 2146another character class like C<\d> or C<[:alpha:]>. The "-" in your false 2147range is interpreted as a literal "-". Consider quoting the "-", "\-". 2148See L<perlre>. 2149 2150=item Filehandle %s opened only for output 2151 2152(W io) You tried to read from a filehandle opened only for writing. If you 2153intended it to be a read/write filehandle, you needed to open it with 2154"+<" or "+>" or "+>>" instead of with "<" or nothing. If 2155you intended only to read from the file, use "<". See 2156L<perlfunc/open>. 2157 2158=item flock() on closed filehandle %s 2159 2160(W closed) The filehandle you're attempting to flock() got itself closed some 2161time before now. Check your logic flow. flock() operates on filehandles. 2162Are you attempting to call flock() on a dirhandle by the same name? 2163 2164=item Global symbol "%s" requires explicit package name 2165 2166(F) You've said "use strict vars", which indicates that all variables 2167must either be lexically scoped (using "my"), declared beforehand using 2168"our", or explicitly qualified to say which package the global variable 2169is in (using "::"). 2170 2171=item Hexadecimal number > 0xffffffff non-portable 2172 2173(W portable) The hexadecimal number you specified is larger than 2**32-1 2174(4294967295) and therefore non-portable between systems. See 2175L<perlport> for more on portability concerns. 2176 2177=item Ill-formed CRTL environ value "%s" 2178 2179(W internal) A warning peculiar to VMS. Perl tried to read the CRTL's internal 2180environ array, and encountered an element without the C<=> delimiter 2181used to separate keys from values. The element is ignored. 2182 2183=item Ill-formed message in prime_env_iter: |%s| 2184 2185(W internal) A warning peculiar to VMS. Perl tried to read a logical name 2186or CLI symbol definition when preparing to iterate over %ENV, and 2187didn't see the expected delimiter between key and value, so the 2188line was ignored. 2189 2190=item Illegal binary digit %s 2191 2192(F) You used a digit other than 0 or 1 in a binary number. 2193 2194=item Illegal binary digit %s ignored 2195 2196(W digit) You may have tried to use a digit other than 0 or 1 in a binary number. 2197Interpretation of the binary number stopped before the offending digit. 2198 2199=item Illegal number of bits in vec 2200 2201(F) The number of bits in vec() (the third argument) must be a power of 2202two from 1 to 32 (or 64, if your platform supports that). 2203 2204=item Integer overflow in %s number 2205 2206(W overflow) The hexadecimal, octal or binary number you have specified either 2207as a literal or as an argument to hex() or oct() is too big for your 2208architecture, and has been converted to a floating point number. On a 220932-bit architecture the largest hexadecimal, octal or binary number 2210representable without overflow is 0xFFFFFFFF, 037777777777, or 22110b11111111111111111111111111111111 respectively. Note that Perl 2212transparently promotes all numbers to a floating point representation 2213internally--subject to loss of precision errors in subsequent 2214operations. 2215 2216=item Invalid %s attribute: %s 2217 2218The indicated attribute for a subroutine or variable was not recognized 2219by Perl or by a user-supplied handler. See L<attributes>. 2220 2221=item Invalid %s attributes: %s 2222 2223The indicated attributes for a subroutine or variable were not recognized 2224by Perl or by a user-supplied handler. See L<attributes>. 2225 2226=item invalid [] range "%s" in regexp 2227 2228The offending range is now explicitly displayed. 2229 2230=item Invalid separator character %s in attribute list 2231 2232(F) Something other than a colon or whitespace was seen between the 2233elements of an attribute list. If the previous attribute 2234had a parenthesised parameter list, perhaps that list was terminated 2235too soon. See L<attributes>. 2236 2237=item Invalid separator character %s in subroutine attribute list 2238 2239(F) Something other than a colon or whitespace was seen between the 2240elements of a subroutine attribute list. If the previous attribute 2241had a parenthesised parameter list, perhaps that list was terminated 2242too soon. 2243 2244=item leaving effective %s failed 2245 2246(F) While under the C<use filetest> pragma, switching the real and 2247effective uids or gids failed. 2248 2249=item Lvalue subs returning %s not implemented yet 2250 2251(F) Due to limitations in the current implementation, array and hash 2252values cannot be returned in subroutines used in lvalue context. 2253See L<perlsub/"Lvalue subroutines">. 2254 2255=item Method %s not permitted 2256 2257See Server error. 2258 2259=item Missing %sbrace%s on \N{} 2260 2261(F) Wrong syntax of character name literal C<\N{charname}> within 2262double-quotish context. 2263 2264=item Missing command in piped open 2265 2266(W pipe) You used the C<open(FH, "| command")> or C<open(FH, "command |")> 2267construction, but the command was missing or blank. 2268 2269=item Missing name in "my sub" 2270 2271(F) The reserved syntax for lexically scoped subroutines requires that they 2272have a name with which they can be found. 2273 2274=item No %s specified for -%c 2275 2276(F) The indicated command line switch needs a mandatory argument, but 2277you haven't specified one. 2278 2279=item No package name allowed for variable %s in "our" 2280 2281(F) Fully qualified variable names are not allowed in "our" declarations, 2282because that doesn't make much sense under existing semantics. Such 2283syntax is reserved for future extensions. 2284 2285=item No space allowed after -%c 2286 2287(F) The argument to the indicated command line switch must follow immediately 2288after the switch, without intervening spaces. 2289 2290=item no UTC offset information; assuming local time is UTC 2291 2292(S) A warning peculiar to VMS. Perl was unable to find the local 2293timezone offset, so it's assuming that local system time is equivalent 2294to UTC. If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL> 2295to translate to the number of seconds which need to be added to UTC to 2296get local time. 2297 2298=item Octal number > 037777777777 non-portable 2299 2300(W portable) The octal number you specified is larger than 2**32-1 (4294967295) 2301and therefore non-portable between systems. See L<perlport> for more 2302on portability concerns. 2303 2304See also L<perlport> for writing portable code. 2305 2306=item panic: del_backref 2307 2308(P) Failed an internal consistency check while trying to reset a weak 2309reference. 2310 2311=item panic: kid popen errno read 2312 2313(F) forked child returned an incomprehensible message about its errno. 2314 2315=item panic: magic_killbackrefs 2316 2317(P) Failed an internal consistency check while trying to reset all weak 2318references to an object. 2319 2320=item Parentheses missing around "%s" list 2321 2322(W parenthesis) You said something like 2323 2324 my $foo, $bar = @_; 2325 2326when you meant 2327 2328 my ($foo, $bar) = @_; 2329 2330Remember that "my", "our", and "local" bind tighter than comma. 2331 2332=item Possible unintended interpolation of %s in string 2333 2334(W ambiguous) It used to be that Perl would try to guess whether you 2335wanted an array interpolated or a literal @. It no longer does this; 2336arrays are now I<always> interpolated into strings. This means that 2337if you try something like: 2338 2339 print "fred@example.com"; 2340 2341and the array C<@example> doesn't exist, Perl is going to print 2342C<fred.com>, which is probably not what you wanted. To get a literal 2343C<@> sign in a string, put a backslash before it, just as you would 2344to get a literal C<$> sign. 2345 2346=item Possible Y2K bug: %s 2347 2348(W y2k) You are concatenating the number 19 with another number, which 2349could be a potential Year 2000 problem. 2350 2351=item pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead 2352 2353(W deprecated) You have written something like this: 2354 2355 sub doit 2356 { 2357 use attrs qw(locked); 2358 } 2359 2360You should use the new declaration syntax instead. 2361 2362 sub doit : locked 2363 { 2364 ... 2365 2366The C<use attrs> pragma is now obsolete, and is only provided for 2367backward-compatibility. See L<perlsub/"Subroutine Attributes">. 2368 2369 2370=item Premature end of script headers 2371 2372See Server error. 2373 2374=item Repeat count in pack overflows 2375 2376(F) You can't specify a repeat count so large that it overflows 2377your signed integers. See L<perlfunc/pack>. 2378 2379=item Repeat count in unpack overflows 2380 2381(F) You can't specify a repeat count so large that it overflows 2382your signed integers. See L<perlfunc/unpack>. 2383 2384=item realloc() of freed memory ignored 2385 2386(S) An internal routine called realloc() on something that had already 2387been freed. 2388 2389=item Reference is already weak 2390 2391(W misc) You have attempted to weaken a reference that is already weak. 2392Doing so has no effect. 2393 2394=item setpgrp can't take arguments 2395 2396(F) Your system has the setpgrp() from BSD 4.2, which takes no arguments, 2397unlike POSIX setpgid(), which takes a process ID and process group ID. 2398 2399=item Strange *+?{} on zero-length expression 2400 2401(W regexp) You applied a regular expression quantifier in a place where it 2402makes no sense, such as on a zero-width assertion. 2403Try putting the quantifier inside the assertion instead. For example, 2404the way to match "abc" provided that it is followed by three 2405repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>. 2406 2407=item switching effective %s is not implemented 2408 2409(F) While under the C<use filetest> pragma, we cannot switch the 2410real and effective uids or gids. 2411 2412=item This Perl can't reset CRTL environ elements (%s) 2413 2414=item This Perl can't set CRTL environ elements (%s=%s) 2415 2416(W internal) Warnings peculiar to VMS. You tried to change or delete an element 2417of the CRTL's internal environ array, but your copy of Perl wasn't 2418built with a CRTL that contained the setenv() function. You'll need to 2419rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see 2420L<perlvms>) so that the environ array isn't the target of the change to 2421%ENV which produced the warning. 2422 2423=item Too late to run %s block 2424 2425(W void) A CHECK or INIT block is being defined during run time proper, 2426when the opportunity to run them has already passed. Perhaps you are 2427loading a file with C<require> or C<do> when you should be using 2428C<use> instead. Or perhaps you should put the C<require> or C<do> 2429inside a BEGIN block. 2430 2431=item Unknown open() mode '%s' 2432 2433(F) The second argument of 3-argument open() is not among the list 2434of valid modes: C<< < >>, C<< > >>, C<<< >> >>>, C<< +< >>, 2435C<< +> >>, C<<< +>> >>>, C<-|>, C<|->. 2436 2437=item Unknown process %x sent message to prime_env_iter: %s 2438 2439(P) An error peculiar to VMS. Perl was reading values for %ENV before 2440iterating over it, and someone else stuck a message in the stream of 2441data Perl expected. Someone's very confused, or perhaps trying to 2442subvert Perl's population of %ENV for nefarious purposes. 2443 2444=item Unrecognized escape \\%c passed through 2445 2446(W misc) You used a backslash-character combination which is not recognized 2447by Perl. The character was understood literally. 2448 2449=item Unterminated attribute parameter in attribute list 2450 2451(F) The lexer saw an opening (left) parenthesis character while parsing an 2452attribute list, but the matching closing (right) parenthesis 2453character was not found. You may need to add (or remove) a backslash 2454character to get your parentheses to balance. See L<attributes>. 2455 2456=item Unterminated attribute list 2457 2458(F) The lexer found something other than a simple identifier at the start 2459of an attribute, and it wasn't a semicolon or the start of a 2460block. Perhaps you terminated the parameter list of the previous attribute 2461too soon. See L<attributes>. 2462 2463=item Unterminated attribute parameter in subroutine attribute list 2464 2465(F) The lexer saw an opening (left) parenthesis character while parsing a 2466subroutine attribute list, but the matching closing (right) parenthesis 2467character was not found. You may need to add (or remove) a backslash 2468character to get your parentheses to balance. 2469 2470=item Unterminated subroutine attribute list 2471 2472(F) The lexer found something other than a simple identifier at the start 2473of a subroutine attribute, and it wasn't a semicolon or the start of a 2474block. Perhaps you terminated the parameter list of the previous attribute 2475too soon. 2476 2477=item Value of CLI symbol "%s" too long 2478 2479(W misc) A warning peculiar to VMS. Perl tried to read the value of an %ENV 2480element from a CLI symbol table, and found a resultant string longer 2481than 1024 characters. The return value has been truncated to 1024 2482characters. 2483 2484=item Version number must be a constant number 2485 2486(P) The attempt to translate a C<use Module n.n LIST> statement into 2487its equivalent C<BEGIN> block found an internal inconsistency with 2488the version number. 2489 2490=back 2491 2492=head1 New tests 2493 2494=over 4 2495 2496=item lib/attrs 2497 2498Compatibility tests for C<sub : attrs> vs the older C<use attrs>. 2499 2500=item lib/env 2501 2502Tests for new environment scalar capability (e.g., C<use Env qw($BAR);>). 2503 2504=item lib/env-array 2505 2506Tests for new environment array capability (e.g., C<use Env qw(@PATH);>). 2507 2508=item lib/io_const 2509 2510IO constants (SEEK_*, _IO*). 2511 2512=item lib/io_dir 2513 2514Directory-related IO methods (new, read, close, rewind, tied delete). 2515 2516=item lib/io_multihomed 2517 2518INET sockets with multi-homed hosts. 2519 2520=item lib/io_poll 2521 2522IO poll(). 2523 2524=item lib/io_unix 2525 2526UNIX sockets. 2527 2528=item op/attrs 2529 2530Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>. 2531 2532=item op/filetest 2533 2534File test operators. 2535 2536=item op/lex_assign 2537 2538Verify operations that access pad objects (lexicals and temporaries). 2539 2540=item op/exists_sub 2541 2542Verify C<exists &sub> operations. 2543 2544=back 2545 2546=head1 Incompatible Changes 2547 2548=head2 Perl Source Incompatibilities 2549 2550Beware that any new warnings that have been added or old ones 2551that have been enhanced are B<not> considered incompatible changes. 2552 2553Since all new warnings must be explicitly requested via the C<-w> 2554switch or the C<warnings> pragma, it is ultimately the programmer's 2555responsibility to ensure that warnings are enabled judiciously. 2556 2557=over 4 2558 2559=item CHECK is a new keyword 2560 2561All subroutine definitions named CHECK are now special. See 2562C</"Support for CHECK blocks"> for more information. 2563 2564=item Treatment of list slices of undef has changed 2565 2566There is a potential incompatibility in the behavior of list slices 2567that are comprised entirely of undefined values. 2568See L</"Behavior of list slices is more consistent">. 2569 2570=item Format of $English::PERL_VERSION is different 2571 2572The English module now sets $PERL_VERSION to $^V (a string value) rather 2573than C<$]> (a numeric value). This is a potential incompatibility. 2574Send us a report via perlbug if you are affected by this. 2575 2576See L</"Improved Perl version numbering system"> for the reasons for 2577this change. 2578 2579=item Literals of the form C<1.2.3> parse differently 2580 2581Previously, numeric literals with more than one dot in them were 2582interpreted as a floating point number concatenated with one or more 2583numbers. Such "numbers" are now parsed as strings composed of the 2584specified ordinals. 2585 2586For example, C<print 97.98.99> used to output C<97.9899> in earlier 2587versions, but now prints C<abc>. 2588 2589See L</"Support for strings represented as a vector of ordinals">. 2590 2591=item Possibly changed pseudo-random number generator 2592 2593Perl programs that depend on reproducing a specific set of pseudo-random 2594numbers may now produce different output due to improvements made to the 2595rand() builtin. You can use C<sh Configure -Drandfunc=rand> to obtain 2596the old behavior. 2597 2598See L</"Better pseudo-random number generator">. 2599 2600=item Hashing function for hash keys has changed 2601 2602Even though Perl hashes are not order preserving, the apparently 2603random order encountered when iterating on the contents of a hash 2604is actually determined by the hashing algorithm used. Improvements 2605in the algorithm may yield a random order that is B<different> from 2606that of previous versions, especially when iterating on hashes. 2607 2608See L</"Better worst-case behavior of hashes"> for additional 2609information. 2610 2611=item C<undef> fails on read only values 2612 2613Using the C<undef> operator on a readonly value (such as $1) has 2614the same effect as assigning C<undef> to the readonly value--it 2615throws an exception. 2616 2617=item Close-on-exec bit may be set on pipe and socket handles 2618 2619Pipe and socket handles are also now subject to the close-on-exec 2620behavior determined by the special variable $^F. 2621 2622See L</"More consistent close-on-exec behavior">. 2623 2624=item Writing C<"$$1"> to mean C<"${$}1"> is unsupported 2625 2626Perl 5.004 deprecated the interpretation of C<$$1> and 2627similar within interpolated strings to mean C<$$ . "1">, 2628but still allowed it. 2629 2630In Perl 5.6.0 and later, C<"$$1"> always means C<"${$1}">. 2631 2632=item delete(), each(), values() and C<\(%h)> 2633 2634operate on aliases to values, not copies 2635 2636delete(), each(), values() and hashes (e.g. C<\(%h)>) 2637in a list context return the actual 2638values in the hash, instead of copies (as they used to in earlier 2639versions). Typical idioms for using these constructs copy the 2640returned values, but this can make a significant difference when 2641creating references to the returned values. Keys in the hash are still 2642returned as copies when iterating on a hash. 2643 2644See also L</"delete(), each(), values() and hash iteration are faster">. 2645 2646=item vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS 2647 2648vec() generates a run-time error if the BITS argument is not 2649a valid power-of-two integer. 2650 2651=item Text of some diagnostic output has changed 2652 2653Most references to internal Perl operations in diagnostics 2654have been changed to be more descriptive. This may be an 2655issue for programs that may incorrectly rely on the exact 2656text of diagnostics for proper functioning. 2657 2658=item C<%@> has been removed 2659 2660The undocumented special variable C<%@> that used to accumulate 2661"background" errors (such as those that happen in DESTROY()) 2662has been removed, because it could potentially result in memory 2663leaks. 2664 2665=item Parenthesized not() behaves like a list operator 2666 2667The C<not> operator now falls under the "if it looks like a function, 2668it behaves like a function" rule. 2669 2670As a result, the parenthesized form can be used with C<grep> and C<map>. 2671The following construct used to be a syntax error before, but it works 2672as expected now: 2673 2674 grep not($_), @things; 2675 2676On the other hand, using C<not> with a literal list slice may not 2677work. The following previously allowed construct: 2678 2679 print not (1,2,3)[0]; 2680 2681needs to be written with additional parentheses now: 2682 2683 print not((1,2,3)[0]); 2684 2685The behavior remains unaffected when C<not> is not followed by parentheses. 2686 2687=item Semantics of bareword prototype C<(*)> have changed 2688 2689The semantics of the bareword prototype C<*> have changed. Perl 5.005 2690always coerced simple scalar arguments to a typeglob, which wasn't useful 2691in situations where the subroutine must distinguish between a simple 2692scalar and a typeglob. The new behavior is to not coerce bareword 2693arguments to a typeglob. The value will always be visible as either 2694a simple scalar or as a reference to a typeglob. 2695 2696See L</"More functional bareword prototype (*)">. 2697 2698=item Semantics of bit operators may have changed on 64-bit platforms 2699 2700If your platform is either natively 64-bit or if Perl has been 2701configured to used 64-bit integers, i.e., $Config{ivsize} is 8, 2702there may be a potential incompatibility in the behavior of bitwise 2703numeric operators (& | ^ ~ << >>). These operators used to strictly 2704operate on the lower 32 bits of integers in previous versions, but now 2705operate over the entire native integral width. In particular, note 2706that unary C<~> will produce different results on platforms that have 2707different $Config{ivsize}. For portability, be sure to mask off 2708the excess bits in the result of unary C<~>, e.g., C<~$x & 0xffffffff>. 2709 2710See L</"Bit operators support full native integer width">. 2711 2712=item More builtins taint their results 2713 2714As described in L</"Improved security features">, there may be more 2715sources of taint in a Perl program. 2716 2717To avoid these new tainting behaviors, you can build Perl with the 2718Configure option C<-Accflags=-DINCOMPLETE_TAINTS>. Beware that the 2719ensuing perl binary may be insecure. 2720 2721=back 2722 2723=head2 C Source Incompatibilities 2724 2725=over 4 2726 2727=item C<PERL_POLLUTE> 2728 2729Release 5.005 grandfathered old global symbol names by providing preprocessor 2730macros for extension source compatibility. As of release 5.6.0, these 2731preprocessor definitions are not available by default. You need to explicitly 2732compile perl with C<-DPERL_POLLUTE> to get these definitions. For 2733extensions still using the old symbols, this option can be 2734specified via MakeMaker: 2735 2736 perl Makefile.PL POLLUTE=1 2737 2738=item C<PERL_IMPLICIT_CONTEXT> 2739 2740This new build option provides a set of macros for all API functions 2741such that an implicit interpreter/thread context argument is passed to 2742every API function. As a result of this, something like C<sv_setsv(foo,bar)> 2743amounts to a macro invocation that actually translates to something like 2744C<Perl_sv_setsv(my_perl,foo,bar)>. While this is generally expected 2745to not have any significant source compatibility issues, the difference 2746between a macro and a real function call will need to be considered. 2747 2748This means that there B<is> a source compatibility issue as a result of 2749this if your extensions attempt to use pointers to any of the Perl API 2750functions. 2751 2752Note that the above issue is not relevant to the default build of 2753Perl, whose interfaces continue to match those of prior versions 2754(but subject to the other options described here). 2755 2756See L<perlguts/"The Perl API"> for detailed information on the 2757ramifications of building Perl with this option. 2758 2759 NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built 2760 with one of -Dusethreads, -Dusemultiplicity, or both. It is not 2761 intended to be enabled by users at this time. 2762 2763=item C<PERL_POLLUTE_MALLOC> 2764 2765Enabling Perl's malloc in release 5.005 and earlier caused the namespace of 2766the system's malloc family of functions to be usurped by the Perl versions, 2767since by default they used the same names. Besides causing problems on 2768platforms that do not allow these functions to be cleanly replaced, this 2769also meant that the system versions could not be called in programs that 2770used Perl's malloc. Previous versions of Perl have allowed this behaviour 2771to be suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor 2772definitions. 2773 2774As of release 5.6.0, Perl's malloc family of functions have default names 2775distinct from the system versions. You need to explicitly compile perl with 2776C<-DPERL_POLLUTE_MALLOC> to get the older behaviour. HIDEMYMALLOC 2777and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now 2778the default. 2779 2780Note that these functions do B<not> constitute Perl's memory allocation API. 2781See L<perlguts/"Memory Allocation"> for further information about that. 2782 2783=back 2784 2785=head2 Compatible C Source API Changes 2786 2787=over 4 2788 2789=item C<PATCHLEVEL> is now C<PERL_VERSION> 2790 2791The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION> 2792are now available by default from perl.h, and reflect the base revision, 2793patchlevel, and subversion respectively. C<PERL_REVISION> had no 2794prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were 2795previously available as C<PATCHLEVEL> and C<SUBVERSION>. 2796 2797The new names cause less pollution of the B<cpp> namespace and reflect what 2798the numbers have come to stand for in common practice. For compatibility, 2799the old names are still supported when F<patchlevel.h> is explicitly 2800included (as required before), so there is no source incompatibility 2801from the change. 2802 2803=back 2804 2805=head2 Binary Incompatibilities 2806 2807In general, the default build of this release is expected to be binary 2808compatible for extensions built with the 5.005 release or its maintenance 2809versions. However, specific platforms may have broken binary compatibility 2810due to changes in the defaults used in hints files. Therefore, please be 2811sure to always check the platform-specific README files for any notes to 2812the contrary. 2813 2814The usethreads or usemultiplicity builds are B<not> binary compatible 2815with the corresponding builds in 5.005. 2816 2817On platforms that require an explicit list of exports (AIX, OS/2 and Windows, 2818among others), purely internal symbols such as parser functions and the 2819run time opcodes are not exported by default. Perl 5.005 used to export 2820all functions irrespective of whether they were considered part of the 2821public API or not. 2822 2823For the full list of public API functions, see L<perlapi>. 2824 2825=head1 Known Problems 2826 2827=head2 Thread test failures 2828 2829The subtests 19 and 20 of lib/thr5005.t test are known to fail due to 2830fundamental problems in the 5.005 threading implementation. These are 2831not new failures--Perl 5.005_0x has the same bugs, but didn't have these 2832tests. 2833 2834=head2 EBCDIC platforms not supported 2835 2836In earlier releases of Perl, EBCDIC environments like OS390 (also 2837known as Open Edition MVS) and VM-ESA were supported. Due to changes 2838required by the UTF-8 (Unicode) support, the EBCDIC platforms are not 2839supported in Perl 5.6.0. 2840 2841=head2 In 64-bit HP-UX the lib/io_multihomed test may hang 2842 2843The lib/io_multihomed test may hang in HP-UX if Perl has been 2844configured to be 64-bit. Because other 64-bit platforms do not 2845hang in this test, HP-UX is suspect. All other tests pass 2846in 64-bit HP-UX. The test attempts to create and connect to 2847"multihomed" sockets (sockets which have multiple IP addresses). 2848 2849=head2 NEXTSTEP 3.3 POSIX test failure 2850 2851In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the 2852operating system libraries is buggy: the %j format numbers the days of 2853a month starting from zero, which, while being logical to programmers, 2854will cause the subtests 19 to 27 of the lib/posix test may fail. 2855 2856=head2 Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc 2857 2858If compiled with gcc 2.95 the lib/sdbm test will fail (dump core). 2859The cure is to use the vendor cc, it comes with the operating system 2860and produces good code. 2861 2862=head2 UNICOS/mk CC failures during Configure run 2863 2864In UNICOS/mk the following errors may appear during the Configure run: 2865 2866 Guessing which symbols your C compiler and preprocessor define... 2867 CC-20 cc: ERROR File = try.c, Line = 3 2868 ... 2869 bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K 2870 ... 2871 4 errors detected in the compilation of "try.c". 2872 2873The culprit is the broken awk of UNICOS/mk. The effect is fortunately 2874rather mild: Perl itself is not adversely affected by the error, only 2875the h2ph utility coming with Perl, and that is rather rarely needed 2876these days. 2877 2878=head2 Arrow operator and arrays 2879 2880When the left argument to the arrow operator C<< -> >> is an array, or 2881the C<scalar> operator operating on an array, the result of the 2882operation must be considered erroneous. For example: 2883 2884 @x->[2] 2885 scalar(@x)->[2] 2886 2887These expressions will get run-time errors in some future release of 2888Perl. 2889 2890=head2 Experimental features 2891 2892As discussed above, many features are still experimental. Interfaces and 2893implementation of these features are subject to change, and in extreme cases, 2894even subject to removal in some future release of Perl. These features 2895include the following: 2896 2897=over 4 2898 2899=item Threads 2900 2901=item Unicode 2902 2903=item 64-bit support 2904 2905=item Lvalue subroutines 2906 2907=item Weak references 2908 2909=item The pseudo-hash data type 2910 2911=item The Compiler suite 2912 2913=item Internal implementation of file globbing 2914 2915=item The DB module 2916 2917=item The regular expression code constructs: 2918 2919C<(?{ code })> and C<(??{ code })> 2920 2921=back 2922 2923=head1 Obsolete Diagnostics 2924 2925=over 4 2926 2927=item Character class syntax [: :] is reserved for future extensions 2928 2929(W) Within regular expression character classes ([]) the syntax beginning 2930with "[:" and ending with ":]" is reserved for future extensions. 2931If you need to represent those character sequences inside a regular 2932expression character class, just quote the square brackets with the 2933backslash: "\[:" and ":\]". 2934 2935=item Ill-formed logical name |%s| in prime_env_iter 2936 2937(W) A warning peculiar to VMS. A logical name was encountered when preparing 2938to iterate over %ENV which violates the syntactic rules governing logical 2939names. Because it cannot be translated normally, it is skipped, and will not 2940appear in %ENV. This may be a benign occurrence, as some software packages 2941might directly modify logical name tables and introduce nonstandard names, 2942or it may indicate that a logical name table has been corrupted. 2943 2944=item In string, @%s now must be written as \@%s 2945 2946The description of this error used to say: 2947 2948 (Someday it will simply assume that an unbackslashed @ 2949 interpolates an array.) 2950 2951That day has come, and this fatal error has been removed. It has been 2952replaced by a non-fatal warning instead. 2953See L</Arrays now always interpolate into double-quoted strings> for 2954details. 2955 2956=item Probable precedence problem on %s 2957 2958(W) The compiler found a bareword where it expected a conditional, 2959which often indicates that an || or && was parsed as part of the 2960last argument of the previous construct, for example: 2961 2962 open FOO || die; 2963 2964=item regexp too big 2965 2966(F) The current implementation of regular expressions uses shorts as 2967address offsets within a string. Unfortunately this means that if 2968the regular expression compiles to longer than 32767, it'll blow up. 2969Usually when you want a regular expression this big, there is a better 2970way to do it with multiple statements. See L<perlre>. 2971 2972=item Use of "$$<digit>" to mean "${$}<digit>" is deprecated 2973 2974(D) Perl versions before 5.004 misinterpreted any type marker followed 2975by "$" and a digit. For example, "$$0" was incorrectly taken to mean 2976"${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. 2977 2978However, the developers of Perl 5.004 could not fix this bug completely, 2979because at least two widely-used modules depend on the old meaning of 2980"$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the 2981old (broken) way inside strings; but it generates this message as a 2982warning. And in Perl 5.005, this special treatment will cease. 2983 2984=back 2985 2986=head1 Reporting Bugs 2987 2988If you find what you think is a bug, you might check the 2989articles recently posted to the comp.lang.perl.misc newsgroup. 2990There may also be information at http://www.perl.com/perl/ , the Perl 2991Home Page. 2992 2993If you believe you have an unreported bug, please run the B<perlbug> 2994program included with your release. Be sure to trim your bug down 2995to a tiny but sufficient test case. Your bug report, along with the 2996output of C<perl -V>, will be sent off to perlbug@perl.org to be 2997analysed by the Perl porting team. 2998 2999=head1 SEE ALSO 3000 3001The F<Changes> file for exhaustive details on what changed. 3002 3003The F<INSTALL> file for how to build Perl. 3004 3005The F<README> file for general stuff. 3006 3007The F<Artistic> and F<Copying> files for copyright information. 3008 3009=head1 HISTORY 3010 3011Written by Gurusamy Sarathy <F<gsar@activestate.com>>, with many 3012contributions from The Perl Porters. 3013 3014Send omissions or corrections to <F<perlbug@perl.org>>. 3015 3016=cut 3017