3 perldelta - what's new for perl v5.6 (as of v5.005_61)
7 This is an unsupported alpha release, meant for intrepid Perl developers
8 only. The included sources may not even build correctly on some platforms.
9 Subscribing to perl5-porters is the best way to monitor and contribute
10 to the progress of development releases (see www.perl.org for info).
12 This document describes differences between the 5.005 release and this one.
14 =head1 Incompatible Changes
16 =head2 Perl Source Incompatibilities
20 =head2 C Source Incompatibilities
26 Release 5.005 grandfathered old global symbol names by providing preprocessor
27 macros for extension source compatibility. As of release 5.6, these
28 preprocessor definitions are not available by default. You need to explicitly
29 compile perl with C<-DPERL_POLLUTE> to get these definitions. For
30 extensions still using the old symbols, this option can be
31 specified via MakeMaker:
33 perl Makefile.PL POLLUTE=1
35 =item C<PERL_IMPLICIT_CONTEXT>
37 This new build option provides a set of macros for all API functions
38 such that an implicit interpreter/thread context argument is passed to
39 every API function. As a result of this, something like C<sv_setsv(foo,bar)>
40 amounts to a macro invocation that actually translates to something like
41 C<Perl_sv_setsv(my_perl,foo,bar)>. While this is generally expected
42 to not have any significant source compatibility issues, the difference
43 between a macro and a real function call will need to be considered.
45 This means that there B<is> a source compatibility issue as a result of
46 this if your extensions attempt to use pointers to any of the Perl API
49 Note that the above issue is not relevant to the default build of
50 Perl, whose interfaces continue to match those of prior versions
51 (but subject to the other options described here).
53 PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
54 with one of -Dusethreads, -Dusemultiplicity, or both.
56 See L<perlguts/"The Perl API"> for detailed information on the
57 ramifications of building Perl using this option.
59 =item C<PERL_POLLUTE_MALLOC>
61 Enabling Perl's malloc in release 5.005 and earlier caused
62 the namespace of system versions of the malloc family of functions to
63 be usurped by the Perl versions, since by default they used the
66 Besides causing problems on platforms that do not allow these functions to
67 be cleanly replaced, this also meant that the system versions could not
68 be called in programs that used Perl's malloc. Previous versions of Perl
69 have allowed this behaviour to be suppressed with the HIDEMYMALLOC and
70 EMBEDMYMALLOC preprocessor definitions.
72 As of release 5.6, Perl's malloc family of functions have default names
73 distinct from the system versions. You need to explicitly compile perl with
74 C<-DPERL_POLLUTE_MALLOC> to get the older behaviour. HIDEMYMALLOC
75 and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
78 Note that these functions do B<not> constitute Perl's memory allocation API.
79 See L<perlguts/"Memory Allocation"> for further information about that.
81 =item C<PL_na> and C<dTHR> Issues
83 The C<PL_na> global is now thread local, so a C<dTHR> declaration is needed
84 in the scope in which the global appears. XSUBs should handle this automatically,
85 but if you have used C<PL_na> in support functions, you either need to
86 change the C<PL_na> to a local variable (which is recommended), or put in
91 =head2 Compatible C Source API Changes
95 =item C<PATCHLEVEL> is now C<PERL_VERSION>
97 The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
98 are now available by default from perl.h, and reflect the base revision,
99 patchlevel, and subversion respectively. C<PERL_REVISION> had no
100 prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
101 previously available as C<PATCHLEVEL> and C<SUBVERSION>.
103 The new names cause less pollution of the B<cpp> namespace and reflect what
104 the numbers have come to stand for in common practice. For compatibility,
105 the old names are still supported when F<patchlevel.h> is explicitly
106 included (as required before), so there is no source incompatibility
111 =head2 Binary Incompatibilities
113 The default build of this release is binary compatible with the 5.005
114 release or its maintenance versions.
116 The usethreads or usemultiplicity builds are B<not> binary compatible
117 with the corresponding builds in 5.005.
121 =head2 Unicode and UTF-8 support
123 Perl can optionally use UTF-8 as its internal representation for character
124 strings. The C<use utf8> pragma enables this support in the current lexical
125 scope. See L<utf8> for more information.
127 =head2 Lexically scoped warning categories
129 You can now control the granularity of warnings emitted by perl at a finer
130 level using the C<use warnings> pragma. See L<warnings> and L<perllexwarn>
133 =head2 Binary numbers supported
135 Binary numbers are now supported as literals, in s?printf formats, and
139 printf "The answer is: %b\n", oct("0b101010");
141 =head2 syswrite() ease-of-use
143 The length argument of C<syswrite()> is now optional.
145 =head2 64-bit support
147 All platforms that have 64-bit integers either (a) natively as longs
148 or ints (b) via special compiler flags (c) using long long are able to
149 use "quads" (64-integers) as follows:
153 =item constants (decimal, hexadecimal, octal, binary) in the code
155 =item arguments to oct() and hex()
157 =item arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
159 =item printed as such
161 =item pack() and unpack() "q" and "Q" formats
163 =item in basic arithmetics: + - * / %
165 =item vec() (but see the below note about bit arithmetics)
169 Note that unless you have the case (a) you will have to configure
170 and compile Perl using the -Duse64bits Configure flag.
172 Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) for numbers are not
173 64-bit clean, they are explictly forced to be 32-bit. Bit arithmetics
174 for bit vectors (created by vec()) are not limited in their width.
176 Last but not least: note that due to Perl's habit of always using
177 floating point numbers the quads are still not true integers.
178 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
179 -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
180 are silently promoted to floating point numbers, after which they will
181 start losing precision (their lower digits).
183 =head2 Large file support
185 If you have filesystems that support "large files" (files larger than
186 2 gigabytes), you may now also be able to create and access them from
187 Perl. You have to use Configure -Duselfs. Turning on the large file
188 support turns on also the 64-bit support, for obvious reasons.
190 Note that in addition to requiring a proper file system to do large
191 files you may also need to adjust your per-process (or your
192 per-system, or per-process-group, or per-user-group) maximum filesize
193 limits before running Perl scripts that try to handle large files,
194 especially if you intend to write such files.
196 Finally, in addition to your process/process group maximum filesize
197 limits, you may have quota limits on your filesystems that stop you
198 (your user id or your user group id) from using large files.
200 Adjusting your process/user/group/file system/operating system limits
201 is outside the scope of Perl core language. For process limits, you
202 may try increasing the limits using your shell's limits/limit/ulimit
203 command before running Perl. The BSD::Resource extension (not
204 included with the standard Perl distribution) may also be of use, it
205 offers the getrlimit/setrlimit interface that can be used to adjust
206 process resource usage limits, including the maximum filesize limit.
210 In some systems you may be able to use long doubles to enhance the
211 range of precision of your double precision floating point numbers
212 (that is, Perl's numbers). Use Configure -Duselongdouble to enable
213 this support (if it is available).
217 You can Configure -Dusemorebits to turn on both the 64-bit support
218 and the long double support.
220 =head2 Better syntax checks on parenthesized unary operators
224 print defined(&foo,&bar,&baz);
225 print uc("foo","bar","baz");
228 used to be accidentally allowed in earlier versions, and produced
229 unpredictable behaviour. Some produced ancillary warnings
230 when used in this way; others silently did the wrong thing.
232 The parenthesized forms of most unary operators that expect a single
233 argument now ensure that they are not called with more than one
234 argument, making the cases shown above syntax errors. The usual
237 print defined &foo, &bar, &baz;
238 print uc "foo", "bar", "baz";
241 remains unchanged. See L<perlop>.
243 =head2 POSIX character class syntax [: :] supported
245 For example to match alphabetic characters use /[[:alpha:]]/.
246 See L<perlre> for details.
248 =head2 Improved C<qw//> operator
250 The C<qw//> operator is now evaluated at compile time into a true list
251 instead of being replaced with a run time call to C<split()>. This
252 removes the confusing misbehaviour of C<qw//> in scalar context, which
253 had inherited that behaviour from split().
257 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
259 now correctly prints "3|a", instead of "2|a".
261 =head2 pack() format 'Z' supported
263 The new format type 'Z' is useful for packing and unpacking null-terminated
264 strings. See L<perlfunc/"pack">.
266 =head2 pack() format modifier '!' supported
268 The new format type modifier '!' is useful for packing and unpacking
269 native shorts, ints, and longs. See L<perlfunc/"pack">.
271 =head2 pack() and unpack() support counted strings
273 The template character '#' can be used to specify a counted string
274 type to be packed or unpacked. See L<perlfunc/"pack">.
276 =head2 $^X variables may now have names longer than one character
278 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
279 error. Now variable names that begin with a control character may be
280 arbitrarily long. However, for compatibility reasons, these variables
281 I<must> be written with explicit braces, as C<${^XY}> for example.
282 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
283 than one control character, such as C<${^XY^Z}>, are illegal.
285 The old syntax has not changed. As before, `^X' may be either a
286 literal control-X character or the two-character sequence `caret' plus
287 `X'. When braces are omitted, the variable name stops after the
288 control character. Thus C<"$^XYZ"> continues to be synonymous with
289 C<$^X . "YZ"> as before.
291 As before, lexical variables may not have names beginning with control
292 characters. As before, variables whose names begin with a control
293 character are always forced to be in package `main'. All such variables
294 are reserved for future extensions, except those that begin with
295 C<^_>, which may be used by user programs and are guaranteed not to
296 acquire special meaning in any future version of Perl.
298 =head2 C<use attrs> implicit in subroutine attributes
300 Formerly, if you wanted to mark a subroutine as being a method call or
301 as requiring an automatic lock() when it is entered, you had to declare
302 that with a C<use attrs> pragma in the body of the subroutine.
303 That can now be accomplished with a declaration syntax, like this:
305 sub mymethod : locked, method ;
307 sub mymethod : locked, method {
311 F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
312 with the stubs they provide. See L<attributes>.
314 =head1 Significant bug fixes
316 =head2 E<lt>HANDLEE<gt> on empty files
318 With C<$/> set to C<undef>, slurping an empty file returns a string of
319 zero length (instead of C<undef>, as it used to) the first time the
320 HANDLE is read. Further reads yield C<undef>.
322 This means that the following will append "foo" to an empty file (it used
325 perl -0777 -pi -e 's/^/foo/' empty_file
329 perl -pi -e 's/^/foo/' empty_file
331 is unchanged (it continues to leave the file empty).
333 =head2 C<eval '...'> improvements
335 Line numbers (as reflected by caller() and most diagnostics) within
336 C<eval '...'> were often incorrect when here documents were involved.
337 This has been corrected.
339 Lexical lookups for variables appearing in C<eval '...'> within
340 functions that were themselves called within an C<eval '...'> were
341 searching the wrong place for lexicals. The lexical search now
342 correctly ends at the subroutine's block boundary.
344 Parsing of here documents used to be flawed when they appeared as
345 the replacement expression in C<eval 's/.../.../e'>. This has
348 =head2 Automatic flushing of output buffers
350 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
351 of all files opened for output when the operation
352 was attempted. This mostly eliminates confusing
353 buffering mishaps suffered by users unaware of how Perl internally
356 =head2 Better diagnostics on meaningless filehandle operations
358 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
359 are compile time errors. Attempting to read from filehandles that
360 were opened only for writing will now produce warnings (just as
361 writing to read-only filehandles does).
363 =head2 Buffered data discarded from input filehandle when dup'ed.
365 C<open(NEW, "E<lt>&OLD")> now discards any data that was previously
366 read and buffered in C<OLD>. The next read operation on C<NEW> will
367 return the same data as the corresponding operation on C<OLD>.
368 Formerly, it would have returned the data from the start of the
369 following disk block instead.
371 =head1 Supported Platforms
377 VM/ESA is now supported.
381 Siemens BS2000 is now supported under the POSIX Shell.
385 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
390 GNU/Hurd is now supported.
394 Rhapsody is now supported.
398 EPOC is is now supported (on Psion 5).
408 Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
412 IO constants (SEEK_*, _IO*).
416 Directory-related IO methods (new, read, close, rewind, tied delete).
418 =item lib/io_multihomed
420 INET sockets with multi-homed hosts.
432 Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
440 Verify operations that access pad objects (lexicals and temporaries).
444 =head1 Modules and Pragmata
452 While used internally by Perl as a pragma, this module also
453 provides a way to fetch subroutine and variable attributes.
458 The ByteLoader is a dedication extension to generate and run
459 Perl bytecode. See L<ByteLoader>.
463 The Perl Compiler suite has been extensively reworked for this
468 Devel::DProf, a Perl source code profiler has been added.
472 Added Dumpvalue module provides screen dumps of Perl data.
476 You can now run tests for I<n> seconds instead of guessing the right
477 number of tests to run: e.g. timethese(-5, ...) will run each
478 code for at least 5 CPU seconds. Zero as the "number of repetitions"
479 means "for at least 3 CPU seconds". The output format has also
480 changed. For example:
482 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
484 will now output something like this:
486 Benchmark: running a, b, each for at least 5 CPU seconds...
487 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
488 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
490 New features: "each for at least N CPU seconds...", "wallclock secs",
491 and the "@ operations/CPU second (n=operations)".
495 The Devel::Peek module provides access to the internal representation
496 of Perl variables and data. It is a data debugging tool for the XS programmer.
500 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
501 large (more than 4G) file access (64-bit support is not yet
502 working, though, so no need to get overly excited), Free/Net/OpenBSD
503 locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
504 O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.
508 New methods have been added to the File::Spec module: devnull() returns
509 the name of the null device (/dev/null on Unix) and tmpdir() the name of
510 the temp directory (normally /tmp on Unix). There are now also methods
511 to convert between absolute and relative filenames: abs2rel() and
512 rel2abs(). For compatibility with operating systems that specify volume
513 names in file paths, the splitpath(), splitdir(), and catdir() methods
516 =item File::Spec::Functions
518 The new File::Spec::Functions modules provides a function interface
519 to the File::Spec module. Allows shorthand
521 $fullname = catfile($dir1, $dir2, $file);
525 $fullname = File::Spec->catfile($dir1, $dir2, $file);
529 The logical operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
530 and C<~> are now supported on bigints.
534 The accessor methods Re, Im, arg, abs, rho, and theta can now also
535 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
539 A little bit of radial trigonometry (cylindrical and spherical),
540 radial coordinate conversions, and the great circle distance were added.
544 An EXISTS method has been added to this module (and sdbm_exists() has
545 been added to the underlying sdbm library), so one can now call exists
546 on an SDBM_File tied hash and get the correct result, rather than a
551 The timelocal() and timegm() functions used to silently return bogus
552 results when the date exceeded the machine's integer range. They
553 now consistently croak() if the date falls in an unsupported range--
554 but on the other hand they now accept "out-of-limits" day-of-month
555 to make "Julian date" conversions easier.
559 The error return value in list context has been changed for all functions
560 that return a list of values. Previously these functions returned a list
561 with a single element C<undef> if an error occurred. Now these functions
562 return the empty list in these situations. This applies to the following
568 The remaining functions are unchanged and continue to return C<undef> on
569 error even in list context.
571 The Win32::SetLastError(ERROR) function has been added as a complement
572 to the Win32::GetLastError() function.
574 The new Win32::GetFullPathName(FILENAME) returns the full absolute
575 pathname for FILENAME in scalar context. In list context it returns
576 a two-element list containing the fully qualified directory name and
581 A new feature called "DBM Filters" has been added to all the
582 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
583 DBM Filters add four new methods to each DBM module:
590 These can be used to filter key-value pairs before the pairs are
591 written to the database or just after they are read from the database.
592 See L<perldbmfilter> for further information.
598 C<use attrs> is now obsolescent, and is only provided for
599 backward-compatibility. It's been replaced by the C<sub : attributes>
600 syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>.
602 C<use utf8> to enable UTF-8 and Unicode support.
604 C<use caller 'encoding'> allows modules to inherit pragmatic attributes
605 from the caller's context. C<encoding> is currently the only supported
608 Lexical warnings pragma, C<use warnings;>, to control optional warnings.
610 C<use filetest> to control the behaviour of filetests (C<-r> C<-w> ...).
611 Currently only one subpragma implemented, "use filetest 'access';",
612 that enables the use of access(2) or equivalent to check
613 permissions instead of using stat(2) as usual. This matters
614 in filesystems where there are ACLs (access control lists): the
615 stat(2) might lie, but access(2) knows better.
617 =head1 Utility Changes
621 =head1 Documentation Changes
625 =item perlopentut.pod
627 A tutorial on using open() effectively.
631 A tutorial that introduces the essentials of references.
635 A tutorial on managing class data for object modules.
639 =head1 New Diagnostics
641 =item "my sub" not yet implemented
643 (F) Lexically scoped subroutines are not yet implemented. Don't try that
646 =item %s package attribute may clash with future reserved word: %s
648 (W) A lowercase attribute name was used that had a package-specific handler.
649 That name might have a meaning to Perl itself some day, even though it
650 doesn't yet. Perhaps you should use a mixed-case attribute name, instead.
653 =item /%s/: Unrecognized escape \\%c passed through
655 (W) You used a backslash-character combination which is not recognized
656 by Perl. This combination appears in an interpolated variable or a
657 C<'>-delimited regular expression.
659 =item Filehandle %s opened only for output
661 (W) You tried to read from a filehandle opened only for writing. If you
662 intended it to be a read-write filehandle, you needed to open it with
663 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
664 you intended only to read from the file, use "E<lt>". See
667 =item Invalid %s attribute: %s
669 The indicated attribute for a subroutine or variable was not recognized
670 by Perl or by a user-supplied handler. See L<attributes>.
672 =item Invalid %s attributes: %s
674 The indicated attributes for a subroutine or variable were not recognized
675 by Perl or by a user-supplied handler. See L<attributes>.
677 =item Invalid separator character %s in attribute list
679 (F) Something other than a comma or whitespace was seen between the
680 elements of an attribute list. If the previous attribute
681 had a parenthesised parameter list, perhaps that list was terminated
682 too soon. See L<attributes>.
684 =item Missing command in piped open
686 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
687 construction, but the command was missing or blank.
689 =item Missing name in "my sub"
691 (F) The reserved syntax for lexically scoped subroutines requires that they
692 have a name with which they can be found.
694 =item Unrecognized escape \\%c passed through
696 (W) You used a backslash-character combination which is not recognized
699 =item Unterminated attribute parameter in attribute list
701 (F) The lexer saw an opening (left) parenthesis character while parsing an
702 attribute list, but the matching closing (right) parenthesis
703 character was not found. You may need to add (or remove) a backslash
704 character to get your parentheses to balance. See L<attributes>.
706 =item Unterminated attribute list
708 (F) The lexer found something other than a simple identifier at the start
709 of an attribute, and it wasn't a semicolon or the start of a
710 block. Perhaps you terminated the parameter list of the previous attribute
711 too soon. See L<attributes>.
713 =item defined(@array) is deprecated
715 (D) defined() is not usually useful on arrays because it checks for an
716 undefined I<scalar> value. If you want to see if the array is empty,
717 just use C<if (@array) { # not empty }> for example.
719 =item defined(%hash) is deprecated
721 (D) defined() is not usually useful on hashes because it checks for an
722 undefined I<scalar> value. If you want to see if the hash is empty,
723 just use C<if (%hash) { # not empty }> for example.
725 =item Invalid separator character %s in subroutine attribute list
727 (F) Something other than a comma or whitespace was seen between the
728 elements of a subroutine attribute list. If the previous attribute
729 had a parenthesised parameter list, perhaps that list was terminated
732 =item Possible Y2K bug: %s
734 (W) You are concatenating the number 19 with another number, which
735 could be a potential Year 2000 problem.
737 =item Unterminated attribute parameter in subroutine attribute list
739 (F) The lexer saw an opening (left) parenthesis character while parsing a
740 subroutine attribute list, but the matching closing (right) parenthesis
741 character was not found. You may need to add (or remove) a backslash
742 character to get your parentheses to balance.
744 =item Unterminated subroutine attribute list
746 (F) The lexer found something other than a simple identifier at the start
747 of a subroutine attribute, and it wasn't a semicolon or the start of a
748 block. Perhaps you terminated the parameter list of the previous attribute
751 =item /%s/ should probably be written as "%s"
753 (W) You have used a pattern where Perl expected to find a string,
754 like in the first argument to C<join>. Perl will treat the true
755 or false result of matching the pattern against $_ as the string,
756 which is probably not what you had in mind.
758 =head1 Obsolete Diagnostics
762 =head1 Configuration Changes
764 =head2 installusrbinperl
766 You can use "Configure -Uinstallusrbinperl" which causes installperl
767 to skip installing perl also as /usr/bin/perl. This is useful if you
768 prefer not to modify /usr/bin for some reason or another but harmful
769 because many scripts assume to find Perl in /usr/bin/perl.
773 You can use "Configure -Dusesocks" which causes Perl to probe
774 for the SOCKS proxy protocol library, http://www.socks.nec.com/
778 You can "post-edit" the Configure variables using the Configure -A
779 flag. The editing happens immediately after the platform specific
780 hints files have been processed but before the actual configuration
781 process starts. Run Configure -h to find out the full -A syntax.
785 If you find what you think is a bug, you might check the headers of
786 articles recently posted to the comp.lang.perl.misc newsgroup.
787 There may also be information at http://www.perl.com/perl/, the Perl
790 If you believe you have an unreported bug, please run the B<perlbug>
791 program included with your release. Make sure to trim your bug down
792 to a tiny but sufficient test case. Your bug report, along with the
793 output of C<perl -V>, will be sent off to perlbug@perl.com to be
794 analysed by the Perl porting team.
798 The F<Changes> file for exhaustive details on what changed.
800 The F<INSTALL> file for how to build Perl.
802 The F<README> file for general stuff.
804 The F<Artistic> and F<Copying> files for copyright information.
808 Written by Gurusamy Sarathy <F<gsar@umich.edu>>, with many contributions
809 from The Perl Porters.
811 Send omissions or corrections to <F<perlbug@perl.com>>.