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 warning> pragma. See L<warning> 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 in the code
155 =item arguments to oct() and hex()
157 =item arguments to print(), printf() and sprintf()
159 =item pack() and unpack() "q" format
161 =item in basic arithmetics
165 Note that unless you have the case (a) you will have to configure
166 and compile Perl using the -Duse64bits Configure flag.
168 Unfortunately, bit operations (&, <<, ...) and vec() do not work,
169 they are limited to 32 bits.
171 Last but not least: note that due to Perl's habit of always using
172 floating point numbers the quads are still not true integers. When
173 quads overflow their limits (18446744073709551615 unsigned,
174 -9223372036854775808...9223372036854775807 signed), they are silently
175 promoted to floating point numbers, after which they will
176 start losing precision (their lower digits).
178 =head2 Large file support
180 If you have filesystems that support "large files" (files larger than
181 2 gigabytes), you may now also be able to create and access them from Perl.
183 Note that in addition to requiring a proper file system to do this you
184 may also need to adjust your per-process (or even your per-system)
185 maximum filesize limits before running Perl scripts that try to handle
186 large files, especially if you intend to write such files.
188 Adjusting your file system/system limits is outside the scope of Perl.
189 For process limits, you may try to increase the limits using your
190 shell's limit/ulimit command before running Perl. The BSD::Resource
191 extension (not included with the standard Perl distribution) may also
194 (Large file support is also related to 64-bit support, for obvious reasons)
196 =head2 Better syntax checks on parenthesized unary operators
200 print defined(&foo,&bar,&baz);
201 print uc("foo","bar","baz");
204 used to be accidentally allowed in earlier versions, and produced
205 unpredictable behaviour. Some produced ancillary warnings
206 when used in this way; others silently did the wrong thing.
208 The parenthesized forms of most unary operators that expect a single
209 argument now ensure that they are not called with more than one
210 argument, making the cases shown above syntax errors. The usual
213 print defined &foo, &bar, &baz;
214 print uc "foo", "bar", "baz";
217 remains unchanged. See L<perlop>.
219 =head2 POSIX character class syntax [: :] supported
221 For example to match alphabetic characters use /[[:alpha:]]/.
222 See L<perlre> for details.
224 =head2 Improved C<qw//> operator
226 The C<qw//> operator is now evaluated at compile time into a true list
227 instead of being replaced with a run time call to C<split()>. This
228 removes the confusing misbehaviour of C<qw//> in scalar context, which
229 had inherited that behaviour from split().
233 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
235 now correctly prints "3|a", instead of "2|a".
237 =head2 pack() format 'Z' supported
239 The new format type 'Z' is useful for packing and unpacking null-terminated
240 strings. See L<perlfunc/"pack">.
242 =head2 pack() format modifier '!' supported
244 The new format type modifier '!' is useful for packing and unpacking
245 native shorts, ints, and longs. See L<perlfunc/"pack">.
247 =head2 pack() and unpack() support counted strings
249 The template character '#' can be used to specify a counted string
250 type to be packed or unpacked. See L<perlfunc/"pack">.
252 =head2 $^X variables may now have names longer than one character
254 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
255 error. Now variable names that begin with a control character may be
256 arbitrarily long. However, for compatibility reasons, these variables
257 I<must> be written with explicit braces, as C<${^XY}> for example.
258 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
259 than one control character, such as C<${^XY^Z}>, are illegal.
261 The old syntax has not changed. As before, `^X' may be either a
262 literal control-X character or the two-character sequence `caret' plus
263 `X'. When braces are omitted, the variable name stops after the
264 control character. Thus C<"$^XYZ"> continues to be synonymous with
265 C<$^X . "YZ"> as before.
267 As before, lexical variables may not have names beginning with control
268 characters. As before, variables whose names begin with a control
269 character are always forced to be in package `main'. All such variables
270 are reserved for future extensions, except those that begin with
271 C<^_>, which may be used by user programs and is guaranteed not to
272 acquire special meaning in any future version of Perl.
274 =head1 Significant bug fixes
276 =head2 E<lt>HANDLEE<gt> on empty files
278 With C<$/> set to C<undef>, slurping an empty file returns a string of
279 zero length (instead of C<undef>, as it used to) the first time the
280 HANDLE is read. Further reads yield C<undef>.
282 This means that the following will append "foo" to an empty file (it used
285 perl -0777 -pi -e 's/^/foo/' empty_file
289 perl -pi -e 's/^/foo/' empty_file
291 is unchanged (it continues to leave the file empty).
293 =head2 C<eval '...'> improvements
295 Line numbers (as reflected by caller() and most diagnostics) within
296 C<eval '...'> were often incorrect when here documents were involved.
297 This has been corrected.
299 Lexical lookups for variables appearing in C<eval '...'> within
300 functions that were themselves called within an C<eval '...'> were
301 searching the wrong place for lexicals. The lexical search now
302 correctly ends at the subroutine's block boundary.
304 Parsing of here documents used to be flawed when they appeared as
305 the replacement expression in C<eval 's/.../.../e'>. This has
308 =head2 Automatic flushing of output buffers
310 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
311 of all files opened for output when the operation
312 was attempted. This mostly eliminates confusing
313 buffering mishaps suffered by users unaware of how Perl internally
316 =head2 Better diagnostics on meaningless filehandle operations
318 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
319 are compile time errors. Attempting to read from filehandles that
320 were opened only for writing will now produce warnings (just as
321 writing to read-only filehandles does).
323 =head2 Buffered data discarded from input filehandle when dup'ed.
325 C<open(NEW, "E<lt>&OLD")> now discards any data that was previously
326 read and buffered in C<OLD>. The next read operation on C<NEW> will
327 return the same data as the corresponding operation on C<OLD>.
328 Formerly, it would have returned the data from the start of the
329 following disk block instead.
331 =head1 Supported Platforms
337 VM/ESA is now supported.
341 Siemens BS2000 is now supported under the POSIX Shell.
345 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
350 GNU/Hurd is now supported.
354 Rhapsody is now supported.
358 EPOC is is now supported (on Psion 5).
368 IO constants (SEEK_*, _IO*).
372 Directory-related IO methods (new, read, close, rewind, tied delete).
374 =item op/io_multihomed
376 INET sockets with multi-homed hosts.
392 Verify operations that access pad objects (lexicals and temporaries).
396 =head1 Modules and Pragmata
404 The ByteLoader is a dedication extension to generate and run
405 Perl bytecode. See L<ByteLoader>.
409 The Perl Compiler suite has been extensively reworked for this
414 Devel::DProf, a Perl source code profiler has been added.
418 Added Dumpvalue module provides screen dumps of Perl data.
422 You can now run tests for I<n> seconds instead of guessing the right
423 number of tests to run: e.g. timethese(-5, ...) will run each
424 code for at least 5 CPU seconds. Zero as the "number of repetitions"
425 means "for at least 3 CPU seconds". The output format has also
426 changed. For example:
428 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
430 will now output something like this:
432 Benchmark: running a, b, each for at least 5 CPU seconds...
433 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
434 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
436 New features: "each for at least N CPU seconds...", "wallclock secs",
437 and the "@ operations/CPU second (n=operations)".
441 The Devel::Peek module provides access to the internal representation
442 of Perl variables and data. It is a data debugging tool for the XS programmer.
446 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
447 large (more than 4G) file access (64-bit support is not yet
448 working, though, so no need to get overly excited), Free/Net/OpenBSD
449 locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
450 O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.
454 New methods have been added to the File::Spec module: devnull() returns
455 the name of the null device (/dev/null on Unix) and tmpdir() the name of
456 the temp directory (normally /tmp on Unix). There are now also methods
457 to convert between absolute and relative filenames: abs2rel() and
458 rel2abs(). For compatibility with operating systems that specify volume
459 names in file paths, the splitpath(), splitdir(), and catdir() methods
462 =item File::Spec::Functions
464 The new File::Spec::Functions modules provides a function interface
465 to the File::Spec module. Allows shorthand
467 $fullname = catfile($dir1, $dir2, $file);
471 $fullname = File::Spec->catfile($dir1, $dir2, $file);
475 The logical operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
476 and C<~> are now supported on bigints.
480 The accessor methods Re, Im, arg, abs, rho, and theta can now also
481 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
485 A little bit of radial trigonometry (cylindrical and spherical),
486 radial coordinate conversions, and the great circle distance were added.
490 An EXISTS method has been added to this module (and sdbm_exists() has
491 been added to the underlying sdbm library), so one can now call exists
492 on an SDBM_File tied hash and get the correct result, rather than a
497 The timelocal() and timegm() functions used to silently return bogus
498 results when the date exceeded the machine's integer range. They
499 now consistently croak() if the date falls in an unsupported range.
503 The error return value in list context has been changed for all functions
504 that return a list of values. Previously these functions returned a list
505 with a single element C<undef> if an error occurred. Now these functions
506 return the empty list in these situations. This applies to the following
512 The remaining functions are unchanged and continue to return C<undef> on
513 error even in list context.
515 The Win32::SetLastError(ERROR) function has been added as a complement
516 to the Win32::GetLastError() function.
518 The new Win32::GetFullPathName(FILENAME) returns the full absolute
519 pathname for FILENAME in scalar context. In list context it returns
520 a two-element list containing the fully qualified directory name and
525 A new feature called "DBM Filters" has been added to all the
526 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
527 DBM Filters add four new methods to each DBM module:
534 These can be used to filter key-value pairs before the pairs are
535 written to the database or just after they are read from the database.
536 See L<perldbmfilter> for further information.
542 C<use utf8> to enable UTF-8 and Unicode support.
544 C<use caller 'encoding'> allows modules to inherit pragmatic attributes
545 from the caller's context. C<encoding> is currently the only supported
548 Lexical warnings pragma, C<use warning;>, to control optional warnings.
550 C<use filetest> to control the behaviour of filetests (C<-r> C<-w> ...).
551 Currently only one subpragma implemented, "use filetest 'access';",
552 that enables the use of access(2) or equivalent to check
553 permissions instead of using stat(2) as usual. This matters
554 in filesystems where there are ACLs (access control lists): the
555 stat(2) might lie, but access(2) knows better.
557 =head1 Utility Changes
561 =head1 Documentation Changes
565 =item perlopentut.pod
567 A tutorial on using open() effectively.
571 A tutorial that introduces the essentials of references.
575 A tutorial on managing class data for object modules.
579 =head1 New Diagnostics
581 =item /%s/: Unrecognized escape \\%c passed through
583 (W) You used a backslash-character combination which is not recognized
584 by Perl. This combination appears in an interpolated variable or a
585 C<'>-delimited regular expression.
587 =item Filehandle %s opened only for output
589 (W) You tried to read from a filehandle opened only for writing. If you
590 intended it to be a read-write filehandle, you needed to open it with
591 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
592 you intended only to read from the file, use "E<lt>". See
595 =item Missing command in piped open
597 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
598 construction, but the command was missing or blank.
600 =item Unrecognized escape \\%c passed through
602 (W) You used a backslash-character combination which is not recognized
605 =item defined(@array) is deprecated
607 (D) defined() is not usually useful on arrays because it checks for an
608 undefined I<scalar> value. If you want to see if the array is empty,
609 just use C<if (@array) { # not empty }> for example.
611 =item defined(%hash) is deprecated
613 (D) defined() is not usually useful on hashes because it checks for an
614 undefined I<scalar> value. If you want to see if the hash is empty,
615 just use C<if (%hash) { # not empty }> for example.
617 =head1 Obsolete Diagnostics
621 =head1 Configuration Changes
623 =head2 installusrbinperl
625 You can use "Configure -Uinstallusrbinperl" which causes installperl
626 to skip installing perl also as /usr/bin/perl. This is useful if you
627 prefer not to modify /usr/bin for some reason or another but harmful
628 because many scripts assume to find Perl in /usr/bin/perl.
632 You can use "Configure -Dusesocks" which causes Perl to probe
633 for the SOCKS proxy protocol library, http://www.socks.nec.com/
637 If you find what you think is a bug, you might check the headers of
638 articles recently posted to the comp.lang.perl.misc newsgroup.
639 There may also be information at http://www.perl.com/perl/, the Perl
642 If you believe you have an unreported bug, please run the B<perlbug>
643 program included with your release. Make sure to trim your bug down
644 to a tiny but sufficient test case. Your bug report, along with the
645 output of C<perl -V>, will be sent off to perlbug@perl.com to be
646 analysed by the Perl porting team.
650 The F<Changes> file for exhaustive details on what changed.
652 The F<INSTALL> file for how to build Perl.
654 The F<README> file for general stuff.
656 The F<Artistic> and F<Copying> files for copyright information.
660 Written by Gurusamy Sarathy <F<gsar@umich.edu>>, with many contributions
661 from The Perl Porters.
663 Send omissions or corrections to <F<perlbug@perl.com>>.