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
163 =item vec() (but see the below note about bit arithmetics)
167 Note that unless you have the case (a) you will have to configure
168 and compile Perl using the -Duse64bits Configure flag.
170 Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) are not 64-bit clean.
172 Last but not least: note that due to Perl's habit of always using
173 floating point numbers the quads are still not true integers.
174 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
175 -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
176 are silently promoted to floating point numbers, after which they will
177 start losing precision (their lower digits).
179 =head2 Large file support
181 If you have filesystems that support "large files" (files larger than
182 2 gigabytes), you may now also be able to create and access them from Perl.
184 Note that in addition to requiring a proper file system to do this you
185 may also need to adjust your per-process (or even your per-system)
186 maximum filesize limits before running Perl scripts that try to handle
187 large files, especially if you intend to write such files.
189 Adjusting your file system/system limits is outside the scope of Perl.
190 For process limits, you may try to increase the limits using your
191 shell's limit/ulimit command before running Perl. The BSD::Resource
192 extension (not included with the standard Perl distribution) may also
195 (Large file support is also related to 64-bit support, for obvious reasons)
197 =head2 Better syntax checks on parenthesized unary operators
201 print defined(&foo,&bar,&baz);
202 print uc("foo","bar","baz");
205 used to be accidentally allowed in earlier versions, and produced
206 unpredictable behaviour. Some produced ancillary warnings
207 when used in this way; others silently did the wrong thing.
209 The parenthesized forms of most unary operators that expect a single
210 argument now ensure that they are not called with more than one
211 argument, making the cases shown above syntax errors. The usual
214 print defined &foo, &bar, &baz;
215 print uc "foo", "bar", "baz";
218 remains unchanged. See L<perlop>.
220 =head2 POSIX character class syntax [: :] supported
222 For example to match alphabetic characters use /[[:alpha:]]/.
223 See L<perlre> for details.
225 =head2 Improved C<qw//> operator
227 The C<qw//> operator is now evaluated at compile time into a true list
228 instead of being replaced with a run time call to C<split()>. This
229 removes the confusing misbehaviour of C<qw//> in scalar context, which
230 had inherited that behaviour from split().
234 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
236 now correctly prints "3|a", instead of "2|a".
238 =head2 pack() format 'Z' supported
240 The new format type 'Z' is useful for packing and unpacking null-terminated
241 strings. See L<perlfunc/"pack">.
243 =head2 pack() format modifier '!' supported
245 The new format type modifier '!' is useful for packing and unpacking
246 native shorts, ints, and longs. See L<perlfunc/"pack">.
248 =head2 pack() and unpack() support counted strings
250 The template character '#' can be used to specify a counted string
251 type to be packed or unpacked. See L<perlfunc/"pack">.
253 =head2 $^X variables may now have names longer than one character
255 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
256 error. Now variable names that begin with a control character may be
257 arbitrarily long. However, for compatibility reasons, these variables
258 I<must> be written with explicit braces, as C<${^XY}> for example.
259 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
260 than one control character, such as C<${^XY^Z}>, are illegal.
262 The old syntax has not changed. As before, `^X' may be either a
263 literal control-X character or the two-character sequence `caret' plus
264 `X'. When braces are omitted, the variable name stops after the
265 control character. Thus C<"$^XYZ"> continues to be synonymous with
266 C<$^X . "YZ"> as before.
268 As before, lexical variables may not have names beginning with control
269 characters. As before, variables whose names begin with a control
270 character are always forced to be in package `main'. All such variables
271 are reserved for future extensions, except those that begin with
272 C<^_>, which may be used by user programs and is guaranteed not to
273 acquire special meaning in any future version of Perl.
275 =head1 Significant bug fixes
277 =head2 E<lt>HANDLEE<gt> on empty files
279 With C<$/> set to C<undef>, slurping an empty file returns a string of
280 zero length (instead of C<undef>, as it used to) the first time the
281 HANDLE is read. Further reads yield C<undef>.
283 This means that the following will append "foo" to an empty file (it used
286 perl -0777 -pi -e 's/^/foo/' empty_file
290 perl -pi -e 's/^/foo/' empty_file
292 is unchanged (it continues to leave the file empty).
294 =head2 C<eval '...'> improvements
296 Line numbers (as reflected by caller() and most diagnostics) within
297 C<eval '...'> were often incorrect when here documents were involved.
298 This has been corrected.
300 Lexical lookups for variables appearing in C<eval '...'> within
301 functions that were themselves called within an C<eval '...'> were
302 searching the wrong place for lexicals. The lexical search now
303 correctly ends at the subroutine's block boundary.
305 Parsing of here documents used to be flawed when they appeared as
306 the replacement expression in C<eval 's/.../.../e'>. This has
309 =head2 Automatic flushing of output buffers
311 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
312 of all files opened for output when the operation
313 was attempted. This mostly eliminates confusing
314 buffering mishaps suffered by users unaware of how Perl internally
317 =head2 Better diagnostics on meaningless filehandle operations
319 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
320 are compile time errors. Attempting to read from filehandles that
321 were opened only for writing will now produce warnings (just as
322 writing to read-only filehandles does).
324 =head2 Buffered data discarded from input filehandle when dup'ed.
326 C<open(NEW, "E<lt>&OLD")> now discards any data that was previously
327 read and buffered in C<OLD>. The next read operation on C<NEW> will
328 return the same data as the corresponding operation on C<OLD>.
329 Formerly, it would have returned the data from the start of the
330 following disk block instead.
332 =head1 Supported Platforms
338 VM/ESA is now supported.
342 Siemens BS2000 is now supported under the POSIX Shell.
346 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
351 GNU/Hurd is now supported.
355 Rhapsody is now supported.
359 EPOC is is now supported (on Psion 5).
369 IO constants (SEEK_*, _IO*).
373 Directory-related IO methods (new, read, close, rewind, tied delete).
375 =item op/io_multihomed
377 INET sockets with multi-homed hosts.
393 Verify operations that access pad objects (lexicals and temporaries).
397 =head1 Modules and Pragmata
405 The ByteLoader is a dedication extension to generate and run
406 Perl bytecode. See L<ByteLoader>.
410 The Perl Compiler suite has been extensively reworked for this
415 Devel::DProf, a Perl source code profiler has been added.
419 Added Dumpvalue module provides screen dumps of Perl data.
423 You can now run tests for I<n> seconds instead of guessing the right
424 number of tests to run: e.g. timethese(-5, ...) will run each
425 code for at least 5 CPU seconds. Zero as the "number of repetitions"
426 means "for at least 3 CPU seconds". The output format has also
427 changed. For example:
429 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
431 will now output something like this:
433 Benchmark: running a, b, each for at least 5 CPU seconds...
434 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
435 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
437 New features: "each for at least N CPU seconds...", "wallclock secs",
438 and the "@ operations/CPU second (n=operations)".
442 The Devel::Peek module provides access to the internal representation
443 of Perl variables and data. It is a data debugging tool for the XS programmer.
447 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
448 large (more than 4G) file access (64-bit support is not yet
449 working, though, so no need to get overly excited), Free/Net/OpenBSD
450 locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
451 O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.
455 New methods have been added to the File::Spec module: devnull() returns
456 the name of the null device (/dev/null on Unix) and tmpdir() the name of
457 the temp directory (normally /tmp on Unix). There are now also methods
458 to convert between absolute and relative filenames: abs2rel() and
459 rel2abs(). For compatibility with operating systems that specify volume
460 names in file paths, the splitpath(), splitdir(), and catdir() methods
463 =item File::Spec::Functions
465 The new File::Spec::Functions modules provides a function interface
466 to the File::Spec module. Allows shorthand
468 $fullname = catfile($dir1, $dir2, $file);
472 $fullname = File::Spec->catfile($dir1, $dir2, $file);
476 The logical operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
477 and C<~> are now supported on bigints.
481 The accessor methods Re, Im, arg, abs, rho, and theta can now also
482 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
486 A little bit of radial trigonometry (cylindrical and spherical),
487 radial coordinate conversions, and the great circle distance were added.
491 An EXISTS method has been added to this module (and sdbm_exists() has
492 been added to the underlying sdbm library), so one can now call exists
493 on an SDBM_File tied hash and get the correct result, rather than a
498 The timelocal() and timegm() functions used to silently return bogus
499 results when the date exceeded the machine's integer range. They
500 now consistently croak() if the date falls in an unsupported range.
504 The error return value in list context has been changed for all functions
505 that return a list of values. Previously these functions returned a list
506 with a single element C<undef> if an error occurred. Now these functions
507 return the empty list in these situations. This applies to the following
513 The remaining functions are unchanged and continue to return C<undef> on
514 error even in list context.
516 The Win32::SetLastError(ERROR) function has been added as a complement
517 to the Win32::GetLastError() function.
519 The new Win32::GetFullPathName(FILENAME) returns the full absolute
520 pathname for FILENAME in scalar context. In list context it returns
521 a two-element list containing the fully qualified directory name and
526 A new feature called "DBM Filters" has been added to all the
527 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
528 DBM Filters add four new methods to each DBM module:
535 These can be used to filter key-value pairs before the pairs are
536 written to the database or just after they are read from the database.
537 See L<perldbmfilter> for further information.
543 C<use utf8> to enable UTF-8 and Unicode support.
545 C<use caller 'encoding'> allows modules to inherit pragmatic attributes
546 from the caller's context. C<encoding> is currently the only supported
549 Lexical warnings pragma, C<use warning;>, to control optional warnings.
551 C<use filetest> to control the behaviour of filetests (C<-r> C<-w> ...).
552 Currently only one subpragma implemented, "use filetest 'access';",
553 that enables the use of access(2) or equivalent to check
554 permissions instead of using stat(2) as usual. This matters
555 in filesystems where there are ACLs (access control lists): the
556 stat(2) might lie, but access(2) knows better.
558 =head1 Utility Changes
562 =head1 Documentation Changes
566 =item perlopentut.pod
568 A tutorial on using open() effectively.
572 A tutorial that introduces the essentials of references.
576 A tutorial on managing class data for object modules.
580 =head1 New Diagnostics
582 =item /%s/: Unrecognized escape \\%c passed through
584 (W) You used a backslash-character combination which is not recognized
585 by Perl. This combination appears in an interpolated variable or a
586 C<'>-delimited regular expression.
588 =item Filehandle %s opened only for output
590 (W) You tried to read from a filehandle opened only for writing. If you
591 intended it to be a read-write filehandle, you needed to open it with
592 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
593 you intended only to read from the file, use "E<lt>". See
596 =item Missing command in piped open
598 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
599 construction, but the command was missing or blank.
601 =item Unrecognized escape \\%c passed through
603 (W) You used a backslash-character combination which is not recognized
606 =item defined(@array) is deprecated
608 (D) defined() is not usually useful on arrays because it checks for an
609 undefined I<scalar> value. If you want to see if the array is empty,
610 just use C<if (@array) { # not empty }> for example.
612 =item defined(%hash) is deprecated
614 (D) defined() is not usually useful on hashes because it checks for an
615 undefined I<scalar> value. If you want to see if the hash is empty,
616 just use C<if (%hash) { # not empty }> for example.
618 =head1 Obsolete Diagnostics
622 =head1 Configuration Changes
624 =head2 installusrbinperl
626 You can use "Configure -Uinstallusrbinperl" which causes installperl
627 to skip installing perl also as /usr/bin/perl. This is useful if you
628 prefer not to modify /usr/bin for some reason or another but harmful
629 because many scripts assume to find Perl in /usr/bin/perl.
633 You can use "Configure -Dusesocks" which causes Perl to probe
634 for the SOCKS proxy protocol library, http://www.socks.nec.com/
638 If you find what you think is a bug, you might check the headers of
639 articles recently posted to the comp.lang.perl.misc newsgroup.
640 There may also be information at http://www.perl.com/perl/, the Perl
643 If you believe you have an unreported bug, please run the B<perlbug>
644 program included with your release. Make sure to trim your bug down
645 to a tiny but sufficient test case. Your bug report, along with the
646 output of C<perl -V>, will be sent off to perlbug@perl.com to be
647 analysed by the Perl porting team.
651 The F<Changes> file for exhaustive details on what changed.
653 The F<INSTALL> file for how to build Perl.
655 The F<README> file for general stuff.
657 The F<Artistic> and F<Copying> files for copyright information.
661 Written by Gurusamy Sarathy <F<gsar@umich.edu>>, with many contributions
662 from The Perl Porters.
664 Send omissions or corrections to <F<perlbug@perl.com>>.