3 perldelta - what's new for perl v5.6 (as of v5.5.58)
7 This document describes differences between the 5.005 release and this one.
9 =head1 Incompatible Changes
11 =head2 Perl Source Incompatibilities
13 None known at this time.
15 =head2 C Source Incompatibilities
21 Release 5.005 grandfathered old global symbol names by providing preprocessor
22 macros for extension source compatibility. As of release 5.6, these
23 preprocessor definitions are not available by default. You need to explicitly
24 compile perl with C<-DPERL_POLLUTE> to get these definitions. For
25 extensions still using the old symbols, this option can be
26 specified via MakeMaker:
28 perl Makefile.PL POLLUTE=1
30 =item C<PERL_POLLUTE_MALLOC>
32 Enabling Perl's malloc in release 5.005 and earlier caused
33 the namespace of system versions of the malloc family of functions to
34 be usurped by the Perl versions, since by default they used the
37 Besides causing problems on platforms that do not allow these functions to
38 be cleanly replaced, this also meant that the system versions could not
39 be called in programs that used Perl's malloc. Previous versions of Perl
40 have allowed this behaviour to be suppressed with the HIDEMYMALLOC and
41 EMBEDMYMALLOC preprocessor definitions.
43 As of release 5.6, Perl's malloc family of functions have default names
44 distinct from the system versions. You need to explicitly compile perl with
45 C<-DPERL_POLLUTE_MALLOC> to get the older behaviour. HIDEMYMALLOC
46 and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
49 Note that these functions do B<not> constitute Perl's memory allocation API.
50 See L<perlguts/"Memory Allocation"> for further information about that.
52 =item C<PL_na> and C<dTHR> Issues
54 The C<PL_na> global is now thread local, so a C<dTHR> declaration is needed
55 in the scope in which the global appears. XSUBs should handle this automatically,
56 but if you have used C<PL_na> in support functions, you either need to
57 change the C<PL_na> to a local variable (which is recommended), or put in
62 =head2 Compatible C Source API Changes
66 =item C<PATCHLEVEL> is now C<PERL_VERSION>
68 The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
69 are now available by default from perl.h, and reflect the base revision,
70 patchlevel, and subversion respectively. C<PERL_REVISION> had no
71 prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
72 previously available as C<PATCHLEVEL> and C<SUBVERSION>.
74 The new names cause less pollution of the B<cpp> namespace and reflect what
75 the numbers have come to stand for in common practice. For compatibility,
76 the old names are still supported when F<patchlevel.h> is explicitly
77 included (as required before), so there is no source incompatibility
82 =head2 Binary Incompatibilities
84 This release is not binary compatible with the 5.005 release or its
89 =head2 Unicode and UTF-8 support
91 Perl can optionally use UTF-8 as its internal representation for character
92 strings. The C<use utf8> pragma enables this support in the current lexical
93 scope. See L<utf8> for more information.
95 =head2 Lexically scoped warning categories
97 You can now control the granularity of warnings emitted by perl at a finer
98 level using the C<use warning> pragma. See L<warning> and L<perllexwarn>
101 =head2 Binary numbers supported
103 Binary numbers are now supported as literals, in s?printf formats, and
107 printf "The answer is: %b\n", oct("0b101010");
109 =head2 Too large hexadecimal, octal, and binary constants more serious
111 Too large hexadecimal, octal, and binary constants now cause fatal errors.
113 =head2 syswrite() ease-of-use
115 The length argument of C<syswrite()> is now optional.
117 =head2 64-bit support
119 Better 64-bit support -- but full support still a distant goal. One
120 must Configure with -Duse64bits to get Configure to probe for the
121 extent of 64-bit support. Depending on the platform (hints file) more
122 or less 64-awareness becomes available. As of 5.005_54 at least
123 somewhat 64-bit aware platforms are HP-UX 11 or better, Solaris 2.6 or
124 better, IRIX 6.2 or better. Naturally 64-bit platforms like Digital
125 Unix and UNICOS also have 64-bit support.
127 =head2 Better syntax checks on parenthesized unary operators
131 print defined(&foo,&bar,&baz);
132 print uc("foo","bar","baz");
135 used to be accidentally allowed in earlier versions, and produced
136 unpredictable behaviour. Some produced ancillary warnings
137 when used in this way; others silently did the wrong thing.
139 The parenthesized forms of most unary operators that expect a single
140 argument now ensure that they are not called with more than one
141 argument, making the cases shown above syntax errors. The usual
144 print defined &foo, &bar, &baz;
145 print uc "foo", "bar", "baz";
148 remains unchanged. See L<perlop>.
150 =head2 POSIX character class syntax [: :] supported
152 For example to match alphabetic characters use /[[:alpha:]]/.
153 See L<perlre> for details.
155 =head2 Improved C<qw//> operator
157 The C<qw//> operator is now evaluated at compile time into a true list
158 instead of being replaced with a run time call to C<split()>. This
159 removes the confusing misbehaviour of C<qw//> in scalar context, which
160 had inherited that behaviour from split().
164 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
166 now correctly prints "3|a", instead of "2|a".
168 =head2 pack() format 'Z' supported
170 The new format type 'Z' is useful for packing and unpacking null-terminated
171 strings. See L<perlfunc/"pack">.
173 =head2 pack() format modifier '!' supported
175 The new format type modifier '!' is useful for packing and unpacking
176 native shorts, ints, and longs. See L<perlfunc/"pack">.
178 =head2 $^X variables may now have names longer than one character
180 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
181 error. Now variable names that begin with a control character may be
182 arbitrarily long. However, for compatibility reasons, these variables
183 I<must> be written with explicit braces, as C<${^XY}> for example.
184 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
185 than one control character, such as C<${^XY^Z}>, are illegal.
187 The old syntax has not changed. As before, `^X' may be either a
188 literal control-X character or the two-character sequence `caret' plus
189 `X'. When braces are omitted, the variable name stops after the
190 control character. Thus C<"$^XYZ"> continues to be synonymous with
191 C<$^X . "YZ"> as before.
193 As before, lexical variables may not have names beginning with control
194 characters. As before, variables whose names begin with a control
195 character are always forced to be in package `main'. All such variables
196 are reserved for future extensions, except those that begin with
197 C<^_>, which may be used by user programs and is guaranteed not to
198 acquire special meaning in any future version of Perl.
200 =head1 Significant bug fixes
202 =head2 E<lt>HANDLEE<gt> on empty files
204 With C<$/> set to C<undef>, slurping an empty file returns a string of
205 zero length (instead of C<undef>, as it used to) the first time the
206 HANDLE is read. Further reads yield C<undef>.
208 This means that the following will append "foo" to an empty file (it used
211 perl -0777 -pi -e 's/^/foo/' empty_file
215 perl -pi -e 's/^/foo/' empty_file
217 is unchanged (it continues to leave the file empty).
219 =head2 C<eval '...'> improvements
221 Line numbers (as reflected by caller() and most diagnostics) within
222 C<eval '...'> were often incorrect when here documents were involved.
223 This has been corrected.
225 Lexical lookups for variables appearing in C<eval '...'> within
226 functions that were themselves called within an C<eval '...'> were
227 searching the wrong place for lexicals. The lexical search now
228 correctly ends at the subroutine's block boundary.
230 Parsing of here documents used to be flawed when they appeared as
231 the replacement expression in C<eval 's/.../.../e'>. This has
234 =head2 Automatic flushing of output buffers
236 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
237 of all files opened for output when the operation
238 was attempted. This mostly eliminates confusing
239 buffering mishaps suffered by users unaware of how Perl internally
242 =head2 Better diagnostics on meaningless filehandle operations
244 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
245 are compile time errors. Attempting to read from filehandles that
246 were opened only for writing will now produce warnings (just as
247 writing to read-only filehandles does).
249 =head1 Supported Platforms
255 VM/ESA is now supported.
259 Siemens BS2000 is now supported under the POSIX Shell.
263 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
268 GNU/Hurd is now supported.
272 Rhapsody is now supported.
276 EPOC is is now supported (on Psion 5).
286 IO constants (SEEK_*, _IO*).
290 Directory-related IO methods (new, read, close, rewind, tied delete).
292 =item op/io_multihomed
294 INET sockets with multi-homed hosts.
310 Verify operations that access pad objects (lexicals and temporaries).
314 =head1 Modules and Pragmata
322 Added Dumpvalue module provides screen dumps of Perl data.
326 You can now run tests for I<n> seconds instead of guessing the right
327 number of tests to run: e.g. timethese(-5, ...) will run each
328 code for at least 5 CPU seconds. Zero as the "number of repetitions"
329 means "for at least 3 CPU seconds". The output format has also
330 changed. For example:
332 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
334 will now output something like this:
336 Benchmark: running a, b, each for at least 5 CPU seconds...
337 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
338 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
340 New features: "each for at least N CPU seconds...", "wallclock secs",
341 and the "@ operations/CPU second (n=operations)".
345 The Devel::Peek module provides access to the internal representation
346 of Perl variables and data. It is a data debugging tool for the XS programmer.
350 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
351 large (more than 4G) file access (64-bit support is not yet
352 working, though, so no need to get overly excited), Free/Net/OpenBSD
353 locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
354 O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.
358 New methods have been added to the File::Spec module: devnull() returns
359 the name of the null device (/dev/null on Unix) and tmpdir() the name of
360 the temp directory (normally /tmp on Unix). There are now also methods
361 to convert between absolute and relative filenames: abs2rel() and
362 rel2abs(). For compatibility with operating systems that specify volume
363 names in file paths, the splitpath(), splitdir(), and catdir() methods
366 =item File::Spec::Functions
368 The new File::Spec::Functions modules provides a function interface
369 to the File::Spec module. Allows shorthand
371 $fullname = catfile($dir1, $dir2, $file);
375 $fullname = File::Spec->catfile($dir1, $dir2, $file);
379 The logical operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
380 and C<~> are now supported on bigints.
384 The accessor methods Re, Im, arg, abs, rho, and theta can now also
385 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
389 A little bit of radial trigonometry (cylindrical and spherical),
390 radial coordinate conversions, and the great circle distance were added.
394 An EXISTS method has been added to this module (and sdbm_exists() has
395 been added to the underlying sdbm library), so one can now call exists
396 on an SDBM_File tied hash and get the correct result, rather than a
401 The timelocal() and timegm() functions used to silently return bogus
402 results when the date exceeded the machine's integer range. They
403 now consistently croak() if the date falls in an unsupported range.
407 The error return value in list context has been changed for all functions
408 that return a list of values. Previously these functions returned a list
409 with a single element C<undef> if an error occurred. Now these functions
410 return the empty list in these situations. This applies to the following
416 The remaining functions are unchanged and continue to return C<undef> on
417 error even in list context.
419 The Win32::SetLastError(ERROR) function has been added as a complement
420 to the Win32::GetLastError() function.
422 The new Win32::GetFullPathName(FILENAME) returns the full absolute
423 pathname for FILENAME in scalar context. In list context it returns
424 a two-element list containing the fully qualified directory name and
429 A new feature called "DBM Filters" has been added to all the
430 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
431 DBM Filters add four new methods to each DBM module:
438 These can be used to filter key-value pairs before the pairs are
439 written to the database or just after they are read from the database.
440 See L<perldbmfilter> for further information.
446 C<use utf8> to enable UTF-8 and Unicode support.
448 C<use caller 'encoding'> allows modules to inherit pragmatic attributes
449 from the caller's context. C<encoding> is currently the only supported
452 Lexical warnings pragma, C<use warning;>, to control optional warnings.
454 C<use filetest> to control the behaviour of filetests (C<-r> C<-w> ...).
455 Currently only one subpragma implemented, "use filetest 'access';",
456 that enables the use of access(2) or equivalent to check
457 permissions instead of using stat(2) as usual. This matters
458 in filesystems where there are ACLs (access control lists): the
459 stat(2) might lie, but access(2) knows better.
461 =head1 Utility Changes
465 =head1 Documentation Changes
469 =item perlopentut.pod
471 A tutorial on using open() effectively.
475 A tutorial that introduces the essentials of references.
479 A tutorial on managing class data for object modules.
483 =head1 New Diagnostics
485 =item /%s/: Unrecognized escape \\%c passed through
487 (W) You used a backslash-character combination which is not recognized
488 by Perl. This combination appears in an interpolated variable or a
489 C<'>-delimited regular expression.
491 =item Filehandle %s opened only for output
493 (W) You tried to read from a filehandle opened only for writing. If you
494 intended it to be a read-write filehandle, you needed to open it with
495 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
496 you intended only to read from the file, use "E<lt>". See
499 =item Missing command in piped open
501 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
502 construction, but the command was missing or blank.
504 =item Unrecognized escape \\%c passed through
506 (W) You used a backslash-character combination which is not recognized
509 =item defined(@array) is deprecated
511 (D) defined() is not usually useful on arrays because it checks for an
512 undefined I<scalar> value. If you want to see if the array is empty,
513 just use C<if (@array) { # not empty }> for example.
515 =item defined(%hash) is deprecated
517 (D) defined() is not usually useful on hashes because it checks for an
518 undefined I<scalar> value. If you want to see if the hash is empty,
519 just use C<if (%hash) { # not empty }> for example.
521 =head1 Obsolete Diagnostics
525 =head1 Configuration Changes
527 =head2 installusrbinperl
529 You can use "Configure -Uinstallusrbinperl" which causes installperl
530 to skip installing perl also as /usr/bin/perl. This is useful if you
531 prefer not to modify /usr/bin for some reason or another but harmful
532 because many scripts assume to find Perl in /usr/bin/perl.
536 You can use "Configure -Dusesocks" which causes Perl to probe
537 for the SOCKS proxy protocol library, http://www.socks.nec.com/
541 If you find what you think is a bug, you might check the headers of
542 articles recently posted to the comp.lang.perl.misc newsgroup.
543 There may also be information at http://www.perl.com/perl/, the Perl
546 If you believe you have an unreported bug, please run the B<perlbug>
547 program included with your release. Make sure to trim your bug down
548 to a tiny but sufficient test case. Your bug report, along with the
549 output of C<perl -V>, will be sent off to perlbug@perl.com to be
550 analysed by the Perl porting team.
554 The F<Changes> file for exhaustive details on what changed.
556 The F<INSTALL> file for how to build Perl.
558 The F<README> file for general stuff.
560 The F<Artistic> and F<Copying> files for copyright information.
564 Written by Gurusamy Sarathy <F<gsar@umich.edu>>, with many contributions
565 from The Perl Porters.
567 Send omissions or corrections to <F<perlbug@perl.com>>.