3 perldelta - what's new for perl5.004
7 This document describes differences between the 5.003 release (as
8 documented in I<Programming Perl>, second edition--the Camel Book) and
11 =head1 Supported Environments
13 Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2,
18 Most importantly, many bugs were fixed. See the F<Changes>
19 file in the distribution for details.
21 =head2 Compilation Option: Binary Compatibility With 5.003
23 There is a new Configure question that asks if you want to maintain
24 binary compatibility with Perl 5.003. If you choose binary
25 compatibility, you do not have to recompile your extensions, but you
26 might have symbol conflicts if you embed Perl in another application,
27 just as in the 5.003 release. By default, binary compatibility
28 is preserved at the expense of symbol table pollution.
30 =head2 Creation of Subroutine argumnets only when necessary
32 In Perl 5.004, array and hash elements used as subroutine parameters
33 are brought into existence if they did not already exist only if the
34 argument is actually assigned to. In Perl versions 5.002 and 5.003,
35 such arguments were always brought into existence. Versions before
36 5.002 never brought such arguments into existence.
40 sub foo { print $_[0] };
45 $a{b} exists but $a[2] does not in Perl5.004; in Perl 5.002 and 5.003
48 =head2 Fixed Parsing of $$<digit>, &$<digit>, etc.
50 A bug in previous versions of Perl 5.0 prevented proper parsing of
51 numeric special variables as symbolic references. That bug has been
52 fixed. As a result, the string "$$0" is no longer equivalent to
53 C<$$."0">, but rather to C<${$0}>. To get the old behavior, change
54 "$$" followed by a digit to "${$}".
56 =head2 No Resetting of $. on Implicit Close
58 The documentation for Perl 5.0 has always stated that C<$.> is I<not>
59 reset when an already-open file handle is re-opened with no intervening
60 call to C<close>. Due to a bug, perl versions 5.000 through 5.0003
61 I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
63 =head2 Changes to Tainting Checks
65 A bug in previous versions may have failed to detect some insecure
66 conditions when taint checks are turned on. (Taint checks are used
67 in setuid or setgid scripts, or when explicitly turned on with the
68 C<-T> invocation option.) Although it's unlikely, this may cause a
69 previously-working script to now fail -- which should be construed
70 as a blessing, since that indicates a potentially-serious security
71 hole was just plugged.
73 =head2 New Opcode Module and Revised Safe Module
75 A new Opcode module supports the creation, manipulation and
76 application of opcode masks. The revised Safe module has a new API
77 and is implemented using the new Opcode module. Please read the new
78 Opcode and Safe documentation.
80 =head2 Embedding Improvements
82 In older versions of Perl it was not possible to create more than one
83 Perl interpreter instance inside a single process without leaking like a
84 sieve and/or crashing. The bugs that caused this behavior have all been
85 fixed. However, you still must take care when embedding Perl in a C
86 program. See the updated perlembed manpage for tips on how to manage
89 =head2 Internal Change: FileHandle Class Based on IO::* Classes
91 File handles are now stored internally as type IO::Handle. The
92 FileHandle module is still supported for backwards compatibility, but
93 it is now merely a front end to the IO::* modules -- specifically,
94 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
95 require, that you use the IO::* modules in new code.
97 In harmony with this change, C<*GLOB{FILEHANDLE}> is now a
98 backward-compatible synonym for C<*STDOUT{IO}>.
100 =head2 Internal Change: PerlIO internal IO abstraction interface
102 It is now possible to build Perl with AT&T's sfio IO package
103 instead of stdio. See L<perlapio> for more details, and
104 the F<INSTALL> file for how to use it.
106 =head2 New and Changed Built-in Variables
112 Extended error message on some platforms. (Also known as
113 $EXTENDED_OS_ERROR if you C<use English>).
117 The current set of syntax checks enabled by C<use strict>. See the
118 documentation of C<strict> for more details. Not actually new, but
120 Because it is intended for internal use by Perl core components,
121 there is no C<use English> long name for this variable.
125 By default, running out of memory it is not trappable. However, if
126 compiled for this, Perl may use the contents of C<$^M> as an emergency
127 pool after die()ing with this message. Suppose that your Perl were
128 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
132 would allocate a 64K buffer for use when in emergency.
133 See the F<INSTALL> file for information on how to enable this option.
134 As a disincentive to casual use of this advanced feature,
135 there is no C<use English> long name for this variable.
139 =head2 New and Changed Built-in Functions
143 =item delete on slices
145 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
149 is now supported on more platforms, prefers fcntl to lockf when
150 emulating, and always flushes before (un)locking.
152 =item printf and sprintf
154 now support "%i" as a synonym for "%d", and the "h" modifier.
155 So "%hi" means "short integer in decimal", and "%ho" means
156 "unsigned short integer as octal".
158 =item keys as an lvalue
160 As an lvalue, C<keys> allows you to increase the number of hash buckets
161 allocated for the given hash. This can gain you a measure of efficiency if
162 you know the hash is going to get big. (This is similar to pre-extending
163 an array by assigning a larger number to $#array.) If you say
167 then C<%hash> will have at least 200 buckets allocated for it. These
168 buckets will be retained even if you do C<%hash = ()>; use C<undef
169 %hash> if you want to free the storage while C<%hash> is still in scope.
170 You can't shrink the number of buckets allocated for the hash using
171 C<keys> in this way (but you needn't worry about doing this by accident,
172 as trying has no effect).
174 =item my() in Control Structures
176 You can now use my() (with or without the parentheses) in the control
177 expressions of control structures such as:
179 while (defined(my $line = <>)) {
185 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
187 } elsif ($answer =~ /^n(o)?$/i) {
191 die "`$answer' is neither `yes' nor `no'";
194 Also, you can declare a foreach loop control variable as lexical by
195 preceding it with the word "my". For example, in:
197 foreach my $i (1, 2, 3) {
201 $i is a lexical variable, and the scope of $i extends to the end of
202 the loop, but not beyond it.
204 Note that you still cannot use my() on global punctuation variables
205 such as $_ and the like.
207 =item unpack() and pack()
209 A new format 'w' represents a BER compressed integer (as defined in
210 ASN.1). Its format is a sequence of one or more bytes, each of which
211 provides seven bits of the total value, with the most significant
212 first. Bit eight of each byte is set, except for the last byte, in
213 which bit eight is clear.
217 If the first argument to C<use> is a number, it is treated as a version
218 number instead of a module name. If the version of the Perl interpreter
219 is less than VERSION, then an error message is printed and Perl exits
220 immediately. Because C<use> occurs at compile time, this check happens
221 immediately during the compilation process, unlike C<require VERSION>,
222 which waits until run-time for the check. This is often useful if you
223 need to check the current Perl version before C<use>ing library modules
224 which have changed in incompatible ways from older versions of Perl.
225 (We try not to do this more than we have to.)
227 =item use Module VERSION LIST
229 If the VERSION argument is present between Module and LIST, then the
230 C<use> will call the VERSION method in class Module with the given
231 version as an argument. The default VERSION method, inherited from
232 the Universal class, croaks if the given version is larger than the
233 value of the variable $Module::VERSION. (Note that there is not a
234 comma after VERSION!)
236 This version-checking mechanism is similar to the one currently used
237 in the Exporter module, but it is faster and can be used with modules
238 that don't use the Exporter. It is the recommended method for new
241 =item prototype(FUNCTION)
243 Returns the prototype of a function as a string (or C<undef> if the
244 function has no prototype). FUNCTION is a reference to or the name of the
245 function whose prototype you want to retrieve.
246 (Not actually new; just never documented before.)
250 The default seed for C<srand>, which used to be C<time>, has been changed.
251 Now it's a heady mix of difficult-to-predict system-dependent values,
252 which should be sufficient for most everyday purposes.
254 Previous to version 5.004, calling C<rand> without first calling C<srand>
255 would yield the same sequence of random numbers on most or all machines.
256 Now, when perl sees that you're calling C<rand> and haven't yet called
257 C<srand>, it calls C<srand> with the default seed. You should still call
258 C<srand> manually if your code might ever be run on a pre-5.004 system,
259 of course, or if you want a seed other than the default.
263 Functions documented in the Camel to default to $_ now in
264 fact do, and all those that do are so documented in L<perlfunc>.
266 =item C<m//g> does not trigger a pos() reset on failure
268 The C<m//g> match iteration construct used to reset the iteration
269 when it failed to match (so that the next C<m//g> match would start at
270 the beginning of the string). You now have to explicitly do a
271 C<pos $str = 0;> to reset the "last match" position, or modify the
272 string in some way. This change makes it practical to chain C<m//g>
273 matches together in conjunction with ordinary matches using the C<\G>
274 zero-width assertion. See L<perlop> and L<perlre>.
276 =item nested C<sub{}> closures work now
278 Prior to the 5.004 release, nested anonymous functions didn't work
281 =item formats work right on changing lexicals
283 Just like anonymous functions that contain lexical variables
284 that change (like a lexical index variable for a C<foreach> loop),
285 formats now work properly. For example, this silently failed
286 before, and is fine now:
289 foreach $i ( 1 .. 10 ) {
299 =head2 New Built-in Methods
301 The C<UNIVERSAL> package automatically contains the following methods that
302 are inherited by all other classes:
308 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
310 C<isa> is also exportable and can be called as a sub with two arguments. This
311 allows the ability to check what a reference points to. Example:
313 use UNIVERSAL qw(isa);
315 if(isa($ref, 'ARRAY')) {
321 C<can> checks to see if its object has a method called C<METHOD>,
322 if it does then a reference to the sub is returned; if it does not then
323 I<undef> is returned.
325 =item VERSION( [NEED] )
327 C<VERSION> returns the version number of the class (package). If the
328 NEED argument is given then it will check that the current version (as
329 defined by the $VERSION variable in the given package) not less than
330 NEED; it will die if this is not the case. This method is normally
331 called as a class method. This method is called automatically by the
332 C<VERSION> form of C<use>.
334 use A 1.2 qw(some imported subs);
340 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
341 C<isa> uses a very similar method and caching strategy. This may cause
342 strange effects if the Perl code dynamically changes @ISA in any package.
344 You may add other methods to the UNIVERSAL class via Perl or XS code.
345 You do not need to C<use UNIVERSAL> in order to make these methods
346 available to your program. This is necessary only if you wish to
347 have C<isa> available as a plain subroutine in the current package.
349 =head2 TIEHANDLE Now Supported
351 See L<perltie> for other kinds of tie()s.
355 =item TIEHANDLE classname, LIST
357 This is the constructor for the class. That means it is expected to
358 return an object of some sort. The reference can be used to
359 hold some internal information.
364 return bless \$i, shift;
367 =item PRINT this, LIST
369 This method will be triggered every time the tied handle is printed to.
370 Beyond its self reference it also expects the list that was passed to
376 return print join( $, => map {uc} @_), $\;
381 This method will be called when the handle is read from via the C<read>
382 or C<sysread> functions.
386 my($buf,$len,$offset) = @_;
387 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
392 This method will be called when the handle is read from. The method
393 should return undef when there is no more data.
397 return "PRINT called $$r times\n"
402 This method will be called when the C<getc> function is called.
404 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
408 As with the other types of ties, this method will be called when the
409 tied handle is about to be destroyed. This is useful for debugging and
410 possibly for cleaning up.
418 =head2 Malloc Enhancements
420 Four new compilation flags are recognized by malloc.c. (They have no
421 effect if perl is compiled with system malloc().)
425 =item -DDEBUGGING_MSTATS
427 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
428 memory statistics at runtime by running Perl thusly:
430 env PERL_DEBUG_MSTATS=2 perl your_script_here
432 The value of 2 means to print statistics after compilation and on
433 exit; with a value of 1, the statistics ares printed only on exit.
434 (If you want the statistics at an arbitrary time, you'll need to
435 install the optional module Devel::Peek.)
437 =item -DEMERGENCY_SBRK
439 If this macro is defined, running out of memory need not be a fatal
440 error: a memory pool can allocated by assigning to the special
441 variable C<$^M>. See L<"$^M">.
445 Perl memory allocation is by bucket with sizes close to powers of two.
446 Because of these malloc overhead may be big, especially for data of
447 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
448 a slightly different algorithm for small allocations (up to 64 bytes
449 long), which makes it possible to have overhead down to 1 byte for
450 allocations which are powers of two (and appear quite often).
452 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
453 about 20% for typical Perl usage. Expected slowdown due to additional
454 malloc overhead is in fractions of a percent (hard to measure, because
455 of the effect of saved memory on speed).
457 =item -DTWO_POT_OPTIMIZE
459 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
460 with size close to a power of two; but this works for big allocations
461 (starting with 16K by default). Such allocations are typical for big
462 hashes and special-purpose scripts, especially image processing.
464 On recent systems, the fact that perl requires 2M from system for 1M
465 allocation will not affect speed of execution, since the tail of such
466 a chunk is not going to be touched (and thus will not require real
467 memory). However, it may result in a premature out-of-memory error.
468 So if you will be manipulating very large blocks with sizes close to
469 powers of two, it would be wise to define this macro.
471 Expected saving of memory is 0-100% (100% in applications which
472 require most memory in such 2**n chunks); expected slowdown is
477 =head2 Miscellaneous Efficiency Enhancements
479 Functions that have an empty prototype and that do nothing but return
480 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
482 Each unique hash key is only allocated once, no matter how many hashes
483 have an entry with that key. So even if you have 100 copies of the
484 same hash, the hash keys never have to be reallocated.
488 Four new pragmatic modules exist:
496 Looks for MakeMaker-like I<'blib'> directory structure starting in
497 I<dir> (or current directory) and working back up to five levels of
500 Intended for use on command line with B<-M> option as a way of testing
501 arbitrary scripts against an uninstalled version of a package.
505 Tells the compiler to enable (or disable) the use of POSIX locales for
508 When C<use locale> is in effect, the current LC_CTYPE locale is used
509 for regular expressions and case mapping; LC_COLLATE for string
510 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
511 (but B<not> in print). LC_NUMERIC is always used in write, since
512 lexical scoping of formats is problematic at best.
514 Each C<use locale> or C<no locale> affects statements to the end of
515 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
516 current file. Locales can be switched and queried with
519 See L<perllocale> for more information.
523 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
527 Enable VMS-specific language features. Currently, there are three
528 VMS-specific features available: 'status', which makes C<$?> and
529 C<system> return genuine VMS status values instead of emulating POSIX;
530 'exit', which makes C<exit> take a genuine VMS status value instead of
531 assuming that C<exit 1> is an error; and 'time', which makes all times
532 relative to the local time zone, in the VMS tradition.
538 =head2 Installation Directories
540 The I<installperl> script now places the Perl source files for
541 extensions in the architecture-specific library directory, which is
542 where the shared libraries for extensions have always been. This
543 change is intended to allow administrators to keep the Perl 5.004
544 library directory unchanged from a previous version, without running
545 the risk of binary incompatibility between extensions' Perl source and
550 New constants in the existing Fcntl modules are now supported,
551 provided that your operating system happens to support them:
554 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
557 These constants are intended for use with the Perl operators sysopen()
558 and fcntl() and the basic database modules like SDBM_File. For the
559 exact meaning of these and other Fcntl constants please refer to your
560 operating system's documentation for fcntl() and open().
562 In addition, the Fcntl module now provides these constants for use
563 with the Perl operator flock():
565 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
567 These constants are defined in all environments (because where there is
568 no flock() system call, Perl emulates it). However, for historical
569 reasons, these constants are not exported unless they are explicitly
570 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
572 =head2 Module Information Summary
574 Brand new modules, arranged by topic rather than strictly
577 CPAN interface to Comprehensive Perl Archive Network
578 CPAN::FirstTime create a CPAN configuration file
579 CPAN::Nox run CPAN while avoiding compiled extensions
581 IO.pm Top-level interface to IO::* classes
582 IO/File.pm IO::File extension Perl module
583 IO/Handle.pm IO::Handle extension Perl module
584 IO/Pipe.pm IO::Pipe extension Perl module
585 IO/Seekable.pm IO::Seekable extension Perl module
586 IO/Select.pm IO::Select extension Perl module
587 IO/Socket.pm IO::Socket extension Perl module
589 Opcode.pm Disable named opcodes when compiling Perl code
591 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
592 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
594 FindBin.pm Find path of currently executing program
596 Class/Template.pm Structure/member template builder
597 File/stat.pm Object-oriented wrapper around CORE::stat
598 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
599 Net/netent.pm Object-oriented wrapper around CORE::getnet*
600 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
601 Net/servent.pm Object-oriented wrapper around CORE::getserv*
602 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
603 Time/localtime.pm Object-oriented wrapper around CORE::localtime
604 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
605 User/grent.pm Object-oriented wrapper around CORE::getgr*
606 User/pwent.pm Object-oriented wrapper around CORE::getpw*
608 Tie/RefHash.pm Base class for tied hashes with references as keys
610 UNIVERSAL.pm Base class for *ALL* classes
614 The IO module provides a simple mechanism to load all of the IO modules at one
615 go. Currently this includes:
623 For more information on any of these modules, please see its
624 respective documentation.
628 The Math::Complex module has been totally rewritten, and now supports
629 more operations. These are overloaded:
631 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
633 And these functions are now exported:
637 tan cotan asin acos atan acotan
638 sinh cosh tanh cotanh asinh acosh atanh acotanh
643 There have been quite a few changes made to DB_File. Here are a few of
650 Fixed a handful of bugs.
654 By public demand, added support for the standard hash function exists().
658 Made it compatible with Berkeley DB 1.86.
662 Made negative subscripts work with RECNO interface.
666 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
667 mode from 0640 to 0666.
671 Made DB_File automatically import the open() constants (O_RDWR,
672 O_CREAT etc.) from Fcntl, if available.
676 Updated documentation.
680 Refer to the HISTORY section in DB_File.pm for a complete list of
681 changes. Everything after DB_File 1.01 has been added since 5.003.
685 Major rewrite - support added for both udp echo and real icmp pings.
687 =head2 Overridden Built-ins
689 Many of the Perl built-ins returning lists now have
690 object-oriented overrides. These are:
702 For example, you can now say
706 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
708 =head1 Utility Changes
714 =item C<void> XSUBs now default to returning nothing
716 Due to a documentation/implementation bug in previous versions of
717 Perl, XSUBs with a return type of C<void> have actually been
718 returning one value. Usually that value was the GV for the XSUB,
719 but sometimes it was some already freed or reused value, which would
720 sometimes lead to program failure.
722 In Perl 5.004, if an XSUB is declared as returning C<void>, it
723 actually returns no value, i.e. an empty list (though there is a
724 backward-compatibility exception; see below). If your XSUB really
725 does return an SV, you should give it a return type of C<SV *>.
727 For backward compatibility, I<xsubpp> tries to guess whether a
728 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
729 It does so by examining the text of the XSUB: if I<xsubpp> finds
730 what looks like an assignment to C<ST(0)>, it assumes that the
731 XSUB's return type is really C<SV *>.
735 =head1 C Language API Changes
739 =item C<gv_fetchmethod> and C<perl_call_sv>
741 The C<gv_fetchmethod> function finds a method for an object, just like
742 in Perl 5.003. The GV it returns may be a method cache entry.
743 However, in Perl 5.004, method cache entries are not visible to users;
744 therefore, they can no longer be passed directly to C<perl_call_sv>.
745 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
746 and pass the CV to C<perl_call_sv>.
748 The most likely symptom of passing the result of C<gv_fetchmethod> to
749 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
750 error on the I<second> call to a given method (since there is no cache
753 =item Extended API for manipulating hashes
755 Internal handling of hash keys has changed. The old hashtable API is
756 still fully supported, and will likely remain so. The additions to the
757 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
758 real scalars as keys rather than plain strings (non-tied hashes still
759 can only use strings as keys). New extensions must use the new hash
760 access functions and macros if they wish to use C<SV*> keys. These
761 additions also make it feasible to manipulate C<HE*>s (hash entries),
762 which can be more efficient. See L<perlguts> for details.
766 =head1 Documentation Changes
768 Many of the base and library pods were updated. These
769 new pods are included in section 1:
779 Locale support (internationalization and localization).
783 Tutorial on Perl OO programming.
787 Perl internal IO abstraction interface.
791 Although not new, this has been massively updated.
795 Although not new, this has been massively updated.
799 =head1 New Diagnostics
801 Several new conditions will trigger warnings that were
802 silent before. Some only affect certain platforms.
803 The following new warnings and errors outline these.
804 These messages are classified as follows (listed in
805 increasing order of desperation):
807 (W) A warning (optional).
808 (D) A deprecation (optional).
809 (S) A severe warning (mandatory).
810 (F) A fatal error (trappable).
811 (P) An internal error you should never see (trappable).
812 (X) A very fatal error (non-trappable).
813 (A) An alien error message (not generated by Perl).
817 =item "my" variable %s masks earlier declaration in same scope
819 (S) A lexical variable has been redeclared in the same scope, effectively
820 eliminating all access to the previous instance. This is almost always
821 a typographical error. Note that the earlier variable will still exist
822 until the end of the scope or until all closure referents to it are
825 =item %s argument is not a HASH element or slice
827 (F) The argument to delete() must be either a hash element, such as
830 $ref->[12]->{"susie"}
832 or a hash slice, such as
834 @foo{$bar, $baz, $xyzzy}
835 @{$ref->[12]}{"susie", "queue"}
837 =item Allocation too large: %lx
839 (X) You can't allocate more than 64K on an MSDOS machine.
841 =item Allocation too large
843 (F) You can't allocate more than 2^31+"small amount" bytes.
845 =item Attempt to free non-existent shared string
847 (P) Perl maintains a reference counted internal table of strings to
848 optimize the storage and access of hash keys and other strings. This
849 indicates someone tried to decrement the reference count of a string
850 that can no longer be found in the table.
852 =item Attempt to use reference as lvalue in substr
854 (W) You supplied a reference as the first argument to substr() used
855 as an lvalue, which is pretty strange. Perhaps you forgot to
856 dereference it first. See L<perlfunc/substr>.
858 =item Unsupported function fork
860 (F) Your version of executable does not support forking.
862 Note that under some systems, like OS/2, there may be different flavors of
863 Perl executables, some of which may support fork, some not. Try changing
864 the name you call Perl by to C<perl_>, C<perl__>, and so on.
866 =item Ill-formed logical name |%s| in prime_env_iter
868 (W) A warning peculiar to VMS. A logical name was encountered when preparing
869 to iterate over %ENV which violates the syntactic rules governing logical
870 names. Since it cannot be translated normally, it is skipped, and will not
871 appear in %ENV. This may be a benign occurrence, as some software packages
872 might directly modify logical name tables and introduce non-standard names,
873 or it may indicate that a logical name table has been corrupted.
875 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
877 (F) Only hard references are allowed by "strict refs". Symbolic references
878 are disallowed. See L<perlref>.
880 =item Constant subroutine %s redefined
882 (S) You redefined a subroutine which had previously been eligible for
883 inlining. See L<perlsub/"Constant Functions"> for commentary and
888 (F) You passed die() an empty string (the equivalent of C<die "">) or
889 you called it with no args and both C<$@> and C<$_> were empty.
891 =item Integer overflow in hex number
893 (S) The literal hex number you have specified is too big for your
894 architecture. On a 32-bit architecture the largest hex literal is
897 =item Integer overflow in octal number
899 (S) The literal octal number you have specified is too big for your
900 architecture. On a 32-bit architecture the largest octal literal is
903 =item Name "%s::%s" used only once: possible typo
905 (W) Typographical errors often show up as unique variable names.
906 If you had a good reason for having a unique name, then just mention
907 it again somehow to suppress the message (the C<use vars> pragma is
908 provided for just this purpose).
910 =item Null picture in formline
912 (F) The first argument to formline must be a valid format picture
913 specification. It was found to be empty, which probably means you
914 supplied it an uninitialized value. See L<perlform>.
916 =item Offset outside string
918 (F) You tried to do a read/write/send/recv operation with an offset
919 pointing outside the buffer. This is difficult to imagine.
920 The sole exception to this is that C<sysread()>ing past the buffer
921 will extend the buffer and zero pad the new area.
923 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
925 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
926 Stubs should never be implicitely created, but explicit calls to C<can>
929 =item Cannot resolve method `%s' overloading `%s' in package `s'
931 (P) Internal error trying to resolve overloading specified by a method
932 name (as opposed to a subroutine reference).
936 (X|F) The malloc() function returned 0, indicating there was insufficient
937 remaining memory (or virtual memory) to satisfy the request.
939 The request was judged to be small, so the possibility to trap it
940 depends on the way Perl was compiled. By default it is not trappable.
941 However, if compiled for this, Perl may use the contents of C<$^M> as
942 an emergency pool after die()ing with this message. In this case the
943 error is trappable I<once>.
945 =item Out of memory during request for %s
947 (F) The malloc() function returned 0, indicating there was insufficient
948 remaining memory (or virtual memory) to satisfy the request. However,
949 the request was judged large enough (compile-time default is 64K), so
950 a possibility to shut down by trapping this error is granted.
952 =item Possible attempt to put comments in qw() list
954 (W) qw() lists contain items separated by whitespace; as with literal
955 strings, comment characters are not ignored, but are instead treated
956 as literal data. (You may have used different delimiters than the
957 exclamation marks parentheses shown here; braces are also frequently
960 You probably wrote something like this:
967 when you should have written this:
974 If you really want comments, build your list the
975 old-fashioned way, with quotes and commas:
979 'b', # another comment
982 =item Possible attempt to separate words with commas
984 (W) qw() lists contain items separated by whitespace; therefore commas
985 aren't needed to separate the items. (You may have used different
986 delimiters than the parentheses shown here; braces are also frequently
989 You probably wrote something like this:
993 which puts literal commas into some of the list items. Write it without
994 commas if you don't want them to appear in your data:
998 =item Scalar value @%s{%s} better written as $%s{%s}
1000 (W) You've used a hash slice (indicated by @) to select a single element of
1001 a hash. Generally it's better to ask for a scalar value (indicated by $).
1002 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1003 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1004 like a list when you assign to it, and provides a list context to its
1005 subscript, which can do weird things if you're expecting only one subscript.
1007 =item untie attempted while %d inner references still exist
1009 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1010 valid when C<untie> was called.
1012 =item Value of %s construct can be "0"; test with defined()
1014 (W) In a conditional expression, you used <HANDLE>, <*> (glob), or
1015 C<readdir> as a boolean value. Each of these constructs can return a
1016 value of "0"; that would make the conditional expression false, which
1017 is probably not what you intended. When using these constructs in
1018 conditional expressions, test their values with the C<defined> operator.
1020 =item Variable "%s" may be unavailable
1022 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1023 subroutine, and outside that is another subroutine; and the anonymous
1024 (innermost) subroutine is referencing a lexical variable defined in
1025 the outermost subroutine. For example:
1027 sub outermost { my $a; sub middle { sub { $a } } }
1029 If the anonymous subroutine is called or referenced (directly or
1030 indirectly) from the outermost subroutine, it will share the variable
1031 as you would expect. But if the anonymous subroutine is called or
1032 referenced when the outermost subroutine is not active, it will see
1033 the value of the shared variable as it was before and during the
1034 *first* call to the outermost subroutine, which is probably not what
1037 In these circumstances, it is usually best to make the middle
1038 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1039 support for shared variables in nested anonymous subroutines; a named
1040 subroutine in between interferes with this feature.
1042 =item Variable "%s" will not stay shared
1044 (W) An inner (nested) I<named> subroutine is referencing a lexical
1045 variable defined in an outer subroutine.
1047 When the inner subroutine is called, it will probably see the value of
1048 the outer subroutine's variable as it was before and during the
1049 *first* call to the outer subroutine; in this case, after the first
1050 call to the outer subroutine is complete, the inner and outer
1051 subroutines will no longer share a common value for the variable. In
1052 other words, the variable will no longer be shared.
1054 Furthermore, if the outer subroutine is anonymous and references a
1055 lexical variable outside itself, then the outer and inner subroutines
1056 will I<never> share the given variable.
1058 This problem can usually be solved by making the inner subroutine
1059 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1060 reference variables in outer subroutines are called or referenced,
1061 they are automatically re-bound to the current values of such
1064 =item Warning: something's wrong
1066 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1067 you called it with no args and C<$_> was empty.
1069 =item Got an error from DosAllocMem
1071 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1072 version of Perl, and this should not happen anyway.
1074 =item Malformed PERLLIB_PREFIX
1076 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1084 with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of
1085 a builtin library search path, prefix2 is substituted. The error may appear
1086 if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">.
1088 =item PERL_SH_DIR too long
1090 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1091 C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">.
1093 =item Process terminated by SIG%s
1095 (W) This is a standard message issued by OS/2 applications, while *nix
1096 applications die in silence. It is considered a feature of the OS/2
1097 port. One can easily disable this by appropriate sighandlers, see
1098 L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">.
1104 If you find what you think is a bug, you might check the headers of
1105 recently posted articles in the comp.lang.perl.misc newsgroup.
1106 There may also be information at http://www.perl.com/perl/, the Perl
1109 If you believe you have an unreported bug, please run the B<perlbug>
1110 program included with your release. Make sure you trim your bug down
1111 to a tiny but sufficient test case. Your bug report, along with the
1112 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1113 analysed by the Perl porting team.
1117 The F<Changes> file for exhaustive details on what changed.
1119 The F<INSTALL> file for how to build Perl. This file has been
1120 significantly updated for 5.004, so even veteran users should
1123 The F<README> file for general stuff.
1125 The F<Copying> file for copyright information.
1129 Constructed by Tom Christiansen, grabbing material with permission
1130 from innumerable contributors, with kibitzing by more than a few Perl
1133 Last update: Sat Mar 8 19:51:26 EST 1997