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 Subroutine Parameters Are Not Autovivified
32 In Perl versions 5.002 and 5.003, array and hash elements used as
33 subroutine parameters were "autovivified"; that is, they were brought
34 into existence if they did not already exist. For example, calling
35 C<func($h{foo})> would create C<$h{foo}> if it did not already exist,
36 causing C<exists $h{foo}> to become true and C<keys %h> to return
39 Perl 5.004 returns to the pre-5.002 behavior of I<not> autovivifying
40 array and hash elements used as subroutine parameters.
42 =head2 Fixed Parsing of $$<digit>, &$<digit>, etc.
44 A bug in previous versions of Perl 5.0 prevented proper parsing of
45 numeric special variables as symbolic references. That bug has been
46 fixed. As a result, the string "$$0" is no longer equivalent to
47 C<$$."0">, but rather to C<${$0}>. To get the old behavior, change
48 "$$" followed by a digit to "${$}".
50 =head2 Changes to Tainting Checks
52 A bug in previous versions may have failed to detect some insecure
53 conditions when taint checks are turned on. (Taint checks are used
54 in setuid or setgid scripts, or when explicitly turned on with the
55 C<-T> invocation option.) Although it's unlikely, this may cause a
56 previously-working script to now fail -- which should be construed
57 as a blessing, since that indicates a potentially-serious security
58 hole was just plugged.
60 =head2 New Opcode Module and Revised Safe Module
62 A new Opcode module supports the creation, manipulation and
63 application of opcode masks. The revised Safe module has a new API
64 and is implemented using the new Opcode module. Please read the new
65 Opcode and Safe documentation.
67 =head2 Internal Change: FileHandle Class Based on IO::* Classes
69 File handles are now stored internally as type IO::Handle. The
70 FileHandle module is still supported for backwards compatibility, but
71 it is now merely a front end to the IO::* modules -- specifically,
72 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
73 require, that you use the IO::* modules in new code.
75 In harmony with this change, C<*GLOB{FILEHANDLE}> is now a
76 backward-compatible synonym for C<*STDOUT{IO}>.
78 =head2 Internal Change: PerlIO internal IO abstraction interface
80 It is now possible to build Perl with AT&T's sfio IO package
81 instead of stdio. See L<perlapio> for more details, and
82 the F<INSTALL> file for how to use it.
84 =head2 New and Changed Built-in Variables
90 Extended error message on some platforms. (Also known as
91 $EXTENDED_OS_ERROR if you C<use English>).
95 The current set of syntax checks enabled by C<use strict>. See the
96 documentation of C<strict> for more details. Not actually new, but
98 Because it is intended for internal use by Perl core components,
99 there is no C<use English> long name for this variable.
103 By default, running out of memory it is not trappable. However, if
104 compiled for this, Perl may use the contents of C<$^M> as an emergency
105 pool after die()ing with this message. Suppose that your Perl were
106 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
110 would allocate a 64K buffer for use when in emergency.
111 See the F<INSTALL> file for information on how to enable this option.
112 As a disincentive to casual use of this advanced feature,
113 there is no C<use English> long name for this variable.
117 =head2 New and Changed Built-in Functions
121 =item delete on slices
123 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
127 is now supported on more platforms, and prefers fcntl
128 to lockf when emulating.
130 =item printf and sprintf
132 now support "%i" as a synonym for "%d", and the "h" modifier.
133 So "%hi" means "short integer in decimal", and "%ho" means
134 "unsigned short integer as octal".
136 =item keys as an lvalue
138 As an lvalue, C<keys> allows you to increase the number of hash buckets
139 allocated for the given hash. This can gain you a measure of efficiency if
140 you know the hash is going to get big. (This is similar to pre-extending
141 an array by assigning a larger number to $#array.) If you say
145 then C<%hash> will have at least 200 buckets allocated for it. These
146 buckets will be retained even if you do C<%hash = ()>; use C<undef
147 %hash> if you want to free the storage while C<%hash> is still in scope.
148 You can't shrink the number of buckets allocated for the hash using
149 C<keys> in this way (but you needn't worry about doing this by accident,
150 as trying has no effect).
152 =item my() in Control Structures
154 You can now use my() (with or without the parentheses) in the control
155 expressions of control structures such as:
157 while (defined(my $line = <>)) {
163 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
165 } elsif ($answer =~ /^n(o)?$/i) {
169 die "`$answer' is neither `yes' nor `no'";
172 Also, you can declare a foreach loop control variable as lexical by
173 preceding it with the word "my". For example, in:
175 foreach my $i (1, 2, 3) {
179 $i is a lexical variable, and the scope of $i extends to the end of
180 the loop, but not beyond it.
182 Note that you still cannot use my() on global punctuation variables
183 such as $_ and the like.
185 =item unpack() and pack()
187 A new format 'w' represents a BER compressed integer (as defined in
188 ASN.1). Its format is a sequence of one or more bytes, each of which
189 provides seven bits of the total value, with the most significant
190 first. Bit eight of each byte is set, except for the last byte, in
191 which bit eight is clear.
195 If the first argument to C<use> is a number, it is treated as a version
196 number instead of a module name. If the version of the Perl interpreter
197 is less than VERSION, then an error message is printed and Perl exits
198 immediately. Because C<use> occurs at compile time, this check happens
199 immediately during the compilation process, unlike C<require VERSION>,
200 which waits until run-time for the check. This is often useful if you
201 need to check the current Perl version before C<use>ing library modules
202 which have changed in incompatible ways from older versions of Perl.
203 (We try not to do this more than we have to.)
205 =item use Module VERSION LIST
207 If the VERSION argument is present between Module and LIST, then the
208 C<use> will call the VERSION method in class Module with the given
209 version as an argument. The default VERSION method, inherited from
210 the Universal class, croaks if the given version is larger than the
211 value of the variable $Module::VERSION. (Note that there is not a
212 comma after VERSION!)
214 This version-checking mechanism is similar to the one currently used
215 in the Exporter module, but it is faster and can be used with modules
216 that don't use the Exporter. It is the recommended method for new
219 =item prototype(FUNCTION)
221 Returns the prototype of a function as a string (or C<undef> if the
222 function has no prototype). FUNCTION is a reference to or the name of the
223 function whose prototype you want to retrieve.
224 (Not actually new; just never documented before.)
228 The default seed for C<srand>, which used to be C<time>, has been changed.
229 Now it's a heady mix of difficult-to-predict system-dependent values,
230 which should be sufficient for most everyday purposes.
232 Previous to version 5.004, calling C<rand> without first calling C<srand>
233 would yield the same sequence of random numbers on most or all machines.
234 Now, when perl sees that you're calling C<rand> and haven't yet called
235 C<srand>, it calls C<srand> with the default seed. You should still call
236 C<srand> manually if your code might ever be run on a pre-5.004 system,
237 of course, or if you want a seed other than the default.
241 Functions documented in the Camel to default to $_ now in
242 fact do, and all those that do are so documented in L<perlfunc>.
244 =item C<m//g> does not trigger a pos() reset on failure
246 The C<m//g> match iteration construct used to reset the iteration
247 when it failed to match (so that the next C<m//g> match would start at
248 the beginning of the string). You now have to explicitly do a
249 C<pos $str = 0;> to reset the "last match" position, or modify the
250 string in some way. This change makes it practical to chain C<m//g>
251 matches together in conjunction with ordinary matches using the C<\G>
252 zero-width assertion. See L<perlop> and L<perlre>.
254 =item nested C<sub{}> closures work now
256 Prior to the 5.004 release, nested anonymous functions didn't work
259 =item formats work right on changing lexicals
261 Just like anonymous functions that contain lexical variables
262 that change (like a lexical index variable for a C<foreach> loop),
263 formats now work properly. For example, this silently failed
264 before, and is fine now:
267 foreach $i ( 1 .. 10 ) {
277 =head2 New Built-in Methods
279 The C<UNIVERSAL> package automatically contains the following methods that
280 are inherited by all other classes:
286 C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS>
288 C<isa> is also exportable and can be called as a sub with two arguments. This
289 allows the ability to check what a reference points to. Example:
291 use UNIVERSAL qw(isa);
293 if(isa($ref, 'ARRAY')) {
299 C<can> checks to see if its object has a method called C<METHOD>,
300 if it does then a reference to the sub is returned; if it does not then
301 I<undef> is returned.
303 =item VERSION( [NEED] )
305 C<VERSION> returns the version number of the class (package). If the
306 NEED argument is given then it will check that the current version (as
307 defined by the $VERSION variable in the given package) not less than
308 NEED; it will die if this is not the case. This method is normally
309 called as a class method. This method is called automatically by the
310 C<VERSION> form of C<use>.
312 use A 1.2 qw(some imported subs);
318 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
319 C<isa> uses a very similar method and caching strategy. This may cause
320 strange effects if the Perl code dynamically changes @ISA in any package.
322 You may add other methods to the UNIVERSAL class via Perl or XS code.
323 You do not need to C<use UNIVERSAL> in order to make these methods
324 available to your program. This is necessary only if you wish to
325 have C<isa> available as a plain subroutine in the current package.
327 =head2 TIEHANDLE Now Supported
329 See L<perltie> for other kinds of tie()s.
333 =item TIEHANDLE classname, LIST
335 This is the constructor for the class. That means it is expected to
336 return an object of some sort. The reference can be used to
337 hold some internal information.
342 return bless \$i, shift;
345 =item PRINT this, LIST
347 This method will be triggered every time the tied handle is printed to.
348 Beyond its self reference it also expects the list that was passed to
354 return print join( $, => map {uc} @_), $\;
359 This method will be called when the handle is read from via the C<read>
360 or C<sysread> functions.
364 my($buf,$len,$offset) = @_;
365 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
370 This method will be called when the handle is read from. The method
371 should return undef when there is no more data.
375 return "PRINT called $$r times\n"
380 This method will be called when the C<getc> function is called.
382 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
386 As with the other types of ties, this method will be called when the
387 tied handle is about to be destroyed. This is useful for debugging and
388 possibly for cleaning up.
396 =head2 Malloc Enhancements
398 Four new compilation flags are recognized by malloc.c. (They have no
399 effect if perl is compiled with system malloc().)
403 =item -DDEBUGGING_MSTATS
405 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
406 memory statistics at runtime by running Perl thusly:
408 env PERL_DEBUG_MSTATS=2 perl your_script_here
410 The value of 2 means to print statistics after compilation and on
411 exit; with a value of 1, the statistics ares printed only on exit.
412 (If you want the statistics at an arbitrary time, you'll need to
413 install the optional module Devel::Peek.)
415 =item -DEMERGENCY_SBRK
417 If this macro is defined, running out of memory need not be a fatal
418 error: a memory pool can allocated by assigning to the special
419 variable C<$^M>. See L<"$^M">.
423 Perl memory allocation is by bucket with sizes close to powers of two.
424 Because of these malloc overhead may be big, especially for data of
425 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
426 a slightly different algorithm for small allocations (up to 64 bytes
427 long), which makes it possible to have overhead down to 1 byte for
428 allocations which are powers of two (and appear quite often).
430 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
431 about 20% for typical Perl usage. Expected slowdown due to additional
432 malloc overhead is in fractions of a percent (hard to measure, because
433 of the effect of saved memory on speed).
435 =item -DTWO_POT_OPTIMIZE
437 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
438 with size close to a power of two; but this works for big allocations
439 (starting with 16K by default). Such allocations are typical for big
440 hashes and special-purpose scripts, especially image processing.
442 On recent systems, the fact that perl requires 2M from system for 1M
443 allocation will not affect speed of execution, since the tail of such
444 a chunk is not going to be touched (and thus will not require real
445 memory). However, it may result in a premature out-of-memory error.
446 So if you will be manipulating very large blocks with sizes close to
447 powers of two, it would be wise to define this macro.
449 Expected saving of memory is 0-100% (100% in applications which
450 require most memory in such 2**n chunks); expected slowdown is
455 =head2 Miscellaneous Efficiency Enhancements
457 Functions that have an empty prototype and that do nothing but return
458 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
460 Each unique hash key is only allocated once, no matter how many hashes
461 have an entry with that key. So even if you have 100 copies of the
462 same hash, the hash keys never have to be re-allocated.
466 Four new pragmatic modules exist:
474 Looks for MakeMaker-like I<'blib'> directory structure starting in
475 I<dir> (or current directory) and working back up to five levels of
478 Intended for use on command line with B<-M> option as a way of testing
479 arbitrary scripts against an uninstalled version of a package.
483 Tells the compiler to enable (or disable) the use of POSIX locales for
486 When C<use locale> is in effect, the current LC_CTYPE locale is used
487 for regular expressions and case mapping; LC_COLLATE for string
488 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
489 (but B<not> in print). LC_NUMERIC is always used in write, since
490 lexical scoping of formats is problematic at best.
492 Each C<use locale> or C<no locale> affects statements to the end of
493 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
494 current file. Locales can be switched and queried with
497 See L<perllocale> for more information.
501 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
505 Enable VMS-specific language features. Currently, there are three
506 VMS-specific features available: 'status', which makes C<$?> and
507 C<system> return genuine VMS status values instead of emulating POSIX;
508 'exit', which makes C<exit> take a genuine VMS status value instead of
509 assuming that C<exit 1> is an error; and 'time', which makes all times
510 relative to the local time zone, in the VMS tradition.
516 =head2 Installation Directories
518 The I<installperl> script now places the Perl source files for
519 extensions in the architecture-specific library directory, which is
520 where the shared libraries for extensions have always been. This
521 change is intended to allow administrators to keep the Perl 5.004
522 library directory unchanged from a previous version, without running
523 the risk of binary incompatibility between extensions' Perl source and
528 New constants in the existing Fcntl modules are now supported,
529 provided that your operating system happens to support them:
532 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
535 These constants are intended for use with the Perl operators sysopen()
536 and fcntl() and the basic database modules like SDBM_File. For the
537 exact meaning of these and other Fcntl constants please refer to your
538 operating system's documentation for fcntl() and open().
540 In addition, the Fcntl module now provides these constants for use
541 with the Perl operator flock():
543 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
545 These constants are defined in all environments (because where there is
546 no flock() system call, Perl emulates it). However, for historical
547 reasons, these constants are not exported unless they are explicitly
548 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
550 =head2 Module Information Summary
552 Brand new modules, arranged by topic rather than strictly
555 CPAN interface to Comprehensive Perl Archive Network
556 CPAN::FirstTime create a CPAN configuration file
557 CPAN::Nox run CPAN while avoiding compiled extensions
559 IO.pm Top-level interface to IO::* classes
560 IO/File.pm IO::File extension Perl module
561 IO/Handle.pm IO::Handle extension Perl module
562 IO/Pipe.pm IO::Pipe extension Perl module
563 IO/Seekable.pm IO::Seekable extension Perl module
564 IO/Select.pm IO::Select extension Perl module
565 IO/Socket.pm IO::Socket extension Perl module
567 Opcode.pm Disable named opcodes when compiling Perl code
569 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
570 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
572 FindBin.pm Find path of currently executing program
574 Class/Template.pm Structure/member template builder
575 File/stat.pm Object-oriented wrapper around CORE::stat
576 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
577 Net/netent.pm Object-oriented wrapper around CORE::getnet*
578 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
579 Net/servent.pm Object-oriented wrapper around CORE::getserv*
580 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
581 Time/localtime.pm Object-oriented wrapper around CORE::localtime
582 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
583 User/grent.pm Object-oriented wrapper around CORE::getgr*
584 User/pwent.pm Object-oriented wrapper around CORE::getpw*
586 Tie/RefHash.pm Base class for tied hashes with references as keys
588 UNIVERSAL.pm Base class for *ALL* classes
592 The IO module provides a simple mechanism to load all of the IO modules at one
593 go. Currently this includes:
601 For more information on any of these modules, please see its
602 respective documentation.
606 The Math::Complex module has been totally rewritten, and now supports
607 more operations. These are overloaded:
609 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
611 And these functions are now exported:
615 tan cotan asin acos atan acotan
616 sinh cosh tanh cotanh asinh acosh atanh acotanh
621 There have been quite a few changes made to DB_File. Here are a few of
628 Fixed a handful of bugs.
632 By public demand, added support for the standard hash function exists().
636 Made it compatible with Berkeley DB 1.86.
640 Made negative subscripts work with RECNO interface.
644 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
645 mode from 0640 to 0666.
649 Made DB_File automatically import the open() constants (O_RDWR,
650 O_CREAT etc.) from Fcntl, if available.
654 Updated documentation.
658 Refer to the HISTORY section in DB_File.pm for a complete list of
659 changes. Everything after DB_File 1.01 has been added since 5.003.
663 Major rewrite - support added for both udp echo and real icmp pings.
665 =head2 Overridden Built-ins
667 Many of the Perl built-ins returning lists now have
668 object-oriented overrides. These are:
680 For example, you can now say
684 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
686 =head1 Utility Changes
692 =item C<void> XSUBs now default to returning nothing
694 Due to a documentation/implementation bug in previous versions of
695 Perl, XSUBs with a return type of C<void> have actually been
696 returning one value. Usually that value was the GV for the XSUB,
697 but sometimes it was some already freed or reused value, which would
698 sometimes lead to program failure.
700 In Perl 5.004, if an XSUB is declared as returning C<void>, it
701 actually returns no value, i.e. an empty list (though there is a
702 backward-compatibility exception; see below). If your XSUB really
703 does return an SV, you should give it a return type of C<SV *>.
705 For backward compatibility, I<xsubpp> tries to guess whether a
706 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
707 It does so by examining the text of the XSUB: if I<xsubpp> finds
708 what looks like an assignment to C<ST(0)>, it assumes that the
709 XSUB's return type is really C<SV *>.
713 =head1 C Language API Changes
717 =item C<gv_fetchmethod> and C<perl_call_sv>
719 The C<gv_fetchmethod> function finds a method for an object, just like
720 in Perl 5.003. The GV it returns may be a method cache entry.
721 However, in Perl 5.004, method cache entries are not visible to users;
722 therefore, they can no longer be passed directly to C<perl_call_sv>.
723 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
724 and pass the CV to C<perl_call_sv>.
726 The most likely symptom of passing the result of C<gv_fetchmethod> to
727 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
728 error on the I<second> call to a given method (since there is no cache
731 =item Extended API for manipulating hashes
733 Internal handling of hash keys has changed. The old hashtable API is
734 still fully supported, and will likely remain so. The additions to the
735 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
736 real scalars as keys rather than plain strings (non-tied hashes still
737 can only use strings as keys). New extensions must use the new hash
738 access functions and macros if they wish to use C<SV*> keys. These
739 additions also make it feasible to manipulate C<HE*>s (hash entries),
740 which can be more efficient. See L<perlguts> for details.
742 =item Embedding improvements
744 In older versions of Perl it was not possible to create more than one
745 instance of a Perl interpreter inside the same process without leaking
746 like mad and/or crashing. The major bugs which caused this behavior
747 have been fixed, however, you still must take care when embedding Perl
748 in a C program. See the updated perlembed manpage for tips on how to
749 manage your interpreters.
753 =head1 Documentation Changes
755 Many of the base and library pods were updated. These
756 new pods are included in section 1:
766 Locale support (internationalization and localization).
770 Tutorial on Perl OO programming.
774 Perl internal IO abstraction interface.
778 Although not new, this has been massively updated.
782 Although not new, this has been massively updated.
786 =head1 New Diagnostics
788 Several new conditions will trigger warnings that were
789 silent before. Some only affect certain platforms.
790 The following new warnings and errors outline these.
791 These messages are classified as follows (listed in
792 increasing order of desperation):
794 (W) A warning (optional).
795 (D) A deprecation (optional).
796 (S) A severe warning (mandatory).
797 (F) A fatal error (trappable).
798 (P) An internal error you should never see (trappable).
799 (X) A very fatal error (non-trappable).
800 (A) An alien error message (not generated by Perl).
804 =item "my" variable %s masks earlier declaration in same scope
806 (S) A lexical variable has been redeclared in the same scope, effectively
807 eliminating all access to the previous instance. This is almost always
808 a typographical error. Note that the earlier variable will still exist
809 until the end of the scope or until all closure referents to it are
812 =item %s argument is not a HASH element or slice
814 (F) The argument to delete() must be either a hash element, such as
817 $ref->[12]->{"susie"}
819 or a hash slice, such as
821 @foo{$bar, $baz, $xyzzy}
822 @{$ref->[12]}{"susie", "queue"}
824 =item Allocation too large: %lx
826 (X) You can't allocate more than 64K on an MSDOS machine.
828 =item Allocation too large
830 (F) You can't allocate more than 2^31+"small amount" bytes.
832 =item Attempt to free non-existent shared string
834 (P) Perl maintains a reference counted internal table of strings to
835 optimize the storage and access of hash keys and other strings. This
836 indicates someone tried to decrement the reference count of a string
837 that can no longer be found in the table.
839 =item Attempt to use reference as lvalue in substr
841 (W) You supplied a reference as the first argument to substr() used
842 as an lvalue, which is pretty strange. Perhaps you forgot to
843 dereference it first. See L<perlfunc/substr>.
845 =item Unsupported function fork
847 (F) Your version of executable does not support forking.
849 Note that under some systems, like OS/2, there may be different flavors of
850 Perl executables, some of which may support fork, some not. Try changing
851 the name you call Perl by to C<perl_>, C<perl__>, and so on.
853 =item Ill-formed logical name |%s| in prime_env_iter
855 (W) A warning peculiar to VMS. A logical name was encountered when preparing
856 to iterate over %ENV which violates the syntactic rules governing logical
857 names. Since it cannot be translated normally, it is skipped, and will not
858 appear in %ENV. This may be a benign occurrence, as some software packages
859 might directly modify logical name tables and introduce non-standard names,
860 or it may indicate that a logical name table has been corrupted.
862 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
864 (F) Only hard references are allowed by "strict refs". Symbolic references
865 are disallowed. See L<perlref>.
867 =item Constant subroutine %s redefined
869 (S) You redefined a subroutine which had previously been eligible for
870 inlining. See L<perlsub/"Constant Functions"> for commentary and
875 (F) You passed die() an empty string (the equivalent of C<die "">) or
876 you called it with no args and both C<$@> and C<$_> were empty.
878 =item Integer overflow in hex number
880 (S) The literal hex number you have specified is too big for your
881 architecture. On a 32-bit architecture the largest hex literal is
884 =item Integer overflow in octal number
886 (S) The literal octal number you have specified is too big for your
887 architecture. On a 32-bit architecture the largest octal literal is
890 =item Name "%s::%s" used only once: possible typo
892 (W) Typographical errors often show up as unique variable names.
893 If you had a good reason for having a unique name, then just mention
894 it again somehow to suppress the message (the C<use vars> pragma is
895 provided for just this purpose).
897 =item Null picture in formline
899 (F) The first argument to formline must be a valid format picture
900 specification. It was found to be empty, which probably means you
901 supplied it an uninitialized value. See L<perlform>.
903 =item Offset outside string
905 (F) You tried to do a read/write/send/recv operation with an offset
906 pointing outside the buffer. This is difficult to imagine.
907 The sole exception to this is that C<sysread()>ing past the buffer
908 will extend the buffer and zero pad the new area.
910 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
912 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
913 Stubs should never be implicitely created, but explicit calls to C<can>
916 =item Cannot resolve method `%s' overloading `%s' in package `s'
918 (P) Internal error trying to resolve overloading specified by a method
919 name (as opposed to a subroutine reference).
923 (X|F) The malloc() function returned 0, indicating there was insufficient
924 remaining memory (or virtual memory) to satisfy the request.
926 The request was judged to be small, so the possibility to trap it
927 depends on the way Perl was compiled. By default it is not trappable.
928 However, if compiled for this, Perl may use the contents of C<$^M> as
929 an emergency pool after die()ing with this message. In this case the
930 error is trappable I<once>.
932 =item Out of memory during request for %s
934 (F) The malloc() function returned 0, indicating there was insufficient
935 remaining memory (or virtual memory) to satisfy the request. However,
936 the request was judged large enough (compile-time default is 64K), so
937 a possibility to shut down by trapping this error is granted.
939 =item Possible attempt to put comments in qw() list
941 (W) qw() lists contain items separated by whitespace; as with literal
942 strings, comment characters are not ignored, but are instead treated
943 as literal data. (You may have used different delimiters than the
944 exclamation marks parentheses shown here; braces are also frequently
947 You probably wrote something like this:
954 when you should have written this:
961 If you really want comments, build your list the
962 old-fashioned way, with quotes and commas:
966 'b', # another comment
969 =item Possible attempt to separate words with commas
971 (W) qw() lists contain items separated by whitespace; therefore commas
972 aren't needed to separate the items. (You may have used different
973 delimiters than the parentheses shown here; braces are also frequently
976 You probably wrote something like this:
980 which puts literal commas into some of the list items. Write it without
981 commas if you don't want them to appear in your data:
985 =item Scalar value @%s{%s} better written as $%s{%s}
987 (W) You've used a hash slice (indicated by @) to select a single element of
988 a hash. Generally it's better to ask for a scalar value (indicated by $).
989 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
990 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
991 like a list when you assign to it, and provides a list context to its
992 subscript, which can do weird things if you're expecting only one subscript.
994 =item untie attempted while %d inner references still exist
996 (W) A copy of the object returned from C<tie> (or C<tied>) was still
997 valid when C<untie> was called.
999 =item Value of %s construct can be "0"; test with defined()
1001 (W) In a conditional expression, you used <HANDLE>, <*> (glob), or
1002 C<readdir> as a boolean value. Each of these constructs can return a
1003 value of "0"; that would make the conditional expression false, which
1004 is probably not what you intended. When using these constructs in
1005 conditional expressions, test their values with the C<defined> operator.
1007 =item Variable "%s" may be unavailable
1009 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1010 subroutine, and outside that is another subroutine; and the anonymous
1011 (innermost) subroutine is referencing a lexical variable defined in
1012 the outermost subroutine. For example:
1014 sub outermost { my $a; sub middle { sub { $a } } }
1016 If the anonymous subroutine is called or referenced (directly or
1017 indirectly) from the outermost subroutine, it will share the variable
1018 as you would expect. But if the anonymous subroutine is called or
1019 referenced when the outermost subroutine is not active, it will see
1020 the value of the shared variable as it was before and during the
1021 *first* call to the outermost subroutine, which is probably not what
1024 In these circumstances, it is usually best to make the middle
1025 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1026 support for shared variables in nested anonymous subroutines; a named
1027 subroutine in between interferes with this feature.
1029 =item Variable "%s" will not stay shared
1031 (W) An inner (nested) I<named> subroutine is referencing a lexical
1032 variable defined in an outer subroutine.
1034 When the inner subroutine is called, it will probably see the value of
1035 the outer subroutine's variable as it was before and during the
1036 *first* call to the outer subroutine; in this case, after the first
1037 call to the outer subroutine is complete, the inner and outer
1038 subroutines will no longer share a common value for the variable. In
1039 other words, the variable will no longer be shared.
1041 Furthermore, if the outer subroutine is anonymous and references a
1042 lexical variable outside itself, then the outer and inner subroutines
1043 will I<never> share the given variable.
1045 This problem can usually be solved by making the inner subroutine
1046 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1047 reference variables in outer subroutines are called or referenced,
1048 they are automatically re-bound to the current values of such
1051 =item Warning: something's wrong
1053 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1054 you called it with no args and C<$_> was empty.
1056 =item Got an error from DosAllocMem
1058 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1059 version of Perl, and this should not happen anyway.
1061 =item Malformed PERLLIB_PREFIX
1063 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1071 with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of
1072 a builtin library search path, prefix2 is substituted. The error may appear
1073 if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">.
1075 =item PERL_SH_DIR too long
1077 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1078 C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">.
1080 =item Process terminated by SIG%s
1082 (W) This is a standard message issued by OS/2 applications, while *nix
1083 applications die in silence. It is considered a feature of the OS/2
1084 port. One can easily disable this by appropriate sighandlers, see
1085 L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">.
1091 If you find what you think is a bug, you might check the headers of
1092 recently posted articles in the comp.lang.perl.misc newsgroup.
1093 There may also be information at http://www.perl.com/perl/, the Perl
1096 If you believe you have an unreported bug, please run the B<perlbug>
1097 program included with your release. Make sure you trim your bug down
1098 to a tiny but sufficient test case. Your bug report, along with the
1099 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1100 analysed by the Perl porting team.
1104 The F<Changes> file for exhaustive details on what changed.
1106 The F<INSTALL> file for how to build Perl. This file has been
1107 significantly updated for 5.004, so even veteran users should
1110 The F<README> file for general stuff.
1112 The F<Copying> file for copyright information.
1116 Constructed by Tom Christiansen, grabbing material with permission
1117 from innumerable contributors, with kibitzing by more than a few Perl
1120 Last update: Sat Mar 8 19:51:26 EST 1997