1PERL5004DELTA(1)       Perl Programmers Reference Guide       PERL5004DELTA(1)
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NAME

6       perl5004delta - what's new for perl5.004
7

DESCRIPTION

9       This document describes differences between the 5.003 release (as
10       documented in Programming Perl, second edition--the Camel Book) and
11       this one.
12

Supported Environments

14       Perl5.004 builds out of the box on Unix, Plan 9, LynxOS, VMS, OS/2,
15       QNX, AmigaOS, and Windows NT.  Perl runs on Windows 95 as well, but it
16       cannot be built there, for lack of a reasonable command interpreter.
17

Core Changes

19       Most importantly, many bugs were fixed, including several security
20       problems.  See the Changes file in the distribution for details.
21
22   List assignment to %ENV works
23       "%ENV = ()" and "%ENV = @list" now work as expected (except on VMS
24       where it generates a fatal error).
25
26   Change to "Can't locate Foo.pm in @INC" error
27       The error "Can't locate Foo.pm in @INC" now lists the contents of @INC
28       for easier debugging.
29
30   Compilation option: Binary compatibility with 5.003
31       There is a new Configure question that asks if you want to maintain
32       binary compatibility with Perl 5.003.  If you choose binary
33       compatibility, you do not have to recompile your extensions, but you
34       might have symbol conflicts if you embed Perl in another application,
35       just as in the 5.003 release.  By default, binary compatibility is
36       preserved at the expense of symbol table pollution.
37
38   $PERL5OPT environment variable
39       You may now put Perl options in the $PERL5OPT environment variable.
40       Unless Perl is running with taint checks, it will interpret this
41       variable as if its contents had appeared on a "#!perl" line at the
42       beginning of your script, except that hyphens are optional.  PERL5OPT
43       may only be used to set the following switches: -[DIMUdmw].
44
45   Limitations on -M, -m, and -T options
46       The "-M" and "-m" options are no longer allowed on the "#!" line of a
47       script.  If a script needs a module, it should invoke it with the "use"
48       pragma.
49
50       The -T option is also forbidden on the "#!" line of a script, unless it
51       was present on the Perl command line.  Due to the way "#!"  works, this
52       usually means that -T must be in the first argument.  Thus:
53
54           #!/usr/bin/perl -T -w
55
56       will probably work for an executable script invoked as "scriptname",
57       while:
58
59           #!/usr/bin/perl -w -T
60
61       will probably fail under the same conditions.  (Non-Unix systems will
62       probably not follow this rule.)  But "perl scriptname" is guaranteed to
63       fail, since then there is no chance of -T being found on the command
64       line before it is found on the "#!" line.
65
66   More precise warnings
67       If you removed the -w option from your Perl 5.003 scripts because it
68       made Perl too verbose, we recommend that you try putting it back when
69       you upgrade to Perl 5.004.  Each new perl version tends to remove some
70       undesirable warnings, while adding new warnings that may catch bugs in
71       your scripts.
72
73   Deprecated: Inherited "AUTOLOAD" for non-methods
74       Before Perl 5.004, "AUTOLOAD" functions were looked up as methods
75       (using the @ISA hierarchy), even when the function to be autoloaded was
76       called as a plain function (e.g. "Foo::bar()"), not a method (e.g.
77       "Foo->bar()" or "$obj->bar()").
78
79       Perl 5.005 will use method lookup only for methods' "AUTOLOAD"s.
80       However, there is a significant base of existing code that may be using
81       the old behavior.  So, as an interim step, Perl 5.004 issues an
82       optional warning when a non-method uses an inherited "AUTOLOAD".
83
84       The simple rule is:  Inheritance will not work when autoloading non-
85       methods.  The simple fix for old code is:  In any module that used to
86       depend on inheriting "AUTOLOAD" for non-methods from a base class named
87       "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
88       startup.
89
90   Previously deprecated %OVERLOAD is no longer usable
91       Using %OVERLOAD to define overloading was deprecated in 5.003.
92       Overloading is now defined using the overload pragma. %OVERLOAD is
93       still used internally but should not be used by Perl scripts. See
94       overload for more details.
95
96   Subroutine arguments created only when they're modified
97       In Perl 5.004, nonexistent array and hash elements used as subroutine
98       parameters are brought into existence only if they are actually
99       assigned to (via @_).
100
101       Earlier versions of Perl vary in their handling of such arguments.
102       Perl versions 5.002 and 5.003 always brought them into existence.  Perl
103       versions 5.000 and 5.001 brought them into existence only if they were
104       not the first argument (which was almost certainly a bug).  Earlier
105       versions of Perl never brought them into existence.
106
107       For example, given this code:
108
109            undef @a; undef %a;
110            sub show { print $_[0] };
111            sub change { $_[0]++ };
112            show($a[2]);
113            change($a{b});
114
115       After this code executes in Perl 5.004, $a{b} exists but $a[2] does
116       not.  In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
117       (but $a[2]'s value would have been undefined).
118
119   Group vector changeable with $)
120       The $) special variable has always (well, in Perl 5, at least)
121       reflected not only the current effective group, but also the group list
122       as returned by the "getgroups()" C function (if there is one).
123       However, until this release, there has not been a way to call the
124       "setgroups()" C function from Perl.
125
126       In Perl 5.004, assigning to $) is exactly symmetrical with examining
127       it: The first number in its string value is used as the effective gid;
128       if there are any numbers after the first one, they are passed to the
129       "setgroups()" C function (if there is one).
130
131   Fixed parsing of $$<digit>, &$<digit>, etc.
132       Perl versions before 5.004 misinterpreted any type marker followed by
133       "$" and a digit.  For example, "$$0" was incorrectly taken to mean
134       "${$}0" instead of "${$0}".  This bug is (mostly) fixed in Perl 5.004.
135
136       However, the developers of Perl 5.004 could not fix this bug
137       completely, because at least two widely-used modules depend on the old
138       meaning of "$$0" in a string.  So Perl 5.004 still interprets
139       "$$<digit>" in the old (broken) way inside strings; but it generates
140       this message as a warning.  And in Perl 5.005, this special treatment
141       will cease.
142
143   Fixed localization of $<digit>, $&, etc.
144       Perl versions before 5.004 did not always properly localize the regex-
145       related special variables.  Perl 5.004 does localize them, as the
146       documentation has always said it should.  This may result in $1, $2,
147       etc. no longer being set where existing programs use them.
148
149   No resetting of $. on implicit close
150       The documentation for Perl 5.0 has always stated that $. is not reset
151       when an already-open file handle is reopened with no intervening call
152       to "close".  Due to a bug, perl versions 5.000 through 5.003 did reset
153       $. under that circumstance; Perl 5.004 does not.
154
155   "wantarray" may return undef
156       The "wantarray" operator returns true if a subroutine is expected to
157       return a list, and false otherwise.  In Perl 5.004, "wantarray" can
158       also return the undefined value if a subroutine's return value will not
159       be used at all, which allows subroutines to avoid a time-consuming
160       calculation of a return value if it isn't going to be used.
161
162   "eval EXPR" determines value of EXPR in scalar context
163       Perl (version 5) used to determine the value of EXPR inconsistently,
164       sometimes incorrectly using the surrounding context for the
165       determination.  Now, the value of EXPR (before being parsed by eval) is
166       always determined in a scalar context.  Once parsed, it is executed as
167       before, by providing the context that the scope surrounding the eval
168       provided.  This change makes the behavior Perl4 compatible, besides
169       fixing bugs resulting from the inconsistent behavior.  This program:
170
171           @a = qw(time now is time);
172           print eval @a;
173           print '|', scalar eval @a;
174
175       used to print something like "timenowis881399109|4", but now (and in
176       perl4) prints "4|4".
177
178   Changes to tainting checks
179       A bug in previous versions may have failed to detect some insecure
180       conditions when taint checks are turned on.  (Taint checks are used in
181       setuid or setgid scripts, or when explicitly turned on with the "-T"
182       invocation option.)  Although it's unlikely, this may cause a
183       previously-working script to now fail, which should be construed as a
184       blessing since that indicates a potentially-serious security hole was
185       just plugged.
186
187       The new restrictions when tainting include:
188
189       No glob() or <*>
190           These operators may spawn the C shell (csh), which cannot be made
191           safe.  This restriction will be lifted in a future version of Perl
192           when globbing is implemented without the use of an external
193           program.
194
195       No spawning if tainted $CDPATH, $ENV, $BASH_ENV
196           These environment variables may alter the behavior of spawned
197           programs (especially shells) in ways that subvert security.  So now
198           they are treated as dangerous, in the manner of $IFS and $PATH.
199
200       No spawning if tainted $TERM doesn't look like a terminal name
201           Some termcap libraries do unsafe things with $TERM.  However, it
202           would be unnecessarily harsh to treat all $TERM values as unsafe,
203           since only shell metacharacters can cause trouble in $TERM.  So a
204           tainted $TERM is considered to be safe if it contains only
205           alphanumerics, underscores, dashes, and colons, and unsafe if it
206           contains other characters (including whitespace).
207
208   New Opcode module and revised Safe module
209       A new Opcode module supports the creation, manipulation and application
210       of opcode masks.  The revised Safe module has a new API and is
211       implemented using the new Opcode module.  Please read the new Opcode
212       and Safe documentation.
213
214   Embedding improvements
215       In older versions of Perl it was not possible to create more than one
216       Perl interpreter instance inside a single process without leaking like
217       a sieve and/or crashing.  The bugs that caused this behavior have all
218       been fixed.  However, you still must take care when embedding Perl in a
219       C program.  See the updated perlembed manpage for tips on how to manage
220       your interpreters.
221
222   Internal change: FileHandle class based on IO::* classes
223       File handles are now stored internally as type IO::Handle.  The
224       FileHandle module is still supported for backwards compatibility, but
225       it is now merely a front end to the IO::* modules, specifically
226       IO::Handle, IO::Seekable, and IO::File.  We suggest, but do not
227       require, that you use the IO::* modules in new code.
228
229       In harmony with this change, *GLOB{FILEHANDLE} is now just a backward-
230       compatible synonym for *GLOB{IO}.
231
232   Internal change: PerlIO abstraction interface
233       It is now possible to build Perl with AT&T's sfio IO package instead of
234       stdio.  See perlapio for more details, and the INSTALL file for how to
235       use it.
236
237   New and changed syntax
238       $coderef->(PARAMS)
239           A subroutine reference may now be suffixed with an arrow and a
240           (possibly empty) parameter list.  This syntax denotes a call of the
241           referenced subroutine, with the given parameters (if any).
242
243           This new syntax follows the pattern of "$hashref->{FOO}" and
244           "$aryref->[$foo]": You may now write "&$subref($foo)" as
245           "$subref->($foo)".  All these arrow terms may be chained; thus,
246           "&{$table->{FOO}}($bar)" may now be written
247           "$table->{FOO}->($bar)".
248
249   New and changed builtin constants
250       __PACKAGE__
251           The current package name at compile time, or the undefined value if
252           there is no current package (due to a "package;" directive).  Like
253           "__FILE__" and "__LINE__", "__PACKAGE__" does not interpolate into
254           strings.
255
256   New and changed builtin variables
257       $^E Extended error message on some platforms.  (Also known as
258           $EXTENDED_OS_ERROR if you "use English").
259
260       $^H The current set of syntax checks enabled by "use strict".  See the
261           documentation of "strict" for more details.  Not actually new, but
262           newly documented.  Because it is intended for internal use by Perl
263           core components, there is no "use English" long name for this
264           variable.
265
266       $^M By default, running out of memory it is not trappable.  However, if
267           compiled for this, Perl may use the contents of $^M as an emergency
268           pool after die()ing with this message.  Suppose that your Perl were
269           compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc.  Then
270
271               $^M = 'a' x (1<<16);
272
273           would allocate a 64K buffer for use when in emergency.  See the
274           INSTALL file for information on how to enable this option.  As a
275           disincentive to casual use of this advanced feature, there is no
276           "use English" long name for this variable.
277
278   New and changed builtin functions
279       delete on slices
280           This now works.  (e.g. "delete @ENV{'PATH', 'MANPATH'}")
281
282       flock
283           is now supported on more platforms, prefers fcntl to lockf when
284           emulating, and always flushes before (un)locking.
285
286       printf and sprintf
287           Perl now implements these functions itself; it doesn't use the C
288           library function sprintf() any more, except for floating-point
289           numbers, and even then only known flags are allowed.  As a result,
290           it is now possible to know which conversions and flags will work,
291           and what they will do.
292
293           The new conversions in Perl's sprintf() are:
294
295              %i   a synonym for %d
296              %p   a pointer (the address of the Perl value, in hexadecimal)
297              %n   special: *stores* the number of characters output so far
298                   into the next variable in the parameter list
299
300           The new flags that go between the "%" and the conversion are:
301
302              #    prefix octal with "0", hex with "0x"
303              h    interpret integer as C type "short" or "unsigned short"
304              V    interpret integer as Perl's standard integer type
305
306           Also, where a number would appear in the flags, an asterisk ("*")
307           may be used instead, in which case Perl uses the next item in the
308           parameter list as the given number (that is, as the field width or
309           precision).  If a field width obtained through "*" is negative, it
310           has the same effect as the '-' flag: left-justification.
311
312           See "sprintf" in perlfunc for a complete list of conversion and
313           flags.
314
315       keys as an lvalue
316           As an lvalue, "keys" allows you to increase the number of hash
317           buckets allocated for the given hash.  This can gain you a measure
318           of efficiency if you know the hash is going to get big.  (This is
319           similar to pre-extending an array by assigning a larger number to
320           $#array.)  If you say
321
322               keys %hash = 200;
323
324           then %hash will have at least 200 buckets allocated for it.  These
325           buckets will be retained even if you do "%hash = ()"; use "undef
326           %hash" if you want to free the storage while %hash is still in
327           scope.  You can't shrink the number of buckets allocated for the
328           hash using "keys" in this way (but you needn't worry about doing
329           this by accident, as trying has no effect).
330
331       my() in Control Structures
332           You can now use my() (with or without the parentheses) in the
333           control expressions of control structures such as:
334
335               while (defined(my $line = <>)) {
336                   $line = lc $line;
337               } continue {
338                   print $line;
339               }
340
341               if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
342                   user_agrees();
343               } elsif ($answer =~ /^n(o)?$/i) {
344                   user_disagrees();
345               } else {
346                   chomp $answer;
347                   die "`$answer' is neither `yes' nor `no'";
348               }
349
350           Also, you can declare a foreach loop control variable as lexical by
351           preceding it with the word "my".  For example, in:
352
353               foreach my $i (1, 2, 3) {
354                   some_function();
355               }
356
357           $i is a lexical variable, and the scope of $i extends to the end of
358           the loop, but not beyond it.
359
360           Note that you still cannot use my() on global punctuation variables
361           such as $_ and the like.
362
363       pack() and unpack()
364           A new format 'w' represents a BER compressed integer (as defined in
365           ASN.1).  Its format is a sequence of one or more bytes, each of
366           which provides seven bits of the total value, with the most
367           significant first.  Bit eight of each byte is set, except for the
368           last byte, in which bit eight is clear.
369
370           If 'p' or 'P' are given undef as values, they now generate a NULL
371           pointer.
372
373           Both pack() and unpack() now fail when their templates contain
374           invalid types.  (Invalid types used to be ignored.)
375
376       sysseek()
377           The new sysseek() operator is a variant of seek() that sets and
378           gets the file's system read/write position, using the lseek(2)
379           system call.  It is the only reliable way to seek before using
380           sysread() or syswrite().  Its return value is the new position, or
381           the undefined value on failure.
382
383       use VERSION
384           If the first argument to "use" is a number, it is treated as a
385           version number instead of a module name.  If the version of the
386           Perl interpreter is less than VERSION, then an error message is
387           printed and Perl exits immediately.  Because "use" occurs at
388           compile time, this check happens immediately during the compilation
389           process, unlike "require VERSION", which waits until runtime for
390           the check.  This is often useful if you need to check the current
391           Perl version before "use"ing library modules which have changed in
392           incompatible ways from older versions of Perl.  (We try not to do
393           this more than we have to.)
394
395       use Module VERSION LIST
396           If the VERSION argument is present between Module and LIST, then
397           the "use" will call the VERSION method in class Module with the
398           given version as an argument.  The default VERSION method,
399           inherited from the UNIVERSAL class, croaks if the given version is
400           larger than the value of the variable $Module::VERSION.  (Note that
401           there is not a comma after VERSION!)
402
403           This version-checking mechanism is similar to the one currently
404           used in the Exporter module, but it is faster and can be used with
405           modules that don't use the Exporter.  It is the recommended method
406           for new code.
407
408       prototype(FUNCTION)
409           Returns the prototype of a function as a string (or "undef" if the
410           function has no prototype).  FUNCTION is a reference to or the name
411           of the function whose prototype you want to retrieve.  (Not
412           actually new; just never documented before.)
413
414       srand
415           The default seed for "srand", which used to be "time", has been
416           changed.  Now it's a heady mix of difficult-to-predict system-
417           dependent values, which should be sufficient for most everyday
418           purposes.
419
420           Previous to version 5.004, calling "rand" without first calling
421           "srand" would yield the same sequence of random numbers on most or
422           all machines.  Now, when perl sees that you're calling "rand" and
423           haven't yet called "srand", it calls "srand" with the default seed.
424           You should still call "srand" manually if your code might ever be
425           run on a pre-5.004 system, of course, or if you want a seed other
426           than the default.
427
428       $_ as Default
429           Functions documented in the Camel to default to $_ now in fact do,
430           and all those that do are so documented in perlfunc.
431
432       "m//gc" does not reset search position on failure
433           The "m//g" match iteration construct has always reset its target
434           string's search position (which is visible through the "pos"
435           operator) when a match fails; as a result, the next "m//g" match
436           after a failure starts again at the beginning of the string.  With
437           Perl 5.004, this reset may be disabled by adding the "c" (for
438           "continue") modifier, i.e. "m//gc".  This feature, in conjunction
439           with the "\G" zero-width assertion, makes it possible to chain
440           matches together.  See perlop and perlre.
441
442       "m//x" ignores whitespace before ?*+{}
443           The "m//x" construct has always been intended to ignore all
444           unescaped whitespace.  However, before Perl 5.004, whitespace had
445           the effect of escaping repeat modifiers like "*" or "?"; for
446           example, "/a *b/x" was (mis)interpreted as "/a\*b/x".  This bug has
447           been fixed in 5.004.
448
449       nested "sub{}" closures work now
450           Prior to the 5.004 release, nested anonymous functions didn't work
451           right.  They do now.
452
453       formats work right on changing lexicals
454           Just like anonymous functions that contain lexical variables that
455           change (like a lexical index variable for a "foreach" loop),
456           formats now work properly.  For example, this silently failed
457           before (printed only zeros), but is fine now:
458
459               my $i;
460               foreach $i ( 1 .. 10 ) {
461                   write;
462               }
463               format =
464                   my i is @#
465                   $i
466               .
467
468           However, it still fails (without a warning) if the foreach is
469           within a subroutine:
470
471               my $i;
472               sub foo {
473                 foreach $i ( 1 .. 10 ) {
474                   write;
475                 }
476               }
477               foo;
478               format =
479                   my i is @#
480                   $i
481               .
482
483   New builtin methods
484       The "UNIVERSAL" package automatically contains the following methods
485       that are inherited by all other classes:
486
487       isa(CLASS)
488           "isa" returns true if its object is blessed into a subclass of
489           "CLASS"
490
491           "isa" is also exportable and can be called as a sub with two
492           arguments. This allows the ability to check what a reference points
493           to. Example:
494
495               use UNIVERSAL qw(isa);
496
497               if(isa($ref, 'ARRAY')) {
498                  ...
499               }
500
501       can(METHOD)
502           "can" checks to see if its object has a method called "METHOD", if
503           it does then a reference to the sub is returned; if it does not
504           then undef is returned.
505
506       VERSION( [NEED] )
507           "VERSION" returns the version number of the class (package).  If
508           the NEED argument is given then it will check that the current
509           version (as defined by the $VERSION variable in the given package)
510           not less than NEED; it will die if this is not the case.  This
511           method is normally called as a class method.  This method is called
512           automatically by the "VERSION" form of "use".
513
514               use A 1.2 qw(some imported subs);
515               # implies:
516               A->VERSION(1.2);
517
518       NOTE: "can" directly uses Perl's internal code for method lookup, and
519       "isa" uses a very similar method and caching strategy. This may cause
520       strange effects if the Perl code dynamically changes @ISA in any
521       package.
522
523       You may add other methods to the UNIVERSAL class via Perl or XS code.
524       You do not need to "use UNIVERSAL" in order to make these methods
525       available to your program.  This is necessary only if you wish to have
526       "isa" available as a plain subroutine in the current package.
527
528   TIEHANDLE now supported
529       See perltie for other kinds of tie()s.
530
531       TIEHANDLE classname, LIST
532           This is the constructor for the class.  That means it is expected
533           to return an object of some sort. The reference can be used to hold
534           some internal information.
535
536               sub TIEHANDLE {
537                   print "<shout>\n";
538                   my $i;
539                   return bless \$i, shift;
540               }
541
542       PRINT this, LIST
543           This method will be triggered every time the tied handle is printed
544           to.  Beyond its self reference it also expects the list that was
545           passed to the print function.
546
547               sub PRINT {
548                   $r = shift;
549                   $$r++;
550                   return print join( $, => map {uc} @_), $\;
551               }
552
553       PRINTF this, LIST
554           This method will be triggered every time the tied handle is printed
555           to with the "printf()" function.  Beyond its self reference it also
556           expects the format and list that was passed to the printf function.
557
558               sub PRINTF {
559                   shift;
560                     my $fmt = shift;
561                   print sprintf($fmt, @_)."\n";
562               }
563
564       READ this LIST
565           This method will be called when the handle is read from via the
566           "read" or "sysread" functions.
567
568               sub READ {
569                   $r = shift;
570                   my($buf,$len,$offset) = @_;
571                   print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
572               }
573
574       READLINE this
575           This method will be called when the handle is read from. The method
576           should return undef when there is no more data.
577
578               sub READLINE {
579                   $r = shift;
580                   return "PRINT called $$r times\n"
581               }
582
583       GETC this
584           This method will be called when the "getc" function is called.
585
586               sub GETC { print "Don't GETC, Get Perl"; return "a"; }
587
588       DESTROY this
589           As with the other types of ties, this method will be called when
590           the tied handle is about to be destroyed. This is useful for
591           debugging and possibly for cleaning up.
592
593               sub DESTROY {
594                   print "</shout>\n";
595               }
596
597   Malloc enhancements
598       If perl is compiled with the malloc included with the perl distribution
599       (that is, if "perl -V:d_mymalloc" is 'define') then you can print
600       memory statistics at runtime by running Perl thusly:
601
602         env PERL_DEBUG_MSTATS=2 perl your_script_here
603
604       The value of 2 means to print statistics after compilation and on exit;
605       with a value of 1, the statistics are printed only on exit.  (If you
606       want the statistics at an arbitrary time, you'll need to install the
607       optional module Devel::Peek.)
608
609       Three new compilation flags are recognized by malloc.c.  (They have no
610       effect if perl is compiled with system malloc().)
611
612       -DPERL_EMERGENCY_SBRK
613           If this macro is defined, running out of memory need not be a fatal
614           error: a memory pool can allocated by assigning to the special
615           variable $^M.  See "$^M".
616
617       -DPACK_MALLOC
618           Perl memory allocation is by bucket with sizes close to powers of
619           two.  Because of these malloc overhead may be big, especially for
620           data of size exactly a power of two.  If "PACK_MALLOC" is defined,
621           perl uses a slightly different algorithm for small allocations (up
622           to 64 bytes long), which makes it possible to have overhead down to
623           1 byte for allocations which are powers of two (and appear quite
624           often).
625
626           Expected memory savings (with 8-byte alignment in "alignbytes") is
627           about 20% for typical Perl usage.  Expected slowdown due to
628           additional malloc overhead is in fractions of a percent (hard to
629           measure, because of the effect of saved memory on speed).
630
631       -DTWO_POT_OPTIMIZE
632           Similarly to "PACK_MALLOC", this macro improves allocations of data
633           with size close to a power of two; but this works for big
634           allocations (starting with 16K by default).  Such allocations are
635           typical for big hashes and special-purpose scripts, especially
636           image processing.
637
638           On recent systems, the fact that perl requires 2M from system for
639           1M allocation will not affect speed of execution, since the tail of
640           such a chunk is not going to be touched (and thus will not require
641           real memory).  However, it may result in a premature out-of-memory
642           error.  So if you will be manipulating very large blocks with sizes
643           close to powers of two, it would be wise to define this macro.
644
645           Expected saving of memory is 0-100% (100% in applications which
646           require most memory in such 2**n chunks); expected slowdown is
647           negligible.
648
649   Miscellaneous efficiency enhancements
650       Functions that have an empty prototype and that do nothing but return a
651       fixed value are now inlined (e.g. "sub PI () { 3.14159 }").
652
653       Each unique hash key is only allocated once, no matter how many hashes
654       have an entry with that key.  So even if you have 100 copies of the
655       same hash, the hash keys never have to be reallocated.
656

Support for More Operating Systems

658       Support for the following operating systems is new in Perl 5.004.
659
660   Win32
661       Perl 5.004 now includes support for building a "native" perl under
662       Windows NT, using the Microsoft Visual C++ compiler (versions 2.0 and
663       above) or the Borland C++ compiler (versions 5.02 and above).  The
664       resulting perl can be used under Windows 95 (if it is installed in the
665       same directory locations as it got installed in Windows NT).  This port
666       includes support for perl extension building tools like
667       ExtUtils::MakeMaker and h2xs, so that many extensions available on the
668       Comprehensive Perl Archive Network (CPAN) can now be readily built
669       under Windows NT.  See http://www.perl.com/ for more information on
670       CPAN and README.win32 in the perl distribution for more details on how
671       to get started with building this port.
672
673       There is also support for building perl under the Cygwin32 environment.
674       Cygwin32 is a set of GNU tools that make it possible to compile and run
675       many Unix programs under Windows NT by providing a mostly Unix-like
676       interface for compilation and execution.  See README.cygwin32 in the
677       perl distribution for more details on this port and how to obtain the
678       Cygwin32 toolkit.
679
680   Plan 9
681       See README.plan9 in the perl distribution.
682
683   QNX
684       See README.qnx in the perl distribution.
685
686   AmigaOS
687       See README.amigaos in the perl distribution.
688

Pragmata

690       Six new pragmatic modules exist:
691
692       use autouse MODULE => qw(sub1 sub2 sub3)
693           Defers "require MODULE" until someone calls one of the specified
694           subroutines (which must be exported by MODULE).  This pragma should
695           be used with caution, and only when necessary.
696
697       use blib
698       use blib 'dir'
699           Looks for MakeMaker-like 'blib' directory structure starting in dir
700           (or current directory) and working back up to five levels of parent
701           directories.
702
703           Intended for use on command line with -M option as a way of testing
704           arbitrary scripts against an uninstalled version of a package.
705
706       use constant NAME => VALUE
707           Provides a convenient interface for creating compile-time
708           constants, See "Constant Functions" in perlsub.
709
710       use locale
711           Tells the compiler to enable (or disable) the use of POSIX locales
712           for builtin operations.
713
714           When "use locale" is in effect, the current LC_CTYPE locale is used
715           for regular expressions and case mapping; LC_COLLATE for string
716           ordering; and LC_NUMERIC for numeric formatting in printf and
717           sprintf (but not in print).  LC_NUMERIC is always used in write,
718           since lexical scoping of formats is problematic at best.
719
720           Each "use locale" or "no locale" affects statements to the end of
721           the enclosing BLOCK or, if not inside a BLOCK, to the end of the
722           current file.  Locales can be switched and queried with
723           POSIX::setlocale().
724
725           See perllocale for more information.
726
727       use ops
728           Disable unsafe opcodes, or any named opcodes, when compiling Perl
729           code.
730
731       use vmsish
732           Enable VMS-specific language features.  Currently, there are three
733           VMS-specific features available: 'status', which makes $? and
734           "system" return genuine VMS status values instead of emulating
735           POSIX; 'exit', which makes "exit" take a genuine VMS status value
736           instead of assuming that "exit 1" is an error; and 'time', which
737           makes all times relative to the local time zone, in the VMS
738           tradition.
739

Modules

741   Required Updates
742       Though Perl 5.004 is compatible with almost all modules that work with
743       Perl 5.003, there are a few exceptions:
744
745           Module   Required Version for Perl 5.004
746           ------   -------------------------------
747           Filter   Filter-1.12
748           LWP      libwww-perl-5.08
749           Tk       Tk400.202 (-w makes noise)
750
751       Also, the majordomo mailing list program, version 1.94.1, doesn't work
752       with Perl 5.004 (nor with perl 4), because it executes an invalid
753       regular expression.  This bug is fixed in majordomo version 1.94.2.
754
755   Installation directories
756       The installperl script now places the Perl source files for extensions
757       in the architecture-specific library directory, which is where the
758       shared libraries for extensions have always been.  This change is
759       intended to allow administrators to keep the Perl 5.004 library
760       directory unchanged from a previous version, without running the risk
761       of binary incompatibility between extensions' Perl source and shared
762       libraries.
763
764   Module information summary
765       Brand new modules, arranged by topic rather than strictly
766       alphabetically:
767
768           CGI.pm               Web server interface ("Common Gateway Interface")
769           CGI/Apache.pm        Support for Apache's Perl module
770           CGI/Carp.pm          Log server errors with helpful context
771           CGI/Fast.pm          Support for FastCGI (persistent server process)
772           CGI/Push.pm          Support for server push
773           CGI/Switch.pm        Simple interface for multiple server types
774
775           CPAN                 Interface to Comprehensive Perl Archive Network
776           CPAN::FirstTime      Utility for creating CPAN configuration file
777           CPAN::Nox            Runs CPAN while avoiding compiled extensions
778
779           IO.pm                Top-level interface to IO::* classes
780           IO/File.pm           IO::File extension Perl module
781           IO/Handle.pm         IO::Handle extension Perl module
782           IO/Pipe.pm           IO::Pipe extension Perl module
783           IO/Seekable.pm       IO::Seekable extension Perl module
784           IO/Select.pm         IO::Select extension Perl module
785           IO/Socket.pm         IO::Socket extension Perl module
786
787           Opcode.pm            Disable named opcodes when compiling Perl code
788
789           ExtUtils/Embed.pm    Utilities for embedding Perl in C programs
790           ExtUtils/testlib.pm  Fixes up @INC to use just-built extension
791
792           FindBin.pm           Find path of currently executing program
793
794           Class/Struct.pm      Declare struct-like datatypes as Perl classes
795           File/stat.pm         By-name interface to Perl's builtin stat
796           Net/hostent.pm       By-name interface to Perl's builtin gethost*
797           Net/netent.pm        By-name interface to Perl's builtin getnet*
798           Net/protoent.pm      By-name interface to Perl's builtin getproto*
799           Net/servent.pm       By-name interface to Perl's builtin getserv*
800           Time/gmtime.pm       By-name interface to Perl's builtin gmtime
801           Time/localtime.pm    By-name interface to Perl's builtin localtime
802           Time/tm.pm           Internal object for Time::{gm,local}time
803           User/grent.pm        By-name interface to Perl's builtin getgr*
804           User/pwent.pm        By-name interface to Perl's builtin getpw*
805
806           Tie/RefHash.pm       Base class for tied hashes with references as keys
807
808           UNIVERSAL.pm         Base class for *ALL* classes
809
810   Fcntl
811       New constants in the existing Fcntl modules are now supported, provided
812       that your operating system happens to support them:
813
814           F_GETOWN F_SETOWN
815           O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
816           O_EXLOCK O_SHLOCK
817
818       These constants are intended for use with the Perl operators sysopen()
819       and fcntl() and the basic database modules like SDBM_File.  For the
820       exact meaning of these and other Fcntl constants please refer to your
821       operating system's documentation for fcntl() and open().
822
823       In addition, the Fcntl module now provides these constants for use with
824       the Perl operator flock():
825
826               LOCK_SH LOCK_EX LOCK_NB LOCK_UN
827
828       These constants are defined in all environments (because where there is
829       no flock() system call, Perl emulates it).  However, for historical
830       reasons, these constants are not exported unless they are explicitly
831       requested with the ":flock" tag (e.g. "use Fcntl ':flock'").
832
833   IO
834       The IO module provides a simple mechanism to load all the IO modules at
835       one go.  Currently this includes:
836
837            IO::Handle
838            IO::Seekable
839            IO::File
840            IO::Pipe
841            IO::Socket
842
843       For more information on any of these modules, please see its respective
844       documentation.
845
846   Math::Complex
847       The Math::Complex module has been totally rewritten, and now supports
848       more operations.  These are overloaded:
849
850            + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
851
852       And these functions are now exported:
853
854           pi i Re Im arg
855           log10 logn ln cbrt root
856           tan
857           csc sec cot
858           asin acos atan
859           acsc asec acot
860           sinh cosh tanh
861           csch sech coth
862           asinh acosh atanh
863           acsch asech acoth
864           cplx cplxe
865
866   Math::Trig
867       This new module provides a simpler interface to parts of Math::Complex
868       for those who need trigonometric functions only for real numbers.
869
870   DB_File
871       There have been quite a few changes made to DB_File. Here are a few of
872       the highlights:
873
874       •   Fixed a handful of bugs.
875
876       •   By public demand, added support for the standard hash function
877           exists().
878
879       •   Made it compatible with Berkeley DB 1.86.
880
881       •   Made negative subscripts work with RECNO interface.
882
883       •   Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the
884           default mode from 0640 to 0666.
885
886       •   Made DB_File automatically import the open() constants (O_RDWR,
887           O_CREAT etc.) from Fcntl, if available.
888
889       •   Updated documentation.
890
891       Refer to the HISTORY section in DB_File.pm for a complete list of
892       changes. Everything after DB_File 1.01 has been added since 5.003.
893
894   Net::Ping
895       Major rewrite - support added for both udp echo and real icmp pings.
896
897   Object-oriented overrides for builtin operators
898       Many of the Perl builtins returning lists now have object-oriented
899       overrides.  These are:
900
901           File::stat
902           Net::hostent
903           Net::netent
904           Net::protoent
905           Net::servent
906           Time::gmtime
907           Time::localtime
908           User::grent
909           User::pwent
910
911       For example, you can now say
912
913           use File::stat;
914           use User::pwent;
915           $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
916

Utility Changes

918   pod2html
919       Sends converted HTML to standard output
920           The pod2html utility included with Perl 5.004 is entirely new.  By
921           default, it sends the converted HTML to its standard output,
922           instead of writing it to a file like Perl 5.003's pod2html did.
923           Use the --outfile=FILENAME option to write to a file.
924
925   xsubpp
926       "void" XSUBs now default to returning nothing
927           Due to a documentation/implementation bug in previous versions of
928           Perl, XSUBs with a return type of "void" have actually been
929           returning one value.  Usually that value was the GV for the XSUB,
930           but sometimes it was some already freed or reused value, which
931           would sometimes lead to program failure.
932
933           In Perl 5.004, if an XSUB is declared as returning "void", it
934           actually returns no value, i.e. an empty list (though there is a
935           backward-compatibility exception; see below).  If your XSUB really
936           does return an SV, you should give it a return type of "SV *".
937
938           For backward compatibility, xsubpp tries to guess whether a "void"
939           XSUB is really "void" or if it wants to return an "SV *".  It does
940           so by examining the text of the XSUB: if xsubpp finds what looks
941           like an assignment to ST(0), it assumes that the XSUB's return type
942           is really "SV *".
943

C Language API Changes

945       "gv_fetchmethod" and "perl_call_sv"
946           The "gv_fetchmethod" function finds a method for an object, just
947           like in Perl 5.003.  The GV it returns may be a method cache entry.
948           However, in Perl 5.004, method cache entries are not visible to
949           users; therefore, they can no longer be passed directly to
950           "perl_call_sv".  Instead, you should use the "GvCV" macro on the GV
951           to extract its CV, and pass the CV to "perl_call_sv".
952
953           The most likely symptom of passing the result of "gv_fetchmethod"
954           to "perl_call_sv" is Perl's producing an "Undefined subroutine
955           called" error on the second call to a given method (since there is
956           no cache on the first call).
957
958       "perl_eval_pv"
959           A new function handy for eval'ing strings of Perl code inside C
960           code.  This function returns the value from the eval statement,
961           which can be used instead of fetching globals from the symbol
962           table.  See perlguts, perlembed and perlcall for details and
963           examples.
964
965       Extended API for manipulating hashes
966           Internal handling of hash keys has changed.  The old hashtable API
967           is still fully supported, and will likely remain so.  The additions
968           to the API allow passing keys as "SV*"s, so that "tied" hashes can
969           be given real scalars as keys rather than plain strings (nontied
970           hashes still can only use strings as keys).  New extensions must
971           use the new hash access functions and macros if they wish to use
972           "SV*" keys.  These additions also make it feasible to manipulate
973           "HE*"s (hash entries), which can be more efficient.  See perlguts
974           for details.
975

Documentation Changes

977       Many of the base and library pods were updated.  These new pods are
978       included in section 1:
979
980       perldelta
981           This document.
982
983       perlfaq
984           Frequently asked questions.
985
986       perllocale
987           Locale support (internationalization and localization).
988
989       perltoot
990           Tutorial on Perl OO programming.
991
992       perlapio
993           Perl internal IO abstraction interface.
994
995       perlmodlib
996           Perl module library and recommended practice for module creation.
997           Extracted from perlmod (which is much smaller as a result).
998
999       perldebug
1000           Although not new, this has been massively updated.
1001
1002       perlsec
1003           Although not new, this has been massively updated.
1004

New Diagnostics

1006       Several new conditions will trigger warnings that were silent before.
1007       Some only affect certain platforms.  The following new warnings and
1008       errors outline these.  These messages are classified as follows (listed
1009       in increasing order of desperation):
1010
1011          (W) A warning (optional).
1012          (D) A deprecation (optional).
1013          (S) A severe warning (mandatory).
1014          (F) A fatal error (trappable).
1015          (P) An internal error you should never see (trappable).
1016          (X) A very fatal error (nontrappable).
1017          (A) An alien error message (not generated by Perl).
1018
1019       "my" variable %s masks earlier declaration in same scope
1020           (W) A lexical variable has been redeclared in the same scope,
1021           effectively eliminating all access to the previous instance.  This
1022           is almost always a typographical error.  Note that the earlier
1023           variable will still exist until the end of the scope or until all
1024           closure referents to it are destroyed.
1025
1026       %s argument is not a HASH element or slice
1027           (F) The argument to delete() must be either a hash element, such as
1028
1029               $foo{$bar}
1030               $ref->[12]->{"susie"}
1031
1032           or a hash slice, such as
1033
1034               @foo{$bar, $baz, $xyzzy}
1035               @{$ref->[12]}{"susie", "queue"}
1036
1037       Allocation too large: %lx
1038           (X) You can't allocate more than 64K on an MS-DOS machine.
1039
1040       Allocation too large
1041           (F) You can't allocate more than 2^31+"small amount" bytes.
1042
1043       Applying %s to %s will act on scalar(%s)
1044           (W) The pattern match (//), substitution (s///), and
1045           transliteration (tr///) operators work on scalar values.  If you
1046           apply one of them to an array or a hash, it will convert the array
1047           or hash to a scalar value (the length of an array or the population
1048           info of a hash) and then work on that scalar value.  This is
1049           probably not what you meant to do.  See "grep" in perlfunc and
1050           "map" in perlfunc for alternatives.
1051
1052       Attempt to free nonexistent shared string
1053           (P) Perl maintains a reference counted internal table of strings to
1054           optimize the storage and access of hash keys and other strings.
1055           This indicates someone tried to decrement the reference count of a
1056           string that can no longer be found in the table.
1057
1058       Attempt to use reference as lvalue in substr
1059           (W) You supplied a reference as the first argument to substr() used
1060           as an lvalue, which is pretty strange.  Perhaps you forgot to
1061           dereference it first.  See "substr" in perlfunc.
1062
1063       Bareword "%s" refers to nonexistent package
1064           (W) You used a qualified bareword of the form "Foo::", but the
1065           compiler saw no other uses of that namespace before that point.
1066           Perhaps you need to predeclare a package?
1067
1068       Can't redefine active sort subroutine %s
1069           (F) Perl optimizes the internal handling of sort subroutines and
1070           keeps pointers into them.  You tried to redefine one such sort
1071           subroutine when it was currently active, which is not allowed.  If
1072           you really want to do this, you should write "sort { &func } @x"
1073           instead of "sort func @x".
1074
1075       Can't use bareword ("%s") as %s ref while "strict refs" in use
1076           (F) Only hard references are allowed by "strict refs".  Symbolic
1077           references are disallowed.  See perlref.
1078
1079       Cannot resolve method `%s' overloading `%s' in package `%s'
1080           (P) Internal error trying to resolve overloading specified by a
1081           method name (as opposed to a subroutine reference).
1082
1083       Constant subroutine %s redefined
1084           (S) You redefined a subroutine which had previously been eligible
1085           for inlining.  See "Constant Functions" in perlsub for commentary
1086           and workarounds.
1087
1088       Constant subroutine %s undefined
1089           (S) You undefined a subroutine which had previously been eligible
1090           for inlining.  See "Constant Functions" in perlsub for commentary
1091           and workarounds.
1092
1093       Copy method did not return a reference
1094           (F) The method which overloads "=" is buggy. See "Copy Constructor"
1095           in overload.
1096
1097       Died
1098           (F) You passed die() an empty string (the equivalent of "die """)
1099           or you called it with no args and both $@ and $_ were empty.
1100
1101       Exiting pseudo-block via %s
1102           (W) You are exiting a rather special block construct (like a sort
1103           block or subroutine) by unconventional means, such as a goto, or a
1104           loop control statement.  See "sort" in perlfunc.
1105
1106       Identifier too long
1107           (F) Perl limits identifiers (names for variables, functions, etc.)
1108           to 252 characters for simple names, somewhat more for compound
1109           names (like $A::B).  You've exceeded Perl's limits.  Future
1110           versions of Perl are likely to eliminate these arbitrary
1111           limitations.
1112
1113       Illegal character %s (carriage return)
1114           (F) A carriage return character was found in the input.  This is an
1115           error, and not a warning, because carriage return characters can
1116           break multi-line strings, including here documents (e.g., "print
1117           <<EOF;").
1118
1119       Illegal switch in PERL5OPT: %s
1120           (X) The PERL5OPT environment variable may only be used to set the
1121           following switches: -[DIMUdmw].
1122
1123       Integer overflow in hex number
1124           (S) The literal hex number you have specified is too big for your
1125           architecture. On a 32-bit architecture the largest hex literal is
1126           0xFFFFFFFF.
1127
1128       Integer overflow in octal number
1129           (S) The literal octal number you have specified is too big for your
1130           architecture. On a 32-bit architecture the largest octal literal is
1131           037777777777.
1132
1133       internal error: glob failed
1134           (P) Something went wrong with the external program(s) used for
1135           "glob" and "<*.c>".  This may mean that your csh (C shell) is
1136           broken.  If so, you should change all of the csh-related variables
1137           in config.sh:  If you have tcsh, make the variables refer to it as
1138           if it were csh (e.g. "full_csh='/usr/bin/tcsh'"); otherwise, make
1139           them all empty (except that "d_csh" should be 'undef') so that Perl
1140           will think csh is missing.  In either case, after editing
1141           config.sh, run "./Configure -S" and rebuild Perl.
1142
1143       Invalid conversion in %s: "%s"
1144           (W) Perl does not understand the given format conversion.  See
1145           "sprintf" in perlfunc.
1146
1147       Invalid type in pack: '%s'
1148           (F) The given character is not a valid pack type.  See "pack" in
1149           perlfunc.
1150
1151       Invalid type in unpack: '%s'
1152           (F) The given character is not a valid unpack type.  See "unpack"
1153           in perlfunc.
1154
1155       Name "%s::%s" used only once: possible typo
1156           (W) Typographical errors often show up as unique variable names.
1157           If you had a good reason for having a unique name, then just
1158           mention it again somehow to suppress the message (the "use vars"
1159           pragma is provided for just this purpose).
1160
1161       Null picture in formline
1162           (F) The first argument to formline must be a valid format picture
1163           specification.  It was found to be empty, which probably means you
1164           supplied it an uninitialized value.  See perlform.
1165
1166       Offset outside string
1167           (F) You tried to do a read/write/send/recv operation with an offset
1168           pointing outside the buffer.  This is difficult to imagine.  The
1169           sole exception to this is that "sysread()"ing past the buffer will
1170           extend the buffer and zero pad the new area.
1171
1172       Out of memory!
1173           (X|F) The malloc() function returned 0, indicating there was
1174           insufficient remaining memory (or virtual memory) to satisfy the
1175           request.
1176
1177           The request was judged to be small, so the possibility to trap it
1178           depends on the way Perl was compiled.  By default it is not
1179           trappable.  However, if compiled for this, Perl may use the
1180           contents of $^M as an emergency pool after die()ing with this
1181           message.  In this case the error is trappable once.
1182
1183       Out of memory during request for %s
1184           (F) The malloc() function returned 0, indicating there was
1185           insufficient remaining memory (or virtual memory) to satisfy the
1186           request. However, the request was judged large enough (compile-time
1187           default is 64K), so a possibility to shut down by trapping this
1188           error is granted.
1189
1190       panic: frexp
1191           (P) The library function frexp() failed, making printf("%f")
1192           impossible.
1193
1194       Possible attempt to put comments in qw() list
1195           (W) qw() lists contain items separated by whitespace; as with
1196           literal strings, comment characters are not ignored, but are
1197           instead treated as literal data.  (You may have used different
1198           delimiters than the parentheses shown here; braces are also
1199           frequently used.)
1200
1201           You probably wrote something like this:
1202
1203               @list = qw(
1204                   a # a comment
1205                   b # another comment
1206               );
1207
1208           when you should have written this:
1209
1210               @list = qw(
1211                   a
1212                   b
1213               );
1214
1215           If you really want comments, build your list the old-fashioned way,
1216           with quotes and commas:
1217
1218               @list = (
1219                   'a',    # a comment
1220                   'b',    # another comment
1221               );
1222
1223       Possible attempt to separate words with commas
1224           (W) qw() lists contain items separated by whitespace; therefore
1225           commas aren't needed to separate the items. (You may have used
1226           different delimiters than the parentheses shown here; braces are
1227           also frequently used.)
1228
1229           You probably wrote something like this:
1230
1231               qw! a, b, c !;
1232
1233           which puts literal commas into some of the list items.  Write it
1234           without commas if you don't want them to appear in your data:
1235
1236               qw! a b c !;
1237
1238       Scalar value @%s{%s} better written as $%s{%s}
1239           (W) You've used a hash slice (indicated by @) to select a single
1240           element of a hash.  Generally it's better to ask for a scalar value
1241           (indicated by $).  The difference is that $foo{&bar} always behaves
1242           like a scalar, both when assigning to it and when evaluating its
1243           argument, while @foo{&bar} behaves like a list when you assign to
1244           it, and provides a list context to its subscript, which can do
1245           weird things if you're expecting only one subscript.
1246
1247       Stub found while resolving method `%s' overloading `%s' in %s
1248           (P) Overloading resolution over @ISA tree may be broken by
1249           importing stubs.  Stubs should never be implicitly created, but
1250           explicit calls to "can" may break this.
1251
1252       Too late for "-T" option
1253           (X) The #! line (or local equivalent) in a Perl script contains the
1254           -T option, but Perl was not invoked with -T in its argument list.
1255           This is an error because, by the time Perl discovers a -T in a
1256           script, it's too late to properly taint everything from the
1257           environment.  So Perl gives up.
1258
1259       untie attempted while %d inner references still exist
1260           (W) A copy of the object returned from "tie" (or "tied") was still
1261           valid when "untie" was called.
1262
1263       Unrecognized character %s
1264           (F) The Perl parser has no idea what to do with the specified
1265           character in your Perl script (or eval).  Perhaps you tried to run
1266           a compressed script, a binary program, or a directory as a Perl
1267           program.
1268
1269       Unsupported function fork
1270           (F) Your version of executable does not support forking.
1271
1272           Note that under some systems, like OS/2, there may be different
1273           flavors of Perl executables, some of which may support fork, some
1274           not. Try changing the name you call Perl by to "perl_", "perl__",
1275           and so on.
1276
1277       Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1278           (D) Perl versions before 5.004 misinterpreted any type marker
1279           followed by "$" and a digit.  For example, "$$0" was incorrectly
1280           taken to mean "${$}0" instead of "${$0}".  This bug is (mostly)
1281           fixed in Perl 5.004.
1282
1283           However, the developers of Perl 5.004 could not fix this bug
1284           completely, because at least two widely-used modules depend on the
1285           old meaning of "$$0" in a string.  So Perl 5.004 still interprets
1286           "$$<digit>" in the old (broken) way inside strings; but it
1287           generates this message as a warning.  And in Perl 5.005, this
1288           special treatment will cease.
1289
1290       Value of %s can be "0"; test with defined()
1291           (W) In a conditional expression, you used <HANDLE>, <*> (glob),
1292           "each()", or "readdir()" as a boolean value.  Each of these
1293           constructs can return a value of "0"; that would make the
1294           conditional expression false, which is probably not what you
1295           intended.  When using these constructs in conditional expressions,
1296           test their values with the "defined" operator.
1297
1298       Variable "%s" may be unavailable
1299           (W) An inner (nested) anonymous subroutine is inside a named
1300           subroutine, and outside that is another subroutine; and the
1301           anonymous (innermost) subroutine is referencing a lexical variable
1302           defined in the outermost subroutine.  For example:
1303
1304              sub outermost { my $a; sub middle { sub { $a } } }
1305
1306           If the anonymous subroutine is called or referenced (directly or
1307           indirectly) from the outermost subroutine, it will share the
1308           variable as you would expect.  But if the anonymous subroutine is
1309           called or referenced when the outermost subroutine is not active,
1310           it will see the value of the shared variable as it was before and
1311           during the *first* call to the outermost subroutine, which is
1312           probably not what you want.
1313
1314           In these circumstances, it is usually best to make the middle
1315           subroutine anonymous, using the "sub {}" syntax.  Perl has specific
1316           support for shared variables in nested anonymous subroutines; a
1317           named subroutine in between interferes with this feature.
1318
1319       Variable "%s" will not stay shared
1320           (W) An inner (nested) named subroutine is referencing a lexical
1321           variable defined in an outer subroutine.
1322
1323           When the inner subroutine is called, it will probably see the value
1324           of the outer subroutine's variable as it was before and during the
1325           *first* call to the outer subroutine; in this case, after the first
1326           call to the outer subroutine is complete, the inner and outer
1327           subroutines will no longer share a common value for the variable.
1328           In other words, the variable will no longer be shared.
1329
1330           Furthermore, if the outer subroutine is anonymous and references a
1331           lexical variable outside itself, then the outer and inner
1332           subroutines will never share the given variable.
1333
1334           This problem can usually be solved by making the inner subroutine
1335           anonymous, using the "sub {}" syntax.  When inner anonymous subs
1336           that reference variables in outer subroutines are called or
1337           referenced, they are automatically rebound to the current values of
1338           such variables.
1339
1340       Warning: something's wrong
1341           (W) You passed warn() an empty string (the equivalent of "warn """)
1342           or you called it with no args and $_ was empty.
1343
1344       Ill-formed logical name |%s| in prime_env_iter
1345           (W) A warning peculiar to VMS.  A logical name was encountered when
1346           preparing to iterate over %ENV which violates the syntactic rules
1347           governing logical names.  Since it cannot be translated normally,
1348           it is skipped, and will not appear in %ENV.  This may be a benign
1349           occurrence, as some software packages might directly modify logical
1350           name tables and introduce nonstandard names, or it may indicate
1351           that a logical name table has been corrupted.
1352
1353       Got an error from DosAllocMem
1354           (P) An error peculiar to OS/2.  Most probably you're using an
1355           obsolete version of Perl, and this should not happen anyway.
1356
1357       Malformed PERLLIB_PREFIX
1358           (F) An error peculiar to OS/2.  PERLLIB_PREFIX should be of the
1359           form
1360
1361               prefix1;prefix2
1362
1363           or
1364
1365               prefix1 prefix2
1366
1367           with nonempty prefix1 and prefix2.  If "prefix1" is indeed a prefix
1368           of a builtin library search path, prefix2 is substituted.  The
1369           error may appear if components are not found, or are too long.  See
1370           "PERLLIB_PREFIX" in README.os2.
1371
1372       PERL_SH_DIR too long
1373           (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find
1374           the "sh"-shell in.  See "PERL_SH_DIR" in README.os2.
1375
1376       Process terminated by SIG%s
1377           (W) This is a standard message issued by OS/2 applications, while
1378           *nix applications die in silence.  It is considered a feature of
1379           the OS/2 port.  One can easily disable this by appropriate
1380           sighandlers, see "Signals" in perlipc.  See also "Process
1381           terminated by SIGTERM/SIGINT" in README.os2.
1382

BUGS

1384       If you find what you think is a bug, you might check the headers of
1385       recently posted articles in the comp.lang.perl.misc newsgroup.  There
1386       may also be information at http://www.perl.com/perl/ , the Perl Home
1387       Page.
1388
1389       If you believe you have an unreported bug, please run the perlbug
1390       program included with your release.  Make sure you trim your bug down
1391       to a tiny but sufficient test case.  Your bug report, along with the
1392       output of "perl -V", will be sent off to <perlbug@perl.com> to be
1393       analysed by the Perl porting team.
1394

SEE ALSO

1396       The Changes file for exhaustive details on what changed.
1397
1398       The INSTALL file for how to build Perl.  This file has been
1399       significantly updated for 5.004, so even veteran users should look
1400       through it.
1401
1402       The README file for general stuff.
1403
1404       The Copying file for copyright information.
1405

HISTORY

1407       Constructed by Tom Christiansen, grabbing material with permission from
1408       innumerable contributors, with kibitzing by more than a few Perl
1409       porters.
1410
1411       Last update: Wed May 14 11:14:09 EDT 1997
1412
1413
1414
1415perl v5.34.0                      2021-10-18                  PERL5004DELTA(1)
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