3 perldeprecation - list Perl deprecations
7 The purpose of this document is to document what has been deprecated
8 in Perl, and by which version the deprecated feature will disappear,
9 or, for already removed features, when it was removed.
11 This document will try to discuss what alternatives for the deprecated
12 features are available.
14 The deprecated features will be grouped by the version of Perl in
15 which they will be removed.
19 =head3 Pod::Html utility functions
21 The definition and documentation of three utility functions previously
22 importable from L<Pod::Html> were moved to new package L<Pod::Html::Util> in
23 Perl 5.36. While they remain importable from L<Pod::Html> in Perl 5.36, as of
24 Perl 5.38 they will only be importable, on request, from L<Pod::Html::Util>.
28 There are no deprecations or fatalizations scheduled for Perl 5.34.
32 =head3 Constants from lexical variables potentially modified elsewhere
34 You wrote something like
37 $sub = sub () { $var };
39 but $var is referenced elsewhere and could be modified after the C<sub>
40 expression is evaluated. Either it is explicitly modified elsewhere
41 (C<$var = 3>) or it is passed to a subroutine or to an operator like
42 C<printf> or C<map>, which may or may not modify the variable.
44 Traditionally, Perl has captured the value of the variable at that
45 point and turned the subroutine into a constant eligible for inlining.
46 In those cases where the variable can be modified elsewhere, this
47 breaks the behavior of closures, in which the subroutine captures
48 the variable itself, rather than its value, so future changes to the
49 variable are reflected in the subroutine's return value.
51 If you intended for the subroutine to be eligible for inlining, then
52 make sure the variable is not referenced elsewhere, possibly by
56 $sub = sub () { $var2 };
58 If you do want this subroutine to be a closure that reflects future
59 changes to the variable that it closes over, add an explicit C<return>:
62 $sub = sub () { return $var };
64 This usage was deprecated and as of Perl 5.32 is no longer allowed.
66 =head3 Use of strings with code points over 0xFF as arguments to C<vec>
68 C<vec> views its string argument as a sequence of bits. A string
69 containing a code point over 0xFF is nonsensical. This usage is
70 deprecated in Perl 5.28, and was removed in Perl 5.32.
72 =head3 Use of code points over 0xFF in string bitwise operators
74 The string bitwise operators, C<&>, C<|>, C<^>, and C<~>, treat their
75 operands as strings of bytes. As such, values above 0xFF are
76 nonsensical. Some instances of these have been deprecated since Perl
77 5.24, and were made fatal in 5.28, but it turns out that in cases where
78 the wide characters did not affect the end result, no deprecation
79 notice was raised, and so remain legal. Now, all occurrences either are
80 fatal or raise a deprecation warning, so that the remaining legal
81 occurrences became fatal in 5.32.
87 The wide character is not used in the C<&> operation because the left
88 operand is shorter. This now throws an exception.
90 =head3 hostname() doesn't accept any arguments
92 The function C<hostname()> in the L<Sys::Hostname> module has always
93 been documented to be called with no arguments. Historically it has not
94 enforced this, and has actually accepted and ignored any arguments. As a
95 result, some users have got the mistaken impression that an argument does
96 something useful. To avoid these bugs, the function is being made strict.
97 Passing arguments was deprecated in Perl 5.28 and became fatal in Perl 5.32.
99 =head3 Unescaped left braces in regular expressions
101 The simple rule to remember, if you want to match a literal C<{>
102 character (U+007B C<LEFT CURLY BRACKET>) in a regular expression
103 pattern, is to escape each literal instance of it in some way.
104 Generally easiest is to precede it with a backslash, like C<\{>
105 or enclose it in square brackets (C<[{]>). If the pattern
106 delimiters are also braces, any matching right brace (C<}>) should
107 also be escaped to avoid confusing the parser, for example,
111 Forcing literal C<{> characters to be escaped will enable the Perl
112 language to be extended in various ways in future releases. To avoid
113 needlessly breaking existing code, the restriction is not enforced in
114 contexts where there are unlikely to ever be extensions that could
115 conflict with the use there of C<{> as a literal. A non-deprecation
116 warning that the left brace is being taken literally is raised in
117 contexts where there could be confusion about it.
119 Literal uses of C<{> were deprecated in Perl 5.20, and some uses of it
120 started to give deprecation warnings since. These cases were made fatal
121 in Perl 5.26. Due to an oversight, not all cases of a use of a literal
122 C<{> got a deprecation warning. Some cases started warning in Perl 5.26,
123 and were made fatal in Perl 5.30. Other cases started in Perl 5.28,
124 and were made fatal in 5.32.
126 =head3 In XS code, use of various macros dealing with UTF-8.
128 The macros below now require an extra parameter than in versions prior
129 to Perl 5.32. The final parameter in each one is a pointer into the
130 string supplied by the first parameter beyond which the input will not
131 be read. This prevents potential reading beyond the end of the buffer.
132 C<isALPHANUMERIC_utf8>,
143 C<isALPHANUMERIC_LC_utf8>,
151 C<isIDFIRST_LC_utf8>,
158 C<isWORDCHAR_LC_utf8>,
166 Since Perl 5.26, this functionality with the extra parameter has been
167 available by using a corresponding macro to each one of these, and whose
168 name is formed by appending C<_safe> to the base name. There is no
169 change to the functionality of those. For example, C<isDIGIT_utf8_safe>
170 corresponds to C<isDIGIT_utf8>, and both now behave identically. All
171 are documented in L<perlapi/Character case changing> and
172 L<perlapi/Character classification>.
174 This change was originally scheduled for 5.30, but was delayed until
177 =head3 C<< File::Glob::glob() >> was removed
179 C<< File::Glob >> has a function called C<< glob >>, which just calls
182 C<< File::Glob::glob() >> was deprecated in Perl 5.8. A deprecation
183 message was issued from Perl 5.26 onwards, and the function has now
184 disappeared in Perl 5.30.
186 Code using C<< File::Glob::glob() >> should call
187 C<< File::Glob::bsd_glob() >> instead.
191 =head3 C<< $* >> is no longer supported
193 Before Perl 5.10, setting C<< $* >> to a true value globally enabled
194 multi-line matching within a string. This relique from the past lost
195 its special meaning in 5.10. Use of this variable will be a fatal error
196 in Perl 5.30, freeing the variable up for a future special meaning.
198 To enable multiline matching one should use the C<< /m >> regexp
199 modifier (possibly in combination with C<< /s >>). This can be set
200 on a per match bases, or can be enabled per lexical scope (including
201 a whole file) with C<< use re '/m' >>.
203 =head3 C<< $# >> is no longer supported
205 This variable used to have a special meaning -- it could be used
206 to control how numbers were formatted when printed. This seldom
207 used functionality was removed in Perl 5.10. In order to free up
208 the variable for a future special meaning, its use will be a fatal
211 To specify how numbers are formatted when printed, one is advised
212 to use C<< printf >> or C<< sprintf >> instead.
214 =head3 Assigning non-zero to C<< $[ >> is fatal
216 This variable (and the corresponding C<array_base> feature and
217 L<arybase> module) allowed changing the base for array and string
220 Setting this to a non-zero value has been deprecated since Perl 5.12 and
221 throws a fatal error as of Perl 5.30.
223 =head3 C<< File::Glob::glob() >> will disappear
225 C<< File::Glob >> has a function called C<< glob >>, which just calls
226 C<< bsd_glob >>. However, its prototype is different from the prototype
227 of C<< CORE::glob >>, and hence, C<< File::Glob::glob >> should not
230 C<< File::Glob::glob() >> was deprecated in Perl 5.8. A deprecation
231 message was issued from Perl 5.26 onwards, and the function will
232 disappear in Perl 5.30.
234 Code using C<< File::Glob::glob() >> should call
235 C<< File::Glob::bsd_glob() >> instead.
237 =head3 Unescaped left braces in regular expressions (for 5.30)
239 See L</Unescaped left braces in regular expressions> above.
241 =head3 Unqualified C<dump()>
243 Use of C<dump()> instead of C<CORE::dump()> was deprecated in Perl 5.8,
244 and an unqualified C<dump()> will no longer be available in Perl 5.30.
246 See L<perlfunc/dump>.
249 =head3 Using my() in false conditional.
251 There has been a long-standing bug in Perl that causes a lexical variable
252 not to be cleared at scope exit when its declaration includes a false
253 conditional. Some people have exploited this bug to achieve a kind of
254 static variable. To allow us to fix this bug, people should not be
255 relying on this behavior.
257 Instead, it's recommended one uses C<state> variables to achieve the
261 sub count {state $counter; return ++ $counter}
262 say count (); # Prints 1
263 say count (); # Prints 2
265 C<state> variables were introduced in Perl 5.10.
267 Alternatively, you can achieve a similar static effect by
268 declaring the variable in a separate block outside the function, e.g.,
270 sub f { my $x if 0; return $x++ }
274 { my $x; sub f { return $x++ } }
276 The use of C<my()> in a false conditional has been deprecated in
277 Perl 5.10, and became a fatal error in Perl 5.30.
280 =head3 Reading/writing bytes from/to :utf8 handles.
282 The sysread(), recv(), syswrite() and send() operators are
283 deprecated on handles that have the C<:utf8> layer, either explicitly, or
284 implicitly, eg., with the C<:encoding(UTF-16LE)> layer.
286 Both sysread() and recv() currently use only the C<:utf8> flag for the stream,
287 ignoring the actual layers. Since sysread() and recv() do no UTF-8
288 validation they can end up creating invalidly encoded scalars.
290 Similarly, syswrite() and send() use only the C<:utf8> flag, otherwise ignoring
291 any layers. If the flag is set, both write the value UTF-8 encoded, even if
292 the layer is some different encoding, such as the example above.
294 Ideally, all of these operators would completely ignore the C<:utf8> state,
295 working only with bytes, but this would result in silently breaking existing
296 code. To avoid this a future version of perl will throw an exception when
297 any of sysread(), recv(), syswrite() or send() are called on handle with the
300 In Perl 5.30, it will no longer be possible to use sysread(), recv(),
301 syswrite() or send() to read or send bytes from/to :utf8 handles.
304 =head3 Use of unassigned code point or non-standalone grapheme for a delimiter.
306 A grapheme is what appears to a native-speaker of a language to be a
307 character. In Unicode (and hence Perl) a grapheme may actually be
308 several adjacent characters that together form a complete grapheme. For
309 example, there can be a base character, like "R" and an accent, like a
310 circumflex "^", that appear to be a single character when displayed,
311 with the circumflex hovering over the "R".
313 As of Perl 5.30, use of delimiters which are non-standalone graphemes is
314 fatal, in order to move the language to be able to accept
315 multi-character graphemes as delimiters.
317 Also, as of Perl 5.30, delimiters which are unassigned code points
318 but that may someday become assigned are prohibited. Otherwise, code
319 that works today would fail to compile if the currently unassigned
320 delimiter ends up being something that isn't a stand-alone grapheme.
321 Because Unicode is never going to assign L<non-character code
322 points|perlunicode/Noncharacter code points>, nor L<code points that are
323 above the legal Unicode maximum|perlunicode/Beyond Unicode code
324 points>, those can be delimiters.
328 =head3 Attributes C<< :locked >> and C<< :unique >>
330 The attributes C<< :locked >> (on code references) and C<< :unique >>
331 (on array, hash and scalar references) have had no effect since
332 Perl 5.005 and Perl 5.8.8 respectively. Their use has been deprecated
335 As of Perl 5.28, these attributes are syntax errors. Since the
336 attributes do not do anything, removing them from your code fixes
337 the syntax error; and removing them will not influence the behaviour
341 =head3 Bare here-document terminators
343 Perl has allowed you to use a bare here-document terminator to have the
344 here-document end at the first empty line. This practise was deprecated
345 in Perl 5.000; as of Perl 5.28, using a bare here-document terminator
346 throws a fatal error.
348 You are encouraged to use the explicitly quoted form if you wish to
349 use an empty line as the terminator of the here-document:
354 # Previous blank line ends the here-document.
357 =head3 Setting $/ to a reference to a non-positive integer
359 You assigned a reference to a scalar to C<$/> where the
360 referenced item is not a positive integer. In older perls this B<appeared>
361 to work the same as setting it to C<undef> but was in fact internally
362 different, less efficient and with very bad luck could have resulted in
363 your file being split by a stringified form of the reference.
365 In Perl 5.20.0 this was changed so that it would be B<exactly> the same as
366 setting C<$/> to undef, with the exception that this warning would be
369 As of Perl 5.28, setting C<$/> to a reference of a non-positive
370 integer throws a fatal error.
372 You are recommended to change your code to set C<$/> to C<undef> explicitly
373 if you wish to slurp the file.
376 =head3 Limit on the value of Unicode code points.
378 Unicode only allows code points up to 0x10FFFF, but Perl allows
379 much larger ones. Up till Perl 5.28, it was allowed to use code
380 points exceeding the maximum value of an integer (C<IV_MAX>).
381 However, that did break the perl interpreter in some constructs,
382 including causing it to hang in a few cases. The known problem
383 areas were in C<tr///>, regular expression pattern matching using
384 quantifiers, as quote delimiters in C<qI<X>...I<X>> (where I<X> is
385 the C<chr()> of a large code point), and as the upper limits in
388 The use of out of range code points was deprecated in Perl 5.24; as of
389 Perl 5.28 using a code point exceeding C<IV_MAX> throws a fatal error.
391 If your code is to run on various platforms, keep in mind that the upper
392 limit depends on the platform. It is much larger on 64-bit word sizes
393 than 32-bit ones. For 32-bit integers, C<IV_MAX> equals C<0x7FFFFFFF>,
394 for 64-bit integers, C<IV_MAX> equals C<0x7FFFFFFFFFFFFFFF>.
397 =head3 Use of comma-less variable list in formats.
399 It was allowed to use a list of variables in a format, without
400 separating them with commas. This usage has been deprecated
401 for a long time, and as of Perl 5.28, this throws a fatal error.
403 =head3 Use of C<\N{}>
405 Use of C<\N{}> with nothing between the braces was deprecated in
406 Perl 5.24, and throws a fatal error as of Perl 5.28.
408 Since such a construct is equivalent to using an empty string,
409 you are recommended to remove such C<\N{}> constructs.
411 =head3 Using the same symbol to open a filehandle and a dirhandle
413 It used to be legal to use C<open()> to associate both a
414 filehandle and a dirhandle to the same symbol (glob or scalar).
415 This idiom is likely to be confusing, and it was deprecated in
418 Using the same symbol to C<open()> a filehandle and a dirhandle
419 throws a fatal error as of Perl 5.28.
421 You should be using two different symbols instead.
423 =head3 ${^ENCODING} is no longer supported.
425 The special variable C<${^ENCODING}> was used to implement
426 the C<encoding> pragma. Setting this variable to anything other
427 than C<undef> was deprecated in Perl 5.22. Full deprecation
428 of the variable happened in Perl 5.25.3.
430 Setting this variable to anything other than an undefined value
431 throws a fatal error as of Perl 5.28.
434 =head3 C<< B::OP::terse >>
436 This method, which just calls C<< B::Concise::b_terse >>, has been
437 deprecated, and disappeared in Perl 5.28. Please use
438 C<< B::Concise >> instead.
442 =head3 Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
444 As an (ahem) accidental feature, C<AUTOLOAD> subroutines were looked
445 up as methods (using the C<@ISA> hierarchy) even when the subroutines
446 to be autoloaded were called as plain functions (e.g. C<Foo::bar()>),
447 not as methods (e.g. C<< Foo->bar() >> or C<< $obj->bar() >>).
449 This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28
450 by using method lookup only for methods' C<AUTOLOAD>s.
452 The simple rule is: Inheritance will not work when autoloading
453 non-methods. The simple fix for old code is: In any module that used
454 to depend on inheriting C<AUTOLOAD> for non-methods from a base class
455 named C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during
458 In code that currently says C<use AutoLoader; @ISA = qw(AutoLoader);>
459 you should remove AutoLoader from @ISA and change C<use AutoLoader;> to
460 C<use AutoLoader 'AUTOLOAD';>.
463 =head3 Use of code points over 0xFF in string bitwise operators
465 The string bitwise operators, C<&>, C<|>, C<^>, and C<~>, treat
466 their operands as strings of bytes. As such, values above 0xFF
467 are nonsensical. Using such code points with these operators
468 was deprecated in Perl 5.24, and is fatal as of Perl 5.28.
470 =head3 In XS code, use of C<to_utf8_case()>
472 This function has been removed as of Perl 5.28; instead convert to call
473 the appropriate one of:
474 L<C<toFOLD_utf8_safe>|perlapi/toFOLD_utf8_safe>.
475 L<C<toLOWER_utf8_safe>|perlapi/toLOWER_utf8_safe>,
476 L<C<toTITLE_utf8_safe>|perlapi/toTITLE_utf8_safe>,
478 L<C<toUPPER_utf8_safe>|perlapi/toUPPER_utf8_safe>.
482 =head3 C<< --libpods >> in C<< Pod::Html >>
484 Since Perl 5.18, the option C<< --libpods >> has been deprecated, and
485 using this option did not do anything other than producing a warning.
487 The C<< --libpods >> option is no longer recognized as of Perl 5.26.
490 =head3 The utilities C<< c2ph >> and C<< pstruct >>
492 These old, perl3-era utilities have been deprecated in favour of
493 C<< h2xs >> for a long time. As of Perl 5.26, they have been removed.
496 =head3 Trapping C<< $SIG {__DIE__} >> other than during program exit.
498 The C<$SIG{__DIE__}> hook is called even inside an C<eval()>. It was
499 never intended to happen this way, but an implementation glitch made
500 this possible. This used to be deprecated, as it allowed strange action
501 at a distance like rewriting a pending exception in C<$@>. Plans to
502 rectify this have been scrapped, as users found that rewriting a
503 pending exception is actually a useful feature, and not a bug.
505 Perl never issued a deprecation warning for this; the deprecation
506 was by documentation policy only. But this deprecation has been
507 lifted as of Perl 5.26.
510 =head3 Malformed UTF-8 string in "%s"
512 This message indicates a bug either in the Perl core or in XS
513 code. Such code was trying to find out if a character, allegedly
514 stored internally encoded as UTF-8, was of a given type, such as
515 being punctuation or a digit. But the character was not encoded
516 in legal UTF-8. The C<%s> is replaced by a string that can be used
517 by knowledgeable people to determine what the type being checked
520 Passing malformed strings was deprecated in Perl 5.18, and
521 became fatal in Perl 5.26.
526 =head3 Use of C<< *glob{FILEHANDLE} >>
528 The use of C<< *glob{FILEHANDLE} >> was deprecated in Perl 5.8.
529 The intention was to use C<< *glob{IO} >> instead, for which
530 C<< *glob{FILEHANDLE} >> is an alias.
532 However, this feature was undeprecated in Perl 5.24.
534 =head3 Calling POSIX::%s() is deprecated
536 The following functions in the C<POSIX> module are no longer available:
537 C<isalnum>, C<isalpha>, C<iscntrl>, C<isdigit>, C<isgraph>, C<islower>,
538 C<isprint>, C<ispunct>, C<isspace>, C<isupper>, and C<isxdigit>. The
539 functions are buggy and don't work on UTF-8 encoded strings. See their
540 entries in L<POSIX> for more information.
542 The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
547 =head3 Use of %s on a handle without * is deprecated
549 It used to be possible to use C<tie>, C<tied> or C<untie> on a scalar
550 while the scalar holds a typeglob. This caused its filehandle to be
551 tied. It left no way to tie the scalar itself when it held a typeglob,
552 and no way to untie a scalar that had had a typeglob assigned to it.
554 This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
556 So now C<tie $scalar> will always tie the scalar, not the handle it holds.
557 To tie the handle, use C<tie *$scalar> (with an explicit asterisk). The same
558 applies to C<tied *$scalar> and C<untie *$scalar>.
563 L<warnings>, L<diagnostics>.