1PERLDEPRECATION(1) Perl Programmers Reference Guide PERLDEPRECATION(1)
2
6 perldeprecation - list Perl deprecations
7
9 The purpose of this document is to document what has been deprecated in
10 Perl, and by which version the deprecated feature will disappear, or,
11 for already removed features, when it was removed.
12 This document will try to discuss what alternatives for the deprecated
14 features are available.
15 The deprecated features will be grouped by the version of Perl in which
17 they will be removed.
18 Perl 5.40
20 Downgrading a "use VERSION" to below v5.11
21 Once Perl has seen a "use VERSION" declaration that requests a version
23 "v5.11" or above, a subsequent second declaration that requests an
24 earlier version will print a deprecation warning. For example,
25 use v5.14;
27 say "We can use v5.14's features here";
28 use v5.10; # This prints a warning
30 This behaviour will be removed in Perl 5.40; such a subsequent request
32 will become a compile-time error.
33 This is because of an intended related change to the interaction
35 between "use VERSION" and "use strict". If you specify a version >=
36 5.11, strict is enabled implicitly. If you request a version < 5.11,
37 strict will become disabled even if you had previously written "use
38 strict". This was not the previous behaviour of "use VERSION", which at
39 present will track explicitly-enabled strictness flags independently.
40 Perl 5.38
42 Pod::Html utility functions
43 The definition and documentation of three utility functions previously
45 importable from Pod::Html were moved to new package Pod::Html::Util in
46 Perl 5.36. While they remain importable from Pod::Html in Perl 5.36,
47 as of Perl 5.38 they will only be importable, on request, from
48 Pod::Html::Util.
49 Perl 5.34
51 There are no deprecations or fatalizations scheduled for Perl 5.34.
52 Perl 5.32
54 Constants from lexical variables potentially modified elsewhere
55 You wrote something like
57 my $var;
59 $sub = sub () { $var };
60 but $var is referenced elsewhere and could be modified after the "sub"
62 expression is evaluated. Either it is explicitly modified elsewhere
63 ("$var = 3") or it is passed to a subroutine or to an operator like
64 "printf" or "map", which may or may not modify the variable.
65 Traditionally, Perl has captured the value of the variable at that
67 point and turned the subroutine into a constant eligible for inlining.
68 In those cases where the variable can be modified elsewhere, this
69 breaks the behavior of closures, in which the subroutine captures the
70 variable itself, rather than its value, so future changes to the
71 variable are reflected in the subroutine's return value.
72 If you intended for the subroutine to be eligible for inlining, then
74 make sure the variable is not referenced elsewhere, possibly by copying
75 it:
76 my $var2 = $var;
78 $sub = sub () { $var2 };
79 If you do want this subroutine to be a closure that reflects future
81 changes to the variable that it closes over, add an explicit "return":
82 my $var;
84 $sub = sub () { return $var };
85 This usage was deprecated and as of Perl 5.32 is no longer allowed.
87 Use of strings with code points over 0xFF as arguments to "vec"
89 "vec" views its string argument as a sequence of bits. A string
91 containing a code point over 0xFF is nonsensical. This usage is
92 deprecated in Perl 5.28, and was removed in Perl 5.32.
93 Use of code points over 0xFF in string bitwise operators
95 The string bitwise operators, "&", "|", "^", and "~", treat their
97 operands as strings of bytes. As such, values above 0xFF are
98 nonsensical. Some instances of these have been deprecated since Perl
99 5.24, and were made fatal in 5.28, but it turns out that in cases where
100 the wide characters did not affect the end result, no deprecation
101 notice was raised, and so remain legal. Now, all occurrences either
102 are fatal or raise a deprecation warning, so that the remaining legal
103 occurrences became fatal in 5.32.
104 An example of this is
106 "" & "\x{100}"
108 The wide character is not used in the "&" operation because the left
110 operand is shorter. This now throws an exception.
111 hostname() doesn't accept any arguments
113 The function "hostname()" in the Sys::Hostname module has always been
115 documented to be called with no arguments. Historically it has not
116 enforced this, and has actually accepted and ignored any arguments. As
117 a result, some users have got the mistaken impression that an argument
118 does something useful. To avoid these bugs, the function is being made
119 strict. Passing arguments was deprecated in Perl 5.28 and became fatal
120 in Perl 5.32.
121 Unescaped left braces in regular expressions
123 The simple rule to remember, if you want to match a literal "{"
125 character (U+007B "LEFT CURLY BRACKET") in a regular expression
126 pattern, is to escape each literal instance of it in some way.
127 Generally easiest is to precede it with a backslash, like "\{" or
128 enclose it in square brackets ("[{]"). If the pattern delimiters are
129 also braces, any matching right brace ("}") should also be escaped to
130 avoid confusing the parser, for example,
131 qr{abc\{def\}ghi}
133 Forcing literal "{" characters to be escaped will enable the Perl
135 language to be extended in various ways in future releases. To avoid
136 needlessly breaking existing code, the restriction is not enforced in
137 contexts where there are unlikely to ever be extensions that could
138 conflict with the use there of "{" as a literal. A non-deprecation
139 warning that the left brace is being taken literally is raised in
140 contexts where there could be confusion about it.
141 Literal uses of "{" were deprecated in Perl 5.20, and some uses of it
143 started to give deprecation warnings since. These cases were made fatal
144 in Perl 5.26. Due to an oversight, not all cases of a use of a literal
145 "{" got a deprecation warning. Some cases started warning in Perl
146 5.26, and were made fatal in Perl 5.30. Other cases started in Perl
147 5.28, and were made fatal in 5.32.
148 In XS code, use of various macros dealing with UTF-8.
150 The macros below now require an extra parameter than in versions prior
152 to Perl 5.32. The final parameter in each one is a pointer into the
153 string supplied by the first parameter beyond which the input will not
154 be read. This prevents potential reading beyond the end of the buffer.
155 "isALPHANUMERIC_utf8", "isASCII_utf8", "isBLANK_utf8", "isCNTRL_utf8",
156 "isDIGIT_utf8", "isIDFIRST_utf8", "isPSXSPC_utf8", "isSPACE_utf8",
157 "isVERTWS_utf8", "isWORDCHAR_utf8", "isXDIGIT_utf8",
158 "isALPHANUMERIC_LC_utf8", "isALPHA_LC_utf8", "isASCII_LC_utf8",
159 "isBLANK_LC_utf8", "isCNTRL_LC_utf8", "isDIGIT_LC_utf8",
160 "isGRAPH_LC_utf8", "isIDCONT_LC_utf8", "isIDFIRST_LC_utf8",
161 "isLOWER_LC_utf8", "isPRINT_LC_utf8", "isPSXSPC_LC_utf8",
162 "isPUNCT_LC_utf8", "isSPACE_LC_utf8", "isUPPER_LC_utf8",
163 "isWORDCHAR_LC_utf8", "isXDIGIT_LC_utf8", "toFOLD_utf8",
164 "toLOWER_utf8", "toTITLE_utf8", and "toUPPER_utf8".
165 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
168 whose name is formed by appending "_safe" to the base name. There is
169 no change to the functionality of those. For example,
170 "isDIGIT_utf8_safe" corresponds to "isDIGIT_utf8", and both now behave
171 identically. All are documented in "Character case changing" in
172 perlapi and "Character classification" in perlapi.
173 This change was originally scheduled for 5.30, but was delayed until
175 5.32.
176 "File::Glob::glob()" was removed
178 "File::Glob" has a function called "glob", which just calls "bsd_glob".
180 "File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message
182 was issued from Perl 5.26 onwards, the function became fatal in Perl
183 5.30, and was removed entirely in Perl 5.32.
184 Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()"
186 instead.
187 Perl 5.30
189 $* is no longer supported
190 Before Perl 5.10, setting $* to a true value globally enabled multi-
192 line matching within a string. This relique from the past lost its
193 special meaning in 5.10. Use of this variable became a fatal error in
194 Perl 5.30, freeing the variable up for a future special meaning.
195 To enable multiline matching one should use the "/m" regexp modifier
197 (possibly in combination with "/s"). This can be set on a per match
198 bases, or can be enabled per lexical scope (including a whole file)
199 with "use re '/m'".
200 $# is no longer supported
202 This variable used to have a special meaning -- it could be used to
204 control how numbers were formatted when printed. This seldom used
205 functionality was removed in Perl 5.10. In order to free up the
206 variable for a future special meaning, its use became a fatal error in
207 Perl 5.30.
208 To specify how numbers are formatted when printed, one is advised to
210 use "printf" or "sprintf" instead.
211 Assigning non-zero to $[ is fatal
213 This variable (and the corresponding "array_base" feature and arybase
215 module) allowed changing the base for array and string indexing
216 operations.
217 Setting this to a non-zero value has been deprecated since Perl 5.12
219 and throws a fatal error as of Perl 5.30.
220 "File::Glob::glob()" will disappear
222 "File::Glob" has a function called "glob", which just calls "bsd_glob".
224 However, its prototype is different from the prototype of "CORE::glob",
225 and hence, "File::Glob::glob" should not be used.
226 "File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message
228 was issued from Perl 5.26 onwards, and in Perl 5.30 this was turned
229 into a fatal error.
230 Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()"
232 instead.
233 Unescaped left braces in regular expressions (for 5.30)
235 See "Unescaped left braces in regular expressions" above.
237 Unqualified "dump()"
239 Use of "dump()" instead of "CORE::dump()" was deprecated in Perl 5.8,
241 and an unqualified "dump()" is no longer available as of Perl 5.30.
242 See "dump" in perlfunc.
244 Using my() in false conditional.
246 There has been a long-standing bug in Perl that causes a lexical
248 variable not to be cleared at scope exit when its declaration includes
249 a false conditional. Some people have exploited this bug to achieve a
250 kind of static variable. To allow us to fix this bug, people should
251 not be relying on this behavior.
252 Instead, it's recommended one uses "state" variables to achieve the
254 same effect:
255 use 5.10.0;
257 sub count {state $counter; return ++ $counter}
258 say count (); # Prints 1
259 say count (); # Prints 2
260 "state" variables were introduced in Perl 5.10.
262 Alternatively, you can achieve a similar static effect by declaring the
264 variable in a separate block outside the function, e.g.,
265 sub f { my $x if 0; return $x++ }
267 becomes
269 { my $x; sub f { return $x++ } }
271 The use of "my()" in a false conditional has been deprecated in Perl
273 5.10, and became a fatal error in Perl 5.30.
274 Reading/writing bytes from/to :utf8 handles.
276 The sysread(), recv(), syswrite() and send() operators are deprecated
278 on handles that have the ":utf8" layer, either explicitly, or
279 implicitly, eg., with the ":encoding(UTF-16LE)" layer.
280 Both sysread() and recv() currently use only the ":utf8" flag for the
282 stream, ignoring the actual layers. Since sysread() and recv() do no
283 UTF-8 validation they can end up creating invalidly encoded scalars.
284 Similarly, syswrite() and send() use only the ":utf8" flag, otherwise
286 ignoring any layers. If the flag is set, both write the value UTF-8
287 encoded, even if the layer is some different encoding, such as the
288 example above.
289 Ideally, all of these operators would completely ignore the ":utf8"
291 state, working only with bytes, but this would result in silently
292 breaking existing code. To avoid this a future version of perl will
293 throw an exception when any of sysread(), recv(), syswrite() or send()
294 are called on handle with the ":utf8" layer.
295 As of Perl 5.30, it is no longer be possible to use sysread(), recv(),
297 syswrite() or send() to read or send bytes from/to :utf8 handles.
298 Use of unassigned code point or non-standalone grapheme for a
300 delimiter.
301 A grapheme is what appears to a native-speaker of a language to be a
303 character. In Unicode (and hence Perl) a grapheme may actually be
304 several adjacent characters that together form a complete grapheme.
305 For example, there can be a base character, like "R" and an accent,
306 like a circumflex "^", that appear to be a single character when
307 displayed, with the circumflex hovering over the "R".
308 As of Perl 5.30, use of delimiters which are non-standalone graphemes
310 is fatal, in order to move the language to be able to accept multi-
311 character graphemes as delimiters.
312 Also, as of Perl 5.30, delimiters which are unassigned code points but
314 that may someday become assigned are prohibited. Otherwise, code that
315 works today would fail to compile if the currently unassigned delimiter
316 ends up being something that isn't a stand-alone grapheme. Because
317 Unicode is never going to assign non-character code points, nor code
318 points that are above the legal Unicode maximum, those can be
319 delimiters.
320 Perl 5.28
322 Attributes ":locked" and ":unique"
323 The attributes ":locked" (on code references) and ":unique" (on array,
325 hash and scalar references) have had no effect since Perl 5.005 and
326 Perl 5.8.8 respectively. Their use has been deprecated since.
327 As of Perl 5.28, these attributes are syntax errors. Since the
329 attributes do not do anything, removing them from your code fixes the
330 syntax error; and removing them will not influence the behaviour of
331 your code.
332 Bare here-document terminators
334 Perl has allowed you to use a bare here-document terminator to have the
336 here-document end at the first empty line. This practise was deprecated
337 in Perl 5.000; as of Perl 5.28, using a bare here-document terminator
338 throws a fatal error.
339 You are encouraged to use the explicitly quoted form if you wish to use
341 an empty line as the terminator of the here-document:
342 print <<"";
344 Print this line.
345 # Previous blank line ends the here-document.
347 Setting $/ to a reference to a non-positive integer
349 You assigned a reference to a scalar to $/ where the referenced item is
351 not a positive integer. In older perls this appeared to work the same
352 as setting it to "undef" but was in fact internally different, less
353 efficient and with very bad luck could have resulted in your file being
354 split by a stringified form of the reference.
355 In Perl 5.20.0 this was changed so that it would be exactly the same as
357 setting $/ to undef, with the exception that this warning would be
358 thrown.
359 As of Perl 5.28, setting $/ to a reference of a non-positive integer
361 throws a fatal error.
362 You are recommended to change your code to set $/ to "undef" explicitly
364 if you wish to slurp the file.
365 Limit on the value of Unicode code points.
367 Unicode only allows code points up to 0x10FFFF, but Perl allows much
369 larger ones. Up till Perl 5.28, it was allowed to use code points
370 exceeding the maximum value of an integer ("IV_MAX"). However, that
371 did break the perl interpreter in some constructs, including causing it
372 to hang in a few cases. The known problem areas were in "tr///",
373 regular expression pattern matching using quantifiers, as quote
374 delimiters in "qX...X" (where X is the "chr()" of a large code point),
375 and as the upper limits in loops.
376 The use of out of range code points was deprecated in Perl 5.24; as of
378 Perl 5.28 using a code point exceeding "IV_MAX" throws a fatal error.
379 If your code is to run on various platforms, keep in mind that the
381 upper limit depends on the platform. It is much larger on 64-bit word
382 sizes than 32-bit ones. For 32-bit integers, "IV_MAX" equals
383 0x7FFFFFFF, for 64-bit integers, "IV_MAX" equals 0x7FFFFFFFFFFFFFFF.
384 Use of comma-less variable list in formats.
386 It was allowed to use a list of variables in a format, without
388 separating them with commas. This usage has been deprecated for a long
389 time, and as of Perl 5.28, this throws a fatal error.
390 Use of "\N{}"
392 Use of "\N{}" with nothing between the braces was deprecated in Perl
394 5.24, and throws a fatal error as of Perl 5.28.
395 Since such a construct is equivalent to using an empty string, you are
397 recommended to remove such "\N{}" constructs.
398 Using the same symbol to open a filehandle and a dirhandle
400 It used to be legal to use "open()" to associate both a filehandle and
402 a dirhandle to the same symbol (glob or scalar). This idiom is likely
403 to be confusing, and it was deprecated in Perl 5.10.
404 Using the same symbol to "open()" a filehandle and a dirhandle throws a
406 fatal error as of Perl 5.28.
407 You should be using two different symbols instead.
409 ${^ENCODING} is no longer supported.
411 The special variable "${^ENCODING}" was used to implement the
413 "encoding" pragma. Setting this variable to anything other than "undef"
414 was deprecated in Perl 5.22. Full deprecation of the variable happened
415 in Perl 5.25.3.
416 Setting this variable to anything other than an undefined value throws
418 a fatal error as of Perl 5.28.
419 "B::OP::terse"
421 This method, which just calls "B::Concise::b_terse", has been
423 deprecated, and disappeared in Perl 5.28. Please use "B::Concise"
424 instead.
425 Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
427 As an (ahem) accidental feature, "AUTOLOAD" subroutines were looked up
429 as methods (using the @ISA hierarchy) even when the subroutines to be
430 autoloaded were called as plain functions (e.g. "Foo::bar()"), not as
431 methods (e.g. "Foo->bar()" or "$obj->bar()").
432 This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28
434 by using method lookup only for methods' "AUTOLOAD"s.
435 The simple rule is: Inheritance will not work when autoloading non-
437 methods. The simple fix for old code is: In any module that used to
438 depend on inheriting "AUTOLOAD" for non-methods from a base class named
439 "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
440 startup.
441 In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);"
443 you should remove AutoLoader from @ISA and change "use AutoLoader;" to
444 "use AutoLoader 'AUTOLOAD';".
445 Use of code points over 0xFF in string bitwise operators
447 The string bitwise operators, "&", "|", "^", and "~", treat their
449 operands as strings of bytes. As such, values above 0xFF are
450 nonsensical. Using such code points with these operators was deprecated
451 in Perl 5.24, and is fatal as of Perl 5.28.
452 In XS code, use of "to_utf8_case()"
454 This function has been removed as of Perl 5.28; instead convert to call
456 the appropriate one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe",
457 "toTITLE_utf8_safe", or "toUPPER_utf8_safe".
458 Perl 5.26
460 "--libpods" in "Pod::Html"
461 Since Perl 5.18, the option "--libpods" has been deprecated, and using
463 this option did not do anything other than producing a warning.
464 The "--libpods" option is no longer recognized as of Perl 5.26.
466 The utilities "c2ph" and "pstruct"
468 These old, perl3-era utilities have been deprecated in favour of "h2xs"
470 for a long time. As of Perl 5.26, they have been removed.
471 Trapping "$SIG {__DIE__}" other than during program exit.
473 The $SIG{__DIE__} hook is called even inside an "eval()". It was never
475 intended to happen this way, but an implementation glitch made this
476 possible. This used to be deprecated, as it allowed strange action at a
477 distance like rewriting a pending exception in $@. Plans to rectify
478 this have been scrapped, as users found that rewriting a pending
479 exception is actually a useful feature, and not a bug.
480 Perl never issued a deprecation warning for this; the deprecation was
482 by documentation policy only. But this deprecation has been lifted as
483 of Perl 5.26.
484 Malformed UTF-8 string in "%s"
486 This message indicates a bug either in the Perl core or in XS code.
488 Such code was trying to find out if a character, allegedly stored
489 internally encoded as UTF-8, was of a given type, such as being
490 punctuation or a digit. But the character was not encoded in legal
491 UTF-8. The %s is replaced by a string that can be used by
492 knowledgeable people to determine what the type being checked against
493 was.
494 Passing malformed strings was deprecated in Perl 5.18, and became fatal
496 in Perl 5.26.
497 Perl 5.24
499 Use of *glob{FILEHANDLE}
500 The use of *glob{FILEHANDLE} was deprecated in Perl 5.8. The intention
502 was to use *glob{IO} instead, for which *glob{FILEHANDLE} is an alias.
503 However, this feature was undeprecated in Perl 5.24.
505 Calling POSIX::%s() is deprecated
507 The following functions in the "POSIX" module are no longer available:
509 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower",
510 "isprint", "ispunct", "isspace", "isupper", and "isxdigit". The
511 functions are buggy and don't work on UTF-8 encoded strings. See their
512 entries in POSIX for more information.
513 The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
515 Perl 5.16
517 Use of %s on a handle without * is deprecated
518 It used to be possible to use "tie", "tied" or "untie" on a scalar
520 while the scalar holds a typeglob. This caused its filehandle to be
521 tied. It left no way to tie the scalar itself when it held a typeglob,
522 and no way to untie a scalar that had had a typeglob assigned to it.
523 This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
525 So now "tie $scalar" will always tie the scalar, not the handle it
527 holds. To tie the handle, use "tie *$scalar" (with an explicit
528 asterisk). The same applies to "tied *$scalar" and "untie *$scalar".
529
531 warnings, diagnostics.
532perl v5.36.3 2023-11-30 PERLDEPRECATION(1)