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 5.34
20 There are no deprecations or fatalizations scheduled for Perl 5.34.
21 Perl 5.32
23 Constants from lexical variables potentially modified elsewhere
24 You wrote something like
26 my $var;
28 $sub = sub () { $var };
29 but $var is referenced elsewhere and could be modified after the "sub"
31 expression is evaluated. Either it is explicitly modified elsewhere
32 ("$var = 3") or it is passed to a subroutine or to an operator like
33 "printf" or "map", which may or may not modify the variable.
34 Traditionally, Perl has captured the value of the variable at that
36 point and turned the subroutine into a constant eligible for inlining.
37 In those cases where the variable can be modified elsewhere, this
38 breaks the behavior of closures, in which the subroutine captures the
39 variable itself, rather than its value, so future changes to the
40 variable are reflected in the subroutine's return value.
41 If you intended for the subroutine to be eligible for inlining, then
43 make sure the variable is not referenced elsewhere, possibly by copying
44 it:
45 my $var2 = $var;
47 $sub = sub () { $var2 };
48 If you do want this subroutine to be a closure that reflects future
50 changes to the variable that it closes over, add an explicit "return":
51 my $var;
53 $sub = sub () { return $var };
54 This usage was deprecated and as of Perl 5.32 is no longer allowed.
56 Use of strings with code points over 0xFF as arguments to "vec"
58 "vec" views its string argument as a sequence of bits. A string
60 containing a code point over 0xFF is nonsensical. This usage is
61 deprecated in Perl 5.28, and was removed in Perl 5.32.
62 Use of code points over 0xFF in string bitwise operators
64 The string bitwise operators, "&", "|", "^", and "~", treat their
66 operands as strings of bytes. As such, values above 0xFF are
67 nonsensical. Some instances of these have been deprecated since Perl
68 5.24, and were made fatal in 5.28, but it turns out that in cases where
69 the wide characters did not affect the end result, no deprecation
70 notice was raised, and so remain legal. Now, all occurrences either
71 are fatal or raise a deprecation warning, so that the remaining legal
72 occurrences became fatal in 5.32.
73 An example of this is
75 "" & "\x{100}"
77 The wide character is not used in the "&" operation because the left
79 operand is shorter. This now throws an exception.
80 hostname() doesn't accept any arguments
82 The function "hostname()" in the Sys::Hostname module has always been
84 documented to be called with no arguments. Historically it has not
85 enforced this, and has actually accepted and ignored any arguments. As
86 a result, some users have got the mistaken impression that an argument
87 does something useful. To avoid these bugs, the function is being made
88 strict. Passing arguments was deprecated in Perl 5.28 and became fatal
89 in Perl 5.32.
90 Unescaped left braces in regular expressions
92 The simple rule to remember, if you want to match a literal "{"
94 character (U+007B "LEFT CURLY BRACKET") in a regular expression
95 pattern, is to escape each literal instance of it in some way.
96 Generally easiest is to precede it with a backslash, like "\{" or
97 enclose it in square brackets ("[{]"). If the pattern delimiters are
98 also braces, any matching right brace ("}") should also be escaped to
99 avoid confusing the parser, for example,
100 qr{abc\{def\}ghi}
102 Forcing literal "{" characters to be escaped will enable the Perl
104 language to be extended in various ways in future releases. To avoid
105 needlessly breaking existing code, the restriction is not enforced in
106 contexts where there are unlikely to ever be extensions that could
107 conflict with the use there of "{" as a literal. A non-deprecation
108 warning that the left brace is being taken literally is raised in
109 contexts where there could be confusion about it.
110 Literal uses of "{" were deprecated in Perl 5.20, and some uses of it
112 started to give deprecation warnings since. These cases were made fatal
113 in Perl 5.26. Due to an oversight, not all cases of a use of a literal
114 "{" got a deprecation warning. Some cases started warning in Perl
115 5.26, and were made fatal in Perl 5.30. Other cases started in Perl
116 5.28, and were made fatal in 5.32.
117 In XS code, use of various macros dealing with UTF-8.
119 The macros below now require an extra parameter than in versions prior
121 to Perl 5.32. The final parameter in each one is a pointer into the
122 string supplied by the first parameter beyond which the input will not
123 be read. This prevents potential reading beyond the end of the buffer.
124 "isALPHANUMERIC_utf8", "isASCII_utf8", "isBLANK_utf8", "isCNTRL_utf8",
125 "isDIGIT_utf8", "isIDFIRST_utf8", "isPSXSPC_utf8", "isSPACE_utf8",
126 "isVERTWS_utf8", "isWORDCHAR_utf8", "isXDIGIT_utf8",
127 "isALPHANUMERIC_LC_utf8", "isALPHA_LC_utf8", "isASCII_LC_utf8",
128 "isBLANK_LC_utf8", "isCNTRL_LC_utf8", "isDIGIT_LC_utf8",
129 "isGRAPH_LC_utf8", "isIDCONT_LC_utf8", "isIDFIRST_LC_utf8",
130 "isLOWER_LC_utf8", "isPRINT_LC_utf8", "isPSXSPC_LC_utf8",
131 "isPUNCT_LC_utf8", "isSPACE_LC_utf8", "isUPPER_LC_utf8",
132 "isWORDCHAR_LC_utf8", "isXDIGIT_LC_utf8", "toFOLD_utf8",
133 "toLOWER_utf8", "toTITLE_utf8", and "toUPPER_utf8".
134 Since Perl 5.26, this functionality with the extra parameter has been
136 available by using a corresponding macro to each one of these, and
137 whose name is formed by appending "_safe" to the base name. There is
138 no change to the functionality of those. For example,
139 "isDIGIT_utf8_safe" corresponds to "isDIGIT_utf8", and both now behave
140 identically. All are documented in "Character case changing" in
141 perlapi and "Character classification" in perlapi.
142 This change was originally scheduled for 5.30, but was delayed until
144 5.32.
145 "File::Glob::glob()" was removed
147 "File::Glob" has a function called "glob", which just calls "bsd_glob".
149 "File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message
151 was issued from Perl 5.26 onwards, and the function has now disappeared
152 in Perl 5.30.
153 Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()"
155 instead.
156 Perl 5.30
158 $* is no longer supported
159 Before Perl 5.10, setting $* to a true value globally enabled multi-
161 line matching within a string. This relique from the past lost its
162 special meaning in 5.10. Use of this variable will be a fatal error in
163 Perl 5.30, freeing the variable up for a future special meaning.
164 To enable multiline matching one should use the "/m" regexp modifier
166 (possibly in combination with "/s"). This can be set on a per match
167 bases, or can be enabled per lexical scope (including a whole file)
168 with "use re '/m'".
169 $# is no longer supported
171 This variable used to have a special meaning -- it could be used to
173 control how numbers were formatted when printed. This seldom used
174 functionality was removed in Perl 5.10. In order to free up the
175 variable for a future special meaning, its use will be a fatal error in
176 Perl 5.30.
177 To specify how numbers are formatted when printed, one is advised to
179 use "printf" or "sprintf" instead.
180 Assigning non-zero to $[ is fatal
182 This variable (and the corresponding "array_base" feature and arybase
184 module) allowed changing the base for array and string indexing
185 operations.
186 Setting this to a non-zero value has been deprecated since Perl 5.12
188 and throws a fatal error as of Perl 5.30.
189 "File::Glob::glob()" will disappear
191 "File::Glob" has a function called "glob", which just calls "bsd_glob".
193 However, its prototype is different from the prototype of "CORE::glob",
194 and hence, "File::Glob::glob" should not be used.
195 "File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message
197 was issued from Perl 5.26 onwards, and the function will disappear in
198 Perl 5.30.
199 Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()"
201 instead.
202 Unescaped left braces in regular expressions (for 5.30)
204 See "Unescaped left braces in regular expressions" above.
206 Unqualified "dump()"
208 Use of "dump()" instead of "CORE::dump()" was deprecated in Perl 5.8,
210 and an unqualified "dump()" will no longer be available in Perl 5.30.
211 See "dump" in perlfunc.
213 Using my() in false conditional.
215 There has been a long-standing bug in Perl that causes a lexical
217 variable not to be cleared at scope exit when its declaration includes
218 a false conditional. Some people have exploited this bug to achieve a
219 kind of static variable. To allow us to fix this bug, people should
220 not be relying on this behavior.
221 Instead, it's recommended one uses "state" variables to achieve the
223 same effect:
224 use 5.10.0;
226 sub count {state $counter; return ++ $counter}
227 say count (); # Prints 1
228 say count (); # Prints 2
229 "state" variables were introduced in Perl 5.10.
231 Alternatively, you can achieve a similar static effect by declaring the
233 variable in a separate block outside the function, e.g.,
234 sub f { my $x if 0; return $x++ }
236 becomes
238 { my $x; sub f { return $x++ } }
240 The use of "my()" in a false conditional has been deprecated in Perl
242 5.10, and became a fatal error in Perl 5.30.
243 Reading/writing bytes from/to :utf8 handles.
245 The sysread(), recv(), syswrite() and send() operators are deprecated
247 on handles that have the ":utf8" layer, either explicitly, or
248 implicitly, eg., with the ":encoding(UTF-16LE)" layer.
249 Both sysread() and recv() currently use only the ":utf8" flag for the
251 stream, ignoring the actual layers. Since sysread() and recv() do no
252 UTF-8 validation they can end up creating invalidly encoded scalars.
253 Similarly, syswrite() and send() use only the ":utf8" flag, otherwise
255 ignoring any layers. If the flag is set, both write the value UTF-8
256 encoded, even if the layer is some different encoding, such as the
257 example above.
258 Ideally, all of these operators would completely ignore the ":utf8"
260 state, working only with bytes, but this would result in silently
261 breaking existing code. To avoid this a future version of perl will
262 throw an exception when any of sysread(), recv(), syswrite() or send()
263 are called on handle with the ":utf8" layer.
264 In Perl 5.30, it will no longer be possible to use sysread(), recv(),
266 syswrite() or send() to read or send bytes from/to :utf8 handles.
267 Use of unassigned code point or non-standalone grapheme for a
269 delimiter.
270 A grapheme is what appears to a native-speaker of a language to be a
272 character. In Unicode (and hence Perl) a grapheme may actually be
273 several adjacent characters that together form a complete grapheme.
274 For example, there can be a base character, like "R" and an accent,
275 like a circumflex "^", that appear to be a single character when
276 displayed, with the circumflex hovering over the "R".
277 As of Perl 5.30, use of delimiters which are non-standalone graphemes
279 is fatal, in order to move the language to be able to accept multi-
280 character graphemes as delimiters.
281 Also, as of Perl 5.30, delimiters which are unassigned code points but
283 that may someday become assigned are prohibited. Otherwise, code that
284 works today would fail to compile if the currently unassigned delimiter
285 ends up being something that isn't a stand-alone grapheme. Because
286 Unicode is never going to assign non-character code points, nor code
287 points that are above the legal Unicode maximum, those can be
288 delimiters.
289 Perl 5.28
291 Attributes ":locked" and ":unique"
292 The attributes ":locked" (on code references) and ":unique" (on array,
294 hash and scalar references) have had no effect since Perl 5.005 and
295 Perl 5.8.8 respectively. Their use has been deprecated since.
296 As of Perl 5.28, these attributes are syntax errors. Since the
298 attributes do not do anything, removing them from your code fixes the
299 syntax error; and removing them will not influence the behaviour of
300 your code.
301 Bare here-document terminators
303 Perl has allowed you to use a bare here-document terminator to have the
305 here-document end at the first empty line. This practise was deprecated
306 in Perl 5.000; as of Perl 5.28, using a bare here-document terminator
307 throws a fatal error.
308 You are encouraged to use the explicitly quoted form if you wish to use
310 an empty line as the terminator of the here-document:
311 print <<"";
313 Print this line.
314 # Previous blank line ends the here-document.
316 Setting $/ to a reference to a non-positive integer
318 You assigned a reference to a scalar to $/ where the referenced item is
320 not a positive integer. In older perls this appeared to work the same
321 as setting it to "undef" but was in fact internally different, less
322 efficient and with very bad luck could have resulted in your file being
323 split by a stringified form of the reference.
324 In Perl 5.20.0 this was changed so that it would be exactly the same as
326 setting $/ to undef, with the exception that this warning would be
327 thrown.
328 As of Perl 5.28, setting $/ to a reference of a non-positive integer
330 throws a fatal error.
331 You are recommended to change your code to set $/ to "undef" explicitly
333 if you wish to slurp the file.
334 Limit on the value of Unicode code points.
336 Unicode only allows code points up to 0x10FFFF, but Perl allows much
338 larger ones. Up till Perl 5.28, it was allowed to use code points
339 exceeding the maximum value of an integer ("IV_MAX"). However, that
340 did break the perl interpreter in some constructs, including causing it
341 to hang in a few cases. The known problem areas were in "tr///",
342 regular expression pattern matching using quantifiers, as quote
343 delimiters in "qX...X" (where X is the "chr()" of a large code point),
344 and as the upper limits in loops.
345 The use of out of range code points was deprecated in Perl 5.24; as of
347 Perl 5.28 using a code point exceeding "IV_MAX" throws a fatal error.
348 If your code is to run on various platforms, keep in mind that the
350 upper limit depends on the platform. It is much larger on 64-bit word
351 sizes than 32-bit ones. For 32-bit integers, "IV_MAX" equals
352 0x7FFFFFFF, for 64-bit integers, "IV_MAX" equals 0x7FFFFFFFFFFFFFFF.
353 Use of comma-less variable list in formats.
355 It was allowed to use a list of variables in a format, without
357 separating them with commas. This usage has been deprecated for a long
358 time, and as of Perl 5.28, this throws a fatal error.
359 Use of "\N{}"
361 Use of "\N{}" with nothing between the braces was deprecated in Perl
363 5.24, and throws a fatal error as of Perl 5.28.
364 Since such a construct is equivalent to using an empty string, you are
366 recommended to remove such "\N{}" constructs.
367 Using the same symbol to open a filehandle and a dirhandle
369 It used to be legal to use "open()" to associate both a filehandle and
371 a dirhandle to the same symbol (glob or scalar). This idiom is likely
372 to be confusing, and it was deprecated in Perl 5.10.
373 Using the same symbol to "open()" a filehandle and a dirhandle throws a
375 fatal error as of Perl 5.28.
376 You should be using two different symbols instead.
378 ${^ENCODING} is no longer supported.
380 The special variable "${^ENCODING}" was used to implement the
382 "encoding" pragma. Setting this variable to anything other than "undef"
383 was deprecated in Perl 5.22. Full deprecation of the variable happened
384 in Perl 5.25.3.
385 Setting this variable to anything other than an undefined value throws
387 a fatal error as of Perl 5.28.
388 "B::OP::terse"
390 This method, which just calls "B::Concise::b_terse", has been
392 deprecated, and disappeared in Perl 5.28. Please use "B::Concise"
393 instead.
394 Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
396 As an (ahem) accidental feature, "AUTOLOAD" subroutines were looked up
398 as methods (using the @ISA hierarchy) even when the subroutines to be
399 autoloaded were called as plain functions (e.g. "Foo::bar()"), not as
400 methods (e.g. "Foo->bar()" or "$obj->bar()").
401 This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28
403 by using method lookup only for methods' "AUTOLOAD"s.
404 The simple rule is: Inheritance will not work when autoloading non-
406 methods. The simple fix for old code is: In any module that used to
407 depend on inheriting "AUTOLOAD" for non-methods from a base class named
408 "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
409 startup.
410 In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);"
412 you should remove AutoLoader from @ISA and change "use AutoLoader;" to
413 "use AutoLoader 'AUTOLOAD';".
414 Use of code points over 0xFF in string bitwise operators
416 The string bitwise operators, "&", "|", "^", and "~", treat their
418 operands as strings of bytes. As such, values above 0xFF are
419 nonsensical. Using such code points with these operators was deprecated
420 in Perl 5.24, and is fatal as of Perl 5.28.
421 In XS code, use of "to_utf8_case()"
423 This function has been removed as of Perl 5.28; instead convert to call
425 the appropriate one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe",
426 "toTITLE_utf8_safe", or "toUPPER_utf8_safe".
427 Perl 5.26
429 "--libpods" in "Pod::Html"
430 Since Perl 5.18, the option "--libpods" has been deprecated, and using
432 this option did not do anything other than producing a warning.
433 The "--libpods" option is no longer recognized as of Perl 5.26.
435 The utilities "c2ph" and "pstruct"
437 These old, perl3-era utilities have been deprecated in favour of "h2xs"
439 for a long time. As of Perl 5.26, they have been removed.
440 Trapping "$SIG {__DIE__}" other than during program exit.
442 The $SIG{__DIE__} hook is called even inside an "eval()". It was never
444 intended to happen this way, but an implementation glitch made this
445 possible. This used to be deprecated, as it allowed strange action at a
446 distance like rewriting a pending exception in $@. Plans to rectify
447 this have been scrapped, as users found that rewriting a pending
448 exception is actually a useful feature, and not a bug.
449 Perl never issued a deprecation warning for this; the deprecation was
451 by documentation policy only. But this deprecation has been lifted as
452 of Perl 5.26.
453 Malformed UTF-8 string in "%s"
455 This message indicates a bug either in the Perl core or in XS code.
457 Such code was trying to find out if a character, allegedly stored
458 internally encoded as UTF-8, was of a given type, such as being
459 punctuation or a digit. But the character was not encoded in legal
460 UTF-8. The %s is replaced by a string that can be used by
461 knowledgeable people to determine what the type being checked against
462 was.
463 Passing malformed strings was deprecated in Perl 5.18, and became fatal
465 in Perl 5.26.
466 Perl 5.24
468 Use of *glob{FILEHANDLE}
469 The use of *glob{FILEHANDLE} was deprecated in Perl 5.8. The intention
471 was to use *glob{IO} instead, for which *glob{FILEHANDLE} is an alias.
472 However, this feature was undeprecated in Perl 5.24.
474 Calling POSIX::%s() is deprecated
476 The following functions in the "POSIX" module are no longer available:
478 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower",
479 "isprint", "ispunct", "isspace", "isupper", and "isxdigit". The
480 functions are buggy and don't work on UTF-8 encoded strings. See their
481 entries in POSIX for more information.
482 The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
484 Perl 5.16
486 Use of %s on a handle without * is deprecated
487 It used to be possible to use "tie", "tied" or "untie" on a scalar
489 while the scalar holds a typeglob. This caused its filehandle to be
490 tied. It left no way to tie the scalar itself when it held a typeglob,
491 and no way to untie a scalar that had had a typeglob assigned to it.
492 This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
494 So now "tie $scalar" will always tie the scalar, not the handle it
496 holds. To tie the handle, use "tie *$scalar" (with an explicit
497 asterisk). The same applies to "tied *$scalar" and "untie *$scalar".
498
500 warnings, diagnostics.
501perl v5.34.1 2022-03-15 PERLDEPRECATION(1)