perldeprecation - list Perl deprecations

The purpose of this document is to document what has been deprecated in Perl, and by which version the deprecated feature will disappear, or, for already removed features, when it was removed.

This document will try to discuss what alternatives for the deprecated features are available.

The deprecated features will be grouped by the version of Perl in which they will be removed.

Some unicode delimiters used to be allowed as single characters, but in the future will be part of a balanced pair. This deprecation category is used to mark the ones that will change from being unpaired to paired.

Category: "deprecated::delimiter_will_be_paired"

The current working directory . used to be automatically included in @INC, but in Perl 5.26 this was removed for security reasons. Ever since then we have produced a warning when a user uses do EXPR and EXPR does not include a path, and the file was not found in any directory in @INC but was located in .. The file will not be loaded but a deprecated warning will be generated.

Category: "deprecated::dot_in_inc"

Various types of unicode property name will generate deprecated warnings when used in a regex pattern. For instance surrogate characters will result in deprecation warnings.

Category: "deprecated::unicode_property_name"

Historically calling import() or unimport() on any class which did not define such a method would be silently ignored. Effectively Perl behaved as though there was an empty method defined in the UNIVERSAL package (even when there was no such method actually defined). As of Perl version 5.39.2 calling such a method with an argument will trigger a warning, and in Perl version 5.44 this warning will be upgraded to an error. (Calling such a method with no arguments at all will always be safe.)

A use VERSION declaration has many implicit effects on the surrounding scope, such as strict and feature flags, or importing builtin functions. Once you have a use VERSION statement in scope, another use VERSION statement with a different version is now deprecated since Perl 5.39.8, due to the increasing complexity of swapping from one prevailing version to another.

Smartmatch is now seen as a failed experiment and was marked as deprecated in Perl 5.37.10. This includes the when and given keywords, as well as the smartmatch operator ~~. The feature will be removed entirely in the Perl 5.42.0 production release.

Category: "deprecated::smartmatch"

goto LABEL; will produce a deprecated warning when jumping into the body of a loop or other block construct from outside. For instance

will produce a warning that this behavior is deprecated. In general you should just avoid doing this; the people that maintain your code will be grateful for your restraint.

Category: "deprecated::goto_construct"

Perl allows use of ' instead of :: to replace the parts of a package or global variable name, for example A::B and A'B are equivalent.

' will no longer be recognized as a name separator in Perl 5.42.

Category: "deprecated::apostrophe_as_package_separator"

Once Perl has seen a use VERSION declaration that requests a version v5.11 or above, a subsequent second declaration that requests an earlier version will print a deprecation warning. For example,

This was deprecated in Perl 5.36 and is now fatal.

This is because of an intended related change to the interaction between use VERSION and use strict. If you specify a version >= 5.11, strict is enabled implicitly. If you request a version < 5.11, strict will become disabled even if you had previously written use strict. This was not the previous behaviour of use VERSION, which at present will track explicitly-enabled strictness flags independently.

Category: "deprecated::version_downgrade"

The definition and documentation of three utility functions previously importable from Pod::Html were moved to new package Pod::Html::Util in Perl 5.36. While they remained importable from Pod::Html in Perl 5.36, as of Perl 5.38 they are only importable, on request, from Pod::Html::Util.

There were no deprecations or fatalizations in Perl 5.34.

You wrote something like

but $var is referenced elsewhere and could be modified after the sub expression is evaluated. Either it is explicitly modified elsewhere ($var = 3) or it is passed to a subroutine or to an operator like printf or map, which may or may not modify the variable.

Traditionally, Perl has captured the value of the variable at that point and turned the subroutine into a constant eligible for inlining. In those cases where the variable can be modified elsewhere, this breaks the behavior of closures, in which the subroutine captures the variable itself, rather than its value, so future changes to the variable are reflected in the subroutine's return value.

If you intended for the subroutine to be eligible for inlining, then make sure the variable is not referenced elsewhere, possibly by copying it:

If you do want this subroutine to be a closure that reflects future changes to the variable that it closes over, add an explicit return:

This usage was deprecated and as of Perl 5.32 is no longer allowed.

vec views its string argument as a sequence of bits. A string containing a code point over 0xFF is nonsensical. This usage is deprecated in Perl 5.28, and was removed in Perl 5.32.

The string bitwise operators, &, |, ^, and ~, treat their operands as strings of bytes. As such, values above 0xFF are nonsensical. Some instances of these have been deprecated since Perl 5.24, and were made fatal in 5.28, but it turns out that in cases where the wide characters did not affect the end result, no deprecation notice was raised, and so remain legal. Now, all occurrences either are fatal or raise a deprecation warning, so that the remaining legal occurrences became fatal in 5.32.

An example of this is

The wide character is not used in the & operation because the left operand is shorter. This now throws an exception.

The function hostname() in the Sys::Hostname module has always been documented to be called with no arguments. Historically it has not enforced this, and has actually accepted and ignored any arguments. As a result, some users have got the mistaken impression that an argument does something useful. To avoid these bugs, the function is being made strict. Passing arguments was deprecated in Perl 5.28 and became fatal in Perl 5.32.

The simple rule to remember, if you want to match a literal { character (U+007B LEFT CURLY BRACKET) in a regular expression pattern, is to escape each literal instance of it in some way. Generally easiest is to precede it with a backslash, like \{ or enclose it in square brackets ([{]). If the pattern delimiters are also braces, any matching right brace (}) should also be escaped to avoid confusing the parser, for example,

Forcing literal { characters to be escaped will enable the Perl language to be extended in various ways in future releases. To avoid needlessly breaking existing code, the restriction is not enforced in contexts where there are unlikely to ever be extensions that could conflict with the use of { as a literal. A non-deprecation warning that the left brace is being taken literally is raised in contexts where there could be confusion about it.

Literal uses of { were deprecated in Perl 5.20, and some uses of it started to give deprecation warnings since. These cases were made fatal in Perl 5.26. Due to an oversight, not all cases of a use of a literal { got a deprecation warning. Some cases started warning in Perl 5.26, and were made fatal in Perl 5.30. Other cases started in Perl 5.28, and were made fatal in 5.32.

The macros below now require an extra parameter compared to versions prior to Perl 5.32. The final parameter in each one is a pointer into the string supplied by the first parameter beyond which the input will not be read. This prevents potential reading beyond the end of the buffer. isALPHANUMERIC_utf8, isASCII_utf8, isBLANK_utf8, isCNTRL_utf8, isDIGIT_utf8, isIDFIRST_utf8, isPSXSPC_utf8, isSPACE_utf8, isVERTWS_utf8, isWORDCHAR_utf8, isXDIGIT_utf8, isALPHANUMERIC_LC_utf8, isALPHA_LC_utf8, isASCII_LC_utf8, isBLANK_LC_utf8, isCNTRL_LC_utf8, isDIGIT_LC_utf8, isGRAPH_LC_utf8, isIDCONT_LC_utf8, isIDFIRST_LC_utf8, isLOWER_LC_utf8, isPRINT_LC_utf8, isPSXSPC_LC_utf8, isPUNCT_LC_utf8, isSPACE_LC_utf8, isUPPER_LC_utf8, isWORDCHAR_LC_utf8, isXDIGIT_LC_utf8, toFOLD_utf8, toLOWER_utf8, toTITLE_utf8, and toUPPER_utf8.

Since Perl 5.26, this functionality with the extra parameter has been available by using a corresponding macro to each one of these, and whose name is formed by appending _safe to the base name. There is no change to the functionality of those. For example, isDIGIT_utf8_safe corresponds to isDIGIT_utf8, and both now behave identically. All are documented in "Character case changing" in perlapi and "Character classification" in perlapi.

This change was originally scheduled for 5.30, but was delayed until 5.32.

File::Glob had a function called glob, which just called bsd_glob.

File::Glob::glob() was deprecated in Perl 5.8. A deprecation message was issued from Perl 5.26 onwards, the function became fatal in Perl 5.30, and was removed entirely in Perl 5.32.

Code using File::Glob::glob() should call File::Glob::bsd_glob() instead.

Before Perl 5.10, setting $* to a true value globally enabled multi-line matching within a string. This relic from the past lost its special meaning in 5.10. Use of this variable became a fatal error in Perl 5.30, freeing the variable up for a future special meaning.

To enable multiline matching one should use the /m regexp modifier (possibly in combination with /s). This can be set on a per match basis, or can be enabled per lexical scope (including a whole file) with use re '/m'.

This variable used to have a special meaning -- it could be used to control how numbers were formatted when printed. This seldom used functionality was removed in Perl 5.10. In order to free up the variable for a future special meaning, its use became a fatal error in Perl 5.30.

To specify how numbers are formatted when printed, one is advised to use printf or sprintf instead.

This variable (and the corresponding array_base feature and arybase module) allowed changing the base for array and string indexing operations.

Setting this to a non-zero value has been deprecated since Perl 5.12 and throws a fatal error as of Perl 5.30.

Use of dump() instead of CORE::dump() was deprecated in Perl 5.8, and an unqualified dump() is no longer available as of Perl 5.30.

See "dump" in perlfunc.

There has been a long-standing bug in Perl that causes a lexical variable not to be cleared at scope exit when its declaration includes a false conditional. Some people have exploited this bug to achieve a kind of static variable. To allow us to fix this bug, people should not be relying on this behavior.

Instead, it's recommended one uses state variables to achieve the same effect:

state variables were introduced in Perl 5.10.

Alternatively, you can achieve a similar static effect by declaring the variable in a separate block outside the function, e.g.,

becomes

The use of my() in a false conditional has been deprecated in Perl 5.10, and became a fatal error in Perl 5.30.

The sysread(), recv(), syswrite() and send() operators are deprecated on handles that have the :utf8 layer, either explicitly, or implicitly, eg., with the :encoding(UTF-16LE) layer.

Both sysread() and recv() currently use only the :utf8 flag for the stream, ignoring the actual layers. Since sysread() and recv() do no UTF-8 validation they can end up creating invalidly encoded scalars.

Similarly, syswrite() and send() use only the :utf8 flag, otherwise ignoring any layers. If the flag is set, both write the value UTF-8 encoded, even if the layer is some different encoding, such as the UTF-16LE example above.

Ideally, all of these operators would completely ignore the :utf8 state, working only with bytes, but this would result in silently breaking existing code. To avoid this a future version of perl will throw an exception when any of sysread(), recv(), syswrite() or send() are called on handles with the :utf8 layer.

As of Perl 5.30, it is no longer possible to use sysread(), recv(), syswrite() or send() to read or send bytes from/to :utf8 handles.

A grapheme is what appears to a native speaker of a language to be a character. In Unicode (and hence Perl) a grapheme may actually be several adjacent characters that together form a complete grapheme. For example, there can be a base character, like "R" and an accent, like a circumflex "^", that appear to be a single character when displayed, with the circumflex hovering over the "R".

As of Perl 5.30, use of delimiters which are non-standalone graphemes is fatal, in order to move the language to be able to accept multi-character graphemes as delimiters.

Also, as of Perl 5.30, delimiters which are unassigned code points but that may someday become assigned are prohibited. Otherwise, code that works today would fail to compile if the currently unassigned delimiter ends up being something that isn't a stand-alone grapheme. Because Unicode is never going to assign non-character code points, nor code points that are above the legal Unicode maximum, those can be delimiters.

The attributes :locked (on code references) and :unique (on array, hash and scalar references) have had no effect since Perl 5.005 and Perl 5.8.8 respectively. Their use has been deprecated since.

As of Perl 5.28, these attributes are syntax errors. Since the attributes do not do anything, removing them from your code fixes the syntax error; and removing them will not influence the behaviour of your code.

Perl has allowed you to use a bare here-document terminator << to have the here-document end at the first empty line. This practise was deprecated in Perl 5.000; as of Perl 5.28, using a bare here-document terminator throws a fatal error.

You are encouraged to use the explicitly quoted form if you wish to use an empty line as the terminator of the here-document:

You assigned a reference to a scalar to $/ where the referenced item is not a positive integer. In older perls this appeared to work the same as setting it to undef but was in fact internally different, less efficient and with very bad luck could have resulted in your file being split by a stringified form of the reference.

In Perl 5.20.0 this was changed so that it would be exactly the same as setting $/ to undef, with the exception that this warning would be thrown.

As of Perl 5.28, setting $/ to a reference to a non-positive integer throws a fatal error.

You are recommended to change your code to set $/ to undef explicitly if you wish to slurp the file.

Unicode only allows code points up to 0x10FFFF, but Perl allows much larger ones. Up till Perl 5.28, it was allowed to use code points exceeding the maximum value of an integer (IV_MAX). However, that did break the perl interpreter in some constructs, including causing it to hang in a few cases. The known problem areas were in tr///, regular expression pattern matching using quantifiers, as quote delimiters in qX...X (where X is the chr() of a large code point), and as the upper limits in loops.

The use of out of range code points was deprecated in Perl 5.24; as of Perl 5.28 using a code point exceeding IV_MAX throws a fatal error.

If your code is to run on various platforms, keep in mind that the upper limit depends on the platform. It is much larger on 64-bit word sizes than 32-bit ones. For 32-bit integers, IV_MAX equals 0x7FFFFFFF; for 64-bit integers, IV_MAX equals 0x7FFFFFFFFFFFFFFF.

It was allowed to use a list of variables in a format, without separating them with commas. This usage has been deprecated for a long time, and as of Perl 5.28, this throws a fatal error.

Use of \N{} with nothing between the braces was deprecated in Perl 5.24, and throws a fatal error as of Perl 5.28.

Since such a construct is equivalent to using an empty string, you are recommended to remove such \N{} constructs.

It used to be legal to use open() to associate both a filehandle and a dirhandle to the same symbol (glob or scalar). This idiom is likely to be confusing, and it was deprecated in Perl 5.10.

Using the same symbol to open() a filehandle and a dirhandle throws a fatal error as of Perl 5.28.

You should be using two different symbols instead.

The special variable ${^ENCODING} was used to implement the encoding pragma. Setting this variable to anything other than undef was deprecated in Perl 5.22. Full deprecation of the variable happened in Perl 5.25.3.

Setting this variable to anything other than an undefined value throws a fatal error as of Perl 5.28.

This method, which just calls B::Concise::b_terse, has been deprecated, and disappeared in Perl 5.28. Please use B::Concise instead.

As an (ahem) accidental feature, AUTOLOAD subroutines were looked up as methods (using the @ISA hierarchy) even when the subroutines to be autoloaded were called as plain functions (e.g. Foo::bar()), not as methods (e.g. Foo->bar() or $obj->bar()).

This bug was deprecated in Perl 5.004 and has been rectified in Perl 5.28 by using method lookup only for methods' AUTOLOADs.

The simple rule is: Inheritance will not work when autoloading non-methods. The simple fix for old code is: In any module that used to depend on inheriting AUTOLOAD for non-methods from a base class named BaseClass, execute *AUTOLOAD = \&BaseClass::AUTOLOAD during startup.

In code that currently says use AutoLoader; @ISA = qw(AutoLoader); you should remove AutoLoader from @ISA and change use AutoLoader; to use AutoLoader 'AUTOLOAD';.

This function has been removed as of Perl 5.28; instead convert to call the appropriate one of: toFOLD_utf8_safe. toLOWER_utf8_safe, toTITLE_utf8_safe, or toUPPER_utf8_safe.

Since Perl 5.18, the option --libpods has been deprecated, and using this option did not do anything other than producing a warning.

The --libpods option is no longer recognized as of Perl 5.26.

These old, perl3-era utilities have been deprecated in favour of h2xs for a long time. As of Perl 5.26, they have been removed.

The $SIG{__DIE__} hook is called even inside an eval(). It was never intended to happen this way, but an implementation glitch made this possible. This used to be deprecated, as it allowed strange action at a distance like rewriting a pending exception in $@. Plans to rectify this have been scrapped, as users found that rewriting a pending exception is actually a useful feature, and not a bug.

Perl never issued a deprecation warning for this; the deprecation was by documentation policy only. But this deprecation has been lifted as of Perl 5.26.

This message indicates a bug either in the Perl core or in XS code. Such code was trying to find out if a character, allegedly stored internally encoded as UTF-8, was of a given type, such as being punctuation or a digit. But the character was not encoded in legal UTF-8. The %s is replaced by a string that can be used by knowledgeable people to determine what the type being checked against was.

Passing malformed strings was deprecated in Perl 5.18, and became fatal in Perl 5.26.

The use of *glob{FILEHANDLE} was deprecated in Perl 5.8. The intention was to use *glob{IO} instead, for which *glob{FILEHANDLE} is an alias.

However, this feature was undeprecated in Perl 5.24.

The following functions in the POSIX module are no longer available: isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, and isxdigit. The functions are buggy and don't work on UTF-8 encoded strings. See their entries in POSIX for more information.

The functions were deprecated in Perl 5.20, and removed in Perl 5.24.

It used to be possible to use tie, tied or untie on a scalar while the scalar holds a typeglob. This caused its filehandle to be tied. It left no way to tie the scalar itself when it held a typeglob, and no way to untie a scalar that had had a typeglob assigned to it.

This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.

So now tie $scalar will always tie the scalar, not the handle it holds. To tie the handle, use tie *$scalar (with an explicit asterisk). The same applies to tied *$scalar and untie *$scalar.