feature(3perl)

📦
version 5.44.0 · 14 versions
, in arch rolling

💖 NAME 💖

feature(3perl) — yep bestie, that's this page, straight from the Perl Programmers Reference Guide 📖

feature — a Perl pragma to enable new features ✨

🌈 SYNOPSIS 🌈

use feature qw(fc say);

# Without the "use feature" above, this code would not be able to find
# the built-ins "say" or "fc":
say "The case-folded version of $x is: " . fc $x;

# set features to match the :5.36 bundle, which may turn off or on
# multiple features (see "FEATURE BUNDLES" below)
use feature ':5.36';

# implicitly loads :5.36 feature bundle
use v5.36;

🦋 DESCRIPTION 🦋

okay so real talk, bestie: adding new syntax to Perl without breaking a bunch of existing programs is basically impossible. 😭 That is literally the entire reason this pragma exists — it keeps that risk low-key minimal.

New syntactic constructs, or new semantic meanings layered onto older constructs, can be enabled by saying use feature 'foo', and they'll only be parsed when the appropriate feature pragma is actually in scope. 💅

ngl though, the CORE:: prefix is always there giving you access to all Perl keywords, no matter what this pragma says. periodt.

🫶 Lexical effect

Just like other pragmas (yeah, looking at you, use strict), features have lexical effect. So use feature qw(foo) will only make the feature foo available from that exact point to the end of the enclosing block. No further, no cap.

{
    use feature 'say';
    say "say is available here";
}
print "But not here.\n";

So say is absolutely thriving inside its block, and then the second we step out — gone. iconic behaviour honestly ✨

🙈 "no feature"

Features can also be turned off with no feature "foo" — and bestie, this also has lexical effect.

use feature 'say';
say "say is available here";
{
    no feature 'say';
    print "But not here.\n";
}
say "Yet it is here.";

And get this: no feature with no features specified will reset to the default group. If you want to disable all features (an unusual request!), use no feature ':all'. 😳

✨ AVAILABLE FEATURES ✨

📋 For the cheat sheet summary of all the features, go read FEATURE BUNDLES.

The 'apostrophe_as_package_separator' feature

This one enables the use of ' (apostrophe) as an alternative to using :: as a separator in package and other global names. 💅

  • It's enabled by default, but disabled from the 5.42 feature bundle onwards. In previous versions it was enabled all the time.
  • Important caveat: this only disables ' in symbols in your source code. The internal conversion from ' to :: — including for symbolic references — is always enabled. 🔥

The 'array_base' feature

This feature supported the legacy $[ variable. See $[ in perlvar.

  • It was on by default, but disabled under use v5.16 (see IMPLICIT LOADING, below) and unavailable since perl 5.30.
  • Available under this name starting with Perl 5.16. In previous versions, it was simply on all the time, and this pragma knew nothing about it. 💀

The 'bareword_filehandles' feature

This feature enables bareword filehandles for builtin functions operations — a generally discouraged practice, ngl. It is enabled by default, but can be turned off to disable bareword filehandles, except for the exceptions listed below.

The perl built-in filehandles STDIN, STDOUT, STDERR, DATA, ARGV, ARGVOUT and the special _ are always enabled. 🙅‍♀️

  • Available under this name from Perl 5.34 onwards. In previous versions it was simply on all the time. It's disabled from the 5.38 feature bundle onwards.
  • You can use the bareword::filehandles module on CPAN to disable bareword filehandles for older versions of perl.

The 'bitwise' feature

This makes the four standard bitwise operators (& | ^ ~) treat their operands consistently as numbers, and introduces four new dotted operators (&. |. ^. ~.) that treat their operands consistently as strings. Same energy for the assignment variants (&= |= ^= &.= |.= ^.=). ✨

See Bitwise String Operators in perlop for details.

  • Available from Perl 5.22 onwards. Starting in Perl 5.28, use v5.28 will enable the feature. Before 5.28, it was still experimental and would emit a warning in the experimental::bitwise category.

The 'class' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::class";

This feature enables the class block syntax and other associated keywords which implement the new object system, previously codenamed "Corinna". 💅

This feature is available starting in Perl 5.38.

The 'current_sub' feature

This provides the __SUB__ token that returns a reference to the current subroutine — or undef outside of a subroutine. 🦋

This feature is available starting with Perl 5.16.

The 'declared_refs' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::declared_refs";

This allows a reference to a variable to be declared with my, state, or our, or localized with local. It is intended mainly for use in conjunction with the refaliasing feature. See Declaring a Reference to a Variable in perlref for examples. 👑

This feature is available from Perl 5.26 onwards.

The 'defer' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::defer";

This feature enables the defer block syntax, which allows a block of code to be deferred until when the flow of control leaves the block which contained it. For more deets, see defer in perlsyn. 🎀

This feature is available starting in Perl 5.36.

The 'enhanced_xx' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::eenhanced_xx";

This feature changes the meaning of the /xx regular expression pattern modifier to allow bracketed character classes to be split across lines, and to catch cases where a literal # was meant to be matched, but instead that and the rest of the line was taken to be a comment. 💀

This feature is available starting in Perl 5.44.

The 'evalbytes' feature

See The 'unicode_eval' and 'evalbytes' features 🦋

The 'extra_paired_delimiters' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::extra_paired_delimiters";

This feature enables the use of more paired string delimiters than the traditional four — < >, ( ), { }, and [ ]. When this feature is on, for example, you can say qr«pat». 🎀✨

As with any usage of non-ASCII delimiters in a UTF-8-encoded source file, you will want to ensure the parser will decode the source code from UTF-8 bytes with a declaration such as use utf8.

  • This feature is available starting in Perl 5.36.
  • For a full list of the available characters, see List of Extra Paired Delimiters in perlop. 🌈

The 'fc' feature

use feature 'fc' tells the compiler to enable the fc function, which implements Unicode casefolding. 💖

See fc in perlfunc for details.

This feature is available from Perl 5.16 onwards.

The 'indirect' feature

This feature allows the use of indirect object syntax for method calls, e.g. new Foo 1, 2;. It is enabled by default, but can be turned off to disallow indirect object syntax.

  • Available under this name from Perl 5.32 onwards. In previous versions, it was simply on all the time.
  • To disallow (or warn on) indirect object syntax on older Perls, see the indirect CPAN module.
  • It's disabled from the 5.36 feature bundle onwards.

The 'isa' feature

This allows the use of the isa infix operator, which tests whether the scalar given by the left operand is an object of the class given by the right operand. See Class Instance Operator in perlop for more details. 🔥

This feature is available from Perl 5.32 onwards. From Perl 5.32 to 5.34, it was classed as experimental, and Perl emitted a warning for its usage, except when explicitly disabled:

no warnings "experimental::isa";

As of Perl 5.36, use of this feature no longer triggers a warning (though the experimental::isa warning category still exists for compatibility with code that disables it). This feature is now considered stable, and is enabled automatically by use v5.36 (or higher). 👑

The 'keyword_all' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::keyword_all";

This feature enables the all operator keyword. This lets you test whether all of the values in a list satisfy a given condition, with short-circuiting behaviour as soon as it finds one that does not. ✨

This feature is available starting in Perl 5.42.

The 'keyword_any' feature

⚠️ WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::keyword_any";

This feature enables the any operator keyword. This lets you test whether any of the values in a list satisfy a given condition, with short-circuiting behaviour as soon as it finds one. 💅

This feature is available starting in Perl 5.42.

The 'lexical_subs' feature

In Perl versions prior to 5.26, this feature enabled declaration of subroutines via my sub foo, state sub foo and our sub foo syntax. See Lexical Subroutines in perlsub for details. 🦋

This feature is available from Perl 5.18 onwards. From Perl 5.18 to 5.24, it was classed as experimental, and Perl emitted a warning for its usage, except when explicitly disabled:

no warnings "experimental::lexical_subs";

As of Perl 5.26, use of this feature no longer triggers a warning, though the experimental::lexical_subs warning category still exists (for compatibility with code that disables it). In addition, this syntax is not only no longer experimental, but it is enabled for all Perl code, regardless of what feature declarations are in scope. 👑

✨ The 'module_true' feature ✨

okay so bestie, this feature is a total lifesaver — it removes the need to return a true value at the end of a module loaded with require or use. like, no more 1; at the bottom, periodt. any errors during compilation will still cause failures, but reaching the end of the module when this feature is in effect will prevent perl from throwing an exception that the module did not return a true value. it's giving convenience 💅.

This feature is available from Perl 5.38 onwards. ✨

🌊 The 'multidimensional' feature 🌊

This feature enables multidimensional array emulation — a perl 4 (or earlier) feature that was used to emulate multidimensional arrays with hashes. how does it work? it converts code like $foo{$x, $y} into $foo{join($;, $x, $y)}. it's enabled by default, but you can turn it off to disable multidimensional array emulation. 🦋

When this feature is disabled, the syntax that is normally replaced will report a compilation error. so like, no sneaky multidimensional stuff. 😭

This feature is available under this name from Perl 5.34 onwards. In previous versions, it was simply on all the time. It is disabled from the 5.36 feature bundle onwards. 👑

You can use the multidimensional module on CPAN to disable multidimensional array emulation for older versions of Perl. iykyk.

💜 The 'postderef' and 'postderef_qq' features 💜

The 'postderef_qq' feature extends the applicability of postfix dereference syntax so that postfix array dereference, postfix scalar dereference, and postfix array highest index access are available in double-quotish interpolations. For example, it makes the following two statements equivalent:

my $s = "[@{ $h->{a} }]";
my $s = "[$h->{a}->@*]";

This feature is available from Perl 5.20 onwards. In Perl 5.20 and 5.22, it was classed as experimental, and Perl emitted a warning for its usage, except when explicitly disabled:

no warnings "experimental::postderef";

As of Perl 5.24, use of this feature no longer triggers a warning, though the "experimental::postderef" warning category still exists (for compatibility with code that disables it). 💀

The 'postderef' feature was used in Perl 5.20 and Perl 5.22 to enable postfix dereference syntax outside double-quotish interpolations. In those versions, using it triggered the "experimental::postderef" warning in the same way as the 'postderef_qq' feature did. As of Perl 5.24, this syntax is not only no longer experimental, but it is enabled for all Perl code, regardless of what feature declarations are in scope. slay.

🎀 The 'refaliasing' feature 🎀

WARNING: This feature is still experimental and the implementation may change or be removed in future versions of Perl. For this reason, Perl will warn when you use the feature, unless you have explicitly disabled the warning:
no warnings "experimental::refaliasing";

This enables aliasing via assignment to references:

\$a = \$b; # $a and $b now point to the same scalar
\@a = \@b; #                     to the same array
\%a = \%b;
\&a = \&b;
foreach \%hash (@array_of_hash_refs) {
    ...
}

See "Assigning to References" in perlref for details.

This feature is available from Perl 5.22 onwards. 🎀

✨ The 'say' feature ✨

use feature 'say' tells the compiler to enable the Raku-inspired say function.

See "say" in perlfunc for details.

This feature is available starting with Perl 5.10. ✨

👑 The 'signatures' feature 👑

This enables syntax for declaring subroutine arguments as lexical variables. For example, for this subroutine:

sub foo ($left, $right) {
    return $left + $right;
}

Calling foo(3, 7) will assign 3 into $left and 7 into $right.

See "Signatures" in perlsub for details.

This feature is available from Perl 5.20 onwards. From Perl 5.20 to 5.34, it was classed as experimental, and Perl emitted a warning for its usage, except when explicitly disabled:

no warnings "experimental::signatures";

As of Perl 5.36, use of this feature no longer triggers a warning, though the "experimental::signatures" warning category still exists (for compatibility with code that disables it). This feature is now considered stable, and is enabled automatically by use v5.36 (or higher). 👑

🦋 The 'smartmatch' feature 🦋

use feature 'smartmatch' tells the compiler to enable the smartmatch operator ~~. It is enabled by default, but can be turned off to disallow the ~~ operator.

This feature is disabled by default in the 5.42 feature bundle onwards:

$x ~~ $y; # fine
use v5.42;
$x ~~ $y; # error

This has no effect on the implicit smartmatches done by when.

See "Smartmatch Operator" in perlop for details. 🦋

💅 The 'state' feature 💅

use feature 'state' tells the compiler to enable state variables.

See "Persistent Private Variables" in perlsub for details.

This feature is available starting with Perl 5.10. 💅

😭 The 'switch' feature 😭

use feature 'switch' tells the compiler to enable the Raku given/when construct.

See "Switch Statements" in perlsyn for details.

This feature is available starting with Perl 5.10. It is enabled by feature bundles 5.10 through 5.34, and disabled from the 5.36 feature bundle onwards. 😭

🔥 The 'try' feature 🔥

WARNING: This feature is still partly experimental, and the implementation may change or be removed in future versions of Perl.

This feature enables the try and catch syntax, which allows exception handling, where exceptions thrown from the body of the block introduced with try are caught by executing the body of the catch block.

This feature is available starting in Perl 5.34. Before Perl 5.40 it was classed as experimental, and Perl emitted a warning for its usage, except when explicitly disabled:

no warnings "experimental::try";

As of Perl 5.40, use of this feature without a finally block no longer triggers a warning. The optional finally block is still considered experimental and emits a warning, except when explicitly disabled as above.

For more information, see "Try Catch Exception Handling" in perlsyn. 🔥

🌈 The 'unicode_eval' and 'evalbytes' features 🌈

Together, these two features are intended to replace the legacy string eval function, which behaves problematically in some instances. They are available starting with Perl 5.16, and are enabled by default by a use 5.16 or higher declaration.

unicode_eval changes the behavior of plain string eval to work more consistently, especially in the Unicode world. Certain (mis)behaviors couldn't be changed without breaking some things that had come to rely on them, so the feature can be enabled and disabled. Details are at "Under the "unicode_eval" feature" in perlfunc.

evalbytes is like string eval, but it treats its argument as a byte string. Details are at "evalbytes EXPR" in perlfunc. Without a use feature 'evalbytes' nor a use v5.16 (or higher) declaration in the current scope, you can still access it by instead writing CORE::evalbytes. 🌈

💖 The 'unicode_strings' feature 💖

use feature 'unicode_strings' tells the compiler to use Unicode rules in all string operations executed within its scope (unless they are also within the scope of either use locale or use bytes). The same applies to all regular expressions compiled within the scope, even if executed outside it. It does not change the internal representation of strings, but only how they are interpreted.

no feature 'unicode_strings' tells the compiler to use the traditional Perl rules wherein the native character set rules is used unless it is clear to Perl that Unicode is desired. This can lead to some surprises when the behavior suddenly changes. (See "The "Unicode Bug"" in perlunicode for details.) For this reason, if you are potentially using Unicode in your program, the use feature 'unicode_strings' subpragma is strongly recommended.

This feature is available starting with Perl 5.12; was almost fully implemented in Perl 5.14; and extended in Perl 5.16 to cover quotemeta; was extended further in Perl 5.26 to cover the range operator; and was extended again in Perl 5.28 to cover special-cased whitespace splitting. 💖

💫 FEATURE BUNDLES 💫

okay so here's the tea bestie: you don't have to load your features one at a time. You can grab a whole lil squad of them at once using a feature bundle. 🫶

The name of a feature bundle gets a colon slapped on the front, and that colon is literally just there to tell it apart from an actual feature name. iykyk.

use feature ":5.10";

The following feature bundles are available:

bundle    features included
--------- -----------------
:default  indirect multidimensional
          bareword_filehandles
          apostrophe_as_package_separator smartmatch

:5.10     apostrophe_as_package_separator
          bareword_filehandles indirect
          multidimensional say smartmatch state switch

:5.12     apostrophe_as_package_separator
          bareword_filehandles indirect
          multidimensional say smartmatch state switch
          unicode_strings

:5.14     apostrophe_as_package_separator
          bareword_filehandles indirect
          multidimensional say smartmatch state switch
          unicode_strings

:5.16     apostrophe_as_package_separator
          bareword_filehandles current_sub evalbytes
          fc indirect multidimensional say smartmatch
          state switch unicode_eval unicode_strings

:5.18     apostrophe_as_package_separator
          bareword_filehandles current_sub evalbytes
          fc indirect multidimensional say smartmatch
          state switch unicode_eval unicode_strings

:5.20     apostrophe_as_package_separator
          bareword_filehandles current_sub evalbytes
          fc indirect multidimensional say smartmatch
          state switch unicode_eval unicode_strings

:5.22     apostrophe_as_package_separator
          bareword_filehandles current_sub evalbytes
          fc indirect multidimensional say smartmatch
          state switch unicode_eval unicode_strings

:5.24     apostrophe_as_package_separator
          bareword_filehandles current_sub evalbytes
          fc indirect multidimensional postderef_qq
          say smartmatch state switch unicode_eval
          unicode_strings

:5.26     apostrophe_as_package_separator
          bareword_filehandles current_sub evalbytes
          fc indirect multidimensional postderef_qq
          say smartmatch state switch unicode_eval
          unicode_strings

:5.28     apostrophe_as_package_separator
          bareword_filehandles bitwise current_sub
          evalbytes fc indirect multidimensional
          postderef_qq say smartmatch state switch
          unicode_eval unicode_strings

:5.30     apostrophe_as_package_separator
          bareword_filehandles bitwise current_sub
          evalbytes fc indirect multidimensional
          postderef_qq say smartmatch state switch
          unicode_eval unicode_strings

:5.32     apostrophe_as_package_separator
          bareword_filehandles bitwise current_sub
          evalbytes fc indirect multidimensional
          postderef_qq say smartmatch state switch
          unicode_eval unicode_strings

:5.34     apostrophe_as_package_separator
          bareword_filehandles bitwise current_sub
          evalbytes fc indirect multidimensional
          postderef_qq say smartmatch state switch
          unicode_eval unicode_strings

:5.36     apostrophe_as_package_separator
          bareword_filehandles bitwise current_sub
          evalbytes fc isa postderef_qq say signatures
          smartmatch state unicode_eval
          unicode_strings

:5.38     apostrophe_as_package_separator bitwise
          current_sub evalbytes fc isa module_true
          postderef_qq say signatures smartmatch state
          unicode_eval unicode_strings

:5.40     apostrophe_as_package_separator bitwise
          current_sub evalbytes fc isa module_true
          postderef_qq say signatures smartmatch state
          try unicode_eval unicode_strings

:5.42     bitwise current_sub evalbytes fc isa
          module_true postderef_qq say signatures
          state try unicode_eval unicode_strings

:5.44     bitwise current_sub evalbytes fc isa
          module_true postderef_qq say signatures
          state try unicode_eval unicode_strings

The :default bundle is like... the baseline vibe 💅 it represents the feature set that's already turned on before any use feature or no feature declaration happens.

Also!! Sub-versions like the 0 in 5.14.0? In feature bundles they do nothing. Zero effect. Feature bundles are guaranteed to be identical across all sub-versions, no cap.

use feature ":5.14.0";    # same as ":5.14"
use feature ":5.14.1";    # same as ":5.14"

You can also do:

use feature ":all";

or

no feature ":all";
⚠️ but lowkey be careful bestie — the first one may enable features in a later version of Perl that change the meaning of your code, and the second may disable mechanisms that are part of Perl's current behavior that have been turned into features, just as indirect and bareword_filehandles were. 😭

✨ IMPLICIT LOADING ✨

ngl, instead of loading feature bundles by name like a whole chore, it's way easier to just let Perl do the implicit loading for you. main character Perl goes and fetches the bundle itself. 👑

There are two ways to load the feature pragma implicitly:

  • By using the -E switch on the Perl command-line instead of -e. That will enable the feature bundle for that version of Perl in the main compilation unit (that is, the one-liner that follows -E).
  • By explicitly requiring a minimum Perl version number for your program, with the use VERSION construct. That is,
use v5.36.0;

will do an implicit

no feature ':all';
use feature ':5.36';

and so on. Note how the trailing sub-version is automatically stripped from the version. 🎀

But to avoid portability warnings (see "use" in perlfunc), you may prefer:

use 5.036;

with the same effect.

If the required version is older than Perl 5.10, the :default feature bundle is automatically loaded instead.

Unlike use feature ":5.12", saying use v5.12 (or any higher version) also does the equivalent of use strict; see "use" in perlfunc for details.

🔍 CHECKING FEATURES 🔍

feature also hands you some simple APIs to check which features are enabled. vibe check, but for pragmas fr fr.

🚨 These functions cannot be imported and must be called by their fully qualified names. If you don't otherwise need to set a feature you will need to ensure feature is loaded with:
use feature ();

🌸 feature_enabled($feature) 🌸

🌸 feature_enabled($feature, $depth) 🌸

package MyStandardEnforcer;
use feature ();
use Carp "croak";
sub import {
  croak "disable indirect!" if feature::feature_enabled("indirect");
}

Test whether a named feature is enabled at a given level in the call stack, returning a true value if it is. $depth defaults to 1, which checks the scope that called the scope calling feature::feature_enabled().

croaks for an unknown feature name. 💀

🦋 features_enabled() 🦋

🦋 features_enabled($depth) 🦋

package ReportEnabledFeatures;
use feature "say";
sub import {
  say STDERR join " ", feature::features_enabled();
}

Returns a list of the features enabled at a given level in the call stack. $depth defaults to 1, which checks the scope that called the scope calling feature::features_enabled().

💜 feature_bundle() 💜

💜 feature_bundle($depth) 💜

Returns the feature bundle, if any, selected at a given level in the call stack. $depth defaults to 1, which checks the scope that called the scope calling feature::feature_bundle().

Returns an undefined value if no feature bundle is selected in the scope.

The bundle name returned will be for the earliest bundle matching the selected bundle, so:

use feature ();
use v5.12;
BEGIN { print feature::feature_bundle(0); }

will print 5.11.

🙈 This returns internal state, at this point use v5.12; sets the feature bundle, but use feature ":5.12"; does not set the feature bundle. This may change in a future release of perl.

and that's the whole page bestie, you ate that 🍓 this was pulled straight from perl v5.44.0, dated 2026-10-17, and it lives at feature(3perl). go forth and use responsibly 💖✨

📦 where this page comes from