PERL56DELTA(1perl)

✨ NAME ✨

perl56delta — bestie, this is the tea on everything new for perl v5.6.0 💖 (and yeah, it's from the Perl Programmers Reference Guide, PERL56DELTA(1perl), iykyk)

💫 DESCRIPTION 💫

This doc tells you every single difference between the 5.005 release and the 5.6.0 release. No cap, that's the whole vibe. 📖✨

---

🔥 Core Enhancements 🔥

🧵 Interpreter cloning, threads, and concurrency

Perl 5.6.0 introduces the beginnings of support for running multiple interpreters concurrently in different threads. Team up with the perl_clone() API call — which can selectively duplicate the state of any given interpreter — and you can compile a piece of code once in an interpreter, clone that interpreter one or more times, and run all the resulting interpreters in distinct threads. Iconic behavior, honestly. 👑

On the Windows platform, this feature is used to emulate fork() at the interpreter level. Peep perlfork for the deets on that.

This feature is still in evolution, lowkey. It's eventually meant to be used to selectively clone a subroutine and data reachable from that subroutine in a separate interpreter, then run the cloned subroutine in a separate thread. Since there is no shared data between the interpreters, little or no locking will be needed (unless parts of the symbol table are explicitly shared). This is obviously intended to be an easy-to-use replacement for the existing threads support. 🦋

Support for cloning interpreters and interpreter concurrency can be enabled using the -Dusethreads Configure option (see win32/Makefile for how to enable it on Windows). The resulting perl executable will be functionally identical to one that was built with -Dmultiplicity, but the perl_clone() API call will only be available in the former.

-Dusethreads enables the cpp macro USE_ITHREADS by default, which in turn enables Perl source code changes that provide a clear separation between the op tree and the data it operates with. The former is immutable, and can therefore be shared between an interpreter and all of its clones, while the latter is considered local to each interpreter, and is therefore copied for each clone.

Note that building Perl with the -Dusemultiplicity Configure option is adequate if you wish to run multiple independent interpreters concurrently in different threads. -Dusethreads only provides the additional functionality of the perl_clone() API call and other support for running cloned interpreters concurrently.

NOTE: This is an experimental feature. Implementation details are subject to change. 🙈

🚨 Lexically scoped warning categories

You can now control the granularity of warnings emitted by perl at a finer level using the use warnings pragma. Not me being able to actually fine-tune my warnings 😭. warnings and perllexwarn have copious documentation on this feature.

🌈 Unicode and UTF-8 support

Perl now uses UTF-8 as its internal representation for character strings. The utf8 and bytes pragmas are used to control this support in the current lexical scope. See perlunicode, utf8 and bytes for more information.

This feature is expected to evolve quickly to support some form of I/O disciplines that can be used to specify the kind of input and output data (bytes or characters). Until that happens, additional modules from CPAN will be needed to complete the toolkit for dealing with Unicode. 🌸

NOTE: This should be considered an experimental feature. Implementation details are subject to change. 💀

🎀 Support for interpolating named characters

The new \N escape interpolates named characters within strings. For example, "Hi! \N{WHITE SMILING FACE}" evaluates to a string with a Unicode smiley face at the end. She's cute, she's functional, slay. 😊✨

👑 "our" declarations

An "our" declaration introduces a value that can be best understood as a lexically scoped symbolic alias to a global variable in the package that was current where the variable was declared. This is mostly useful as an alternative to the "vars" pragma, but also provides the opportunity to introduce typing and other attributes for such variables. See "our" in perlfunc.

🍓 Support for strings represented as a vector of ordinals

Literals of the form "v1.2.3.4" are now parsed as a string composed of characters with the specified ordinals. This is an alternative, more readable way to construct (possibly Unicode) strings instead of interpolating characters, as in "\x{1}\x{2}\x{3}\x{4}". The leading "v" may be omitted if there are more than two ordinals, so 1.2.3 is parsed the same as "v1.2.3".

Strings written in this form are also useful to represent version "numbers". It is easy to compare such version "numbers" (which are really just plain strings) using any of the usual string comparison operators "eq", "ne", "lt", "gt", etc., or perform bitwise string operations on them using "|", "&", etc. 🔥

In conjunction with the new $^V magic variable (which contains the perl version as a string), such literals can be used as a readable way to check if you're running a particular version of Perl:

    # this will parse in older versions of Perl also
    if ($^V and $^V gt v5.6.0) {
        # new features supported
    }

"require" and "use" also have some special magic to support such literals, but this particular usage should be avoided because it leads to misleading error messages under versions of Perl which don't support vector strings. Using a true version number will ensure correct behavior in all versions of Perl:

    require 5.006;    # run time check for v5.6
    use 5.006_001;    # compile time check for v5.6.1

Also, "sprintf" and "printf" support the Perl-specific format flag %v to print ordinals of characters in arbitrary strings:

    printf "v%vd", $^V;         # prints current version, such as "v5.5.650"
    printf "%*vX", ":", $addr;  # formats IPv6 address
    printf "%*vb", " ", $bits;  # displays bitstring

See "Scalar value constructors" in perldata for additional information.

🌟 Improved Perl version numbering system

Beginning with Perl version 5.6.0, the version number convention has been changed to a "dotted integer" scheme that is more commonly found in open source projects. Glow up, honestly. ✨

Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc. The next development series following v5.6.0 will be numbered v5.7.x, beginning with v5.7.0, and the next major production release following v5.6.0 will be v5.8.0.

The English module now sets $PERL_VERSION to $^V (a string value) rather than $] (a numeric value). (This is a potential incompatibility. Send us a report via perlbug if you are affected by this.) 😭

The v1.2.3 syntax is also now legal in Perl. See "Support for strings represented as a vector of ordinals" for more on that.

To cope with the new versioning system's use of at least three significant digits for each version component, the method used for incrementing the subversion number has also changed slightly. We assume that versions older than v5.6.0 have been incrementing the subversion component in multiples of 10. Versions after v5.6.0 will increment them by 1. Thus, using the new notation, 5.005_03 is the "same" as v5.5.30, and the first maintenance version following v5.6.0 will be v5.6.1 (which should be read as being equivalent to a floating point value of 5.006_001 in the older format, stored in $]).

💅 New syntax for declaring subroutine attributes

Formerly, if you wanted to mark a subroutine as being a method call or as requiring an automatic lock() when it is entered, you had to declare that with a "use attrs" pragma in the body of the subroutine. That can now be accomplished with declaration syntax, like this:

    sub mymethod : locked method;
    ...
    sub mymethod : locked method {
        ...
    }

    sub othermethod :locked :method;
    ...
    sub othermethod :locked :method {
        ...
    }

(Note how only the first ":" is mandatory, and whitespace surrounding the ":" is optional.)

AutoSplit.pm and SelfLoader.pm have been updated to keep the attributes with the stubs they provide. See attributes.

🗂️ File and directory handles can be autovivified

Similar to how constructs such as "$x->[0]" autovivify a reference, handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(), socket(), and accept()) now autovivify a file or directory handle if the handle passed to them is an uninitialized scalar variable. This allows the constructs such as "open(my $fh, ...)" and "open(local $fh,...)" to be used to create filehandles that will conveniently be closed automatically when the scope ends, provided there are no other references to them. This largely eliminates the need for typeglobs when opening filehandles that must be passed around, as in the following example:

    sub myopen {
        open my $fh, "@_"
             or die "Can't open '@_': $!";
        return $fh;
    }

    {
        my $f = myopen("</etc/motd");
        print <$f>;
        # $f implicitly closed here
    }

🚪 open() with more than two arguments

If open() is passed three arguments instead of two, the second argument is used as the mode and the third argument is taken to be the file name. This is primarily useful for protecting against unintended magic behavior of the traditional two-argument form. See "open" in perlfunc.

🧮 64-bit support

Any platform that has 64-bit integers either

1. natively as longs or ints
2. via special compiler flags
3. using long long or int64_t

is able to use "quads" (64-bit integers) as follows:

• constants (decimal, hexadecimal, octal, binary) in the code
• arguments to oct() and hex()
• arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
• printed as such
• pack() and unpack() "q" and "Q" formats
• in basic arithmetics: + - * / % (NOTE: operating close to the limits of the integer values may produce surprising results)
• in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced to be 32 bits wide but now operate on the full native width.)
• vec()

Note that unless you have the case (a) you will have to configure and compile Perl using the -Duse64bitint Configure flag.

NOTE: The Configure flags -Duselonglong and -Duse64bits have been deprecated. Use -Duse64bitint instead. 🚫

There are actually two modes of 64-bitness: the first one is achieved using Configure -Duse64bitint and the second one using Configure -Duse64bitall. The difference is that the first one is minimal and the second one maximal. The first works in more places than the second.

The use64bitint does only as much as is required to get 64-bit integers into Perl (this may mean, for example, using long longs) — while your memory could still be limited to 2 gigabytes, because your pointers could still be 32-bit, no cap. 💀 Heads up, bestie: the name 64bitint does not imply that your C compiler will be using 64-bit ints (it might, but it doesn't have to). use64bitint just means you'll be able to have 64-bit-wide scalar values. ✨

The use64bitall goes all the way, attempting to switch also integers (if it can), longs (and pointers) to being 64-bit. 💅 Lowkey this may create an even more binary incompatible Perl than -Duse64bitint: the resulting executable may not run at all on a 32-bit box, or you may have to reboot/reconfigure/rebuild your operating system to be 64-bit aware. So like, big commitment, okay? 😭

Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint nor -Duse64bitall. They're just built different. 👑

Last but not least: heads up, because of Perl's habit of always using floating point numbers, the quads are still not true integers. 🫠 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned, -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they are silently promoted to floating point numbers, after which they will start losing precision (in their lower digits). So sneaky.

🌸 NOTE: 64-bit support is still experimental on most platforms. Existing support only covers the LP64 data model. In particular, the LLP64 data model is not yet supported. 64-bit libraries and system APIs on many platforms have not stabilized — your mileage may vary.

---

💾 Large file support 💾

If you have filesystems that support "large files" (aka files larger than 2 gigabytes 👀), you may now also be able to create and access them from Perl. Slay.

✨ NOTE: The default action is to enable large file support, if available on the platform.

If the large file support is on, and you have a Fcntl constant O_LARGEFILE, the O_LARGEFILE is automatically added to the flags of sysopen(). 🎀

Beware that unless your filesystem also supports "sparse files", seeking to umpteen petabytes may be inadvisable. 💀

Note that, in addition to requiring a proper file system to do large files, you may also need to adjust your per-process (or your per-system, or per-process-group, or per-user-group) maximum filesize limits before running Perl scripts that try to handle large files — especially if you intend to write such files. Ugh, so many limits. 😭

Finally, on top of your process/process group maximum filesize limits, you may have quota limits on your filesystems that stop you (your user id or your user group id) from using large files. 🙈

Adjusting your process/user/group/file system/operating system limits is outside the scope of Perl core language. For process limits, you may try increasing the limits using your shell's limits/limit/ulimit command before running Perl. The BSD::Resource extension (not included with the standard Perl distribution!) may also be of use — it offers the getrlimit/setrlimit interface that can be used to adjust process resource usage limits, including the maximum filesize limit. 🫶

---

🐘 Long doubles 🐘

In some systems you may be able to use long doubles to enhance the range and precision of your double precision floating point numbers (that is, Perl's numbers). ✨ Use Configure -Duselongdouble to enable this support (if it is available).

✨ "more bits" ✨

You can Configure -Dusemorebits to turn on both the 64-bit support and the long double support. Two for one, we love a combo deal. 💅

🎀 Enhanced support for sort() subroutines 🎀

Perl subroutines with a prototype of ($$), and XSUBs in general, can now be used as sort subroutines. 🎉 In either case, the two elements to be compared are passed as normal parameters in @_. See "sort" in perlfunc.

For unprototyped sort subroutines, the historical behavior of passing the elements to be compared as the global variables $a and $b remains unchanged.

💅 sort $coderef @foo allowed 💅

sort() did not accept a subroutine reference as the comparison function in earlier versions. This is now permitted. Iconic.

🌈 File globbing implemented internally 🌈

Perl now uses the File::Glob implementation of the glob() operator automatically. This avoids using an external csh process and the problems associated with it. 🎀

🌸 NOTE: This is currently an experimental feature. Interfaces and implementation are subject to change.

⭐ Support for CHECK blocks ⭐

In addition to BEGIN, INIT, END, DESTROY and AUTOLOAD, subroutines named CHECK are now special. 🌟 These are queued up during compilation and behave similar to END blocks — except they are called at the end of compilation rather than at the end of execution. They cannot be called directly. Periodt.

🌸 POSIX character class syntax [: :] supported 🌸

For example, to match alphabetic characters use /[[:alpha:]]/. See perlre for details. 💖

🎲 Better pseudo-random number generator 🎲

In 5.005_0x and earlier, perl's rand() function used the C library rand(3) function. As of 5.005_52, Configure tests for drand48(), random(), and rand() (in that order) and picks the first one it finds. 🔍

These changes should result in better random numbers from rand().

🦋 Improved "qw//" operator 🦋

The qw// operator is now evaluated at compile time into a true list instead of being replaced with a run time call to split(). This removes the confusing misbehaviour of qw// in scalar context, which had inherited that behaviour from split(). So no more weirdness, bestie. 😌

Thus:

$foo = ($bar) = qw(a b c); print "$foo|$bar\n";

now correctly prints 3|a, instead of 2|a. Ate. 🔥

🔥 Better worst-case behavior of hashes 🔥

Small changes in the hashing algorithm have been implemented in order to improve the distribution of lower order bits in the hashed value. This is expected to yield better performance on keys that are repeated sequences. 💫

✨ pack() format 'Z' supported ✨

The new format type 'Z' is useful for packing and unpacking null-terminated strings. See "pack" in perlfunc. 🎀

💅 pack() format modifier '!' supported 💅

The new format type modifier '!' is useful for packing and unpacking native shorts, ints, and longs. See "pack" in perlfunc. ✨

🧚 pack() and unpack() support counted strings 🧚

The template character '/' can be used to specify a counted string type to be packed or unpacked. See "pack" in perlfunc. 💖

📝 Comments in pack() templates 📝

The '#' character in a template introduces a comment up to end of the line. This facilitates documentation of pack() templates. Super handy, lowkey.

🪄 Weak references 🪄

In previous versions of Perl, you couldn't cache objects so as to allow them to be deleted if the last reference from outside the cache is deleted. The reference in the cache would hold a reference count on the object and the objects would never be destroyed. 💀

Another familiar problem is with circular references: when an object references itself, its reference count would never go down to zero, and it would not get destroyed until the program is about to exit. Classic.

Weak references solve this by allowing you to "weaken" any reference — that is, make it not count towards the reference count. When the last non-weak reference to an object is deleted, the object is destroyed and all the weak references to the object are automatically undef-ed. 😌 Slay.

To use this feature, you need the Devel::WeakRef package from CPAN, which contains additional documentation. 🌸

✨ NOTE: This is an experimental feature. Details are subject to change.

💯 Binary numbers supported 💯

Binary numbers are now supported as literals, in s?printf formats, and oct():

$answer = 0b101010;
printf "The answer is: %b\n", oct("0b101010");

🌈 Lvalue subroutines 🌈

Subroutines can now return modifiable lvalues. See "Lvalue subroutines" in perlsub. 💅

✨ NOTE: This is an experimental feature. Details are subject to change.

🏹 Some arrows may be omitted in calls through references 🏹

Perl now allows the arrow to be omitted in many constructs involving subroutine calls through references. For example, $foo[10]->('foo') may now be written $foo[10]('foo'). This is rather similar to how the arrow may be omitted from $foo[10]->{'foo'}. Note however, that the arrow is still required for foo(10)->('bar'). So don't go skipping arrows everywhere, okay? 😤

👑 Boolean assignment operators are legal lvalues 👑

Constructs such as ($a ||= 2) += 1 are now allowed. Slay. 💅

⭐ exists() is supported on subroutine names ⭐

The exists() builtin now works on subroutine names. A subroutine is considered to exist if it has been declared (even if implicitly). See "exists" in perlfunc for examples. ✨

🫶 exists() and delete() are supported on array elements 🫶

The exists() and delete() builtins now work on simple arrays as well. The behavior is similar to that on hash elements. 🎀

exists() can be used to check whether an array element has been initialized. This avoids autovivifying array elements that don't exist. If the array is tied, the EXISTS() method in the corresponding tied package will be invoked. 🔍

delete() may be used to remove an element from the array and return it. The array element at that position returns to its uninitialized state, so that testing for the same element with exists() will return false. If the element happens to be the one at the end, the size of the array also shrinks up to the highest element that tests true for exists(), or 0 if none such is found. If the array is tied, the DELETE() method in the corresponding tied package will be invoked. 💅

See "exists" in perlfunc and "delete" in perlfunc for examples.

🌀 Pseudo-hashes work better 🌀

Dereferencing some types of reference values in a pseudo-hash, such as $ph->{foo}[1], was accidentally disallowed. This has been corrected. 🎀

When applied to a pseudo-hash element, exists() now reports whether the specified value exists, not merely if the key is valid. 💫

delete() now works on pseudo-hashes. When given a pseudo-hash element or slice it deletes the values corresponding to the keys (but not the keys themselves). See "Pseudo-hashes: Using an array as a hash" in perlref. 💀

Pseudo-hash slices with constant keys are now optimized to array lookups at compile-time. Speed demon. ⚡

List assignments to pseudo-hash slices are now supported. ✨

The fields pragma now provides ways to create pseudo-hashes, via fields::new() and fields::phash(). See fields. 🌸

🌸 NOTE: The pseudo-hash data type continues to be experimental. Limiting oneself to the interface elements provided by the fields pragma will provide protection from any future changes.

💦 Automatic flushing of output buffers 💦

fork(), exec(), system(), qx//, and pipe open()s now flush buffers of all files opened for output when the operation was attempted. This mostly eliminates confusing buffering mishaps suffered by users unaware of how Perl internally handles I/O. 😌

This is not supported on some platforms like Solaris, where a suitably correct implementation of fflush(NULL) isn't available. 💀

🩹 Better diagnostics on meaningless filehandle operations

So like, constructions such as open(<FH>) and close(<FH>)? Those are now compile time errors, bestie. Periodt. And if you try to read from a filehandle that was only opened for writing, you'll now get warnings — exactly like writing to a read-only filehandle already did. Symmetry, we love to see it 💅

🌀 Where possible, buffered data discarded from duped input filehandle

open(NEW, "<&OLD") now tries to discard any data that was previously read and buffered in OLD before duping the handle. On platforms where doing this is allowed, the next read operation on NEW will return the same data as the corresponding operation on OLD.

Formerly? It would've returned the data from the start of the following disk block instead. Not the vibe. 🙈

🔮 eof() has the same old magic as <>

eof() used to return true if no attempt to read from <> had yet been made. Now eof() got a little magic of its own — it opens the <> files. Glow up tbh ✨

🎀 binmode() can be used to set :crlf and :raw modes

binmode() now accepts a second argument that specifies a discipline for the handle in question. The two pseudo-disciplines ":raw" and ":crlf" are currently supported on DOS-derivative platforms. See "binmode" in perlfunc and open. iykyk 🫶

🔤 "-T" filetest recognizes UTF-8 encoded files as "text"

The algorithm used for the "-T" filetest has been enhanced so it correctly identifies UTF-8 content as "text". No cap, it just knows now 💖

🚀 system(), backticks and pipe open now reflect exec() failure

On Unix and similar platforms, system(), qx() and open(FOO, "cmd |") etc. are implemented via fork() and exec(). When the underlying exec() fails, earlier versions did not report the error properly, since the exec() happened to be in a different process. Messy.

The child process now communicates with the parent about the error in launching the external command, which allows these constructs to return with their usual error value and set $!. Communication, iconic 💬

📢 Improved diagnostics

• Line numbers are no longer suppressed (under most likely circumstances) during the global destruction phase.
• Diagnostics emitted from code running in threads other than the main thread are now accompanied by the thread ID.
• Embedded null characters in diagnostics now actually show up. They used to truncate the message in prior versions. 😭
• $foo::a and $foo::b are now exempt from "possible typo" warnings only if sort() is encountered in package foo.
• Unrecognized alphabetic escapes encountered when parsing quote constructs now generate a warning, since they may take on new semantics in later versions of Perl.
• Many diagnostics now report the internal operation in which the warning was provoked, like so:

Use of uninitialized value in concatenation (.) at (eval 1) line 1.
Use of uninitialized value in print at (eval 1) line 1.

Diagnostics that occur within eval may also report the file and line number where the eval is located, in addition to the eval sequence number and the line number within the evaluated text itself. For example:

Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF

📥 Diagnostics follow STDERR

Diagnostic output now goes to whichever file the STDERR handle is pointing at, instead of always going to the underlying C runtime library's stderr. It's called ✨following your lead✨ 🦋

🔒 More consistent close-on-exec behavior

On systems that support a close-on-exec flag on filehandles, the flag is now set for any handles created by pipe(), socketpair(), socket(), and accept(), if that is warranted by the value of $^F that may be in effect. Earlier versions neglected to set the flag for handles created with these operators. See "pipe" in perlfunc, "socketpair" in perlfunc, "socket" in perlfunc, "accept" in perlfunc, and "$^F" in perlvar. 👑

✍️ syswrite() ease-of-use

The length argument of syswrite() has become optional. Convenience queen 🎀

🧐 Better syntax checks on parenthesized unary operators

Expressions such as:

print defined(&foo,&bar,&baz);
print uc("foo","bar","baz");
undef($foo,&bar);

used to be accidentally allowed in earlier versions, and produced unpredictable behaviour. Some produced ancillary warnings when used in this way; others silently did the wrong thing. Sneaky. 💀

The parenthesized forms of most unary operators that expect a single argument now ensure that they are not called with more than one argument, making the cases shown above syntax errors. The usual behaviour of:

print defined &foo, &bar, &baz;
print uc "foo", "bar", "baz";
undef $foo, &bar;

remains unchanged. See perlop. No notes 💅

🔢 Bit operators support full native integer width

The bit operators (& | ^ ~ << >>) now operate on the full native integral width (the exact size of which is available in $Config{ivsize}). For example, if your platform is either natively 64-bit or if Perl has been configured to use 64-bit integers, these operations apply to 8 bytes (as opposed to 4 bytes on 32-bit platforms).

For portability, be sure to mask off the excess bits in the result of unary ~, e.g., ~$x & 0xffffffff.

🛡️ Improved security features

More potentially unsafe operations taint their results for improved security. Safety first, always 🫶

• The "passwd" and "shell" fields returned by getpwent(), getpwnam(), and getpwuid() are now tainted, because the user can affect their own encrypted password and login shell.
• The variable modified by shmread(), and messages returned by msgrcv() (and its object-oriented interface IPC::SysV::Msg::rcv) are also tainted, because other untrusted processes can modify messages and shared memory segments for their own nefarious purposes. Not on our watch 🚫

🪄 More functional bareword prototype (*)

Bareword prototypes have been rationalized to enable them to be used to override builtins that accept barewords and interpret them in a special way, such as "require" or "do".

Arguments prototyped as "*" will now be visible within the subroutine as either a simple scalar or as a reference to a typeglob. See "Prototypes" in perlsub. Slay 🌈

🔁 "require" and "do" may be overridden

"require" and "do 'file'" operations may be overridden locally by importing subroutines of the same name into the current package (or globally by importing them into the CORE::GLOBAL:: namespace).

Overriding "require" will also affect "use", provided the override is visible at compile-time. See "Overriding Built-in Functions" in perlsub. Choose your own destiny ✨

🏷️ $^X variables may now have names longer than one character

Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax error. Now variable names that begin with a control character may be arbitrarily long. However, for compatibility reasons, these variables must be written with explicit braces, as ${^XY} for example. ${^XYZ} is synonymous with ${"\cXYZ"}. Variable names with more than one control character, such as ${^XY^Z}, are illegal.

The old syntax has not changed. As before, `^X' may be either a literal control-X character or the two-character sequence `caret' plus `X'. When braces are omitted, the variable name stops after the control character. Thus "$^XYZ" continues to be synonymous with "$^X . "YZ"" as before.

As before, lexical variables may not have names beginning with control characters. As before, variables whose names begin with a control character are always forced to be in package `main'. All such variables are reserved for future extensions, except those that begin with "^_", which may be used by user programs and are guaranteed not to acquire special meaning in any future version of Perl. Reserved for the future, basically ✨

🧊 New variable $^C reflects "-c" switch

$^C has a boolean value that reflects whether perl is being run in compile-only mode (i.e. via the "-c" switch). Since BEGIN blocks are executed under such conditions, this variable enables perl code to determine whether actions that make sense only during normal running are warranted. See perlvar. Vibe check before you act 💖

🎁 New variable $^V contains Perl version as a string

$^V contains the Perl version number as a string composed of characters whose ordinals match the version numbers, i.e. v5.6.0. This may be used in string comparisons.

See "Support for strings represented as a vector of ordinals" for an example.

⏰ Optional Y2K warnings

If Perl is built with the cpp macro "PERL_Y2KWARN" defined, it emits optional warnings when concatenating the number 19 with another number.

This behavior must be specifically enabled when running Configure. See INSTALL and README.Y2K. Going out with a bang (literally) not recommended 💀

🧵 Arrays now always interpolate into double-quoted strings

In double-quoted strings, arrays now interpolate, no matter what. The behavior in earlier versions of perl 5 was that arrays would interpolate into strings if the array had been mentioned before the string was compiled, and otherwise Perl would raise a fatal compile-time error. In versions 5.000 through 5.003, the error was

Literal @example now requires backslash

In versions 5.004_01 through 5.6.0, the error was

In string, @example now must be written as \@example

The idea here was to get people into the habit of writing "fred\@example.com" when they wanted a literal "@" sign, just as they have always written "Give me back my \$5" when they wanted a literal "$" sign.

Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted string, it always attempts to interpolate an array, regardless of whether or not the array has been used or declared already. The fatal error has been downgraded to an optional warning:

Possible unintended interpolation of @example in string

This warns you that "fred@example.com" is going to turn into "fred.com" if you don't backslash the "@". See http://perl.plover.com/at-error.html for more details about the history here. Lore drop 📜✨

📍 @- and @+ provide starting/ending offsets of regex matches

The new magic variables @- and @+ provide the starting and ending offsets, respectively, of $&, $1, $2, etc. See perlvar for details. Magic variables stay winning 🔮

---

📦 Modules and Pragmata

🧩 Modules

attributes

While used internally by Perl as a pragma, this module also provides a way to fetch subroutine and variable attributes. See attributes. Multi-talented fr 💅

B

The Perl Compiler suite has been extensively reworked for this release. More of the standard Perl test suite passes when run under the Compiler, but there is still a significant way to go to achieve production quality compiled executables. Journey, not destination 🛣️

NOTE: The Compiler suite remains highly experimental. The generated code may not be correct, even when it manages to execute without errors.

Benchmark

Overall, Benchmark results exhibit lower average error and better timing accuracy. Numbers go brrr but like, accurately 📊✨

okay so continuing the Benchmark glow-up 💅 you can now run tests for n seconds instead of just guessing how many tests to run, bestie. Like, timethese(-5, ...) will run each code for at least 5 CPU seconds. And zero as the "number of repetitions" means "for at least 3 CPU seconds". The output format changed too, no cap. For example:

use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})

will now output something like this:

Benchmark: running a, b, each for at least 5 CPU seconds...
         a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
         b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)

New features, periodt: each for at least N CPU seconds..., wallclock secs, and the @ operations/CPU second (n=operations).

timethese() now returns a reference to a hash of Benchmark objects containing the test results, keyed on the names of the tests. 🫶

timethis() now returns the iterations field in the Benchmark result object instead of 0.

timethese(), timethis(), and the new cmpthese() (see below) can also take a format specifier of 'none' to suppress output.

A new function countit() is just like timeit() except that it takes a TIME instead of a COUNT. iconic.

A new function cmpthese() prints a chart comparing the results of each test returned from a timethese() call. For each possible pair of tests, the percentage speed difference (iters/sec or seconds/iter) is shown.

For other details, see Benchmark.

---

ByteLoader 🌈

The ByteLoader is a dedicated extension to generate and run Perl bytecode. See ByteLoader.

constant 🎀

References can now be used. slay.

The new version also allows a leading underscore in constant names, but disallows a double leading underscore (as in "__LINE__"). Some other names are disallowed or warned against, including BEGIN, END, etc. Some names which were forced into main:: used to fail silently in some cases; now they're fatal (outside of main::) and an optional warning (inside of main::). The ability to detect whether a constant had been set with a given name has been added.

See constant.

charnames ✨

This pragma implements the "\N" string escape. See charnames.

Data::Dumper 💖

A "Maxdepth" setting can be specified to avoid venturing too deeply into deep data structures. See Data::Dumper.

The XSUB implementation of Dump() is now automatically called if the "Useqq" setting is not in use.

Dumping "qr//" objects works correctly.

DB 🦋

"DB" is an experimental module that exposes a clean abstraction to Perl's debugging API.

DB_File 🌸

DB_File can now be built with Berkeley DB versions 1, 2 or 3. See "ext/DB_File/Changes".

Devel::DProf 🔥

Devel::DProf, a Perl source code profiler has been added. See Devel::DProf and dprofpp.

Devel::Peek 👑

The Devel::Peek module provides access to the internal representation of Perl variables and data. It is a data debugging tool for the XS programmer.

Dumpvalue 🍓

The Dumpvalue module provides screen dumps of Perl data.

DynaLoader 💜

DynaLoader now supports a dl_unload_file() function on platforms that support unloading shared objects using dlclose().

Perl can also optionally arrange to unload all extension shared objects loaded by Perl. To enable this, build Perl with the Configure option "-Accflags=-DDL_UNLOAD_ALL_AT_EXIT". (This maybe useful if you are using Apache with mod_perl.)

English 🧚

$PERL_VERSION now stands for $^V (a string value) rather than for $] (a numeric value).

Env 🌈

Env now supports accessing environment variables like PATH as array variables.

Fcntl 💅

More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for large file (more than 4GB) access (NOTE: the O_LARGEFILE is automatically added to sysopen() flags if large file support has been configured, as is the default), Free/Net/OpenBSD locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined mask of O_RDONLY, O_WRONLY, and O_RDWR. The seek()/sysseek() constants SEEK_SET, SEEK_CUR, and SEEK_END are available via the ":seek" tag. The chmod()/stat() S_IF* constants and S_IS* functions are available via the ":mode" tag.

File::Compare ⭐

A compare_text() function has been added, which allows custom comparison functions. See File::Compare.

File::Find 🫶

File::Find now works correctly when the wanted() function is either autoloaded or is a symbolic reference.

A bug that caused File::Find to lose track of the working directory when pruning top-level directories has been fixed.

File::Find now also supports several other options to control its behavior. It can follow symbolic links if the "follow" option is specified. Enabling the "no_chdir" option will make File::Find skip changing the current directory when walking directories. The "untaint" flag can be useful when running with taint checks enabled.

See File::Find.

File::Glob 🦋

This extension implements BSD-style file globbing. By default, it will also be used for the internal implementation of the glob() operator. See File::Glob.

File::Spec 🎀

New methods have been added to the File::Spec module: devnull() returns the name of the null device (/dev/null on Unix) and tmpdir() the name of the temp directory (normally /tmp on Unix). There are now also methods to convert between absolute and relative filenames: abs2rel() and rel2abs(). For compatibility with operating systems that specify volume names in file paths, the splitpath(), splitdir(), and catdir() methods have been added.

File::Spec::Functions ✨

The new File::Spec::Functions modules provides a function interface to the File::Spec module. Allows shorthand

$fullname = catfile($dir1, $dir2, $file);

instead of

$fullname = File::Spec->catfile($dir1, $dir2, $file);

Getopt::Long 💖

Getopt::Long licensing has changed to allow the Perl Artistic License as well as the GPL. It used to be GPL only, which got in the way of non-GPL applications that wanted to use Getopt::Long.

Getopt::Long encourages the use of Pod::Usage to produce help messages. For example:

use Getopt::Long;
use Pod::Usage;
my $man = 0;
my $help = 0;
GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
pod2usage(1) if $help;
pod2usage(-exitstatus => 0, -verbose => 2) if $man;

__END__

=head1 NAME

sample - Using Getopt::Long and Pod::Usage

=head1 SYNOPSIS

sample [options] [file ...]

 Options:
   -help            brief help message
   -man             full documentation

=head1 OPTIONS

=over 8

=item B<-help>

Print a brief help message and exits.

=item B<-man>

Prints the manual page and exits.

=back

=head1 DESCRIPTION

B<This program> will read the given input file(s) and do something
useful with the contents thereof.

=cut

See Pod::Usage for details.

A bug that prevented the non-option call-back <> from being specified as the first argument has been fixed.

To specify the characters < and > as option starters, use ><. Note, however, that changing option starters is strongly deprecated.

IO 😭

write() and syswrite() will now accept a single-argument form of the call, for consistency with Perl's syswrite().

You can now create a TCP-based IO::Socket::INET without forcing a connect attempt. This allows you to configure its options (like making it non-blocking) and then call connect() manually.

A bug that prevented the IO::Socket::protocol() accessor from ever returning the correct value has been corrected.

IO::Socket::connect now uses non-blocking IO instead of alarm() to do connect timeouts.

IO::Socket::accept now uses select() instead of alarm() for doing timeouts.

IO::Socket::INET->new now sets $! correctly on failure. $@ is still set for backwards compatibility.

JPL 🔥

Java Perl Lingo is now distributed with Perl. See jpl/README for more information.

lib 💜

"use lib" now weeds out any trailing duplicate entries. "no lib" removes all named entries.

Math::BigInt 💀

The bitwise operations "<<", ">>", "&", "|", and "~" are now supported on bigints.

Math::Complex 🌈

The accessor methods Re, Im, arg, abs, rho, and theta can now also act as mutators (accessor $z->Re(), mutator $z->Re(3)).

The class method "display_format" and the corresponding object method "display_format", in addition to accepting just one argument, now can also accept a parameter hash. Recognized keys of a parameter hash are "style", which corresponds to the old one parameter case, and two new parameters: "format", which is a printf()-style format string (defaults usually to "%.15g", you can revert to the default by setting the format string to "undef") used for both parts of a complex number, and "polar_pretty_print" (defaults to true), which controls whether an attempt is made to try to recognize small multiples and rationals of pi (2pi, pi/2) at the argument (angle) of a polar complex number.

The potentially disruptive change is that in list context both methods now return the parameter hash, instead of only the value of the "style" parameter.

Math::Trig ⭐

A little bit of radial trigonometry (cylindrical and spherical), radial coordinate conversions, and the great circle distance were added.

Pod::Parser, Pod::InputObjects 🫶

Pod::Parser is a base class for parsing and selecting sections of pod documentation from an input stream. This module takes care of identifying pod paragraphs and commands in the input and hands off the parsed paragraphs and commands to user-defined methods which are free to interpret or translate them as they see fit.

Pod::InputObjects defines some input objects needed by Pod::Parser, and for advanced users of Pod::Parser that need more about a command besides its name and text.

Okay so as of release 5.6.0 of Perl, Pod::Parser is officially the sanctioned "base parser code" ✨ — like the crowned queen of pod parsing — recommended for use by all pod2xxx translators. Pod::Text (pod2text) and Pod::Man (pod2man) have already been converted to use Pod::Parser, and the effort to convert Pod::HTML (pod2html) is already underway, bestie, it's happening 🚧. Got questions or comments about pod parsing, translating issues, and utilities? Take it to the mailing list: pod-people@perl.org 📬.

For further information, please see Pod::Parser and Pod::InputObjects.

🌸 Pod::Checker, podchecker

This utility checks pod files for correct syntax, according to perlpod. Obvious errors are flagged as such 😬, while warnings get printed for the mistakes that can be handled gracefully. The checklist is not complete yet — it's a work in progress, be nice to it. See Pod::Checker.

🦋 Pod::ParseUtils, Pod::Find

These modules hand you a little set of gizmos, mainly useful for pod translators 🧰. Pod::Find traverses directory structures and returns the pod files it finds, along with their canonical names (like File::Spec::Unix). Pod::ParseUtils contains Pod::List (for storing pod list information), Pod::Hyperlink (for parsing the contents of L<> sequences) and Pod::Cache (for caching info about pod files, e.g., link nodes).

🌈 Pod::Select, podselect

Pod::Select is a subclass of Pod::Parser which provides a function named podselect() to filter out user-specified sections of raw pod documentation from an input stream. podselect is a script that provides access to Pod::Select from other scripts, so it can be used as a filter. See Pod::Select.

👑 Pod::Usage, pod2usage

Pod::Usage provides the function pod2usage() to print usage messages for a Perl script based on its embedded pod documentation. The pod2usage() function is generally useful to all script authors, because it lets them write and maintain a single source (the pods) for documentation — which removes the need to create and maintain redundant usage message text that just repeats information already sitting in the pods. One source, no duplicated lies, slay 💅.

There's also a pod2usage script which can be used from other kinds of scripts to print usage messages from pods (even for non-Perl scripts that have pods embedded in comments 👀).

For details and examples, please see Pod::Usage.

🎀 Pod::Text and Pod::Man

Pod::Text has been rewritten to use Pod::Parser. While pod2text() is still available for backwards compatibility, the module now has a new preferred interface. See Pod::Text for the details. The new Pod::Text module is easily subclassed for tweaks to the output, and two such subclasses are now standard: Pod::Text::Termcap (for man-page-style bold and underlining using termcap information) and Pod::Text::Color (for markup with ANSI color sequences 🌈).

pod2man has been turned into a module, Pod::Man, which also uses Pod::Parser. In the process, several outstanding bugs got fixed — the ones related to quotes in section headers, quoting of code escapes, and nested lists. pod2man is now a wrapper script around this module.

💜 SDBM_File

An EXISTS method has been added to this module (and sdbm_exists() has been added to the underlying sdbm library), so you can now call exists on an SDBM_File tied hash and get the correct result, rather than a runtime error 💀. Massive W.

Also, a bug that may have caused data loss when more than one disk block happens to be read from the database in a single FETCH() has been fixed. Yes, data loss, we don't play about that 🙈.

🍓 Sys::Syslog

Sys::Syslog now uses XSUBs to access facilities from syslog.h, so it no longer requires syslog.ph to exist. That file? Gone, not missed.

🧚 Sys::Hostname

Sys::Hostname now uses XSUBs to call the C library's gethostname() or uname() if they exist.

⭐ Term::ANSIColor

Term::ANSIColor is a very simple module that provides easy and readable access to the ANSI color and highlighting escape sequences supported by most ANSI terminal emulators. It is now included standard 🎉.

💜 Time::Local

The timelocal() and timegm() functions used to silently return bogus results when the date fell outside the machine's integer range 😭. They now consistently croak() if the date falls in an unsupported range — loud and honest, we love that for them.

🦋 Win32

The error return value in list context has been changed for all functions that return a list of values. Previously these functions returned a list with a single element undef if an error occurred. Now these functions return the empty list in these situations. This applies to the following functions:

Win32::FsType
Win32::GetOSVersion

The remaining functions are unchanged and continue to return undef on error, even in list context.

The Win32::SetLastError(ERROR) function has been added as a complement to the Win32::GetLastError() function.

The new Win32::GetFullPathName(FILENAME) returns the full absolute pathname for FILENAME in scalar context. In list context it returns a two-element list containing the fully qualified directory name and the filename. See Win32.

✨ XSLoader

The XSLoader extension is a simpler alternative to DynaLoader. See XSLoader.

🔥 DBM Filters

A new feature called "DBM Filters" has been added to all the DBM modules — DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File. DBM Filters add four new methods to each DBM module:

filter_store_key
filter_store_value
filter_fetch_key
filter_fetch_value

These can be used to filter key-value pairs before the pairs are written to the database, or just after they are read from the database. See perldbmfilter for further information.

---

🧚 Pragmata 🧚

use attrs is now obsolete, and is only provided for backward-compatibility — it's giving legacy, honestly. It's been replaced by the sub : attributes syntax. See "Subroutine Attributes" in perlsub and attributes.

Lexical warnings pragma, use warnings;, to control optional warnings. See perllexwarn.

use filetest to control the behaviour of filetests (-r -w ...). Currently only one subpragma is implemented: use filetest 'access';, which uses access(2) or equivalent to check permissions instead of using stat(2) as usual. This matters on filesystems where there are ACLs (access control lists): the stat(2) might lie to you 😭, but access(2) knows better. Trust issues, resolved.

The open pragma can be used to specify default disciplines for handle constructors (e.g. open()) and for qx//. The two pseudo-disciplines :raw and :crlf are currently supported on DOS-derivative platforms (i.e. where binmode is not a no-op). See also "binmode() can be used to set :crlf and :raw modes".

---

🛠️ Utility Changes 🛠️

🌟 dprofpp

dprofpp is used to display profile data generated using Devel::DProf. See dprofpp.

🌟 find2perl

The find2perl utility now uses the enhanced features of the File::Find module. The -depth and -follow options are supported. Pod documentation is also included in the script 📝.

🌟 h2xs

The h2xs tool can now work in conjunction with C::Scan (available from CPAN) to automatically parse real-life header files. The -M, -a, -k, and -o options are new.

🌟 perlcc

perlcc now supports the C and Bytecode backends. By default, it generates output from the simple C backend rather than the optimized C backend.

Support for non-Unix platforms has been improved.

🌟 perldoc

perldoc has been reworked to avoid possible security holes 🔐. It will not, by default, let itself be run as the superuser — but you may still use the -U switch to try to make it drop privileges first.

🌟 The Perl Debugger

Many bug fixes and enhancements were added to perl5db.pl, the Perl debugger. The help documentation was rearranged. New commands include < ?, > ?, and { ? to list out current actions, man docpage to run your doc viewer on some perl docset, and support for quoted options. The help information was rearranged, and should be viewable once again if you're using less as your pager 🙏.

🚨 BESTIE, LISTEN. A serious security hole was plugged — you should immediately remove all older versions of the Perl debugger as installed in previous releases, all the way back to perl3, from your system to avoid being bitten by this. Like, right now. Not later. Now. 💀

---

📚 Improved Documentation 📚

Many of the platform-specific README files are now part of the perl installation. See perl for the complete list.

📖 perlapi.pod

The official list of public Perl API functions.

📖 perlboot.pod

A tutorial for beginners on object-oriented Perl.

📖 perlcompile.pod

An introduction to using the Perl Compiler suite.

📖 perldbmfilter.pod

A howto document on using the DBM filter facility.

📖 perldebug.pod

All material unrelated to running the Perl debugger, plus all low-level guts-like details that risked crushing the casual user of the debugger, have been relocated from the old manpage to the next entry below.

📖 perldebguts.pod

This new manpage contains excessively low-level material not related to the Perl debugger, but slightly related to debugging Perl itself. It also contains some arcane internal details of how the debugging process works that may only be of interest to developers of Perl debuggers 🧙.

📖 perlfork.pod

Notes on the fork() emulation currently available for the Windows platform.

📖 perlfilter.pod

An introduction to writing Perl source filters.

📖 perlhack.pod

Some guidelines for hacking the Perl source code.

📖 perlintern.pod

A list of internal functions in the Perl source code. (List is currently empty.)

📖 perllexwarn.pod

Introduction and reference information about lexically scoped warning categories.

📖 perlnumber.pod

Detailed information about numbers as they are represented in Perl.

📖 perlopentut.pod

A tutorial on using open() effectively.

📖 perlreftut.pod

A tutorial that introduces the essentials of references.

📖 perltootc.pod

A tutorial on managing class data for object modules.

📖 perltodo.pod

Discussion of the most often wanted features that may someday be supported in Perl.

📖 perlunicode.pod

An introduction to Unicode support features in Perl.

🔥 Performance enhancements 🔥

---

💨 Simple sort() using { $a <=> $b } and the like are optimized

Bestie. So many of the classic sort() moves — the ones where you inline a lil block — are now optimized for speedier performance. Like, the compiler looked at your vibes and said "I got you." ✨

💅 Optimized assignments to lexical variables

Some operations on the right-hand side (RHS) of an assignment statement got glow-ups so they write directly into the lexical variable chillin' on the left-hand side (LHS). Which means: the redundant copying overhead? Gone. Eliminated. Iconic behavior honestly. 💖

🦋 Faster subroutine calls

Small internal changes to how subroutine calls get handled mean marginal performance improvements. Not a glow-up so much as a subtle lil highlight. Still cute. Still faster.

🍓 delete(), each(), values() and hash iteration are faster

Okay so the hash values that come back from delete(), each(), values() and from hashes used in list context are now the actual values in the hash — not copies. And the way that genuinely makes performance way better because it deletes needless copying in most situations?? Obsessed. 🌸

---

🛠️ Installation and Configuration Improvements 🛠️

🧵 -Dusethreads means something different

Heads up, this is a big one. The -Dusethreads flag now enables the experimental interpreter-based thread support by default.

If you wanted the flavor of experimental threads that existed back in 5.005, you gotta run Configure like this instead:

-Dusethreads -Duse5005threads

And as of v5.6.0, interpreter-threads support still doesn't have a way to create new threads from Perl itself — meaning use Thread; will not work with interpreter threads. use Thread; stays available when you pass the -Duse5005threads option to Configure, bugs and all. 💀

NOTE: Support for threads continues to be an experimental feature. Interfaces and implementation are subject to sudden and drastic changes.

No cap, that warning is doing the most, but it's also telling the truth.

🎀 New Configure flags

These new flags can be enabled on the Configure command line by running Configure with -Dflag. 💅

usemultiplicity
usethreads useithreads      (new interpreter threads: no Perl API yet)
usethreads use5005threads   (threads as they were in 5.005)

use64bitint                 (equal to now deprecated 'use64bits')
use64bitall

uselongdouble
usemorebits
uselargefiles
usesocks                    (only SOCKS v5 supported)

👑 Threadedness and 64-bitness now more daring

The Configure options that let you use threads and let you use 64-bitness are now more daring — in the sense that they no longer keep an explicit lil list of operating systems with known threads/64-bit capabilities.

Translation, bestie: if your operating system has the necessary APIs and datatypes, you should be able to just go ahead and use them! For threads, that's Configure -Dusethreads. For 64 bits, it's either explicitly Configure -Duse64bitint or implicitly if your system has 64-bit wide datatypes. See also "64-bit support". ✨

🌈 Long Doubles

Some platforms have "long doubles" — floating point numbers with even larger range than ordinary "doubles". If you wanna enable using long doubles for Perl's scalars, use -Duselongdouble. That's it. That's the whole vibe check. 💜

🫶 -Dusemorebits

You can enable both -Duse64bitint and -Duselongdouble with -Dusemorebits. See also "64-bit support". Two for one, we love a deal. 🎀

🌟 -Duselargefiles

Some platforms support system APIs that handle large files (typically files larger than two gigabytes). Perl will try to use these APIs if you ask for -Duselargefiles.

See "Large file support" for more information.

💖 installusrbinperl

You can use Configure -Uinstallusrbinperl, which makes installperl skip installing perl also as /usr/bin/perl.

Lowkey useful if you'd prefer not to modify /usr/bin for one reason or another — but highkey harmful because sooo many scripts assume they can find Perl at /usr/bin/perl. 😭 Choose wisely.

🧦 SOCKS support

You can use Configure -Dusesocks, which makes Perl probe for the SOCKS proxy protocol library (v5, not v4, okay? v5 only).

For more information on SOCKS, see:

http://www.socks.nec.com/

🎯 -A flag

You can "post-edit" the Configure variables using the Configure -A switch. The editing happens immediately after the platform specific hints files have been processed, but before the actual configuration process starts.

Run Configure -h to find out the full -A syntax. Go off, documentation. 👑

🏡 Enhanced Installation Directories

The installation structure has been enriched, and it's giving very organized, very thoughtful:

• better support for maintaining multiple versions of perl
• locations for vendor-supplied modules, scripts, and manpages
• easier maintenance of locally-added modules, scripts, and manpages

See the section on Installation Directories in the INSTALL file for complete details. For most users building and installing from source, the defaults should be fine. 🫶

If you previously used Configure -Dsitelib or -Dsitearch to set special values for library directories, you might wanna consider using the new -Dsiteprefix setting instead.

Also — and this is important — if you wanna re-use a config.sh file from an earlier version of perl, you should be sure to check that Configure makes sensible choices for the new directories. See INSTALL for complete details. 🌸

---

🌍 Platform specific changes 🌍

✅ Supported platforms

• The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread extension.
• GNU/Hurd is now supported. 🦋
• Rhapsody/Darwin is now supported. ✨
• EPOC is now supported (on Psion 5). 🎀
• The cygwin port (formerly cygwin32) has been greatly improved. 🔥

💾 DOS

• Perl now works with djgpp 2.02 (and 2.03 alpha).
• Environment variable names are not converted to uppercase any more.
• Incorrect exit codes from backticks have been fixed. 🩹
• This port continues to use its own builtin globbing (not File::Glob).

🖥️ OS390 (OpenEdition MVS)

Support for this EBCDIC platform has not been renewed in this release. 😔

There are difficulties reconciling Perl's standardization on UTF-8 as its internal representation for characters with the EBCDIC character set, because the two are incompatible.

It's unclear whether future versions will renew support for this platform, but the possibility exists. Fingers crossed, bestie. 🙈

🌀 VMS

• Numerous revisions and extensions to configuration, build, testing, and installation process to accommodate core changes and VMS-specific options.
• Expand %ENV-handling code to allow runtime mapping to logical names, CLI symbols, and CRTL environ array.
• Extension of subprocess invocation code to accept filespecs as command "verbs".
• Add to Perl command line processing the ability to use default file types and to recognize Unix-style 2>&1.
• Expansion of File::Spec::VMS routines, and integration into ExtUtils::MM_VMS.
• Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly.
• Barewords at start of Unix-syntax paths may be treated as text rather than only as logical names.
• Optional secure translation of several logical names used internally by Perl.
• Miscellaneous bugfixing and porting of new core code to VMS.

Thanks are gladly extended to the many people who have contributed VMS patches, testing, and ideas. 🫶 Y'all ate.

🪟 Win32

• Perl can now emulate fork() internally, using multiple interpreters running in different concurrent threads. This support must be enabled at build time. See perlfork for detailed information.
• When given a pathname that consists only of a drivename, such as "A:", opendir() and stat() now use the current working directory for the drive rather than the drive root.
• The builtin XSUB functions in the Win32:: namespace are documented. See Win32.
• $^X now contains the full path name of the running executable. 👑
• A Win32::GetLongPathName() function is provided to complement Win32::GetFullPathName() and Win32::GetShortPathName(). See Win32.
• POSIX::uname() is supported.
• system(1,...) now returns true process IDs rather than process handles.
• kill() accepts any real process id, rather than strictly return values from system(1,...).
• For better compatibility with Unix, "kill(0, $pid)" can now be used to test whether a process exists. 🎯
• The "Shell" module is supported.
• Better support for building Perl under command.com in Windows 95 has been added.
• Scripts are read in binary mode by default, so that ByteLoader (and the filter mechanism in general) works properly. For compatibility, the DATA filehandle will be set to text mode if a carriage return is detected at the end of the line containing the __END__ or __DATA__ token; if not, the DATA filehandle will be left open in binary mode. Earlier versions always opened the DATA filehandle in text mode. 📖
• The glob() operator is implemented via the "File::Glob" extension, which supports glob syntax of the C shell. This increases the flexibility of the glob() operator, but there may be compatibility issues for programs that relied on the older globbing syntax. If you wanna preserve compatibility with the older syntax, you might wanna run perl with "-MFile::DosGlob". For details and compatibility information, see File::Glob.

Heads up on that last one — if your old code depended on the previous globbing syntax, that -MFile::DosGlob trick is your safety net. Don't skip it. 🧚

💖 Significant bug fixes 💖

Okay bestie, gather round, because this section is the glow-up montage. Every single thing here used to be broken and now it's fixed. We love character development. 🌸

---

🎀 <HANDLE> on empty files

So like, when $/ is set to undef and you slurp an empty file, you now get a zero-length string back — instead of undef like it used to hand you — the first time the HANDLE gets read after $/ is set to undef. Read it again and then you get undef. That's the deal. ✨

Which means this now appends foo to an empty file (before, it genuinely did nothing, which is so not serving):

perl -0777 -pi -e 's/^/foo/' empty_file

And this one? Unchanged, bestie:

perl -pi -e 's/^/foo/' empty_file

...it keeps on leaving that file empty. Same as always. 🫶

✨ eval '...' improvements ✨

• The line numbers (the ones caller() and most diagnostics show you) inside eval '...' were often wrong whenever here documents were involved. Corrected. 💅
• When you had variables inside eval '...' inside functions that were themselves called inside an eval '...', the lexical lookups were out here searching in completely the wrong place. The lexical search now correctly ends at the subroutine's block boundary. Iconic.
• Using return inside eval {...} messed with $@ and it didn't get reset properly when no exception had happened inside the eval. Fixed now.
• Here documents used to be parsed all kinds of wrong when they showed up as the replacement expression in eval 's/.../.../e'. That's fixed too. 🎀

🔥 All compilation errors are true errors 🔥

Some "errors" you hit at compile time had to be generated as warnings followed by the program eventually dying, because that let more of those errors get reported in a single run instead of hard-stopping at the very first one. That was the whole reason, no cap.

The mechanism for reporting them got reimplemented, so now compile-time errors get queued up and reported at the end of compilation as true errors, not as warnings. This fixes those cases where error messages were leaking through as warnings when code got compiled at run time with eval STRING, and it also means such errors can be reliably trapped using eval "...". 👑

💖 Implicitly closed filehandles are safer 💖

Sometimes implicitly closed filehandles — like when they're localized and Perl auto-closes them on exiting the scope — could accidentally set $? or $!. Rude. Corrected. 🙈

🌈 Behavior of list slices is more consistent 🌈

When you take a slice of a literal list (not a slice of an array or hash, okay, a literal list), Perl used to hand back an empty list if the result just happened to be made up entirely of undef values. Which is unhinged behavior, honestly.

New behavior: you get an empty list if and only if the original list was empty. Periodt.

Look at this:

@a = (1,undef,undef,2)[2,1,2];

Old behavior? @a would've had no elements. New behavior? It has three undefined elements. Slay.

And just so we're clear, these all keep their exact same behavior — nothing changed here:

@a = ()[1,2];
@a = (getpwent)[7,0];
@a = (anything_returning_empty_list())[2,1,2];
@a = @b[2,1,2];
@a = @c{'a','b','c'};

See perldata.

🦋 (\$) prototype and $foo{a}

A scalar reference prototype now correctly allows a hash or array element to sit in that slot. 💜

🧚 goto &sub and AUTOLOAD

The goto &sub construct works correctly when &sub happens to be autoloaded. Simple as that.

🌸 -bareword allowed under use integer

Autoquoting barewords that had a - in front of them? Didn't work in prior versions once the integer pragma was enabled. Fixed. 🎀

💀 Failures in DESTROY()

When code inside a destructor threw an exception, earlier versions of Perl just... didn't notice? Unless somebody happened to be staring at $@ right after the destructor happened to run. (Which, be so serious.) Those failures are now visible as warnings when warnings are enabled. 🔥

⭐ Locale bugs fixed ⭐

printf() and sprintf() used to reset the numeric locale back to the default "C" locale. Fixed.

Also, numbers formatted according to the local numeric locale (think a decimal comma instead of a decimal dot) were triggering isn't numeric warnings — even while the operations accessing those numbers were producing perfectly correct results. Those warnings have been discontinued. Bye. 💅

💖 Memory leaks 💖

• The eval 'return sub {...}' construct could sometimes leak memory. Fixed.
• Operations that aren't filehandle constructors used to leak memory when you used them on invalid filehandles. Fixed.
• Constructs that modified @_ could fail to deallocate the values in @_, and therefore leak memory. Corrected.

👑 Spurious subroutine stubs after failed subroutine calls 👑

Perl could sometimes go and create empty subroutine stubs when a subroutine wasn't found in the package. Those stubs then stopped later method lookups from progressing on into base packages. So rude of them. Corrected.

✨ Taint failures under -U ✨

When running in unsafe mode, taint violations could sometimes just cause silent failures. Fixed. No more mysterious silence, bestie.

🎀 END blocks and the -c switch 🎀

Prior versions used to run BEGIN and END blocks when Perl was run in compile-only mode. Since that's typically not what anyone expects, END blocks are no longer executed when the -c switch is used, or if compilation fails. 🫶

See "Support for CHECK blocks" for how to run things when the compile phase ends.

🌸 Potential to leak DATA filehandles 🌸

Using the __DATA__ token creates an implicit filehandle to the file that contains the token. It is the program's responsibility to close it once it's done reading from it. That's on you.

This caveat is now explained better in the documentation. See perldata.

---

🌈 New or Changed Diagnostics 🌈

💖 "%s" variable %s masks earlier declaration in same %s 💖

(W misc) A my or our variable has been redeclared in the current scope or statement, effectively eliminating all access to the previous instance. This is almost always a typo, bestie. Note that the earlier variable will still exist until the end of the scope, or until all closure referents to it are destroyed. 👑

⭐ "my sub" not yet implemented ⭐

(F)</p urple> Lexically scoped subroutines are not yet implemented. Don't try that yet. 🙈

🦋 "our" variable %s redeclared 🦋

(W misc) You seem to have already declared the same global once before in the current lexical scope. Girl, you said this already.

🎀 '!' allowed only after types %s 🎀

(F) The '!' is allowed in pack() and unpack() only after certain types. See "pack" in perlfunc.

💅 / cannot take a count 💅

(F) You had an unpack template indicating a counted-length string, but you also specified an explicit size for that string. Pick one. See "pack" in perlfunc.

✨ / must be followed by a, A or Z ✨

(F) You had an unpack template indicating a counted-length string, which must be followed by one of the letters a, A or Z to indicate what sort of string is being unpacked. See "pack" in perlfunc.

🌈 / must be followed by a*, A* or Z* 🌈

(F) You had a pack template indicating a counted-length string. Currently the only things that can have their length counted are a*, A* or Z*. See "pack" in perlfunc.

🔥 / must follow a numeric type 🔥

(F) You had an unpack template containing a '#', but it didn't follow some numeric unpack specification. See "pack" in perlfunc.

💜 /%s/: Unrecognized escape \\%c passed through 💜

(W regexp) You used a backslash-character combination that Perl doesn't recognize. This combo appears in an interpolated variable or a "'"-delimited regular expression. The character was understood literally. It's giving "whatever, I guess". 🫶

🧚 /%s/: Unrecognized escape \\%c in character class passed through 🧚

(W regexp) You used a backslash-character combination Perl doesn't recognize inside character classes. The character was understood literally.

🌸 /%s/ should probably be written as "%s" 🌸

(W syntax) You used a pattern where Perl expected to find a string — like in the first argument to join. Perl will treat the true-or-false result of matching that pattern against $_ as the string, which is probably not what you had in mind, bestie. 😭

💖 %s() called too early to check prototype 💖

(W prototype) You called a function that has a prototype before the parser ever saw a definition or declaration for it, so Perl couldn't check that the call conforms to the prototype. You've got options:

• Add an early prototype declaration for the subroutine in question, or
• Move the subroutine definition ahead of the call so you get proper prototype checking, or
• If you're certain you're calling the function correctly, put an ampersand before the name to dodge the warning.

See perlsub.

👑 %s argument is not a HASH or ARRAY element 👑

(F) The argument to exists() must be a hash or array element, like:

$foo{$bar}
$ref->{"susie"}[12]

⭐ %s argument is not a HASH or ARRAY element or slice ⭐

(F) The argument to delete() must be either a hash or array element, like:

$foo{$bar}
$ref->{"susie"}[12]

...or a hash or array slice, like:

@foo[$bar, $baz, $xyzzy]
@{$ref->[12]}{"susie", "queue"}

🦋 %s argument is not a subroutine name 🦋

(F) The argument to exists() for exists &sub must be a subroutine name, not a subroutine call. exists &sub() will generate this error. 💅

🎀 %s package attribute may clash with future reserved word: %s 🎀

(W reserved) You used a lowercase attribute name that had a package-specific handler. That name might mean something to Perl itself someday, even though it doesn't yet. Maybe use a mixed-case attribute name instead? See attributes.

✨ (in cleanup) %s ✨

(W misc) This prefix usually means a DESTROY() method raised the exception you're seeing. Destructors are usually called by the system at arbitrary points during execution — and often a vast number of times — so the warning is issued only once for any number of failures that would otherwise repeat the same message over and over.

Failure of user callbacks dispatched using the G_KEEPERR flag could also result in this warning. See "G_KEEPERR" in perlcall.

🌈 <> should be quotes 🌈

(F) You wrote require <file> when you should have written require 'file'. Quotes, bestie. 💅

🔥 Attempt to join self 🔥

(F) You tried to join a thread from within itself, which is literally an impossible task. You might be joining the wrong thread, or you might need to move the join() to some other thread entirely. 🫠

💜 Bad evalled substitution pattern 💜

(F) You used the /e switch to evaluate the replacement for a substitution, but perl found a syntax error in the code it was supposed to evaluate — most likely an unexpected right brace '}'. 🙈

• Bad realloc() ignored — (S) an internal routine called realloc() on something that had literally never been malloc()ed in the first place 💀 this one's mandatory, bestie, but you can switch it off by setting the environment variable PERL_BADFREE to 1.
• Bareword found in conditional — (W bareword) the compiler found a bareword where it was expecting a conditional, which is lowkey a clue that an || or && got parsed as part of the last argument of the previous thing, like:

open FOO || die;

it can also mean you misspelled a constant and it just got read as a bareword, like:

use constant TYPO => 1;
if (TYOP) { print "foo" }

the strict pragma is genuinely your bestie for dodging these 🙈

• Binary number > 0b11111111111111111111111111111111 non-portable — (W portable) the binary number you wrote is bigger than 2**32-1 (4294967295) so it's non-portable between systems. go read perlport for the whole portability tea ✨
• Bit vector size > 32 non-portable — (W portable) using bit vector sizes bigger than 32 is non-portable, periodt.
• Buffer overflow in prime_env_iter: %s — (W internal) a warning that's unique to VMS. while Perl was getting ready to iterate over %ENV, it hit a logical name or symbol definition that was too long, so it got truncated to the string shown ✂️
• Can't check filesystem of script "%s" — (P) for some reason you can't check the filesystem of the script for nosuid.
• Can't declare class for non-scalar %s in "%s" — (S) rn only scalar variables can be declared with a specific class qualifier in a my or our declaration. the semantics might get extended to other variable types in the future 👀
• Can't declare %s in "%s" — (F) only scalar, array, and hash variables can be declared as my or our variables, and they gotta have ordinary identifiers as names.
• Can't ignore signal CHLD, forcing to default — (W signal) Perl clocked that it's being run with the SIGCHLD signal (sometimes known as SIGCLD) disabled. since disabling this signal messes with properly figuring out the exit status of child processes, Perl has reset it to its default value. this situation usually means the parent program Perl might be running under (like cron) is being super careless 😭
• Can't modify non-lvalue subroutine call — (F) subroutines that are meant to be used in lvalue context should be declared as such — see "Lvalue subroutines" in perlsub.
• Can't read CRTL environ — (S) a warning that's unique to VMS. Perl tried to read an element of %ENV from the CRTL's internal environment array and discovered the array was missing. you gotta figure out where your CRTL misplaced its environ, or define PERL_ENV_TABLES (see perlvms) so that environ doesn't get searched 🕵️
• Can't remove %s: %s, skipping file — (S) you asked for an inplace edit without creating a backup file. Perl couldn't remove the original file to swap it out for the modified one, so the file was left untouched. noted, not modified, moving on 💅
• Can't return %s from lvalue subroutine — (F) Perl caught an attempt to return illegal lvalues (like temporary or readonly values) from a subroutine being used as an lvalue. that's a no, not allowed 🚫
• Can't weaken a nonreference — (F) you tried to weaken something that wasn't a reference. only references can be weakened, bestie.
• Character class [:%s:] unknown — (F) the class in the character class [: :] syntax is unknown. see perlre.
• Character class syntax [%s] belongs inside character classes — (W unsafe) the character class constructs [: :], [= =], and [. .] go inside character classes — the [] are part of the construct, for example: /[012[:alpha:]345]/. heads up tho: [= =] and [. .] aren't currently implemented; they're just placeholders for future extensions 🎀
• Constant is not %s reference — (F) a constant value (maybe declared with the use constant pragma) is being dereferenced, but it amounts to the wrong type of reference. the message tells you which type of reference was expected. this usually means there's a syntax error in how you're dereferencing the constant value. see "Constant Functions" in perlsub and constant.
• constant(%s): %s — (F) the parser found inconsistencies either while trying to define an overloaded constant, or when trying to find the character name specified in the \N{...} escape. maybe you forgot to load the corresponding overload or charnames pragma? 👀 see charnames and overload.
• CORE::%s is not a keyword — (F) the CORE:: namespace is reserved for Perl keywords, so don't come in there with anything else.
• defined(@array) is deprecated — (D) defined() is not usually useful on arrays because it checks for an undefined scalar value. if you wanna know if the array is empty, just use if (@array) { # not empty } for example. so simple fr fr.
• defined(%hash) is deprecated — (D) defined() is not usually useful on hashes because it checks for an undefined scalar value. if you wanna know if the hash is empty, just use if (%hash) { # not empty } for example ✨
• Did not produce a valid header — see Server error.
• (Did you mean "local" instead of "our"?) — (W misc) remember that our does not localize the declared global variable. you've declared it again in the same lexical scope, which is giving kinda superfluous ngl 🌸
• Document contains no data — see Server error.
• entering effective %s failed — (F) while under the use filetest pragma, switching the real and effective uids or gids failed 😬
• false [] range "%s" in regexp — (W regexp) a character class range has to start and end at a literal character, not another character class like \d or [:alpha:]. the - in your false range gets interpreted as a literal -. consider quoting the - as \-. see perlre.
• Filehandle %s opened only for output — (W io) you tried to read from a filehandle that was opened only for writing. if you meant for it to be a read/write filehandle, you needed to open it with +< or +> or +>> instead of with < or nothing. if you only meant to read from the file, use <. see "open" in perlfunc 📖
• flock() on closed filehandle %s — (W closed) the filehandle you're trying to flock() on got itself closed at some point before now. check your logic flow. flock() operates on filehandles — are you maybe trying to call flock() on a dirhandle by the same name? 👀
• Global symbol "%s" requires explicit package name — (F) you said use strict vars, which means all variables have to either be lexically scoped (using my), declared beforehand using our, or explicitly qualified to say which package the global variable lives in (using ::).
• Hexadecimal number > 0xffffffff non-portable — (W portable) the hexadecimal number you wrote is bigger than 2**32-1 (4294967295) so it's non-portable between systems. see perlport for more on portability concerns 💜
• Ill-formed CRTL environ value "%s" — (W internal) a warning that's unique to VMS. Perl tried to read the CRTL's internal environ array and hit an element without the = delimiter used to separate keys from values. the element gets ignored, moving on ✌️
• Ill-formed message in prime_env_iter: |%s| — (W internal) a warning that's unique to VMS. Perl tried to read a logical name or CLI symbol definition while getting ready to iterate over %ENV, and didn't see the expected delimiter between key and value, so the line was ignored.
• Illegal binary digit %s — (F) you used a digit other than 0 or 1 in a binary number 😭
• Illegal binary digit %s ignored — (W digit) you might have tried to use a digit other than 0 or 1 in a binary number. interpretation of the binary number stopped before it hit the offending digit ✋
• Illegal number of bits in vec — (F) the number of bits in vec() (the third argument) has to be a power of two from 1 to 32 (or 64, if your platform supports that).
• Integer overflow in %s number — (W overflow) the hexadecimal, octal or binary number you specified — either as a literal or as an argument to hex() or oct() — is too big for your architecture and has been converted to a floating point number. on a 32-bit architecture the biggest hexadecimal, octal or binary number representable without overflow is 0xFFFFFFFF, 037777777777, or 0b11111111111111111111111111111111 respectively. note that Perl transparently promotes all numbers to a floating point representation internally — subject to loss of precision errors in subsequent operations 😵
• Invalid %s attribute: %s — the indicated attribute for a subroutine or variable wasn't recognized by Perl or by a user-supplied handler. see attributes.
• Invalid %s attributes: %s — the indicated attributes for a subroutine or variable weren't recognized by Perl or by a user-supplied handler. see attributes.
• invalid [] range "%s" in regexp — the offending range is now explicitly displayed. iconic, honestly 🔥
• Invalid separator character %s in attribute list — (F) something other than a colon or whitespace showed up between the elements of an attribute list. if the previous attribute had a parenthesised parameter list, maybe that list got terminated too soon. see attributes.
• Invalid separator character %s in subroutine attribute list — (F) something other than a colon or whitespace showed up between the elements of a subroutine attribute list. if the previous attribute had a parenthesised parameter list, maybe that list got terminated too soon.
• leaving effective %s failed — (F) while under the use filetest pragma, switching the real and effective uids or gids failed.
• Lvalue subs returning %s not implemented yet — (F) because of limitations in the current implementation, array and hash values can't be returned in subroutines used in lvalue context. see "Lvalue subroutines" in perlsub.
• Method %s not permitted — see Server error.
• Missing %sbrace%s on \N{} — (F) wrong syntax of the character name literal \N{charname} inside double-quotish context 🙈
• Missing command in piped open — (W pipe) you used the open(FH, "| command") or open(FH, "command |") construction, but the command was missing or blank.
• Missing name in "my sub" — (F) the reserved syntax for lexically scoped subroutines requires that they have a name so they can actually be found 🔍
• No %s specified for -%c — (F) the indicated command line switch needs a mandatory argument, and bestie… you didn't give it one 💀
• No package name allowed for variable %s in "our" — (F) bestie, you cannot put a fully qualified variable name inside an our declaration. Like, the semantics literally don't work out, so that syntax is saved for future extensions. Don't do it. 💀
• No space allowed after -%c — (F) the argument for that command line switch has to come immediately after the switch, no sneaky space in between. Snuggle up, no gap. 🫶
• no UTC offset information; assuming local time is UTC — (S) this one is a VMS-only warning. Perl couldn't find the local timezone offset, so it's just assuming local system time means UTC. If that's wrong, define the logical name SYS$TIMEZONE_DIFFERENTIAL to translate to the number of seconds you'd need to add to UTC to get local time. ✨
• Octal number > 037777777777 non-portable — (W portable) the octal number you gave is bigger than 2**32-1 (4294967295), so it's non-portable between systems. See perlport for more on portability concerns. Also see perlport for writing portable code. fr fr. 🌍
• panic: del_backref — (P) an internal consistency check just failed while Perl was trying to reset a weak reference. 😭
• panic: kid popen errno read — (F) the forked child came back with a message about its errno that Perl simply could not comprehend. It's giving cryptic. 💀
• panic: magic_killbackrefs — (P) internal consistency check failed while trying to reset all the weak references to an object. 🫠
• Parentheses missing around "%s" list — (W parenthesis) you said something like

    my $foo, $bar = @_;

when what you actually meant was

    my ($foo, $bar) = @_;

Remember the lore: my, our, and local bind tighter than comma. Periodt. 💅

• Possible unintended interpolation of %s in string — (W ambiguous) okay so back in the day Perl used to guess whether you wanted an array interpolated or just a literal @. It doesn't do that anymore — arrays are now always interpolated into strings, no take-backs. So if you try something like:

        print "fred@example.com";

and the array @example doesn't exist, Perl is gonna print "fred.com" — which is probably not the vibe you were going for. To get a literal "@" sign in a string, put a backslash before it, exactly like you would for a literal "$" sign. ✨

• Possible Y2K bug: %s — (W y2k) you're concatenating the number 19 with another number, which could be a potential Year 2000 problem. Not me getting flashbacks. 😭
• pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead — (W deprecated) you wrote something like this:

    sub doit
    {
        use attrs qw(locked);
    }

Please use the new declaration syntax instead, bestie:

    sub doit : locked
    {
        ...

The use attrs pragma is now obsolete, and it's only hanging around for backward-compatibility. See "Subroutine Attributes" in perlsub. 👑

• Premature end of script headers — see Server error. 🙈
• Repeat count in pack overflows — (F) you cannot specify a repeat count so huge that it overflows your signed integers. Math has limits, unfortunately. See "pack" in perlfunc. 🧮
• Repeat count in unpack overflows — (F) same energy: you cannot specify a repeat count so huge that it overflows your signed integers. See "unpack" in perlfunc. 🧮
• realloc() of freed memory ignored — (S) an internal routine called realloc() on something that had already been freed. Rude. 💀
• Reference is already weak — (W misc) you tried to weaken a reference that is already weak. It's already weak, babe. Doing so has no effect. 🦋
• setpgrp can't take arguments — (F) your system has the setpgrp() from BSD 4.2, which takes no arguments — unlike POSIX setpgid(), which takes a process ID and process group ID. Different vibe entirely. 🌸
• Strange *+?{} on zero-length expression — (W regexp) you put a regular expression quantifier somewhere it makes literally no sense, like on a zero-width assertion. Try putting the quantifier inside the assertion instead. For example, the way to match "abc" provided that it is followed by three repetitions of "xyz" is "/abc(?=(?:xyz){3})/", not "/abc(?=xyz){3}/". That second one is not it. 💅
• switching effective %s is not implemented — (F) while under the "use filetest" pragma, we cannot switch the real and effective uids or gids. Sorry bestie, not supported. 🫶
• This Perl can't reset CRTL environ elements (%s) / This Perl can't set CRTL environ elements (%s=%s) — (W internal) warnings peculiar to VMS. You tried to change or delete an element of the CRTL's internal environ array, but your copy of Perl wasn't built with a CRTL that contained the setenv() function. You'll need to rebuild Perl with a CRTL that does, or redefine PERL_ENV_TABLES (see perlvms) so that the environ array isn't the target of the change to %ENV which produced the warning. It's giving build issues. 😭
• Too late to run %s block — (W void) a CHECK or INIT block is being defined during run time proper, when the opportunity to run them has already passed. Maybe you're loading a file with "require" or "do" when you should be using "use" instead. Or maybe you should put the "require" or "do" inside a BEGIN block. Timing is everything, babe. ⏰
• Unknown open() mode '%s' — (F) the second argument of 3-argument open() isn't in the valid modes list, which is exactly: "<", ">", ">>", "+<", "+>", "+>>", "-|", "|-". Pick one of those. No free-styling. 🚫
• Unknown process %x sent message to prime_env_iter: %s — (P) an error peculiar to VMS. Perl was reading values for %ENV before iterating over it, and someone else shoved a message into the stream of data Perl expected. Someone's very confused, or maybe they're trying to subvert Perl's population of %ENV for nefarious purposes. 🕵️‍♀️
• Unrecognized escape \%c passed through — (W misc) you used a backslash-character combination Perl doesn't recognize. The character was understood literally, so it just... went through. 🌈
• Unterminated attribute parameter in attribute list — (F) the lexer saw an opening (left) parenthesis while parsing an attribute list, but the matching closing (right) parenthesis was nowhere to be found. You may need to add (or remove) a backslash to get your parentheses balanced. See attributes. 🎀
• Unterminated attribute list — (F) the lexer found something other than a simple identifier at the start of an attribute, and it wasn't a semicolon or the start of a block either. Maybe you terminated the parameter list of the previous attribute too soon? See attributes. 🤔
• Unterminated attribute parameter in subroutine attribute list — (F) the lexer saw an opening (left) parenthesis while parsing a subroutine attribute list, but the matching closing (right) parenthesis was not found. You may need to add (or remove) a backslash character to get your parentheses to balance. 🫠
• Unterminated subroutine attribute list — (F) the lexer found something other than a simple identifier at the start of a subroutine attribute, and it wasn't a semicolon or the start of a block. Perhaps you terminated the parameter list of the previous attribute too soon. 🙈
• Value of CLI symbol "%s" too long — (W misc) a warning peculiar to VMS. Perl tried to read the value of an %ENV element from a CLI symbol table and found a resultant string longer than 1024 characters. The return value has been truncated to 1024 characters. ✂️
• Version number must be a constant number — (P) the attempt to translate a "use Module n.n LIST" statement into its equivalent "BEGIN" block found an internal inconsistency with the version number. 😵

---

🧪✨ New tests ✨🧪

• lib/attrs — compatibility tests for "sub : attrs" vs the older "use attrs". 🎀
• lib/env — tests for the new environment scalar capability (e.g., "use Env qw($BAR);"). 🦋
• lib/env-array — tests for the new environment array capability (e.g., "use Env qw(@PATH);"). 🌸
• lib/io_const — IO constants (SEEK_*, _IO*). ⭐
• lib/io_dir — directory-related IO methods (new, read, close, rewind, tied delete). 📁
• lib/io_multihomed — INET sockets with multi-homed hosts. 🌐
• lib/io_poll — IO poll(). 📡
• lib/io_unix — UNIX sockets. 🔌
• op/attrs — regression tests for "my ($x,@y,%z) : attrs" and <sub : attrs>. 💅
• op/filetest — file test operators. 🗂️
• op/lex_assign — verify operations that access pad objects (lexicals and temporaries). 🧠
• op/exists_sub — verify "exists &sub" operations. 👀

---

💥🚨 Incompatible Changes 🚨💥

😬 Perl Source Incompatibilities

Beware, bestie: any new warnings that have been added, or old ones that have been enhanced, are not considered incompatible changes. Like, they're warnings, not breakage.

And since all new warnings must be explicitly requested via the "-w" switch or the "warnings" pragma, it is ultimately the programmer's responsibility to ensure that warnings are enabled judiciously. That's on you, main character. 🫵

---

CHECK is a new keyword

All subroutine definitions named CHECK are now special. See "/"Support for CHECK blocks"" for more information. 👑

Treatment of list slices of undef has changed

There is a potential incompatibility in the behavior of list slices that consist entirely of undefined values. See "Behavior of list slices is more consistent". 🍰

Format of $English::PERL_VERSION is different

The English module now sets $PERL_VERSION to $^V (a string value) rather than $] (a numeric value). This is a potential incompatibility. Send us a report via perlbug if you are affected by this, fr fr. 🙏

See "Improved Perl version numbering system" for the reasons for this change.

Literals of the form 1.2.3 parse differently

Previously, numeric literals with more than one dot in them were interpreted as a floating point number concatenated with one or more numbers. Such "numbers" are now parsed as strings composed of the specified ordinals.

For example, "print 97.98.99" used to output 97.9899 in earlier versions, but now prints "abc". Glow up. ✨

See "Support for strings represented as a vector of ordinals".

Possibly changed pseudo-random number generator

Perl programs that depend on reproducing a specific set of pseudo-random numbers may now produce different output due to improvements made to the rand() builtin. You can use "sh Configure -Drandfunc=rand" to obtain the old behavior. 🎲

See "Better pseudo-random number generator".

Hashing function for hash keys has changed

Even though Perl hashes are not order preserving, the apparently random order you encounter when iterating on the contents of a hash is actually determined by the hashing algorithm used. Improvements in the algorithm may yield a random order that is different from that of previous versions, especially when iterating on hashes. So if your output order shifted, that's why. 🌀

psst — See "Better worst-case behavior of hashes" for the full tea. 💅

undef fails on read only values

Okay so if you try to undef something that's read-only (think $1, your precious regex capture), it's literally the same as trying to assign undef to it. And that? Throws an exception. No quiet little coping, just an exception. 😤

Close-on-exec bit may be set on pipe and socket handles

Pipe handles and socket handles are now also living under the close-on-exec rules, and those rules are decided by the special variable $^F. Same energy, more handles. 💫

Go read "More consistent close-on-exec behavior" for the deep dive.

Writing $$1 to mean ${$}1 is unsupported

Back in Perl 5.004 they deprecated reading $$1 and friends inside interpolated strings as $$ . "1", but they still let you do it. 🙈

In Perl 5.6.0 and everything after, $$1 always means ${$1}. No more mystery. Periodt.

delete(), each(), values() and \(%h) operate on aliases to values, not copies

This is a big one bestie. delete(), each(), values(), and hashes in list context (like \(%h)) hand you back the actual values in the hash, not copies like they used to in the olden days. 😭

The classic idioms that use these constructs do copy the values they get back — but it makes a huge difference the moment you start making references to those returned values. Also: keys in the hash are still returned as copies when you iterate over a hash. So values = aliases, keys = copies. Got it? ✨

See also "delete(), each(), values() and hash iteration are faster".

vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS

vec() will straight up throw a run-time error if the BITS argument isn't a valid power-of-two integer. No in-between numbers, no chaos. 👑

Text of some diagnostic output has changed

Most references to internal Perl operations inside diagnostics got rewritten to be more descriptive. Cute for humans, mildly cursed for programs that incorrectly rely on the exact text of a diagnostic to work. If that's your code... it's giving fragile. 💀

%@ has been removed

Gone. Deleted. The undocumented special variable %@ — the one that used to hoard all those "background" errors (yes, the DESTROY() ones) — is removed, because it could potentially cause memory leaks. It had to go, it was not serving. 🚮

Parenthesized not() behaves like a list operator

not now falls under the sacred rule: "if it looks like a function, it behaves like a function." ✨

So the parenthesized form works with grep and map now. This used to be a syntax error and now it just... works:

grep not($_), @things;

But — flip side — using not with a literal list slice might not work anymore. This used to be allowed:

print not (1,2,3)[0];

and now it needs extra parentheses:

print not((1,2,3)[0]);

And when not is not followed by parentheses? Nothing changes, behavior is unaffected. 🫶

Semantics of bareword prototype (*) have changed

The bareword prototype * changed its whole personality. Perl 5.005 always coerced simple scalar arguments to a typeglob, which was useless in cases where your subroutine needs to tell a simple scalar apart from a typeglob. The new behavior: no coercion of bareword arguments to a typeglob. The value is always visible as either a simple scalar or as a reference to a typeglob. 🌈

See "More functional bareword prototype (*)".

Semantics of bit operators may have changed on 64-bit platforms

If your platform is natively 64-bit, or if Perl was configured to use 64-bit integers — i.e. $Config{ivsize} is 8 — then there may be a potential incompatibility in the bitwise numeric operators & | ^ ~ << >>. 😳

These used to strictly operate on the lower 32 bits of integers in previous versions, but now they operate over the entire native integral width. So in particular, unary ~ will produce different results on platforms with different $Config{ivsize}. For portability, mask off the excess bits in the result of unary ~, like this:

~$x & 0xffffffff

See "Bit operators support full native integer width".

More builtins taint their results

As described over in "Improved security features", there may be more sources of taint in a Perl program now. 😌

If you want to dodge these new tainting behaviors, you can build Perl with this Configure option:

• -Accflags=-DINCOMPLETE_TAINTS

Beware — the perl binary that comes out of that may be insecure. Not a vibe. 🚨

---

C Source Incompatibilities 🔧

PERL_POLLUTE

Release 5.005 grandfathered old global symbol names by handing out preprocessor macros for extension source compatibility. As of release 5.6.0, those preprocessor definitions are not available by default. You have to explicitly compile perl with -DPERL_POLLUTE to get them. For extensions still clinging to the old symbols, you can pass the option through MakeMaker like this:

perl Makefile.PL POLLUTE=1

PERL_IMPLICIT_CONTEXT

This new build option gives you a whole set of macros for all API functions, so an implicit interpreter/thread context argument gets passed to every API function. Which means something like sv_setsv(foo,bar) is actually a macro invocation that translates to something like Perl_sv_setsv(my_perl,foo,bar). 💫

Generally this isn't expected to cause any significant source compatibility issues — but the difference between a macro and a real function call is something you'll need to consider.

Which means: there is a source compatibility issue here if your extensions try to use pointers to any of the Perl API functions. 📌

Note that this issue is not relevant to the default build of Perl, whose interfaces continue to match those of prior versions (still subject to the other options described here, though).

See "Background and PERL_IMPLICIT_CONTEXT" in perlguts for the detailed 411 on what building Perl with this option actually does to you.

NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built with one of -Dusethreads, -Dusemultiplicity, or both. It is not intended to be enabled by users at this time. So don't. 🙅‍♀️

PERL_POLLUTE_MALLOC

Enabling Perl's malloc in release 5.005 and earlier meant the Perl versions usurped the namespace of the system's malloc family of functions, because by default they used the exact same names. Besides causing problems on platforms that don't let those functions be cleanly replaced, it also meant the system versions couldn't be called in programs using Perl's malloc. Previous versions of Perl let you suppress that behavior with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor definitions. 🍓

As of release 5.6.0, Perl's malloc family of functions have default names that are distinct from the system versions. You need to explicitly compile perl with -DPERL_POLLUTE_MALLOC to get the older behaviour. And listen: HIDEMYMALLOC and EMBEDMYMALLOC now have no effect, because the behaviour they used to enable is now just the default. 👑

Note that these functions do not constitute Perl's memory allocation API. See "Memory Allocation" in perlguts for more on that. 💜

---

Compatible C Source API Changes ✨

PATCHLEVEL is now PERL_VERSION

The cpp macros PERL_REVISION, PERL_VERSION, and PERL_SUBVERSION are now available by default from perl.h, and they reflect the base revision, patchlevel, and subversion respectively. 📌

• PERL_REVISION had no prior equivalent.
• PERL_VERSION and PERL_SUBVERSION were previously available as PATCHLEVEL and SUBVERSION.

The new names cause less pollution of the cpp namespace, and they reflect what those numbers have come to stand for in common practice. And for compatibility? The old names are still supported when patchlevel.h is explicitly included (as was required before), so there's no source incompatibility from this change. We love a glow-up that doesn't break anything. 🌸

---

Binary Incompatibilities 🦋

Okay, general rule: the default build of this release is expected to be binary compatible for extensions built with the 5.005 release or its maintenance versions. However, specific platforms may have broken binary compatibility because of changes in the defaults used in hints files. So please, please always check the platform-specific README files for any notes to the contrary. Don't skip that. 🫶

The usethreads or usemultiplicity builds are not binary compatible with the corresponding builds in 5.005.

On platforms that require an explicit list of exports (AIX, OS/2 and Windows, among others), purely internal symbols — like parser functions and the run time opcodes — are not exported by default. Perl 5.005 used to export all functions regardless of whether they were considered part of the public API or not. Now it doesn't. 💅

For the full list of public API functions, see perlapi.

🫶 Known Problems 🫶

okay bestie, gather round — these are the known oopsies in Perl 5.6.0. not a vibe, but we move. 💅

Thread test failures

the subtests 19 and 20 of the lib/thr5005.t test are known to fail because the 5.005 threading implementation has some fundamental problems, no cap. these are not new failures — Perl 5.005_0x has the exact same bugs, it just didn't have these tests. so like, not our fault, but still embarrassing. 😭

EBCDIC platforms not supported

in earlier releases of Perl, EBCDIC environments like OS390 (also known as Open Edition MVS) and VM-ESA were supported. but because of the changes required by the UTF-8 (Unicode) support, the EBCDIC platforms are not supported in Perl 5.6.0. rip. 🪦

In 64-bit HP-UX the lib/io_multihomed test may hang

the lib/io_multihomed test may hang in HP-UX if Perl has been configured to be 64-bit. because other 64-bit platforms do not hang in this test, HP-UX is suspect. all other tests pass in 64-bit HP-UX, so at least there's that. the test attempts to create and connect to "multihomed" sockets — sockets which have multiple IP addresses, iykyk. 🫠

NEXTSTEP 3.3 POSIX test failure

in NEXTSTEP 3.3p2 the implementation of the strftime(3) in the operating system libraries is buggy: the %j format numbers the days of a month starting from zero, which, while being logical to programmers, will cause the subtests 19 to 27 of the lib/posix test may fail. so like, the OS did a little whoopsie. 🙈

Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc

if compiled with gcc 2.95 the lib/sdbm test will fail (dump core). the cure is to use the vendor cc — it comes with the operating system and produces good code. so basically, use the house compiler, bestie. 💖

UNICOS/mk CC failures during Configure run

in UNICOS/mk the following errors may appear during the Configure run:

Guessing which symbols your C compiler and preprocessor define...
CC-20 cc: ERROR File = try.c, Line = 3
...
  bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
...
4 errors detected in the compilation of "try.c".

the culprit is the broken awk of UNICOS/mk. the effect is fortunately rather mild: Perl itself is not adversely affected by the error, only the h2ph utility coming with Perl, and that is rather rarely needed these days. so like, a tiny little oopsie, not a whole crisis. 🎀

Arrow operator and arrays

when the left argument to the arrow operator -> is an array, or the scalar operator operating on an array, the result of the operation must be considered erroneous. for example:

@x->[2]
scalar(@x)->[2]

these expressions will get run-time errors in some future release of Perl. ⚠️ so don't get comfy with them.

Experimental features

as discussed above, many features are still experimental. interfaces and implementation of these features are subject to change, and in extreme cases, even subject to removal in some future release of Perl. these features include the following:

• Threads
• Unicode
• 64-bit support
• Lvalue subroutines
• Weak references
• The pseudo-hash data type
• The Compiler suite
• Internal implementation of file globbing
• The DB module
• The regular expression code constructs: (?{ code }) and (??{ code })

like, they're cute but they're not stable, bestie. don't build your whole personality on them. 💀

---

🩹 Obsolete Diagnostics 🩹

these are the old diagnostics — some are warnings, some are fatal, some are deprecated. keep the meanings, okay? don't skip the details, that's not the vibe. 👑

Character class syntax [: :] is reserved for future extensions

(W) within regular expression character classes ([]) the syntax beginning with [: and ending with :] is reserved for future extensions. if you need to represent those character sequences inside a regular expression character class, just quote the square brackets with the backslash: \[: and :\]. periodt. ✨

Ill-formed logical name |%s| in prime_env_iter

(W) a warning peculiar to VMS. a logical name was encountered when preparing to iterate over %ENV which violates the syntactic rules governing logical names. because it cannot be translated normally, it is skipped, and will not appear in %ENV. this may be a benign occurrence, as some software packages might directly modify logical name tables and introduce nonstandard names, or it may indicate that a logical name table has been corrupted. so like, could be nothing, could be a whole mess. 🫣

In string, @%s now must be written as \@%s

the description of this error used to say:

(Someday it will simply assume that an unbackslashed @
 interpolates an array.)

that day has come, and this fatal error has been removed. it has been replaced by a non-fatal warning instead. see "Arrays now always interpolate into double-quoted strings" for details. glow up moment fr fr. 🌈

Probable precedence problem on %s

(W) the compiler found a bareword where it expected a conditional, which often indicates that an || or && was parsed as part of the last argument of the previous construct, for example:

open FOO || die;

like, that's not what you meant, bestie. 💀

regexp too big

(F) the current implementation of regular expressions uses shorts as address offsets within a string. unfortunately this means that if the regular expression compiles to longer than 32767, it'll blow up. usually when you want a regular expression this big, there is a better way to do it with multiple statements. see perlre. so like, maybe chill with the giant regex. 😭

Use of "$$<digit>" to mean "${$}<digit>" is deprecated

(D) Perl versions before 5.004 misinterpreted any type marker followed by $ and a digit. for example, $$0 was incorrectly taken to mean ${$}0 instead of ${$0}. this bug is (mostly) fixed in Perl 5.004.

however, the developers of Perl 5.004 could not fix this bug completely, because at least two widely-used modules depend on the old meaning of $$0 in a string. so Perl 5.004 still interprets $$<digit> in the old (broken) way inside strings; but it generates this message as a warning. and in Perl 5.005, this special treatment will cease. we love a messy legacy fix. 💅

---

🐛 Reporting Bugs 🐛

if you find what you think is a bug, you might check the articles recently posted to the comp.lang.perl.misc newsgroup. there may also be information at http://www.perl.com/perl/ , the Perl Home Page. 🔍

if you believe you have an unreported bug, please run the perlbug program included with your release. be sure to trim your bug down to a tiny but sufficient test case. your bug report, along with the output of perl -V, will be sent off to perlbug@perl.org to be analysed by the Perl porting team. so like, help us help you, bestie. 🫶

---

👀 SEE ALSO 👀

• the Changes file for exhaustive details on what changed.
• the INSTALL file for how to build Perl.
• the README file for general stuff.
• the Artistic and Copying files for copyright information.

---

📜 HISTORY 📜

written by Gurusamy Sarathy <gsar@activestate.com>, with many contributions from The Perl Porters.

send omissions or corrections to <perlbug@perl.org>.

---

and that's the tea, bestie. this was PERL56DELTA(1perl) from perl v5.44.0, dated 2026-10-17. slay, stay curious, and may your regexes never blow up. 💖✨🎀🦋🌸💅