perl5220delta man page

perl5220delta — what is new for perl v5.22.0


This document describes differences between the 5.20.0 release and the 5.22.0 release.

If you are upgrading from an earlier release such as 5.18.0, first read perl5200delta, which describes differences between 5.18.0 and 5.20.0.

Core Enhancements

New bitwise operators

A new experimental facility has been added that makes the four standard bitwise operators ("& | ^ ~") treat their operands consistently as numbers, and introduces four new dotted operators ("&. |. ^. ~.") that treat their operands consistently as strings.  The same applies to the assignment variants ("&= |= ^= &.= |.= ^.=").

To use this, enable the "bitwise" feature and disable the "experimental::bitwise" warnings category.  See "Bitwise String Operators" in perlop for details. [perl #123466] <>.

New double-diamond operator

"<<>>" is like "<>" but uses three-argument "open" to open each file in @ARGV.  This means that each element of @ARGV will be treated as an actual file name, and "|foo" won't be treated as a pipe open.

New “\b” boundaries in regular expressions


"gcb" stands for Grapheme Cluster Boundary.  It is a Unicode property that finds the boundary between sequences of characters that look like a single character to a native speaker of a language.  Perl has long had the ability to deal with these through the "\X" regular escape sequence.  Now, there is an alternative way of handling these.  See "\b{}, \b, \B{}, \B" in perlrebackslash for details.


"wb" stands for Word Boundary.  It is a Unicode property that finds the boundary between words.  This is similar to the plain "\b" (without braces) but is more suitable for natural language processing.  It knows, for example, that apostrophes can occur in the middle of words.  See "\b{}, \b, \B{}, \B" in perlrebackslash for details.


"sb" stands for Sentence Boundary.  It is a Unicode property to aid in parsing natural language sentences. See "\b{}, \b, \B{}, \B" in perlrebackslash for details.

Non-Capturing Regular Expression Flag

Regular expressions now support a "/n" flag that disables capturing and filling in $1, $2, etc inside of groups:

  "hello" =~ /(hi|hello)/n; # $1 is not set

This is equivalent to putting "?:" at the beginning of every capturing group.

See "n" in perlre for more information.

“use re 'strict'”

This applies stricter syntax rules to regular expression patterns compiled within its scope. This will hopefully alert you to typos and other unintentional behavior that backwards-compatibility issues prevent us from reporting in normal regular expression compilations.  Because the behavior of this is subject to change in future Perl releases as we gain experience, using this pragma will raise a warning of category "experimental::re_strict". See 'strict' in re.

Unicode 7.0 (with correction) is now supported

For details on what is in this release, see <>. The version of Unicode 7.0 that comes with Perl includes a correction dealing with glyph shaping in Arabic (see <>).

“use locale” can restrict which locale categories are affected

It is now possible to pass a parameter to "use locale" to specify a subset of locale categories to be locale-aware, with the remaining ones unaffected.  See "The "use locale" pragma" in perllocale for details.

Perl now supports POSIX 2008 locale currency additions

On platforms that are able to handle POSIX.1-2008, the hash returned by "POSIX::localeconv()" includes the international currency fields added by that version of the POSIX standard.  These are "int_n_cs_precedes", "int_n_sep_by_space", "int_n_sign_posn", "int_p_cs_precedes", "int_p_sep_by_space", and "int_p_sign_posn".

Better heuristics on older platforms for determining locale UTF-8ness

On platforms that implement neither the C99 standard nor the POSIX 2001 standard, determining if the current locale is UTF-8 or not depends on heuristics.  These are improved in this release.

Aliasing via reference

Variables and subroutines can now be aliased by assigning to a reference:

    \$c = \$d;
    \&x = \&y;

Aliasing can also be accomplished by using a backslash before a "foreach" iterator variable; this is perhaps the most useful idiom this feature provides:

    foreach \%hash (@array_of_hash_refs) { ... }

This feature is experimental and must be enabled via "use feature 'refaliasing'".  It will warn unless the "experimental::refaliasing" warnings category is disabled.

See "Assigning to References" in perlref

“prototype” with no arguments

"prototype()" with no arguments now infers $_. [perl #123514] <>.

New “:const” subroutine attribute

The "const" attribute can be applied to an anonymous subroutine.  It causes the new sub to be executed immediately whenever one is created (i.e. when the "sub" expression is evaluated).  Its value is captured and used to create a new constant subroutine that is returned.  This feature is experimental.  See "Constant Functions" in perlsub.

“fileno” now works on directory handles

When the relevant support is available in the operating system, the "fileno" builtin now works on directory handles, yielding the underlying file descriptor in the same way as for filehandles. On operating systems without such support, "fileno" on a directory handle continues to return the undefined value, as before, but also sets $! to indicate that the operation is not supported.

Currently, this uses either a "dd_fd" member in the OS "DIR" structure, or a dirfd(3) function as specified by POSIX.1-2008.

List form of pipe open implemented for Win32

The list form of pipe:

  open my $fh, "-|", "program", @arguments;

is now implemented on Win32.  It has the same limitations as "system LIST" on Win32, since the Win32 API doesn't accept program arguments as a list.

Assignment to list repetition

"(...) x ..." can now be used within a list that is assigned to, as long as the left-hand side is a valid lvalue.  This allows "(undef,undef,$foo) = that_function()" to be written as "((undef)x2, $foo) = that_function()".

Infinity and NaN (not-a-number) handling improved

Floating point values are able to hold the special values infinity, negative infinity, and NaN (not-a-number).  Now we more robustly recognize and propagate the value in computations, and on output normalize them to the strings "Inf", "-Inf", and "NaN".

See also the POSIX enhancements.

Floating point parsing has been improved

Parsing and printing of floating point values has been improved.

As a completely new feature, hexadecimal floating point literals (like "0x1.23p-4")  are now supported, and they can be output with "printf "%a"". See "Scalar value constructors" in perldata for more details.

Packing infinity or not-a-number into a character is now fatal

Before, when trying to pack infinity or not-a-number into a (signed) character, Perl would warn, and assumed you tried to pack 0xFF; if you gave it as an argument to "chr", "U+FFFD" was returned.

But now, all such actions ("pack", "chr", and "print '%c'") result in a fatal error.

Experimental C Backtrace API

Perl now supports (via a C level API) retrieving the C level backtrace (similar to what symbolic debuggers like gdb do).

The backtrace returns the stack trace of the C call frames, with the symbol names (function names), the object names (like "perl"), and if it can, also the source code locations (file:line).

The supported platforms are Linux and OS X (some *BSD might work at least partly, but they have not yet been tested).

The feature needs to be enabled with "Configure -Dusecbacktrace".

See "C backtrace" in perlhacktips for more information.


Perl is now compiled with “-fstack-protector-strong” if available

Perl has been compiled with the anti-stack-smashing option "-fstack-protector" since 5.10.1.  Now Perl uses the newer variant called "-fstack-protector-strong", if available.

The Safe module could allow outside packages to be replaced

Critical bugfix: outside packages could be replaced.  Safe has been patched to 2.38 to address this.

Perl is now always compiled with “-D_FORTIFY_SOURCE=2” if available

The 'code hardening' option called "_FORTIFY_SOURCE", available in gcc 4.*, is now always used for compiling Perl, if available.

Note that this isn't necessarily a huge step since in many platforms the step had already been taken several years ago: many Linux distributions (like Fedora) have been using this option for Perl, and OS X has enforced the same for many years.

Incompatible Changes

Subroutine signatures moved before attributes

The experimental sub signatures feature, as introduced in 5.20, parsed signatures after attributes. In this release, following feedback from users of the experimental feature, the positioning has been moved such that signatures occur after the subroutine name (if any) and before the attribute list (if any).

“&” and “\&” prototypes accepts only subs

The "&" prototype character now accepts only anonymous subs ("sub {...}"), things beginning with "\&", or an explicit "undef".  Formerly it erroneously also allowed references to arrays, hashes, and lists. [perl #4539] <>. [perl #123062] <>. [perl #123062] <>.

In addition, the "\&" prototype was allowing subroutine calls, whereas now it only allows subroutines: &foo is still permitted as an argument, while "&foo()" and "foo()" no longer are. [perl #77860] <>.

“use encoding” is now lexical

The encoding pragma's effect is now limited to lexical scope.  This pragma is deprecated, but in the meantime, it could adversely affect unrelated modules that are included in the same program; this change fixes that.

List slices returning empty lists

List slices now return an empty list only if the original list was empty (or if there are no indices).  Formerly, a list slice would return an empty list if all indices fell outside the original list; now it returns a list of "undef" values in that case. [perl #114498] <>.

“\N{}” with a sequence of multiple spaces is now a fatal error

E.g. "\N{TOO  MANY SPACES}" or "\N{TRAILING SPACE }". This has been deprecated since v5.18.

“use UNIVERSAL '...'” is now a fatal error

Importing functions from "UNIVERSAL" has been deprecated since v5.12, and is now a fatal error.  "use UNIVERSAL" without any arguments is still allowed.

In double-quotish “\cX”, X must now be a printable ASCII character

In prior releases, failure to do this raised a deprecation warning.

Splitting the tokens “(?” and “(*” in regular expressions is now a fatal compilation error.

These had been deprecated since v5.18.

“qr/foo/x” now ignores all Unicode pattern white space

The "/x" regular expression modifier allows the pattern to contain white space and comments (both of which are ignored) for improved readability.  Until now, not all the white space characters that Unicode designates for this purpose were handled.  The additional ones now recognized are:

    U+0085 NEXT LINE

The use of these characters with "/x" outside bracketed character classes and when not preceded by a backslash has raised a deprecation warning since v5.18.  Now they will be ignored.

Comment lines within “(?[ ])” are now ended only by a “\n”

"(?[ ])"  is an experimental feature, introduced in v5.18.  It operates as if "/x" is always enabled.  But there was a difference: comment lines (following a "#" character) were terminated by anything matching "\R" which includes all vertical whitespace, such as form feeds.  For consistency, this is now changed to match what terminates comment lines outside "(?[ ])", namely a "\n" (even if escaped), which is the same as what terminates a heredoc string and formats.

“(?[...])” operators now follow standard Perl precedence

This experimental feature allows set operations in regular expression patterns. Prior to this, the intersection operator had the same precedence as the other binary operators.  Now it has higher precedence.  This could lead to different outcomes than existing code expects (though the documentation has always noted that this change might happen, recommending fully parenthesizing the expressions).  See "Extended Bracketed Character Classes" in perlrecharclass.

Omitting “%” and “@” on hash and array names is no longer permitted

Really old Perl let you omit the "@" on array names and the "%" on hash names in some spots.  This has issued a deprecation warning since Perl 5.000, and is no longer permitted.

“$!” text is now in English outside the scope of “use locale”

Previously, the text, unlike almost everything else, always came out based on the current underlying locale of the program.  (Also affected on some systems is "$^E".)  For programs that are unprepared to handle locale differences, this can cause garbage text to be displayed. It's better to display text that is translatable via some tool than garbage text which is much harder to figure out.

“$!” text will be returned in UTF-8 when appropriate

The stringification of $! and $^E will have the UTF-8 flag set when the text is actually non-ASCII UTF-8.  This will enable programs that are set up to be locale-aware to properly output messages in the user's native language.  Code that needs to continue the 5.20 and earlier behavior can do the stringification within the scopes of both "use bytes" and "use locale ":messages"".  Within these two scopes, no other Perl operations will be affected by locale; only $! and $^E stringification.  The "bytes" pragma causes the UTF-8 flag to not be set, just as in previous Perl releases.  This resolves [perl #112208] <>.

Support for “?PATTERN?” without explicit operator has been removed

The "m?PATTERN?" construct, which allows matching a regex only once, previously had an alternative form that was written directly with a question mark delimiter, omitting the explicit "m" operator.  This usage has produced a deprecation warning since 5.14.0.  It is now a syntax error, so that the question mark can be available for use in new operators.

“defined(@array)” and “defined(%hash)” are now fatal errors

These have been deprecated since v5.6.1 and have raised deprecation warnings since v5.16.

Using a hash or an array as a reference are now fatal errors

For example, "%foo->{"bar"}" now causes a fatal compilation error.  These have been deprecated since before v5.8, and have raised deprecation warnings since then.

Changes to the “*” prototype

The "*" character in a subroutine's prototype used to allow barewords to take precedence over most, but not all, subroutine names.  It was never consistent and exhibited buggy behavior.

Now it has been changed, so subroutines always take precedence over barewords, which brings it into conformity with similarly prototyped built-in functions:

    sub splat(*) { ... }
    sub foo { ... }
    splat(foo); # now always splat(foo())
    splat(bar); # still splat('bar') as before
    close(foo); # close(foo())
    close(bar); # close('bar')


Setting “${^ENCODING}” to anything but “undef”

This variable allows Perl scripts to be written in an encoding other than ASCII or UTF-8.  However, it affects all modules globally, leading to wrong answers and segmentation faults.  New scripts should be written in UTF-8; old scripts should be converted to UTF-8, which is easily done with the piconv utility.

Use of non-graphic characters in single-character variable names

The syntax for single-character variable names is more lenient than for longer variable names, allowing the one-character name to be a punctuation character or even invisible (a non-graphic).  Perl v5.20 deprecated the ASCII-range controls as such a name.  Now, all non-graphic characters that formerly were allowed are deprecated. The practical effect of this occurs only when not under "use utf8", and affects just the C1 controls (code points 0x80 through 0xFF), NO-BREAK SPACE, and SOFT HYPHEN.

Inlining of “sub () { $var }” with observable side-effects

In many cases Perl makes "sub () { $var }" into an inlinable constant subroutine, capturing the value of $var at the time the "sub" expression is evaluated.  This can break the closure behavior in those cases where $var is subsequently modified, since the subroutine won't return the changed value. (Note that this all only applies to anonymous subroutines with an empty prototype ("sub ()").)

This usage is now deprecated in those cases where the variable could be modified elsewhere.  Perl detects those cases and emits a deprecation warning.  Such code will likely change in the future and stop producing a constant.

If your variable is only modified in the place where it is declared, then Perl will continue to make the sub inlinable with no warnings.

    sub make_constant {
        my $var = shift;
        return sub () { $var }; # fine

    sub make_constant_deprecated {
        my $var;
        $var = shift;
        return sub () { $var }; # deprecated

    sub make_constant_deprecated2 {
        my $var = shift;
        log_that_value($var); # could modify $var
        return sub () { $var }; # deprecated

In the second example above, detecting that $var is assigned to only once is too hard to detect.  That it happens in a spot other than the "my" declaration is enough for Perl to find it suspicious.

This deprecation warning happens only for a simple variable for the body of the sub.  (A "BEGIN" block or "use" statement inside the sub is ignored, because it does not become part of the sub's body.)  For more complex cases, such as "sub () { do_something() if 0; $var }" the behavior has changed such that inlining does not happen if the variable is modifiable elsewhere.  Such cases should be rare.

Use of multiple “/x” regexp modifiers

It is now deprecated to say something like any of the following:

    use re qw(/amxx);

That is, now "x" should only occur once in any string of contiguous regular expression pattern modifiers.  We do not believe there are any occurrences of this in all of CPAN.  This is in preparation for a future Perl release having "/xx" permit white-space for readability in bracketed character classes (those enclosed in square brackets: "[...]").

Using a NO-BREAK space in a character alias for “\N{...}” is now deprecated

This non-graphic character is essentially indistinguishable from a regular space, and so should not be allowed.  See "CUSTOM ALIASES" in charnames.

A literal “{” should now be escaped in a pattern

If you want a literal left curly bracket (also called a left brace) in a regular expression pattern, you should now escape it by either preceding it with a backslash ("\{") or enclosing it within square brackets "[{]", or by using "\Q"; otherwise a deprecation warning will be raised.  This was first announced as forthcoming in the v5.16 release; it will allow future extensions to the language to happen.

Making all warnings fatal is discouraged

The documentation for fatal warnings notes that "use warnings FATAL => 'all'" is discouraged, and provides stronger language about the risks of fatal warnings in general.

Performance Enhancements

Modules and Pragmata

Updated Modules and Pragmata

Many of the libraries distributed with perl have been upgraded since v5.20.0. For a complete list of changes, run:

  corelist --diff 5.20.0 5.22.0

You can substitute your favorite version in place of 5.20.0, too.

Some notable changes include:

  • Archive::Tar has been upgraded to version 2.04.

    Tests can now be run in parallel.

  • attributes has been upgraded to version 0.27.

    The usage of "memEQs" in the XS has been corrected. [perl #122701] <>

    Avoid reading beyond the end of a buffer. [perl #122629]

  • B has been upgraded to version 1.58.

    It provides a new "B::safename" function, based on the existing "B::GV->SAFENAME", that converts "\cOPEN" to "^OPEN".

    Nulled COPs are now of class "B::COP", rather than "B::OP".

    "B::REGEXP" objects now provide a "qr_anoncv" method for accessing the implicit CV associated with "qr//" things containing code blocks, and a "compflags" method that returns the pertinent flags originating from the "qr//blahblah" op.

    "B::PMOP" now provides a "pmregexp" method returning a "B::REGEXP" object. Two new classes, "B::PADNAME" and "B::PADNAMELIST", have been introduced.

    A bug where, after an ithread creation or psuedofork, special/immortal SVs in the child ithread/psuedoprocess did not have the correct class of "B::SPECIAL", has been fixed. The "id" and "outid" PADLIST methods have been added.

  • B::Concise has been upgraded to version 0.996.

    Null ops that are part of the execution chain are now given sequence numbers.

    Private flags for nulled ops are now dumped with mnemonics as they would be for the non-nulled counterparts.

  • B::Deparse has been upgraded to version 1.35.

    It now deparses "+sub : attr { ... }" correctly at the start of a statement.  Without the initial "+", "sub" would be a statement label.

    "BEGIN" blocks are now emitted in the right place most of the time, but the change unfortunately introduced a regression, in that "BEGIN" blocks occurring just before the end of the enclosing block may appear below it instead.

    "B::Deparse" no longer puts erroneous "local" here and there, such as for "LIST = tr/a//d".  [perl #119815]

    Adjacent "use" statements are no longer accidentally nested if one contains a "do" block.  [perl #115066]

    Parenthesised arrays in lists passed to "\" are now correctly deparsed with parentheses (e.g., "\(@a, (@b), @c)" now retains the parentheses around @b), thus preserving the flattening behavior of referenced parenthesised arrays.  Formerly, it only worked for one array: "\(@a)".

    "local our" is now deparsed correctly, with the "our" included.

    "for($foo; !$bar; $baz) {...}" was deparsed without the "!" (or "not"). This has been fixed.

    Core keywords that conflict with lexical subroutines are now deparsed with the "CORE::" prefix.

    "foreach state $x (...) {...}" now deparses correctly with "state" and not "my".

    "our @array = split(...)" now deparses correctly with "our" in those cases where the assignment is optimized away.

    It now deparses "our(LIST)" and typed lexical ("my Dog $spot") correctly.

    Deparse $#_ as that instead of as $#{_}. [perl #123947] <>

    BEGIN blocks at the end of the enclosing scope are now deparsed in the right place.  [perl #77452]

    BEGIN blocks were sometimes deparsed as __ANON__, but are now always called BEGIN.

    Lexical subroutines are now fully deparsed.  [perl #116553]

    "Anything =~ y///r" with "/r" no longer omits the left-hand operand.

    The op trees that make up regexp code blocks are now deparsed for real. Formerly, the original string that made up the regular expression was used. That caused problems with "qr/(?{<<heredoc})/" and multiline code blocks, which were deparsed incorrectly.  [perl #123217] [perl #115256]

    $; at the end of a statement no longer loses its semicolon. [perl #123357]

    Some cases of subroutine declarations stored in the stash in shorthand form were being omitted.

    Non-ASCII characters are now consistently escaped in strings, instead of some of the time.  (There are still outstanding problems with regular expressions and identifiers that have not been fixed.)

    When prototype sub calls are deparsed with "&" (e.g., under the -P option), "scalar" is now added where appropriate, to force the scalar context implied by the prototype.

    "require(foo())", "do(foo())", "goto(foo())" and similar constructs with loop controls are now deparsed correctly.  The outer parentheses are not optional.

    Whitespace is no longer escaped in regular expressions, because it was getting erroneously escaped within "(?x:...)" sections.

    "sub foo { foo() }" is now deparsed with those mandatory parentheses.

    "/@array/" is now deparsed as a regular expression, and not just @array.

    "/@{-}/", "/@{+}/" and $#{1} are now deparsed with the braces, which are mandatory in these cases.

    In deparsing feature bundles, "B::Deparse" was emitting "no feature;" first instead of "no feature ':all';".  This has been fixed.

    "chdir FH" is now deparsed without quotation marks.

    "\my @a" is now deparsed without parentheses.  (Parenthese would flatten the array.)

    "system" and "exec" followed by a block are now deparsed correctly. Formerly there was an erroneous "do" before the block.

    "use constant QR => qr/.../flags" followed by """ =~ QR" is no longer without the flags.

    Deparsing "BEGIN { undef &foo }" with the -w switch enabled started to emit 'uninitialized' warnings in Perl 5.14.  This has been fixed.

    Deparsing calls to subs with a "(;+)" prototype resulted in an infinite loop.  The "(;$") "(_)" and "(;_)" prototypes were given the wrong precedence, causing "foo($a<$b)" to be deparsed without the parentheses.

    Deparse now provides a defined state sub in inner subs.

  • B::Op_private has been added.

    B::Op_private provides detailed information about the flags used in the "op_private" field of perl opcodes.

  • bigint, bignum, bigrat have been upgraded to version 0.39.

    Document in CAVEATS that using strings as numbers won't always invoke the big number overloading, and how to invoke it.  [ #123064]

  • Carp has been upgraded to version 1.36.

    "Carp::Heavy" now ignores version mismatches with Carp if Carp is newer than 1.12, since "Carp::Heavy"'s guts were merged into Carp at that point. [perl #121574] <>

    Carp now handles non-ASCII platforms better.

    Off-by-one error fix for Perl < 5.14.

  • constant has been upgraded to version 1.33.

    It now accepts fully-qualified constant names, allowing constants to be defined in packages other than the caller.

  • CPAN has been upgraded to version 2.11.

    Add support for "Cwd::getdcwd()" and introduce workaround for a misbehavior seen on Strawberry Perl 5.20.1.

    Fix "chdir()" after building dependencies bug.

    Introduce experimental support for plugins/hooks.

    Integrate the "App::Cpan" sources.

    Do not check recursion on optional dependencies.

    Sanity check META.yml to contain a hash. [cpan #95271] <>

  • CPAN::Meta::Requirements has been upgraded to version 2.132.

    Works around limitations in "version::vpp" detecting v-string magic and adds support for forthcoming ExtUtils::MakeMaker bootstrap for Perls older than 5.10.0.

  • Data::Dumper has been upgraded to version 2.158.

    Fixes CVE-2014-4330 by adding a configuration variable/option to limit recursion when dumping deep data structures.

    Changes to resolve Coverity issues. XS dumps incorrectly stored the name of code references stored in a GLOB. [perl #122070] <>

  • DynaLoader has been upgraded to version 1.32.

    Remove "dl_nonlazy" global if unused in Dynaloader. [perl #122926]

  • Encode has been upgraded to version 2.72.

    "piconv" now has better error handling when the encoding name is nonexistent, and a build breakage when upgrading Encode in perl-5.8.2 and earlier has been fixed.

    Building in C++ mode on Windows now works.

  • Errno has been upgraded to version 1.23.

    Add "-P" to the preprocessor command-line on GCC 5.  GCC added extra line directives, breaking parsing of error code definitions.  [ #123784]

  • experimental has been upgraded to version 0.013.

    Hardcodes features for Perls older than 5.15.7.

  • ExtUtils::CBuilder has been upgraded to version 0.280221.

    Fixes a regression on Android. [perl #122675] <>

  • ExtUtils::Manifest has been upgraded to version 1.70.

    Fixes a bug with "maniread()"'s handling of quoted filenames and improves "manifind()" to follow symlinks. [perl #122415] <>

  • ExtUtils::ParseXS has been upgraded to version 3.28.

    Only declare "file" unused if we actually define it. Improve generated "RETVAL" code generation to avoid repeated references to ST(0).  [perl #123278] Broaden and document the "/OBJ$/" to "/REF$/" typemap optimization for the "DESTROY" method.  [perl #123418]

  • Fcntl has been upgraded to version 1.13.

    Add support for the Linux pipe buffer size "fcntl()" commands.

  • File::Find has been upgraded to version 1.29.

    "find()" and "finddepth()" will now warn if passed inappropriate or misspelled options.

  • File::Glob has been upgraded to version 1.24.

    Avoid "SvIV()" expanding to call "get_sv()" three times in a few places. [perl #123606]

  • HTTP::Tiny has been upgraded to version 0.054.

    "keep_alive" is now fork-safe and thread-safe.

  • IO has been upgraded to version 1.35.

    The XS implementation has been fixed for the sake of older Perls.

  • IO::Socket has been upgraded to version 1.38.

    Document the limitations of the "connected()" method.  [perl #123096]

  • IO::Socket::IP has been upgraded to version 0.37.

    A better fix for subclassing "connect()". [cpan #95983] <> [cpan #97050] <>

    Implements Timeout for "connect()". [cpan #92075] <>

  • The libnet collection of modules has been upgraded to version 3.05.

    Support for IPv6 and SSL to "Net::FTP", "Net::NNTP", "Net::POP3" and "Net::SMTP". Improvements in "Net::SMTP" authentication.

  • Locale::Codes has been upgraded to version 3.34.

    Fixed a bug in the scripts used to extract data from spreadsheets that prevented the SHP currency code from being found. [cpan #94229] <>

    New codes have been added.

  • Math::BigInt has been upgraded to version 1.9997.

    Synchronize POD changes from the CPAN release. "Math::BigFloat->blog(x)" would sometimes return "blog(2*x)" when the accuracy was greater than 70 digits. The result of "Math::BigFloat->bdiv()" in list context now satisfies "x = quotient * divisor + remainder".

    Correct handling of subclasses. [cpan #96254] <> [cpan #96329] <>

  • Module::Metadata has been upgraded to version 1.000026.

    Support installations on older perls with an ExtUtils::MakeMaker earlier than 6.63_03

  • overload has been upgraded to version 1.26.

    A redundant "ref $sub" check has been removed.

  • The PathTools module collection has been upgraded to version 3.56.

    A warning from the gcc compiler is now avoided when building the XS.

    Don't turn leading "//" into "/" on Cygwin. [perl #122635]

  • has been upgraded to version 1.49.

    The debugger would cause an assertion failure. [perl #124127] <>

    "fork()" in the debugger under "tmux" will now create a new window for the forked process. [perl #121333] <>

    The debugger now saves the current working directory on startup and restores it when you restart your program with "R" or "rerun". [perl #121509] <>

  • PerlIO::scalar has been upgraded to version 0.22.

    Reading from a position well past the end of the scalar now correctly returns end of file.  [perl #123443]

    Seeking to a negative position still fails, but no longer leaves the file position set to a negation location.

    "eof()" on a "PerlIO::scalar" handle now properly returns true when the file position is past the 2GB mark on 32-bit systems.

    Attempting to write at file positions impossible for the platform now fail early rather than wrapping at 4GB.

  • Pod::Perldoc has been upgraded to version 3.25.

    Filehandles opened for reading or writing now have ":encoding(UTF-8)" set. [cpan #98019] <>

  • POSIX has been upgraded to version 1.53.

    The C99 math functions and constants (for example "acosh", "isinf", "isnan", "round", "trunc"; "M_E", "M_SQRT2", "M_PI") have been added.

    "POSIX::tmpnam()" now produces a deprecation warning.  [perl #122005]

  • Safe has been upgraded to version 2.39.

    "reval" was not propagating void context properly.

  • Scalar-List-Utils has been upgraded to version 1.41.

    A new module, Sub::Util, has been added, containing functions related to CODE refs, including "subname" (inspired by "Sub::Identity") and "set_subname" (copied and renamed from "Sub::Name"). The use of "GetMagic" in "List::Util::reduce()" has also been fixed. [cpan #63211] <>

  • SDBM_File has been upgraded to version 1.13.

    Simplified the build process.  [perl #123413]

  • Time::Piece has been upgraded to version 1.29.

    When pretty printing negative "Time::Seconds", the "minus" is no longer lost.

  • Unicode::Collate has been upgraded to version 1.12.

    Version 0.67's improved discontiguous contractions is invalidated by default and is supported as a parameter "long_contraction".

  • Unicode::Normalize has been upgraded to version 1.18.

    The XSUB implementation has been removed in favor of pure Perl.

  • Unicode::UCD has been upgraded to version 0.61.

    A new function property_values() has been added to return a given property's possible values.

    A new function charprop() has been added to return the value of a given property for a given code point.

    A new function charprops_all() has been added to return the values of all Unicode properties for a given code point.

    A bug has been fixed so that propaliases() returns the correct short and long names for the Perl extensions where it was incorrect.

    A bug has been fixed so that prop_value_aliases() returns "undef" instead of a wrong result for properties that are Perl extensions.

    This module now works on EBCDIC platforms.

  • utf8 has been upgraded to version 1.17

    A mismatch between the documentation and the code in "utf8::downgrade()" was fixed in favor of the documentation. The optional second argument is now correctly treated as a perl boolean (true/false semantics) and not as an integer.

  • version has been upgraded to version 0.9909.

    Numerous changes.  See the Changes file in the CPAN distribution for details.

  • Win32 has been upgraded to version 0.51.

    "GetOSName()" now supports Windows 8.1, and building in C++ mode now works.

  • Win32API::File has been upgraded to version 0.1202

    Building in C++ mode now works.

  • XSLoader has been upgraded to version 0.20.

    Allow XSLoader to load modules from a different namespace. [perl #122455]

Removed Modules and Pragmata

The following modules (and associated modules) have been removed from the core perl distribution:

  • CGI
  • Module::Build


New Documentation


This document, by Tom Christiansen, provides examples of handling Unicode in Perl.

Changes to Existing Documentation


  • A note on long doubles has been added.


  • Note that "SvSetSV" doesn't do set magic.
  • "sv_usepvn_flags" - fix documentation to mention the use of "Newx" instead of "malloc".

    [perl #121869] <>

  • Clarify where "NUL" may be embedded or is required to terminate a string.
  • Some documentation that was previously missing due to formatting errors is now included.
  • Entries are now organized into groups rather than by the file where they are found.
  • Alphabetical sorting of entries is now done consistently (automatically by the POD generator) to make entries easier to find when scanning.


  • The syntax of single-character variable names has been brought up-to-date and more fully explained.
  • Hexadecimal floating point numbers are described, as are infinity and NaN.


  • This document has been significantly updated in the light of recent improvements to EBCDIC support.


  • Added a LIMITATIONS section.


  • Mention that "study()" is currently a no-op.
  • Calling "delete" or "exists" on array values is now described as "strongly discouraged" rather than "deprecated".
  • Improve documentation of "our".
  • "-l" now notes that it will return false if symlinks aren't supported by the file system. [perl #121523] <>
  • Note that "exec LIST" and "system LIST" may fall back to the shell on Win32. Only the indirect-object syntax "exec PROGRAM LIST" and "system PROGRAM LIST" will reliably avoid using the shell.

    This has also been noted in perlport.

    [perl #122046] <>


  • The OOK example has been updated to account for COW changes and a change in the storage of the offset.
  • Details on C level symbols and libperl.t added.
  • Information on Unicode handling has been added
  • Information on EBCDIC handling has been added


  • A note has been added about running on platforms with non-ASCII character sets
  • A note has been added about performance testing


  • Documentation has been added illustrating the perils of assuming that there is no change to the contents of static memory pointed to by the return values of Perl's wrappers for C library functions.
  • Replacements for "tmpfile", "atoi", "strtol", and "strtoul" are now recommended.
  • Updated documentation for the "test.valgrind" "make" target. [perl #121431] <>
  • Information is given about writing test files portably to non-ASCII platforms.
  • A note has been added about how to get a C language stack backtrace.


  • Note that the message "Redeclaration of "sendpath" with a different storage class specifier" is harmless.


  • Updated for the enhancements in v5.22, along with some clarifications.


  • Instead of pointing to the module list, we are now pointing to PrePAN <>.


  • Updated for the enhancements in v5.22, along with some clarifications.


  • The specification of the pod language is changing so that the default encoding of pods that aren't in UTF-8 (unless otherwise indicated) is CP1252 instead of ISO 8859-1 (Latin1).


  • We now have a code of conduct for the p5p mailing list, as documented in "STANDARDS OF CONDUCT" in perlpolicy.
  • The conditions for marking an experimental feature as non-experimental are now set out.
  • Clarification has been made as to what sorts of changes are permissible in maintenance releases.


  • Out-of-date VMS-specific information has been fixed and/or simplified.
  • Notes about EBCDIC have been added.


  • The description of the "/x" modifier has been clarified to note that comments cannot be continued onto the next line by escaping them; and there is now a list of all the characters that are considered whitespace by this modifier.
  • The new "/n" modifier is described.
  • A note has been added on how to make bracketed character class ranges portable to non-ASCII machines.


  • Added documentation of "\b{sb}", "\b{wb}", "\b{gcb}", and "\b{g}".


  • Clarifications have been added to "Character Ranges" in perlrecharclass to the effect "[A-Z]", "[a-z]", "[0-9]" and any subranges thereof in regular expression bracketed character classes are guaranteed to match exactly what a naive English speaker would expect them to match, even on platforms (such as EBCDIC) where perl has to do extra work to accomplish this.
  • The documentation of Bracketed Character Classes has been expanded to cover the improvements in "qr/[\N{named sequence}]/" (see under "Selected Bug Fixes").


  • A new section has been added Assigning to References


  • Comments added on algorithmic complexity and tied hashes.



  • This has had extensive revisions to bring it up-to-date with current Unicode support and to make it more readable.  Notable is that Unicode 7.0 changed what it should do with non-characters.  Perl retains the old way of handling for reasons of backward compatibility.  See "Noncharacter code points" in perlunicode.


  • Advice for how to make sure your strings and regular expression patterns are interpreted as Unicode has been updated.


  • $] is no longer listed as being deprecated.  Instead, discussion has been added on the advantages and disadvantages of using it versus $^V.  $OLD_PERL_VERSION was re-added to the documentation as the long form of $].
  • "${^ENCODING}" is now marked as deprecated.
  • The entry for "%^H" has been clarified to indicate it can only handle simple values.


  • Out-of-date and/or incorrect material has been removed.
  • Updated documentation on environment and shell interaction in VMS.


  • Added a discussion of locale issues in XS code.


The following additions or changes have been made to diagnostic output, including warnings and fatal error messages.  For the complete list of diagnostic messages, see perldiag.

New Diagnostics

New Errors

  • Bad symbol for scalar

    (P) An internal request asked to add a scalar entry to something that wasn't a symbol table entry.

  • Can't use a hash as a reference

    (F) You tried to use a hash as a reference, as in "%foo->{"bar"}" or "%$ref->{"hello"}".  Versions of perl <= 5.6.1 used to allow this syntax, but shouldn't have.

  • Can't use an array as a reference

    (F) You tried to use an array as a reference, as in "@foo->[23]" or "@$ref->[99]".  Versions of perl <= 5.6.1 used to allow this syntax, but shouldn't have.

  • Can't use 'defined(@array)' (Maybe you should just omit the defined()?)

    (F) "defined()" is not useful on arrays because it checks for an undefined scalar value.  If you want to see if the array is empty, just use "if (@array) { # not empty }" for example.

  • Can't use 'defined(%hash)' (Maybe you should just omit the defined()?)

    (F) "defined()" is not usually right on hashes.

    Although "defined %hash" is false on a plain not-yet-used hash, it becomes true in several non-obvious circumstances, including iterators, weak references, stash names, even remaining true after "undef %hash". These things make "defined %hash" fairly useless in practice, so it now generates a fatal error.

    If a check for non-empty is what you wanted then just put it in boolean context (see "Scalar values" in perldata):

        if (%hash) {
           # not empty

    If you had "defined %Foo::Bar::QUUX" to check whether such a package variable exists then that's never really been reliable, and isn't a good way to enquire about the features of a package, or whether it's loaded, etc.

  • Cannot chr %f

    (F) You passed an invalid number (like an infinity or not-a-number) to "chr".

  • Cannot compress %f in pack

    (F) You tried converting an infinity or not-a-number to an unsigned character, which makes no sense.

  • Cannot pack %f with '%c'

    (F) You tried converting an infinity or not-a-number to a character, which makes no sense.

  • Cannot print %f with '%c'

    (F) You tried printing an infinity or not-a-number as a character (%c), which makes no sense.  Maybe you meant '%s', or just stringifying it?

  • charnames alias definitions may not contain a sequence of multiple spaces

    (F) You defined a character name which had multiple space characters in a row.  Change them to single spaces.  Usually these names are defined in the ":alias" import argument to "use charnames", but they could be defined by a translator installed into $^H{charnames}. See "CUSTOM ALIASES" in charnames.

  • charnames alias definitions may not contain trailing white-space

    (F) You defined a character name which ended in a space character.  Remove the trailing space(s).  Usually these names are defined in the ":alias" import argument to "use charnames", but they could be defined by a translator installed into $^H{charnames}. See "CUSTOM ALIASES" in charnames.

  • :const is not permitted on named subroutines

    (F) The "const" attribute causes an anonymous subroutine to be run and its value captured at the time that it is cloned.  Named subroutines are not cloned like this, so the attribute does not make sense on them.

  • Hexadecimal float: internal error

    (F) Something went horribly bad in hexadecimal float handling.

  • Hexadecimal float: unsupported long double format

    (F) You have configured Perl to use long doubles but the internals of the long double format are unknown, therefore the hexadecimal float output is impossible.

  • Illegal suidscript

    (F) The script run under suidperl was somehow illegal.

  • In '(?...)', the '(' and '?' must be adjacent in regex; marked by <-- HERE in m/%s/

    (F) The two-character sequence "(?" in this context in a regular expression pattern should be an indivisible token, with nothing intervening between the "(" and the "?", but you separated them.

  • In '(*VERB...)', the '(' and '*' must be adjacent in regex; marked by <-- HERE in m/%s/

    (F) The two-character sequence "(*" in this context in a regular expression pattern should be an indivisible token, with nothing intervening between the "(" and the "*", but you separated them.

  • Invalid quantifier in {,} in regex; marked by <-- HERE in m/%s/

    (F) The pattern looks like a {min,max} quantifier, but the min or max could not be parsed as a valid number: either it has leading zeroes, or it represents too big a number to cope with.  The <-- HERE shows where in the regular expression the problem was discovered.  See perlre.

  • '%s' is an unknown bound type in regex

    (F) You used "\b{...}" or "\B{...}" and the "..." is not known to Perl.  The current valid ones are given in "\b{}, \b, \B{}, \B" in perlrebackslash.

  • Missing or undefined argument to require

    (F) You tried to call "require" with no argument or with an undefined value as an argument.  "require" expects either a package name or a file-specification as an argument.  See "require" in perlfunc.

    Formerly, "require" with no argument or "undef" warned about a Null filename.

New Warnings

  • \C is deprecated in regex

    (D deprecated) The "/\C/" character class was deprecated in v5.20, and now emits a warning. It is intended that it will become an error in v5.24. This character class matches a single byte even if it appears within a multi-byte character, breaks encapsulation, and can corrupt UTF-8 strings.

  • "%s" is more clearly written simply as "%s" in regex; marked by <-- HERE in m/%s/

    (W regexp) (only under "use re 'strict'" or within "(?[...])")

    You specified a character that has the given plainer way of writing it, and which is also portable to platforms running with different character sets.

  • Argument "%s" treated as 0 in increment (++)

    (W numeric) The indicated string was fed as an argument to the "++" operator which expects either a number or a string matching "/^[a-zA-Z]*[0-9]*\z/". See "Auto-increment and Auto-decrement" in perlop for details.

  • Both or neither range ends should be Unicode in regex; marked by <-- HERE in m/%s/

    (W regexp) (only under "use re 'strict'" or within "(?[...])")

    In a bracketed character class in a regular expression pattern, you had a range which has exactly one end of it specified using "\N{}", and the other end is specified using a non-portable mechanism.  Perl treats the range as a Unicode range, that is, all the characters in it are considered to be the Unicode characters, and which may be different code points on some platforms Perl runs on.  For example, "[\N{U+06}-\x08]" is treated as if you had instead said "[\N{U+06}-\N{U+08}]", that is it matches the characters whose code points in Unicode are 6, 7, and 8. But that "\x08" might indicate that you meant something different, so the warning gets raised.

  • Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".

    (W locale) You are 1) running under ""use locale""; 2) the current locale is not a UTF-8 one; 3) you tried to do the designated case-change operation on the specified Unicode character; and 4) the result of this operation would mix Unicode and locale rules, which likely conflict.

    The warnings category "locale" is new.

  • :const is experimental

    (S experimental::const_attr) The "const" attribute is experimental. If you want to use the feature, disable the warning with "no warnings 'experimental::const_attr'", but know that in doing so you are taking the risk that your code may break in a future Perl version.

  • gmtime(%f) failed

    (W overflow) You called "gmtime" with a number that it could not handle: too large, too small, or NaN.  The returned value is "undef".

  • Hexadecimal float: exponent overflow

    (W overflow) The hexadecimal floating point has larger exponent than the floating point supports.

  • Hexadecimal float: exponent underflow

    (W overflow) The hexadecimal floating point has smaller exponent than the floating point supports.

  • Hexadecimal float: mantissa overflow

    (W overflow) The hexadecimal floating point literal had more bits in the mantissa (the part between the "0x" and the exponent, also known as the fraction or the significand) than the floating point supports.

  • Hexadecimal float: precision loss

    (W overflow) The hexadecimal floating point had internally more digits than could be output.  This can be caused by unsupported long double formats, or by 64-bit integers not being available (needed to retrieve the digits under some configurations).

  • Locale '%s' may not work well.%s

    (W locale) You are using the named locale, which is a non-UTF-8 one, and which perl has determined is not fully compatible with what it can handle.  The second %s gives a reason.

    The warnings category "locale" is new.

  • localtime(%f) failed

    (W overflow) You called "localtime" with a number that it could not handle: too large, too small, or NaN.  The returned value is "undef".

  • Negative repeat count does nothing

    (W numeric) You tried to execute the "x" repetition operator fewer than 0 times, which doesn't make sense.

  • NO-BREAK SPACE in a charnames alias definition is deprecated

    (D deprecated) You defined a character name which contained a no-break space character.  Change it to a regular space.  Usually these names are defined in the ":alias" import argument to "use charnames", but they could be defined by a translator installed into $^H{charnames}.  See "CUSTOM ALIASES" in charnames.

  • Non-finite repeat count does nothing

    (W numeric) You tried to execute the "x" repetition operator "Inf" (or "-Inf") or NaN times, which doesn't make sense.

  • PerlIO layer ':win32' is experimental

    (S experimental::win32_perlio) The ":win32" PerlIO layer is experimental.  If you want to take the risk of using this layer, simply disable this warning:

        no warnings "experimental::win32_perlio";
  • Ranges of ASCII printables should be some subset of "0-9", "A-Z", or "a-z" in regex; marked by <-- HERE in m/%s/

    (W regexp) (only under "use re 'strict'" or within "(?[...])")

    Stricter rules help to find typos and other errors.  Perhaps you didn't even intend a range here, if the "-" was meant to be some other character, or should have been escaped (like "\-").  If you did intend a range, the one that was used is not portable between ASCII and EBCDIC platforms, and doesn't have an obvious meaning to a casual reader.

     [3-7]    # OK; Obvious and portable
     [d-g]    # OK; Obvious and portable
     [A-Y]    # OK; Obvious and portable
     [A-z]    # WRONG; Not portable; not clear what is meant
     [a-Z]    # WRONG; Not portable; not clear what is meant
     [%-.]    # WRONG; Not portable; not clear what is meant
     [\x41-Z] # WRONG; Not portable; not obvious to non-geek

    (You can force portability by specifying a Unicode range, which means that the endpoints are specified by "\N{...}", but the meaning may still not be obvious.) The stricter rules require that ranges that start or stop with an ASCII character that is not a control have all their endpoints be a literal character, and not some escape sequence (like "\x41"), and the ranges must be all digits, or all uppercase letters, or all lowercase letters.

  • Ranges of digits should be from the same group in regex; marked by <-- HERE in m/%s/

    (W regexp) (only under "use re 'strict'" or within "(?[...])")

    Stricter rules help to find typos and other errors.  You included a range, and at least one of the end points is a decimal digit.  Under the stricter rules, when this happens, both end points should be digits in the same group of 10 consecutive digits.

  • Redundant argument in %s

    (W redundant) You called a function with more arguments than were needed, as indicated by information within other arguments you supplied (e.g. a printf format). Currently only emitted when a printf-type format required fewer arguments than were supplied, but might be used in the future for e.g. "pack" in perlfunc.

    The warnings category "redundant" is new. See also [perl #121025] <>.

  • Replacement list is longer than search list

    This is not a new diagnostic, but in earlier releases was accidentally not displayed if the transliteration contained wide characters.  This is now fixed, so that you may see this diagnostic in places where you previously didn't (but should have).

  • Use of \b{} for non-UTF-8 locale is wrong.  Assuming a UTF-8 locale

    (W locale) You are matching a regular expression using locale rules, and a Unicode boundary is being matched, but the locale is not a Unicode one.  This doesn't make sense.  Perl will continue, assuming a Unicode (UTF-8) locale, but the results could well be wrong except if the locale happens to be ISO-8859-1 (Latin1) where this message is spurious and can be ignored.

    The warnings category "locale" is new.

  • Using /u for '%s' instead of /%s in regex; marked by <-- HERE in m/%s/

    (W regexp) You used a Unicode boundary ("\b{...}" or "\B{...}") in a portion of a regular expression where the character set modifiers "/a" or "/aa" are in effect.  These two modifiers indicate an ASCII interpretation, and this doesn't make sense for a Unicode definition. The generated regular expression will compile so that the boundary uses all of Unicode.  No other portion of the regular expression is affected.

  • The bitwise feature is experimental

    (S experimental::bitwise) This warning is emitted if you use bitwise operators ("& | ^ ~ &. |. ^. ~.") with the "bitwise" feature enabled. Simply suppress the warning if you want to use the feature, but know that in doing so you are taking the risk of using an experimental feature which may change or be removed in a future Perl version:

        no warnings "experimental::bitwise";
        use feature "bitwise";
        $x |.= $y;
  • Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/%s/

    (D deprecated, regexp) You used a literal "{" character in a regular expression pattern. You should change to use "\{" instead, because a future version of Perl (tentatively v5.26) will consider this to be a syntax error.  If the pattern delimiters are also braces, any matching right brace ("}") should also be escaped to avoid confusing the parser, for example,

  • Use of literal non-graphic characters in variable names is deprecated

    (D deprecated) Using literal non-graphic (including control) characters in the source to refer to the ^FOO variables, like $^X and "${^GLOBAL_PHASE}" is now deprecated.

  • Useless use of attribute "const"

    (W misc) The "const" attribute has no effect except on anonymous closure prototypes.  You applied it to a subroutine via  This is only useful inside an attribute handler for an anonymous subroutine.

  • Useless use of /d modifier in transliteration operator

    This is not a new diagnostic, but in earlier releases was accidentally not displayed if the transliteration contained wide characters.  This is now fixed, so that you may see this diagnostic in places where you previously didn't (but should have).

  • "use re 'strict'" is experimental

    (S experimental::re_strict) The things that are different when a regular expression pattern is compiled under 'strict' are subject to change in future Perl releases in incompatible ways; there are also proposals to change how to enable strict checking instead of using this subpragma. This means that a pattern that compiles today may not in a future Perl release.  This warning is to alert you to that risk.

  • Warning: unable to close filehandle properly: %s

    Warning: unable to close filehandle %s properly: %s

    (S io) Previously, perl silently ignored any errors when doing an implicit close of a filehandle, i.e. where the reference count of the filehandle reached zero and the user's code hadn't already called "close()"; e.g.

            open my $fh, '>', $file  or die "open: '$file': $!\n";
            print $fh, $data  or die;
        } # implicit close here

    In a situation such as disk full, due to buffering, the error may only be detected during the final close, so not checking the result of the close is dangerous.

    So perl now warns in such situations.

  • Wide character (U+%X) in %s

    (W locale) While in a single-byte locale (i.e., a non-UTF-8 one), a multi-byte character was encountered.   Perl considers this character to be the specified Unicode code point.  Combining non-UTF-8 locales and Unicode is dangerous.  Almost certainly some characters will have two different representations.  For example, in the ISO 8859-7 (Greek) locale, the code point 0xC3 represents a Capital Gamma.  But so also does 0x393.  This will make string comparisons unreliable.

    You likely need to figure out how this multi-byte character got mixed up with your single-byte locale (or perhaps you thought you had a UTF-8 locale, but Perl disagrees).

    The warnings category "locale" is new.

Changes to Existing Diagnostics

  • <> should be quotes

    This warning has been changed to <> at require-statement should be quotes to make the issue more identifiable.

  • Argument "%s" isn't numeric%s

    The perldiag entry for this warning has added this clarifying note:

     Note that for the Inf and NaN (infinity and not-a-number) the
     definition of "numeric" is somewhat unusual: the strings themselves
     (like "Inf") are considered numeric, and anything following them is
     considered non-numeric.
  • Global symbol "%s" requires explicit package name

    This message has had '(did you forget to declare "my %s"?)' appended to it, to make it more helpful to new Perl programmers. [perl #121638] <>

  • '"my" variable &foo::bar can't be in a package' has been reworded to say 'subroutine' instead of 'variable'.
  • \N{} in character class restricted to one character in regex; marked by <-- HERE in m/%s/

    This message has had character class changed to inverted character class or as a range end-point is to reflect improvements in "qr/[\N{named sequence}]/" (see under "Selected Bug Fixes").

  • panic: frexp

    This message has had ': %f' appended to it, to show what the offending floating point number is.

  • Possible precedence problem on bitwise %c operator reworded as Possible precedence problem on bitwise %s operator.
  • Unsuccessful %s on filename containing newline

    This warning is now only produced when the newline is at the end of the filename.

  • "Variable %s will not stay shared" has been changed to say "Subroutine" when it is actually a lexical sub that will not stay shared.
  • Variable length lookbehind not implemented in regex m/%s/

    The perldiag entry for this warning has had information about Unicode behavior added.

Diagnostic Removals

Utility Changes

find2perl, s2p and a2p removal

  • The x2p/ directory has been removed from the Perl core.

    This removes find2perl, s2p and a2p. They have all been released to CPAN as separate distributions ("App::find2perl", "App::s2p", "App::a2p").



  • No longer depends on non-core modules.

Configuration and Compilation


Platform Support

Regained Platforms

IRIX and Tru64 platforms are working again.

Some "make test" failures remain: [perl #123977] <> and [perl #125298] <> for IRIX; [perl #124212] <>, [cpan #99605] <>, and [cpan #104836] <> for Tru64.

z/OS running EBCDIC Code Page 1047

Core perl now works on this EBCDIC platform.  Earlier perls also worked, but, even though support wasn't officially withdrawn, recent perls would not compile and run well.  Perl 5.20 would work, but had many bugs which have now been fixed.  Many CPAN modules that ship with Perl still fail tests, including "Pod::Simple".  However the version of "Pod::Simple" currently on CPAN should work; it was fixed too late to include in Perl 5.22.  Work is under way to fix many of the still-broken CPAN modules, which likely will be installed on CPAN when completed, so that you may not have to wait until Perl 5.24 to get a working version.

Discontinued Platforms


NeXTSTEP was a proprietary operating system bundled with NeXT's workstations in the early to mid 90s; OPENSTEP was an API specification that provided a NeXTSTEP-like environment on a non-NeXTSTEP system.  Both are now long dead, so support for building Perl on them has been removed.

Platform-Specific Notes


Special handling is required of the perl interpreter on EBCDIC platforms to get "qr/[i-j]/" to match only "i" and "j", since there are 7 characters between the code points for "i" and "j".  This special handling had only been invoked when both ends of the range are literals.  Now it is also invoked if any of the "\N{...}" forms for specifying a character by name or Unicode code point is used instead of a literal.  See "Character Ranges" in perlrecharclass.


The archname now distinguishes use64bitint from use64bitall.


Build support has been improved for cross-compiling in general and for Android in particular.

  • When spawning a subprocess without waiting, the return value is now the correct PID.
  • Fix a prototype so linking doesn't fail under the VMS C++ compiler.
  • "finite", "finitel", and "isfinite" detection has been added to "", environment handling has had some minor changes, and a fix for legacy feature checking status.
  • miniperl.exe is now built with "-fno-strict-aliasing", allowing 64-bit builds to complete on GCC 4.8. [perl #123976] <>
  • "nmake minitest" now works on Win32.  Due to dependency issues you need to build "nmake test-prep" first, and a small number of the tests fail. [perl #123394] <>
  • Perl can now be built in C++ mode on Windows by setting the makefile macro "USE_CPLUSPLUS" to the value "define".
  • The list form of piped open has been implemented for Win32.  Note: unlike "system LIST" this does not fall back to the shell. [perl #121159] <>
  • New "DebugSymbols" and "DebugFull" configuration options added to Windows makefiles.
  • Previously, compiling XS modules (including CPAN ones) using Visual C++ for Win64 resulted in around a dozen warnings per file from hv_func.h.  These warnings have been silenced.
  • Support for building without PerlIO has been removed from the Windows makefiles.  Non-PerlIO builds were all but deprecated in Perl 5.18.0 and are already not supported by Configure on POSIX systems.
  • Between 2 and 6 milliseconds and seven I/O calls have been saved per attempt to open a perl module for each path in @INC.
  • Intel C builds are now always built with C99 mode on.
  • %I64d is now being used instead of %lld for MinGW.
  • In the experimental ":win32" layer, a crash in "open" was fixed. Also opening /dev/null (which works under Win32 Perl's default ":unix" layer) was implemented for ":win32". [perl #122224] <>
  • A new makefile option, "USE_LONG_DOUBLE", has been added to the Windows dmake makefile for gcc builds only.  Set this to "define" if you want perl to use long doubles to give more accuracy and range for floating point numbers.

On OpenBSD, Perl will now default to using the system "malloc" due to the security features it provides. Perl's own malloc wrapper has been in use since v5.14 due to performance reasons, but the OpenBSD project believes the tradeoff is worth it and would prefer that users who need the speed specifically ask for it.

[perl #122000] <>.

  • We now look for the Sun Studio compiler in both /opt/solstudio* and /opt/solarisstudio*.
  • Builds on Solaris 10 with "-Dusedtrace" would fail early since make didn't follow implied dependencies to build "perldtrace.h".  Added an explicit dependency to "depend". [perl #120120] <>
  • C99 options have been cleaned up; hints look for "solstudio" as well as "SUNWspro"; and support for native "setenv" has been added.

Internal Changes

Selected Bug Fixes

Known Problems


Brian McCauley died on May 8, 2015.  He was a frequent poster to Usenet, Perl Monks, and other Perl forums, and made several CPAN contributions under the nick NOBULL, including to the Perl FAQ.  He attended almost every YAPC::Europe, and indeed, helped organise YAPC::Europe 2006 and the QA Hackathon 2009.  His wit and his delight in intricate systems were particularly apparent in his love of board games; many Perl mongers will have fond memories of playing Fluxx and other games with Brian.  He will be missed.


Perl 5.22.0 represents approximately 12 months of development since Perl 5.20.0 and contains approximately 590,000 lines of changes across 2,400 files from 94 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 370,000 lines of changes to 1,500 .pm, .t, .c and .h files.

Perl continues to flourish into its third decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.22.0:

Aaron Crane, Abhijit Menon-Sen, Abigail, Alberto Simo~es, Alex Solovey, Alex Vandiver, Alexandr Ciornii, Alexandre (Midnite) Jousset, Andreas Koenig, Andreas Voegele, Andrew Fresh, Andy Dougherty, Anthony Heading, Aristotle Pagaltzis, brian d foy, Brian Fraser, Chad Granum, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsaaker, Daniel Dragan, Darin McBride, Dave Rolsky, David Golden, David Mitchell, David Wheeler, Dmitri Tikhonov, Doug Bell, E. Choroba, Ed J, Eric Herman, Father Chrysostomos, George Greer, Glenn D. Golden, Graham Knop, H.Merijn Brand, Herbert Breunung, Hugo van der Sanden, James E Keenan, James McCoy, James Raspass, Jan Dubois, Jarkko Hietaniemi, Jasmine Ngan, Jerry D. Hedden, Jim Cromie, John Goodyear, kafka, Karen Etheridge, Karl Williamson, Kent Fredric, kmx, Lajos Veres, Leon Timmermans, Lukas Mai, Mathieu Arnold, Matthew Horsfall, Max Maischein, Michael Bunk, Nicholas Clark, Niels Thykier, Niko Tyni, Norman Koch, Olivier Mengue, Peter John Acklam, Peter Martini, Petr PisaX, Philippe Bruhat (BooK), Pierre Bogossian, Rafael Garcia-Suarez, Randy Stauner, Reini Urban, Ricardo Signes, Rob Hoelz, Rostislav Skudnov, Sawyer X, Shirakata Kentaro, Shlomi Fish, Sisyphus, Slaven Rezic, Smylers, Steffen Mueller, Steve Hay, Sullivan Beck, syber, Tadeusz SoXnierz, Thomas Sibley, Todd Rinaldo, Tony Cook, Vincent Pit, Vladimir Marek, Yaroslav Kuzmin, Yves Orton, AEvar Arnfjoerð Bjarmason.

The list above is almost certainly incomplete as it is automatically generated from version control history. In particular, it does not include the names of the (very much appreciated) contributors who reported issues to the Perl bug tracker.

Many of the changes included in this version originated in the CPAN modules included in Perl's core. We're grateful to the entire CPAN community for helping Perl to flourish.

For a more complete list of all of Perl's historical contributors, please see the AUTHORS file in the Perl source distribution.

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 and the perl bug database at <>.  There may also be information at <>, 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 to be analysed by the Perl porting team.

If the bug you are reporting has security implications, which make it inappropriate to send to a publicly archived mailing list, then please send it to  This points to a closed subscription unarchived mailing list, which includes all the core committers, who will be able to help assess the impact of issues, figure out a resolution, and help co-ordinate the release of patches to mitigate or fix the problem across all platforms on which Perl is supported.  Please only use this address for security issues in the Perl core, not for modules independently distributed on CPAN.

See Also

The Changes file for an explanation of how to view 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.


2016-07-14 perl v5.24.1 Perl Programmers Reference Guide