=encoding utf8 =head1 NAME perl5240delta - what is new for perl v5.24.0 =head1 DESCRIPTION This document describes the differences between the 5.22.0 release and the 5.24.0 release. =head1 Core Enhancements =head2 Postfix dereferencing is no longer experimental Using the C and C features no longer emits a warning. Existing code that disables the C warning category that they previously used will continue to work. The C feature has no effect; all Perl code can use postfix dereferencing, regardless of what feature declarations are in scope. The C<5.24> feature bundle now includes the C feature. =head2 Unicode 8.0 is now supported For details on what is in this release, see L. =head2 perl will now croak when closing an in-place output file fails Until now, failure to close the output file for an in-place edit was not detected, meaning that the input file could be clobbered without the edit being successfully completed. Now, when the output file cannot be closed successfully, an exception is raised. =head2 New C<\b{lb}> boundary in regular expressions C stands for Line Break. It is a Unicode property that determines where a line of text is suitable to break (typically so that it can be output without overflowing the available horizontal space). This capability has long been furnished by the L module, but now a light-weight, non-customizable version that is suitable for many purposes is in core Perl. =head2 C now works in UTF-8 locales L now will successfully compile when S> is in effect. The compiled pattern will use standard Unicode rules. If the runtime locale is not a UTF-8 one, a warning is raised and standard Unicode rules are used anyway. No tainting is done since the outcome does not actually depend on the locale. =head2 Integer shift (C<< << >> and C<< >> >>) now more explicitly defined Negative shifts are reverse shifts: left shift becomes right shift, and right shift becomes left shift. Shifting by the number of bits in a native integer (or more) is zero, except when the "overshift" is right shifting a negative value under C, in which case the result is -1 (arithmetic shift). Until now negative shifting and overshifting have been undefined because they have relied on whatever the C implementation happens to do. For example, for the overshift a common C behavior is "modulo shift": 1 >> 64 == 1 >> (64 % 64) == 1 >> 0 == 1 # Common C behavior. # And the same for <<, while Perl now produces 0 for both. Now these behaviors are well-defined under Perl, regardless of what the underlying C implementation does. Note, however, that you are still constrained by the native integer width: you need to know how far left you can go. You can use for example: use Config; my $wordbits = $Config{uvsize} * 8; # Or $Config{uvsize} << 3. If you need a more bits on the left shift, you can use for example the C pragma, or the C module from CPAN. =head2 printf and sprintf now allow reordered precision arguments That is, C<< sprintf '|%.*2$d|', 2, 3 >> now returns C<|002|>. This extends the existing reordering mechanism (which allows reordering for arguments that are used as format fields, widths, and vector separators). =head2 More fields provided to C callback with C When passing the C flag to L, the C, C, C, C, C and C fields are now included in the hash passed to the handler, if supported by the platform. =head2 Hashbang redirection to Perl 6 Previously perl would redirect to another interpreter if it found a hashbang path unless the path contains "perl" (see L). To improve compatibility with Perl 6 this behavior has been extended to also redirect if "perl" is followed by "6". =head1 Security =head2 Set proper umask before calling C In 5.22 perl started setting umask to 0600 before calling C and restoring it afterwards. This wrongfully tells C to strip the owner read and write bits from the given mode before applying it, rather than the intended negation of leaving only those bits in place. Systems that use mode 0666 in C (like old versions of glibc) create a file with permissions 0066, leaving world read and write permissions regardless of current umask. This has been fixed by using umask 0177 instead. [perl #127322] =head2 Fix out of boundary access in Win32 path handling This is CVE-2015-8608. For more information see L<[perl #126755]|https://rt.perl.org/Ticket/Display.html?id=126755> =head2 Fix loss of taint in canonpath This is CVE-2015-8607. For more information see L<[perl #126862]|https://rt.perl.org/Ticket/Display.html?id=126862> =head2 Avoid accessing uninitialized memory in win32 C Added validation that will detect both a short salt and invalid characters in the salt. L<[perl #126922]|https://rt.perl.org/Ticket/Display.html?id=126922> =head2 Remove duplicate environment variables from C Previously, if an environment variable appeared more than once in C, C<%ENV> would contain the last entry for that name, while a typical C would return the first entry. We now make sure C<%ENV> contains the same as what C returns. Second, we remove duplicates from C, so if a setting with that name is set in C<%ENV>, we won't pass an unsafe value to a child process. [CVE-2016-2381] =head1 Incompatible Changes =head2 The C feature has been removed The experimental C feature (which allowed calling C, C, C, C, C, C, C, and C on a scalar argument) has been deemed unsuccessful. It has now been removed; trying to use the feature (or to disable the C warning it previously triggered) now yields an exception. =head2 Lexical $_ has been removed C was introduced in Perl 5.10, and subsequently caused much confusion with no obvious solution. In Perl 5.18.0, it was made experimental on the theory that it would either be removed or redesigned in a less confusing (but backward-incompatible) way. Over the following years, no alternatives were proposed. The feature has now been removed and will fail to compile. =head2 C is now tailored to Perl expectations This is now more suited to be a drop-in replacement for plain C<\b>, but giving better results for parsing natural language. Previously it strictly followed the current Unicode rules which calls for it to match between each white space character. Now it doesn't generally match within spans of white space, behaving like C<\b> does. See L =head2 Regular expression compilation errors Some regular expression patterns that had runtime errors now don't compile at all. Almost all Unicode properties using the C<\p{}> and C<\P{}> regular expression pattern constructs are now checked for validity at pattern compilation time, and invalid ones will cause the program to not compile. In earlier releases, this check was often deferred until run time. Whenever an error check is moved from run- to compile time, erroneous code is caught 100% of the time, whereas before it would only get caught if and when the offending portion actually gets executed, which for unreachable code might be never. =head2 C now disallowed under C An empty C<\N{}> makes no sense, but for backwards compatibility is accepted as doing nothing, though a deprecation warning is raised by default. But now this is a fatal error under the experimental feature L. =head2 Nested declarations are now disallowed A C, C, or C declaration is no longer allowed inside of another C, C, or C declaration. For example, these are now fatal: my ($x, my($y)); our (my $x); L<[perl #125587]|https://rt.perl.org/Ticket/Display.html?id=125587> L<[perl #121058]|https://rt.perl.org/Ticket/Display.html?id=121058> =head2 The C character class has been removed. This regular expression character class was deprecated in v5.20.0 and has produced a deprecation warning since v5.22.0. It is now a compile-time error. If you need to examine the individual bytes that make up a UTF8-encoded character, then use C on the string (or a copy) first. =head2 C no longer chdirs home Using C or C to chdir home has been deprecated since perl v5.8, and will now fail. Use C instead. =head2 ASCII characters in variable names must now be all visible It was legal until now on ASCII platforms for variable names to contain non-graphical ASCII control characters (ordinals 0 through 31, and 127, which are the C0 controls and C). This usage has been deprecated since v5.20, and as of now causes a syntax error. The variables these names referred to are special, reserved by Perl for whatever use it may choose, now, or in the future. Each such variable has an alternative way of spelling it. Instead of the single non-graphic control character, a two character sequence beginning with a caret is used, like C<$^]> and C<${^GLOBAL_PHASE}>. Details are at L. It remains legal, though unwise and deprecated (raising a deprecation warning), to use certain non-graphic non-ASCII characters in variables names when not under S>. No code should do this, as all such variables are reserved by Perl, and Perl doesn't currently define any of them (but could at any time, without notice). =head2 An off by one issue in C<$Carp::MaxArgNums> has been fixed C<$Carp::MaxArgNums> is supposed to be the number of arguments to display. Prior to this version, it was instead showing C<$Carp::MaxArgNums> + 1 arguments, contrary to the documentation. =head2 Only blanks and tabs are now allowed within C<[...]> within C<(?[...])>. The experimental Extended Bracketed Character Classes can contain regular bracketed character classes within them. These differ from regular ones in that white space is generally ignored, unless escaped by preceding it with a backslash. The white space that is ignored is now limited to just tab C<\t> and SPACE characters. Previously, it was any white space. See L. =head1 Deprecations =head2 Using code points above the platform's C is now deprecated Unicode defines code points in the range C<0..0x10FFFF>. Some standards at one time defined them up to 2**31 - 1, but Perl has allowed them to be as high as anything that will fit in a word on the platform being used. However, use of those above the platform's C is broken in some constructs, notably C, regular expression patterns involving quantifiers, and in some arithmetic and comparison operations, such as being the upper limit of a loop. Now the use of such code points raises a deprecation warning, unless that warning category is turned off. C is typically 2**31 -1 on 32-bit platforms, and 2**63-1 on 64-bit ones. =head2 Doing bitwise operations on strings containing code points above 0xFF is deprecated The string bitwise operators treat their operands as strings of bytes, and values beyond 0xFF are nonsensical in this context. To operate on encoded bytes, first encode the strings. To operate on code points' numeric values, use C and C