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perl5178delta - what is new for perl v5.17.8


This document describes differences between the 5.17.7 release and the 5.17.8 release.

If you are upgrading from an earlier release such as 5.17.6, first read perl5177delta, which describes differences between 5.17.6 and 5.17.7.

Core Enhancements

Regular Expression Set Operations

This is an experimental feature to allow matching against the union, intersection, etc., of sets of code points, similar to Unicode::Regex::Set. It can also be used to extend /x processing to [bracketed] character classes, and as a replacement of user-defined properties, allowing more complex expressions than they do. See "(?[ ])" in perlre.


Deprecated modules

The Pod::LaTeX module is now deprecated, and due to be moved out of the Perl core in 5.20. Until then, using the core-installed version will produce a warning. You can suppress the warning by installing the module from CPAN.

User-defined charnames with surprising whitespace

A user-defined character name with trailing or multiple spaces in a row is likely a typo. This now generates a warning when defined, on the assumption that uses of it will be unlikely to include the excess whitespace.

Various XS-callable functions are now deprecated

All the functions used to classify characters will be removed from a future version of Perl, and should not be used. With participating C compilers (e.g., gcc), compiling any file that uses any of these will generate a warning. These were not intended for public use; there are equivalent, faster, macros for most of them. See "Character classes" in perlapi. The complete list (including some that were deprecated in 5.17.7) is: is_uni_alnum, is_uni_alnumc, is_uni_alnumc_lc, is_uni_alnum_lc, is_uni_alpha, is_uni_alpha_lc, is_uni_ascii, is_uni_ascii_lc, is_uni_blank, is_uni_blank_lc, is_uni_cntrl, is_uni_cntrl_lc, is_uni_digit, is_uni_digit_lc, is_uni_graph, is_uni_graph_lc, is_uni_idfirst, is_uni_idfirst_lc, is_uni_lower, is_uni_lower_lc, is_uni_print, is_uni_print_lc, is_uni_punct, is_uni_punct_lc, is_uni_space, is_uni_space_lc, is_uni_upper, is_uni_upper_lc, is_uni_xdigit, is_uni_xdigit_lc, is_utf8_alnum, is_utf8_alnumc, is_utf8_alpha, is_utf8_ascii, is_utf8_blank, is_utf8_char, is_utf8_cntrl, is_utf8_digit, is_utf8_graph, is_utf8_idcont, is_utf8_idfirst, is_utf8_lower, is_utf8_mark, is_utf8_perl_space, is_utf8_perl_word, is_utf8_posix_digit, is_utf8_print, is_utf8_punct, is_utf8_space, is_utf8_upper, is_utf8_xdigit, is_utf8_xidcont, is_utf8_xidfirst.

In addition these three functions that have never worked properly are deprecated: to_uni_lower_lc, to_uni_title_lc, and to_uni_upper_lc.

Certain rare uses of backslashes within regexes are now deprectated

There are three pairs of characters that Perl recognizes as metacharacters in regular expression patterns: {}, [], and (). These can be used as well to delimit patterns, as in:


Since they are metacharacters, they have special meaning to regular expression patterns, and it turns out that you can't turn off that special meaning by the normal means of preceding them with a backslash, if you use them, paired, within a pattern delimitted by them. For example, in


the backslashes do not change the behavior, and this matches "f o" followed by one to three more occurrences of "o".

Usages like this, where they are interpreted as metacharacters, are exceedingly rare; we think there are none, for example, in all of CPAN. Hence, this deprecation should affect very little code. It does give notice, however, that any such code needs to change, which will in turn allow us to change the behavior in future Perl versions so that the backslashes do have an effect, and without fear that we are silently breaking any existing code.

Modules and Pragmata

Selected Updates to Modules and Pragmata

  • Several modules have had their version number changed to one with no underscore, since such version numbers are usually interpreted to mean "development-only version". No other changes have been made in these cases. The affected modules are:

  • Digest::SHA has been upgraded from version 5.80 to 5.81. This fixes a double-free bug, which might have caused vulnerabilities in some cases.

  • Module::CoreList has been upgraded from 2.79 to 2.80.

  • Socket has been upgraded from 2.006_001 to 2.009. This fixes an uninitialized memory read.


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 Warnings


  • Many more of the core's tests now have descriptions.

  • Thread stress-tests now adapt to the speed of the machine running the tests, thus reducing the incidence of false failures.

Platform Support

Discontinued Platforms


Support for Rhapsody has been removed.

Platform-Specific Notes


Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for Windows Desktop) in win32/Makefile.


Perl should now work out of the box on Haiku R1 Alpha 4.

Internal Changes

  • A synonym for the misleadingly named av_len() has been created: av_top(). Both of these return the number of the highest index in the array, not the number of elements it contains.

Selected Bug Fixes

  • A bug in the core typemap caused any C types that map to the T_BOOL core typemap entry to not be set, updated, or modified when the T_BOOL variable was used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT: section was not affected. Using a T_BOOL return type for an XSUB (RETVAL) was not affected. A side effect of fixing this bug is, if a T_BOOL is specified in the OUTPUT: section (which previous did nothing to the SV), and a read only SV (literal) is passed to the XSUB, croaks like "Modification of a read-only value attempted" will happen. [perl #115796]

  • On many platforms, providing a directory name as the script name caused perl to do nothing and report success. It should now universally report an error and exit nonzero. [perl #61362]

Known Problems

  • Perl 5.17.7 introduced a new internal copy-on-write mechanism, in the interests of speed. An flaw in the implementation means that some regexp matches which previously completed very fast, without invoking the full regexp engine, now run much slower than before. We expect this performance problem to be resolved before 5.18.0 is released.

  • The POSIX module may yield test failures when building on a ZFS filesystem under FreeBSD.


Perl 5.17.8 represents approximately 5 weeks of development since Perl 5.17.7 and contains approximately 18,000 lines of changes across 280 files from 24 authors.

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 5.17.8:

Aaron Crane, Andy Dougherty, Augustina Blair, Chris 'BinGOs' Williams, Craig A. Berry, Daniel Dragan, Dave Rolsky, David Mitchell, Eric Brine, Father Chrysostomos, H.Merijn Brand, James E Keenan, Jerry D. Hedden, Jesse Luehrs, Karl Williamson, Matthew Horsfall, Nicholas Clark, Renee Baecker, Ricardo Signes, Shlomi Fish, Steffen Müller, Steve Hay, Steven Schubiger, Tony Cook.

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 http://rt.perl.org/perlbug/ . There may also be information at http://www.perl.org/ , 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.

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 perl5-security-report@perl.org. 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.


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.