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5.22
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5.18
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5.16
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5.14
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5.12
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5.10
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5.8
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5.6
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<h1 class='page-title'> Perl 5 version documentation</h1>
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<h1>perl5100delta</h1>
<!-- -->
<ul><li><a href="#NAME">NAME</a></li><li><a href="#DESCRIPTION">DESCRIPTION</a></li><li><a href="#Core-Enhancements">Core Enhancements</a></li><ul><li><a href="#The-feature-pragma">The feature pragma</a></li><li><a href="#New-*-E*-command-line-switch">New *-E* command-line switch</a></li><li><a href="#Defined-or-operator">Defined-or operator</a></li><li><a href="#Switch-and-Smart-Match-operator">Switch and Smart Match operator</a></li><li><a href="#Regular-expressions">Regular expressions</a></li><li><a href="#say()">say()</a></li><li><a href="#Lexical-%24_">Lexical $_</a></li><li><a href="#The-_-prototype">The _ prototype</a></li><li><a href="#UNITCHECK-blocks">UNITCHECK blocks</a></li><li><a href="#New-Pragma%2c-mro">New Pragma, mro</a></li><li><a href="#readdir()-may-return-a-%22short-filename%22-on-Windows">readdir() may return a "short filename" on Windows</a></li><li><a href="#readpipe()-is-now-overridable">readpipe() is now overridable</a></li><li><a href="#Default-argument-for-readline()">Default argument for readline()</a></li><li><a href="#state()-variables">state() variables</a></li><li><a href="#Stacked-filetest-operators">Stacked filetest operators</a></li><li><a href="#UNIVERSAL%3a%3aDOES()">UNIVERSAL::DOES()</a></li><li><a href="#Formats">Formats</a></li><li><a href="#Byte-order-modifiers-for-pack()-and-unpack()">Byte-order modifiers for pack() and unpack()</a></li><li><a href="#no-VERSION">no VERSION</a></li><li><a href="#chdir%2c-chmod-and-chown-on-filehandles">chdir, chmod and chown on filehandles</a></li><li><a href="#OS-groups">OS groups</a></li><li><a href="#Recursive-sort-subs">Recursive sort subs</a></li><li><a href="#Exceptions-in-constant-folding">Exceptions in constant folding</a></li><li><a href="#Source-filters-in-%40INC">Source filters in @INC</a></li><li><a href="#New-internal-variables">New internal variables</a></li><li><a href="#Miscellaneous">Miscellaneous</a></li><li><a href="#UCD-5.0.0">UCD 5.0.0</a></li><li><a href="#MAD">MAD</a></li><li><a href="#kill()-on-Windows">kill() on Windows</a></li></ul><li><a href="#Incompatible-Changes">Incompatible Changes</a></li><ul><li><a href="#Packing-and-UTF-8-strings">Packing and UTF-8 strings</a></li><li><a href="#Byte%2fcharacter-count-feature-in-unpack()">Byte/character count feature in unpack()</a></li><li><a href="#The-%24*-and-%24%23-variables-have-been-removed">The $* and $# variables have been removed</a></li><li><a href="#substr()-lvalues-are-no-longer-fixed-length">substr() lvalues are no longer fixed-length</a></li><li><a href="#Parsing-of--f-_">Parsing of -f _</a></li><li><a href="#%3aunique">:unique</a></li><li><a href="#Effect-of-pragmas-in-eval">Effect of pragmas in eval</a></li><li><a href="#chdir-FOO">chdir FOO</a></li><li><a href="#Handling-of-.pmc-files">Handling of .pmc files</a></li><li><a href="#%24%5eV-is-now-a-version-object-instead-of-a-v-string">$^V is now a version object instead of a v-string</a></li><li><a href="#%40--and-%40%2b-in-patterns">@- and @+ in patterns</a></li><li><a href="#%24AUTOLOAD-can-now-be-tainted">$AUTOLOAD can now be tainted</a></li><li><a href="#Tainting-and-printf">Tainting and printf</a></li><li><a href="#undef-and-signal-handlers">undef and signal handlers</a></li><li><a href="#strictures-and-dereferencing-in-defined()">strictures and dereferencing in defined()</a></li><li><a href="#(%3fp%7b%7d)-has-been-removed">(?p{}) has been removed</a></li><li><a href="#Pseudo-hashes-have-been-removed">Pseudo-hashes have been removed</a></li><li><a href="#Removal-of-the-bytecode-compiler-and-of-perlcc">Removal of the bytecode compiler and of perlcc</a></li><li><a href="#Removal-of-the-JPL">Removal of the JPL</a></li><li><a href="#Recursive-inheritance-detected-earlier">Recursive inheritance detected earlier</a></li><li><a href="#warnings%3a%3aenabled-and-warnings%3a%3awarnif-changed-to-favor-users-of-modules">warnings::enabled and warnings::warnif changed to favor users of modules</a></li></ul><li><a href="#Modules-and-Pragmata">Modules and Pragmata</a></li><ul><li><a href="#Upgrading-individual-core-modules">Upgrading individual core modules</a></li><li><a href="#Pragmata-Changes">Pragmata Changes</a></li><li><a href="#New-modules">New modules</a></li><li><a href="#Selected-Changes-to-Core-Modules">Selected Changes to Core Modules</a></li></ul><li><a href="#Utility-Changes">Utility Changes</a></li><li><a href="#New-Documentation">New Documentation</a></li><li><a href="#Performance-Enhancements">Performance Enhancements</a></li><ul><li><a href="#In-place-sorting">In-place sorting</a></li><li><a href="#Lexical-array-access">Lexical array access</a></li><li><a href="#XS-assisted-SWASHGET">XS-assisted SWASHGET</a></li><li><a href="#Constant-subroutines">Constant subroutines</a></li><li><a href="#PERL_DONT_CREATE_GVSV">PERL_DONT_CREATE_GVSV</a></li><li><a href="#Weak-references-are-cheaper">Weak references are cheaper</a></li><li><a href="#sort()-enhancements">sort() enhancements</a></li><li><a href="#Memory-optimisations">Memory optimisations</a></li><li><a href="#UTF-8-cache-optimisation">UTF-8 cache optimisation</a></li><li><a href="#Sloppy-stat-on-Windows">Sloppy stat on Windows</a></li><li><a href="#Regular-expressions-optimisations">Regular expressions optimisations</a></li></ul><li><a href="#Installation-and-Configuration-Improvements">Installation and Configuration Improvements</a></li><ul><li><a href="#Configuration-improvements">Configuration improvements</a></li><li><a href="#Compilation-improvements">Compilation improvements</a></li><li><a href="#Installation-improvements">Installation improvements</a></li><li><a href="#New-Or-Improved-Platforms">New Or Improved Platforms</a></li></ul><li><a href="#Selected-Bug-Fixes">Selected Bug Fixes</a></li><li><a href="#New-or-Changed-Diagnostics">New or Changed Diagnostics</a></li><li><a href="#Changed-Internals">Changed Internals</a></li><ul><li><a href="#Reordering-of-SVt_*-constants">Reordering of SVt_* constants</a></li><li><a href="#Elimination-of-SVt_PVBM">Elimination of SVt_PVBM</a></li><li><a href="#New-type-SVt_BIND">New type SVt_BIND</a></li><li><a href="#Removal-of-CPP-symbols">Removal of CPP symbols</a></li><li><a href="#Less-space-is-used-by-ops">Less space is used by ops</a></li><li><a href="#New-parser">New parser</a></li><li><a href="#Use-of-const">Use of const</a></li><li><a href="#Mathoms">Mathoms</a></li><li><a href="#AvFLAGS-has-been-removed">AvFLAGS has been removed</a></li><li><a href="#av_*-changes">av_* changes</a></li><li><a href="#%24%5eH-and-%25%5eH">$^H and %^H</a></li><li><a href="#B%3a%3a-modules-inheritance-changed">B:: modules inheritance changed</a></li><li><a href="#Anonymous-hash-and-array-constructors">Anonymous hash and array constructors</a></li></ul><li><a href="#Known-Problems">Known Problems</a></li><ul><li><a href="#UTF-8-problems">UTF-8 problems</a></li></ul><li><a href="#Platform-Specific-Problems">Platform Specific Problems</a></li><li><a href="#Reporting-Bugs">Reporting Bugs</a></li><li><a href="#SEE-ALSO">SEE ALSO</a></li></ul><a id="NAME"></a><h2 class='h2' >NAME</h2>
<p>perl5100delta - what is new for perl 5.10.0</p>
<a id="DESCRIPTION"></a><h2 class='h2' >DESCRIPTION</h2>
<p>This document describes the differences between the 5.8.8 release and
the 5.10.0 release.</p>
<p>Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
releases; they are not duplicated here and are documented in the set of
man pages named perl58[1-8]?delta.</p>
<a id="Core-Enhancements"></a><h2 class='h2' >Core Enhancements</h2>
<a id="The-feature-pragma"></a><h3 class='h3' >The <code class="inline"><span class="w">feature</span></code>
pragma</h3>
<p>The <code class="inline"><span class="w">feature</span></code>
pragma is used to enable new syntax that would break Perl's
backwards-compatibility with older releases of the language. It's a lexical
pragma, like <code class="inline"><span class="w">strict</span></code>
or <code class="inline"><span class="w">warnings</span></code>
.</p>
<p>Currently the following new features are available: <code class="inline">switch</code>
(adds a
switch statement), <code class="inline"><a class="l_k" href="functions/say.html">say</a></code> (adds a <code class="inline"><a class="l_k" href="functions/say.html">say</a></code> built-in function), and <code class="inline"><a class="l_k" href="functions/state.html">state</a></code>
(adds a <code class="inline"><a class="l_k" href="functions/state.html">state</a></code> keyword for declaring "static" variables). Those
features are described in their own sections of this document.</p>
<p>The <code class="inline"><span class="w">feature</span></code>
pragma is also implicitly loaded when you require a minimal
perl version (with the <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">VERSION</span></code>
construct) greater than, or equal
to, 5.9.5. See <a href="feature.html">feature</a> for details.</p>
<a id="New-*-E*-command-line-switch"></a><h3 class='h3' >New <strong>-E</strong> command-line switch</h3>
<p><strong>-E</strong> is equivalent to <strong>-e</strong>, but it implicitly enables all
optional features (like <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">feature</span> <span class="q">":5.10"</span></code>
).</p>
<a id="Defined-or-operator"></a><h3 class='h3' >Defined-or operator</h3>
<p>A new operator <code class="inline"><span class="q">//</span></code>
(defined-or) has been implemented.
The following expression:</p>
<pre class="verbatim"><ol><li> <span class="i">$a</span> // <span class="i">$b</span></li></ol></pre><p>is merely equivalent to</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/defined.html">defined</a> <span class="i">$a</span> ? <span class="i">$a</span> <span class="co">:</span> <span class="i">$b</span></li></ol></pre><p>and the statement</p>
<pre class="verbatim"><ol><li> <span class="i">$c</span> //= <span class="i">$d</span><span class="sc">;</span></li></ol></pre><p>can now be used instead of</p>
<pre class="verbatim"><ol><li> <span class="i">$c</span> = <span class="i">$d</span> <a class="l_k" href="functions/unless.html">unless</a> <a class="l_k" href="functions/defined.html">defined</a> <span class="i">$c</span><span class="sc">;</span></li></ol></pre><p>The <code class="inline"><span class="q">//</span></code>
operator has the same precedence and associativity as <code class="inline">||</code>
.
Special care has been taken to ensure that this operator Do What You Mean
while not breaking old code, but some edge cases involving the empty
regular expression may now parse differently. See <a href="perlop.html">perlop</a> for
details.</p>
<a id="Switch-and-Smart-Match-operator"></a><h3 class='h3' >Switch and Smart Match operator</h3>
<p>Perl 5 now has a switch statement. It's available when <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">feature</span>
<span class="q">'switch'</span></code>
is in effect. This feature introduces three new keywords,
<code class="inline"><a class="l_k" href="functions/given.html">given</a></code>, <code class="inline"><a class="l_k" href="functions/when.html">when</a></code>, and <code class="inline"><a class="l_k" href="functions/default.html">default</a></code>:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/given.html">given</a> <span class="s">(</span><span class="i">$foo</span><span class="s">)</span> <span class="s">{</span></li><li> <a class="l_k" href="functions/when.html">when</a> <span class="s">(</span><span class="q">/^abc/</span><span class="s">)</span> <span class="s">{</span> <span class="i">$abc</span> = <span class="n">1</span><span class="sc">;</span> <span class="s">}</span></li><li> <a class="l_k" href="functions/when.html">when</a> <span class="s">(</span><span class="q">/^def/</span><span class="s">)</span> <span class="s">{</span> <span class="i">$def</span> = <span class="n">1</span><span class="sc">;</span> <span class="s">}</span></li><li> <a class="l_k" href="functions/when.html">when</a> <span class="s">(</span><span class="q">/^xyz/</span><span class="s">)</span> <span class="s">{</span> <span class="i">$xyz</span> = <span class="n">1</span><span class="sc">;</span> <span class="s">}</span></li><li> <span class="i">default</span> <span class="s">{</span> <span class="i">$nothing</span> = <span class="n">1</span><span class="sc">;</span> <span class="s">}</span></li><li> <span class="s">}</span></li></ol></pre><p>A more complete description of how Perl matches the switch variable
against the <code class="inline"><a class="l_k" href="functions/when.html">when</a></code> conditions is given in <a href="perlsyn.html#Switch-statements">Switch statements in perlsyn</a>.</p>
<p>This kind of match is called <i>smart match</i>, and it's also possible to use
it outside of switch statements, via the new <code class="inline">~~</code>
operator. See
<a href="perlsyn.html#Smart-matching-in-detail">Smart matching in detail in perlsyn</a>.</p>
<p>This feature was contributed by Robin Houston.</p>
<a id="Regular-expressions"></a><h3 class='h3' >Regular expressions</h3>
<ul>
<li><a id="Recursive-Patterns"></a><strong>Recursive Patterns</strong>
<p>It is now possible to write recursive patterns without using the <code class="inline"><span class="s">(</span><span class="q">??</span><span class="s">{</span><span class="s">}</span><span class="s">)</span></code>
construct. This new way is more efficient, and in many cases easier to
read.</p>
<p>Each capturing parenthesis can now be treated as an independent pattern
that can be entered by using the <code class="inline"><span class="s">(</span><span class="q">?PARNO)</span></code>
syntax (<code class="inline"><span class="w">PARNO</span></code>
standing for
"parenthesis number"). For example, the following pattern will match
nested balanced angle brackets:</p>
<pre class="verbatim"><ol><li> <span class="q">/</span></li><li> <span class="q"> ^ # start of line</span></li><li> <span class="q"> ( # start capture buffer 1</span></li><li> <span class="q"> < # match an opening angle bracket</span></li><li> <span class="q"> (?: # match one of:</span></li><li> <span class="q"> (?> # don't backtrack over the inside of this group</span></li><li> <span class="q"> [^<>]+ # one or more non angle brackets</span></li><li> <span class="q"> ) # end non backtracking group</span></li><li> <span class="q"> | # ... or ...</span></li><li> <span class="q"> (?1) # recurse to bracket 1 and try it again</span></li><li> <span class="q"> )* # 0 or more times.</span></li><li> <span class="q"> > # match a closing angle bracket</span></li><li> <span class="q"> ) # end capture buffer one</span></li><li> <span class="q"> $ # end of line</span></li><li> <span class="q"> /x</span></li></ol></pre><p>PCRE users should note that Perl's recursive regex feature allows
backtracking into a recursed pattern, whereas in PCRE the recursion is
atomic or "possessive" in nature. As in the example above, you can
add (?>) to control this selectively. (Yves Orton)</p>
</li>
<li><a id="Named-Capture-Buffers"></a><strong>Named Capture Buffers</strong>
<p>It is now possible to name capturing parenthesis in a pattern and refer to
the captured contents by name. The naming syntax is <code class="inline"><span class="s">(</span><span class="q">?<NAME>....)</span></code>
.
It's possible to backreference to a named buffer with the <code class="inline">\<span class="w">k</span><span class="q"><NAME></span></code>
syntax. In code, the new magical hashes <code class="inline"><span class="i">%+</span></code>
and <code class="inline"><span class="i">%-</span></code>
can be used to
access the contents of the capture buffers.</p>
<p>Thus, to replace all doubled chars with a single copy, one could write</p>
<pre class="verbatim"><ol><li> <span class="q">s/(?<letter>.)\k<letter>/$+{letter}/g</span></li></ol></pre><p>Only buffers with defined contents will be "visible" in the <code class="inline"><span class="i">%+</span></code>
hash, so
it's possible to do something like</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/foreach.html">foreach</a> <a class="l_k" href="functions/my.html">my</a> <span class="i">$name</span> <span class="s">(</span><a class="l_k" href="functions/keys.html">keys</a> <span class="i">%+</span><span class="s">)</span> <span class="s">{</span></li><li> <a class="l_k" href="functions/print.html">print</a> <span class="q">"content of buffer '$name' is $+{$name}\n"</span><span class="sc">;</span></li><li> <span class="s">}</span></li></ol></pre><p>The <code class="inline"><span class="i">%-</span></code>
hash is a bit more complete, since it will contain array refs
holding values from all capture buffers similarly named, if there should
be many of them.</p>
<p><code class="inline"><span class="i">%+</span></code>
and <code class="inline"><span class="i">%-</span></code>
are implemented as tied hashes through the new module
<code class="inline"><span class="w">Tie::Hash::NamedCapture</span></code>
.</p>
<p>Users exposed to the .NET regex engine will find that the perl
implementation differs in that the numerical ordering of the buffers
is sequential, and not "unnamed first, then named". Thus in the pattern</p>
<pre class="verbatim"><ol><li> <span class="q">/(A)(?<B>B)(C)(?<D>D)/</span></li></ol></pre><p>$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
$1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
would expect. This is considered a feature. :-) (Yves Orton)</p>
</li>
<li><a id="Possessive-Quantifiers"></a><strong>Possessive Quantifiers</strong>
<p>Perl now supports the "possessive quantifier" syntax of the "atomic match"
pattern. Basically a possessive quantifier matches as much as it can and never
gives any back. Thus it can be used to control backtracking. The syntax is
similar to non-greedy matching, except instead of using a '?' as the modifier
the '+' is used. Thus <code class="inline"><span class="q">?+</span></code>
, <code class="inline"><span class="i">*+</span></code>
, <code class="inline">++</code>
, <code class="inline"><span class="s">{</span><span class="w">min</span><span class="cm">,</span><span class="w">max</span><span class="s">}</span>+</code>
are now legal
quantifiers. (Yves Orton)</p>
</li>
<li><a id="Backtracking-control-verbs"></a><strong>Backtracking control verbs</strong>
<p>The regex engine now supports a number of special-purpose backtrack
control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
and (*ACCEPT). See <a href="perlre.html">perlre</a> for their descriptions. (Yves Orton)</p>
</li>
<li><a id="Relative-backreferences"></a><strong>Relative backreferences</strong>
<p>A new syntax <code class="inline">\<span class="i">g</span><span class="s">{</span><span class="w">N</span><span class="s">}</span></code>
or <code class="inline">\<span class="w">gN</span></code>
where "N" is a decimal integer allows a
safer form of back-reference notation as well as allowing relative
backreferences. This should make it easier to generate and embed patterns
that contain backreferences. See <a href="perlre.html#Capture-buffers">Capture buffers in perlre</a>. (Yves Orton)</p>
</li>
<li><a id="%5cK-escape"></a><strong><code class="inline">\<span class="w">K</span></code>
escape</strong>
<p>The functionality of Jeff Pinyan's module Regexp::Keep has been added to
the core. In regular expressions you can now use the special escape <code class="inline">\<span class="w">K</span></code>
as a way to do something like floating length positive lookbehind. It is
also useful in substitutions like:</p>
<pre class="verbatim"><ol><li> <span class="q">s/(foo)bar/$1/g</span></li></ol></pre><p>that can now be converted to</p>
<pre class="verbatim"><ol><li> <span class="q">s/foo\Kbar//g</span></li></ol></pre><p>which is much more efficient. (Yves Orton)</p>
</li>
<li><a id="Vertical-and-horizontal-whitespace%2c-and-linebreak"></a><strong>Vertical and horizontal whitespace, and linebreak</strong>
<p>Regular expressions now recognize the <code class="inline">\<span class="w">v</span></code>
and <code class="inline">\<span class="w">h</span></code>
escapes that match
vertical and horizontal whitespace, respectively. <code class="inline">\<span class="w">V</span></code>
and <code class="inline">\<span class="w">H</span></code>
logically match their complements.</p>
<p><code class="inline">\<span class="w">R</span></code>
matches a generic linebreak, that is, vertical whitespace, plus
the multi-character sequence <code class="inline"><span class="q">"\x0D\x0A"</span></code>
.</p>
</li>
<li><a id="Optional-pre-match-and-post-match-captures-with-the-%2fp-flag"></a><strong>Optional pre-match and post-match captures with the /p flag</strong>
<p>There is a new flag <code class="inline"><span class="q">/p</span></code>
for regular expressions. Using this
makes the engine preserve a copy of the part of the matched string before
the matching substring to the new special variable <code class="inline"><span class="i">$</span>{<span class="w">^PREMATCH</span>}</code>
, the
part after the matching substring to <code class="inline"><span class="i">$</span>{<span class="w">^POSTMATCH</span>}</code>
, and the matched
substring itself to <code class="inline"><span class="i">$</span>{<span class="w">^MATCH</span>}</code>
.</p>
<p>Perl is still able to store these substrings to the special variables
<code class="inline"><span class="i">$`</span></code>
, <code class="inline"><span class="i">$'</span></code>
, <code class="inline"><span class="i">$&</span></code>
, but using these variables anywhere in the program
adds a penalty to all regular expression matches, whereas if you use
the <code class="inline"><span class="q">/p</span></code>
flag and the new special variables instead, you pay only for
the regular expressions where the flag is used.</p>
<p>For more detail on the new variables, see <a href="perlvar.html">perlvar</a>; for the use of
the regular expression flag, see <a href="perlop.html">perlop</a> and <a href="perlre.html">perlre</a>.</p>
</li>
</ul>
<a id="say()"></a><h3 class='h3' ><code class="inline"><a class="l_k" href="functions/say.html">say()</a></code></h3>
<p>say() is a new built-in, only available when <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">feature</span> <span class="q">'say'</span></code>
is in
effect, that is similar to print(), but that implicitly appends a newline
to the printed string. See <a href="functions/say.html">say</a>. (Robin Houston)</p>
<a id="Lexical-%24_"></a><h3 class='h3' >Lexical <code class="inline"><span class="i">$_</span></code>
</h3>
<p>The default variable <code class="inline"><span class="i">$_</span></code>
can now be lexicalized, by declaring it like
any other lexical variable, with a simple</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/my.html">my</a> <span class="i">$_</span><span class="sc">;</span></li></ol></pre><p>The operations that default on <code class="inline"><span class="i">$_</span></code>
will use the lexically-scoped
version of <code class="inline"><span class="i">$_</span></code>
when it exists, instead of the global <code class="inline"><span class="i">$_</span></code>
.</p>
<p>In a <code class="inline"><a class="l_k" href="functions/map.html">map</a></code> or a <code class="inline"><a class="l_k" href="functions/grep.html">grep</a></code> block, if <code class="inline"><span class="i">$_</span></code>
was previously my'ed, then the
<code class="inline"><span class="i">$_</span></code>
inside the block is lexical as well (and scoped to the block).</p>
<p>In a scope where <code class="inline"><span class="i">$_</span></code>
has been lexicalized, you can still have access to
the global version of <code class="inline"><span class="i">$_</span></code>
by using <code class="inline"><span class="i">$::_</span></code>
, or, more simply, by
overriding the lexical declaration with <code class="inline"><a class="l_k" href="functions/our.html">our</a> <span class="i">$_</span></code>
. (Rafael Garcia-Suarez)</p>
<a id="The-_-prototype"></a><h3 class='h3' >The <code class="inline"><span class="w">_</span></code>
prototype</h3>
<p>A new prototype character has been added. <code class="inline"><span class="w">_</span></code>
is equivalent to <code class="inline"><span class="i">$</span></code>
but
defaults to <code class="inline"><span class="i">$_</span></code>
if the corresponding argument isn't supplied (both <code class="inline"><span class="i">$</span></code>
and <code class="inline"><span class="w">_</span></code>
denote a scalar). Due to the optional nature of the argument,
you can only use it at the end of a prototype, or before a semicolon.</p>
<p>This has a small incompatible consequence: the prototype() function has
been adjusted to return <code class="inline"><span class="w">_</span></code>
for some built-ins in appropriate cases (for
example, <code class="inline"><a class="l_k" href="functions/prototype.html">prototype('CORE::rmdir')</a></code>). (Rafael Garcia-Suarez)</p>
<a id="UNITCHECK-blocks"></a><h3 class='h3' >UNITCHECK blocks</h3>
<p><code class="inline"><a class="l_k" href="functions/UNITCHECK.html">UNITCHECK</a></code>, a new special code block has been introduced, in addition to
<code class="inline"><a class="l_k" href="functions/BEGIN.html">BEGIN</a></code>, <code class="inline"><a class="l_k" href="functions/CHECK.html">CHECK</a></code>, <code class="inline"><a class="l_k" href="functions/INIT.html">INIT</a></code> and <code class="inline"><a class="l_k" href="functions/END.html">END</a></code>.</p>
<p><code class="inline"><a class="l_k" href="functions/CHECK.html">CHECK</a></code> and <code class="inline"><a class="l_k" href="functions/INIT.html">INIT</a></code> blocks, while useful for some specialized purposes,
are always executed at the transition between the compilation and the
execution of the main program, and thus are useless whenever code is
loaded at runtime. On the other hand, <code class="inline"><a class="l_k" href="functions/UNITCHECK.html">UNITCHECK</a></code> blocks are executed
just after the unit which defined them has been compiled. See <a href="perlmod.html">perlmod</a>
for more information. (Alex Gough)</p>
<a id="New-Pragma%2c-mro"></a><h3 class='h3' >New Pragma, <code class="inline"><span class="w">mro</span></code>
</h3>
<p>A new pragma, <code class="inline"><span class="w">mro</span></code>
(for Method Resolution Order) has been added. It
permits to switch, on a per-class basis, the algorithm that perl uses to
find inherited methods in case of a multiple inheritance hierarchy. The
default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
available: the C3 algorithm. See <a href="mro.html">mro</a> for more information.
(Brandon Black)</p>
<p>Note that, due to changes in the implementation of class hierarchy search,
code that used to undef the <code class="inline"><span class="i">*ISA</span></code>
glob will most probably break. Anyway,
undef'ing <code class="inline"><span class="i">*ISA</span></code>
had the side-effect of removing the magic on the @ISA
array and should not have been done in the first place. Also, the
cache <code class="inline"><span class="i">*::ISA::CACHE::</span></code>
no longer exists; to force reset the @ISA cache,
you now need to use the <code class="inline"><span class="w">mro</span></code>
API, or more simply to assign to @ISA
(e.g. with <code class="inline"><span class="i">@ISA</span> = <span class="i">@ISA</span></code>
).</p>
<a id="readdir()-may-return-a-%22short-filename%22-on-Windows"></a><h3 class='h3' >readdir() may return a "short filename" on Windows</h3>
<p>The readdir() function may return a "short filename" when the long
filename contains characters outside the ANSI codepage. Similarly
Cwd::cwd() may return a short directory name, and glob() may return short
names as well. On the NTFS file system these short names can always be
represented in the ANSI codepage. This will not be true for all other file
system drivers; e.g. the FAT filesystem stores short filenames in the OEM
codepage, so some files on FAT volumes remain unaccessible through the
ANSI APIs.</p>
<p>Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make
sure all paths are valid in the ANSI codepage (if possible).</p>
<p>The Win32::GetLongPathName() function now returns the UTF-8 encoded
correct long file name instead of using replacement characters to force
the name into the ANSI codepage. The new Win32::GetANSIPathName()
function can be used to turn a long pathname into a short one only if the
long one cannot be represented in the ANSI codepage.</p>
<p>Many other functions in the <code class="inline"><span class="w">Win32</span></code>
module have been improved to accept
UTF-8 encoded arguments. Please see <a href="Win32.html">Win32</a> for details.</p>
<a id="readpipe()-is-now-overridable"></a><h3 class='h3' >readpipe() is now overridable</h3>
<p>The built-in function readpipe() is now overridable. Overriding it permits
also to override its operator counterpart, <code class="inline"><a class="l_k" href="functions/qx.html">qx//</a></code> (a.k.a. <code class="inline"><span class="q">``</span></code>
).
Moreover, it now defaults to <code class="inline"><span class="i">$_</span></code>
if no argument is provided. (Rafael
Garcia-Suarez)</p>
<a id="Default-argument-for-readline()"></a><h3 class='h3' >Default argument for readline()</h3>
<p>readline() now defaults to <code class="inline"><span class="i">*ARGV</span></code>
if no argument is provided. (Rafael
Garcia-Suarez)</p>
<a id="state()-variables"></a><h3 class='h3' >state() variables</h3>
<p>A new class of variables has been introduced. State variables are similar
to <code class="inline"><a class="l_k" href="functions/my.html">my</a></code> variables, but are declared with the <code class="inline"><a class="l_k" href="functions/state.html">state</a></code> keyword in place of
<code class="inline"><a class="l_k" href="functions/my.html">my</a></code>. They're visible only in their lexical scope, but their value is
persistent: unlike <code class="inline"><a class="l_k" href="functions/my.html">my</a></code> variables, they're not undefined at scope entry,
but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)</p>
<p>To use state variables, one needs to enable them by using</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/use.html">use</a> <span class="w">feature</span> <span class="q">'state'</span><span class="sc">;</span></li></ol></pre><p>or by using the <code class="inline">-<span class="w">E</span></code>
command-line switch in one-liners.
See <a href="perlsub.html#Persistent-Private-Variables">Persistent Private Variables in perlsub</a>.</p>
<a id="Stacked-filetest-operators"></a><h3 class='h3' >Stacked filetest operators</h3>
<p>As a new form of syntactic sugar, it's now possible to stack up filetest
operators. You can now write <code class="inline">-f -w -x <span class="i">$file</span></code>
in a row to mean
<code class="inline">-x <span class="i">$file</span> && -w <span class="i">_</span> && -f <span class="i">_</span></code>
. See <a href="functions/-X.html">-X</a>.</p>
<a id="UNIVERSAL%3a%3aDOES()"></a><h3 class='h3' >UNIVERSAL::DOES()</h3>
<p>The <code class="inline"><span class="w">UNIVERSAL</span></code>
class has a new method, <code class="inline"><span class="i">DOES</span><span class="s">(</span><span class="s">)</span></code>
. It has been added to
solve semantic problems with the <code class="inline"><span class="i">isa</span><span class="s">(</span><span class="s">)</span></code>
method. <code class="inline"><span class="i">isa</span><span class="s">(</span><span class="s">)</span></code>
checks for
inheritance, while <code class="inline"><span class="i">DOES</span><span class="s">(</span><span class="s">)</span></code>
has been designed to be overridden when
module authors use other types of relations between classes (in addition
to inheritance). (chromatic)</p>
<p>See <a href="UNIVERSAL.html#%24obj-%3eDOES(-ROLE-)">$obj->DOES( ROLE ) in UNIVERSAL</a>.</p>
<a id="Formats"></a><h3 class='h3' >Formats</h3>
<p>Formats were improved in several ways. A new field, <code class="inline">^<span class="i">*</span></code>
, can be used for
variable-width, one-line-at-a-time text. Null characters are now handled
correctly in picture lines. Using <code class="inline"><span class="i">@#</span></code>
and <code class="inline">~~</code>
together will now
produce a compile-time error, as those format fields are incompatible.
<a href="perlform.html">perlform</a> has been improved, and miscellaneous bugs fixed.</p>
<a id="Byte-order-modifiers-for-pack()-and-unpack()"></a><h3 class='h3' >Byte-order modifiers for pack() and unpack()</h3>
<p>There are two new byte-order modifiers, <code class="inline">></code>
(big-endian) and <code class="inline"><</code>
(little-endian), that can be appended to most pack() and unpack() template
characters and groups to force a certain byte-order for that type or group.
See <a href="functions/pack.html">pack</a> and <a href="perlpacktut.html">perlpacktut</a> for details.</p>
<a id="no-VERSION"></a><h3 class='h3' ><code class="inline"><a class="l_k" href="functions/no.html">no</a> <span class="w">VERSION</span></code>
</h3>
<p>You can now use <code class="inline"><a class="l_k" href="functions/no.html">no</a></code> followed by a version number to specify that you
want to use a version of perl older than the specified one.</p>
<a id="chdir%2c-chmod-and-chown-on-filehandles"></a><h3 class='h3' ><code class="inline"><a class="l_k" href="functions/chdir.html">chdir</a></code>, <code class="inline"><a class="l_k" href="functions/chmod.html">chmod</a></code> and <code class="inline"><a class="l_k" href="functions/chown.html">chown</a></code> on filehandles</h3>
<p><code class="inline"><a class="l_k" href="functions/chdir.html">chdir</a></code>, <code class="inline"><a class="l_k" href="functions/chmod.html">chmod</a></code> and <code class="inline"><a class="l_k" href="functions/chown.html">chown</a></code> can now work on filehandles as well as
filenames, if the system supports respectively <code class="inline"><span class="w">fchdir</span></code>
, <code class="inline"><span class="w">fchmod</span></code>
and
<code class="inline"><span class="w">fchown</span></code>
, thanks to a patch provided by Gisle Aas.</p>
<a id="OS-groups"></a><h3 class='h3' >OS groups</h3>
<p><code class="inline"><span class="i">$(</span></code>
and <code class="inline"><span class="i">$)</span></code>
now return groups in the order where the OS returns them,
thanks to Gisle Aas. This wasn't previously the case.</p>
<a id="Recursive-sort-subs"></a><h3 class='h3' >Recursive sort subs</h3>
<p>You can now use recursive subroutines with sort(), thanks to Robin Houston.</p>
<a id="Exceptions-in-constant-folding"></a><h3 class='h3' >Exceptions in constant folding</h3>
<p>The constant folding routine is now wrapped in an exception handler, and
if folding throws an exception (such as attempting to evaluate 0/0), perl
now retains the current optree, rather than aborting the whole program.
Without this change, programs would not compile if they had expressions that
happened to generate exceptions, even though those expressions were in code
that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)</p>
<a id="Source-filters-in-%40INC"></a><h3 class='h3' >Source filters in @INC</h3>
<p>It's possible to enhance the mechanism of subroutine hooks in @INC by
adding a source filter on top of the filehandle opened and returned by the
hook. This feature was planned a long time ago, but wasn't quite working
until now. See <a href="functions/require.html">require</a> for details. (Nicholas Clark)</p>
<a id="New-internal-variables"></a><h3 class='h3' >New internal variables</h3>
<ul>
<li><a id="%24%7b%5eRE_DEBUG_FLAGS%7d"></a><strong><code class="inline"><span class="i">$</span>{<span class="w">^RE_DEBUG_FLAGS</span>}</code>
</strong>
<p>This variable controls what debug flags are in effect for the regular
expression engine when running under <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">re</span> <span class="q">"debug"</span></code>
. See <a href="re.html">re</a> for
details.</p>
</li>
<li><a id="%24%7b%5eCHILD_ERROR_NATIVE%7d"></a><strong><code class="inline"><span class="i">$</span>{<span class="w">^CHILD_ERROR_NATIVE</span>}</code>
</strong>
<p>This variable gives the native status returned by the last pipe close,
backtick command, successful call to wait() or waitpid(), or from the
system() operator. See <a href="perlvar.html">perlvar</a> for details. (Contributed by Gisle Aas.)</p>
</li>
<li><a id="%24%7b%5eRE_TRIE_MAXBUF%7d"></a><strong><code class="inline"><span class="i">$</span>{<span class="w">^RE_TRIE_MAXBUF</span>}</code>
</strong>
<p>See <a href="#Trie-optimisation-of-literal-string-alternations">Trie optimisation of literal string alternations</a>.</p>
</li>
<li><a id="%24%7b%5eWIN32_SLOPPY_STAT%7d"></a><strong><code class="inline"><span class="i">$</span>{<span class="w">^WIN32_SLOPPY_STAT</span>}</code>
</strong>
<p>See <a href="#Sloppy-stat-on-Windows">Sloppy stat on Windows</a>.</p>
</li>
</ul>
<a id="Miscellaneous"></a><h3 class='h3' >Miscellaneous</h3>
<p><code class="inline"><a class="l_k" href="functions/unpack.html">unpack()</a></code> now defaults to unpacking the <code class="inline"><span class="i">$_</span></code>
variable.</p>
<p><code class="inline"><a class="l_k" href="functions/mkdir.html">mkdir()</a></code> without arguments now defaults to <code class="inline"><span class="i">$_</span></code>
.</p>
<p>The internal dump output has been improved, so that non-printable characters
such as newline and backspace are output in <code class="inline">\<span class="w">x</span></code>
notation, rather than
octal.</p>
<p>The <strong>-C</strong> option can no longer be used on the <code class="inline"><span class="c">#!</span></code>
line. It wasn't
working there anyway, since the standard streams are already set up
at this point in the execution of the perl interpreter. You can use
binmode() instead to get the desired behaviour.</p>
<a id="UCD-5.0.0"></a><h3 class='h3' >UCD 5.0.0</h3>
<p>The copy of the Unicode Character Database included in Perl 5 has
been updated to version 5.0.0.</p>
<a id="MAD"></a><h3 class='h3' >MAD</h3>
<p>MAD, which stands for <i>Miscellaneous Attribute Decoration</i>, is a
still-in-development work leading to a Perl 5 to Perl 6 converter. To
enable it, it's necessary to pass the argument <code class="inline">-<span class="w">Dmad</span></code>
to Configure. The
obtained perl isn't binary compatible with a regular perl 5.10, and has
space and speed penalties; moreover not all regression tests still pass
with it. (Larry Wall, Nicholas Clark)</p>
<a id="kill()-on-Windows"></a><h3 class='h3' >kill() on Windows</h3>
<p>On Windows platforms, <code class="inline"><a class="l_k" href="functions/kill.html">kill</a><span class="s">(</span><span class="n">-9</span><span class="cm">,</span> <span class="i">$pid</span><span class="s">)</span></code>
now kills a process tree.
(On Unix, this delivers the signal to all processes in the same process
group.)</p>
<a id="Incompatible-Changes"></a><h2 class='h2' >Incompatible Changes</h2>
<a id="Packing-and-UTF-8-strings"></a><h3 class='h3' >Packing and UTF-8 strings</h3>
<p>The semantics of pack() and unpack() regarding UTF-8-encoded data has been
changed. Processing is now by default character per character instead of
byte per byte on the underlying encoding. Notably, code that used things
like <code class="inline"><a class="l_k" href="functions/pack.html">pack</a><span class="s">(</span><span class="q">"a*"</span><span class="cm">,</span> <span class="i">$string</span><span class="s">)</span></code>
to see through the encoding of string will now
simply get back the original $string. Packed strings can also get upgraded
during processing when you store upgraded characters. You can get the old
behaviour by using <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">bytes</span></code>
.</p>
<p>To be consistent with pack(), the <code class="inline"><span class="w">C0</span></code>
in unpack() templates indicates
that the data is to be processed in character mode, i.e. character by
character; on the contrary, <code class="inline"><span class="w">U0</span></code>
in unpack() indicates UTF-8 mode, where
the packed string is processed in its UTF-8-encoded Unicode form on a byte
by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
between pack() and unpack().</p>
<p>Moreover, <code class="inline"><span class="w">C0</span></code>
and <code class="inline"><span class="w">U0</span></code>
can also be used in pack() templates to specify
respectively character and byte modes.</p>
<p><code class="inline"><span class="w">C0</span></code>
and <code class="inline"><span class="w">U0</span></code>
in the middle of a pack or unpack format now switch to the
specified encoding mode, honoring parens grouping. Previously, parens were
ignored.</p>
<p>Also, there is a new pack() character format, <code class="inline"><span class="w">W</span></code>
, which is intended to
replace the old <code class="inline"><span class="w">C</span></code>
. <code class="inline"><span class="w">C</span></code>
is kept for unsigned chars coded as bytes in
the strings internal representation. <code class="inline"><span class="w">W</span></code>
represents unsigned (logical)
character values, which can be greater than 255. It is therefore more
robust when dealing with potentially UTF-8-encoded data (as <code class="inline"><span class="w">C</span></code>
will wrap
values outside the range 0..255, and not respect the string encoding).</p>
<p>In practice, that means that pack formats are now encoding-neutral, except
<code class="inline"><span class="w">C</span></code>
.</p>
<p>For consistency, <code class="inline"><span class="w">A</span></code>
in unpack() format now trims all Unicode whitespace
from the end of the string. Before perl 5.9.2, it used to strip only the
classical ASCII space characters.</p>
<a id="Byte%2fcharacter-count-feature-in-unpack()"></a><h3 class='h3' >Byte/character count feature in unpack()</h3>
<p>A new unpack() template character, <code class="inline"><span class="q">"."</span></code>
, returns the number of bytes or
characters (depending on the selected encoding mode, see above) read so far.</p>
<a id="The-%24*-and-%24%23-variables-have-been-removed"></a><h3 class='h3' >The <code class="inline"><span class="i">$*</span></code>
and <code class="inline"><span class="i">$#</span></code>
variables have been removed</h3>
<p><code class="inline"><span class="i">$*</span></code>
, which was deprecated in favor of the <code class="inline"><span class="q">/s</span></code>
and <code class="inline"><span class="q">/m</span></code>
regexp
modifiers, has been removed.</p>
<p>The deprecated <code class="inline"><span class="i">$#</span></code>
variable (output format for numbers) has been
removed.</p>
<p>Two new severe warnings, <code class="inline"><span class="i">$#</span>/<span class="i">$*</span> <span class="w">is</span> <a class="l_k" href="functions/no.html">no</a> <span class="w">longer</span> <span class="w">supported</span></code>
, have been added.</p>
<a id="substr()-lvalues-are-no-longer-fixed-length"></a><h3 class='h3' >substr() lvalues are no longer fixed-length</h3>
<p>The lvalues returned by the three argument form of substr() used to be a
"fixed length window" on the original string. In some cases this could
cause surprising action at distance or other undefined behaviour. Now the
length of the window adjusts itself to the length of the string assigned to
it.</p>
<a id="Parsing-of--f-_"></a><h3 class='h3' >Parsing of <code class="inline">-f <span class="i">_</span></code>
</h3>
<p>The identifier <code class="inline"><span class="w">_</span></code>
is now forced to be a bareword after a filetest
operator. This solves a number of misparsing issues when a global <code class="inline"><span class="w">_</span></code>
subroutine is defined.</p>
<a id="%3aunique"></a><h3 class='h3' ><code class="inline"><span class="j">:</span><span class="w">unique</span></code>
</h3>
<p>The <code class="inline"><span class="j">:</span><span class="w">unique</span></code>
attribute has been made a no-op, since its current
implementation was fundamentally flawed and not threadsafe.</p>
<a id="Effect-of-pragmas-in-eval"></a><h3 class='h3' >Effect of pragmas in eval</h3>
<p>The compile-time value of the <code class="inline"><span class="i">%^H</span></code>
hint variable can now propagate into
eval("")uated code. This makes it more useful to implement lexical
pragmas.</p>
<p>As a side-effect of this, the overloaded-ness of constants now propagates
into eval("").</p>
<a id="chdir-FOO"></a><h3 class='h3' >chdir FOO</h3>
<p>A bareword argument to chdir() is now recognized as a file handle.
Earlier releases interpreted the bareword as a directory name.
(Gisle Aas)</p>
<a id="Handling-of-.pmc-files"></a><h3 class='h3' >Handling of .pmc files</h3>
<p>An old feature of perl was that before <code class="inline"><a class="l_k" href="functions/require.html">require</a></code> or <code class="inline"><a class="l_k" href="functions/use.html">use</a></code> look for a
file with a <i>.pm</i> extension, they will first look for a similar filename
with a <i>.pmc</i> extension. If this file is found, it will be loaded in
place of any potentially existing file ending in a <i>.pm</i> extension.</p>
<p>Previously, <i>.pmc</i> files were loaded only if more recent than the
matching <i>.pm</i> file. Starting with 5.9.4, they'll be always loaded if
they exist.</p>
<a id="%24%5eV-is-now-a-version-object-instead-of-a-v-string"></a><h3 class='h3' >$^V is now a <code class="inline"><span class="w">version</span></code>
object instead of a v-string</h3>
<p>$^V can still be used with the <code class="inline"><span class="i">%vd</span></code>
format in printf, but any
character-level operations will now access the string representation
of the <code class="inline"><span class="w">version</span></code>
object and not the ordinals of a v-string.
Expressions like <code class="inline"><a class="l_k" href="functions/substr.html">substr</a><span class="s">(</span><span class="i">$^V</span><span class="cm">,</span> <span class="n">0</span><span class="cm">,</span> <span class="n">2</span><span class="s">)</span></code>
or <code class="inline"><a class="l_k" href="functions/split.html">split</a> <span class="q">//</span><span class="cm">,</span> <span class="i">$^V</span></code>
no longer work and must be rewritten.</p>
<a id="%40--and-%40%2b-in-patterns"></a><h3 class='h3' >@- and @+ in patterns</h3>
<p>The special arrays <code class="inline"><span class="i">@-</span></code>
and <code class="inline"><span class="i">@+</span></code>
are no longer interpolated in regular
expressions. (Sadahiro Tomoyuki)</p>
<a id="%24AUTOLOAD-can-now-be-tainted"></a><h3 class='h3' >$AUTOLOAD can now be tainted</h3>
<p>If you call a subroutine by a tainted name, and if it defers to an
AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
(Rick Delaney)</p>
<a id="Tainting-and-printf"></a><h3 class='h3' >Tainting and printf</h3>
<p>When perl is run under taint mode, <code class="inline"><a class="l_k" href="functions/printf.html">printf()</a></code> and <code class="inline"><a class="l_k" href="functions/sprintf.html">sprintf()</a></code> will now
reject any tainted format argument. (Rafael Garcia-Suarez)</p>
<a id="undef-and-signal-handlers"></a><h3 class='h3' >undef and signal handlers</h3>
<p>Undefining or deleting a signal handler via <code class="inline"><a class="l_k" href="functions/undef.html">undef</a> <span class="i">$SIG</span>{<span class="w">FOO</span>}</code>
is now
equivalent to setting it to <code class="inline"><span class="q">'DEFAULT'</span></code>
. (Rafael Garcia-Suarez)</p>
<a id="strictures-and-dereferencing-in-defined()"></a><h3 class='h3' >strictures and dereferencing in defined()</h3>
<p><code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">'refs'</span></code>
was ignoring taking a hard reference in an argument
to defined(), as in :</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">'refs'</span><span class="sc">;</span></li><li> <a class="l_k" href="functions/my.html">my</a> <span class="i">$x</span> = <span class="q">'foo'</span><span class="sc">;</span></li><li> <a class="l_k" href="functions/if.html">if</a> <span class="s">(</span><a class="l_k" href="functions/defined.html">defined</a> <span class="i">$$x</span><span class="s">)</span> <span class="s">{</span>...<span class="s">}</span></li></ol></pre><p>This now correctly produces the run-time error <code class="inline"><span class="w">Can't</span> <a class="l_k" href="functions/use.html">use</a> <span class="w">string</span> <span class="w">as</span> <span class="w">a</span>
<span class="w">SCALAR</span> <a class="l_k" href="functions/ref.html">ref</a> <a class="l_k" href="functions/while.html">while</a> <span class="q">"strict refs"</span> <span class="w">in</span> <a class="l_k" href="functions/use.html">use</a></code>
.</p>
<p><code class="inline"><a class="l_k" href="functions/defined.html">defined</a> <span class="i">@$foo</span></code>
and <code class="inline"><a class="l_k" href="functions/defined.html">defined</a> <span class="i">%$bar</span></code>
are now also subject to <code class="inline"><span class="w">strict</span>
<span class="q">'refs'</span></code>
(that is, <code class="inline"><span class="i">$foo</span></code>
and <code class="inline"><span class="i">$bar</span></code>
shall be proper references there.)
(<code class="inline"><a class="l_k" href="functions/defined.html">defined(@foo)</a></code> and <code class="inline"><a class="l_k" href="functions/defined.html">defined(%bar)</a></code> are discouraged constructs anyway.)
(Nicholas Clark)</p>
<a id="(%3fp%7b%7d)-has-been-removed"></a><h3 class='h3' ><code class="inline"><span class="s">(</span><span class="q">?p{})</span></code>
has been removed</h3>
<p>The regular expression construct <code class="inline"><span class="s">(</span><span class="q">?p{})</span></code>
, which was deprecated in perl
5.8, has been removed. Use <code class="inline"><span class="s">(</span><span class="q">??</span><span class="s">{</span><span class="s">}</span><span class="s">)</span></code>
instead. (Rafael Garcia-Suarez)</p>
<a id="Pseudo-hashes-have-been-removed"></a><h3 class='h3' >Pseudo-hashes have been removed</h3>
<p>Support for pseudo-hashes has been removed from Perl 5.9. (The <code class="inline"><span class="w">fields</span></code>
pragma remains here, but uses an alternate implementation.)</p>
<a id="Removal-of-the-bytecode-compiler-and-of-perlcc"></a><h3 class='h3' >Removal of the bytecode compiler and of perlcc</h3>
<p><code class="inline"><span class="w">perlcc</span></code>
, the byteloader and the supporting modules (B::C, B::CC,
B::Bytecode, etc.) are no longer distributed with the perl sources. Those
experimental tools have never worked reliably, and, due to the lack of
volunteers to keep them in line with the perl interpreter developments, it
was decided to remove them instead of shipping a broken version of those.
The last version of those modules can be found with perl 5.9.4.</p>
<p>However the B compiler framework stays supported in the perl core, as with
the more useful modules it has permitted (among others, B::Deparse and
B::Concise).</p>
<a id="Removal-of-the-JPL"></a><h3 class='h3' >Removal of the JPL</h3>
<p>The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.</p>
<a id="Recursive-inheritance-detected-earlier"></a><h3 class='h3' >Recursive inheritance detected earlier</h3>
<p>Perl will now immediately throw an exception if you modify any package's
<code class="inline"><span class="i">@ISA</span></code>
in such a way that it would cause recursive inheritance.</p>
<p>Previously, the exception would not occur until Perl attempted to make
use of the recursive inheritance while resolving a method or doing a
<code class="inline"><span class="i">$foo</span><span class="i">->isa</span><span class="s">(</span><span class="i">$bar</span><span class="s">)</span></code>
lookup.</p>
<a id="warnings%3a%3aenabled-and-warnings%3a%3awarnif-changed-to-favor-users-of-modules"></a><h3 class='h3' >warnings::enabled and warnings::warnif changed to favor users of modules</h3>
<p>The behaviour in 5.10.x favors the person using the module;
The behaviour in 5.8.x favors the module writer;</p>
<p>Assume the following code:</p>
<pre class="verbatim"><ol><li> <span class="w">main</span> <span class="w">calls</span> <span class="i">Foo::Bar::baz</span><span class="s">(</span><span class="s">)</span></li><li> <span class="w">Foo::Bar</span> <span class="w">inherits</span> <span class="w">from</span> <span class="w">Foo::Base</span></li><li> <span class="i">Foo::Bar::baz</span><span class="s">(</span><span class="s">)</span> <span class="w">calls</span> <span class="i">Foo::Base::_bazbaz</span><span class="s">(</span><span class="s">)</span></li><li> <span class="i">Foo::Base::_bazbaz</span><span class="s">(</span><span class="s">)</span> <span class="w">calls</span><span class="co">:</span> <span class="i">warnings::warnif</span><span class="s">(</span><span class="q">'substr'</span><span class="cm">,</span> <span class="q">'some warning </span></li><li><span class="q">message'</span><span class="s">)</span><span class="sc">;</span></li></ol></pre><p>On 5.8.x, the code warns when Foo::Bar contains <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">warnings</span><span class="sc">;</span></code>
It does not matter if Foo::Base or main have warnings enabled
to disable the warning one has to modify Foo::Bar.</p>
<p>On 5.10.0 and newer, the code warns when main contains <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">warnings</span><span class="sc">;</span></code>
It does not matter if Foo::Base or Foo::Bar have warnings enabled
to disable the warning one has to modify main.</p>
<a id="Modules-and-Pragmata"></a><h2 class='h2' >Modules and Pragmata</h2>
<a id="Upgrading-individual-core-modules"></a><h3 class='h3' >Upgrading individual core modules</h3>
<p>Even more core modules are now also available separately through the
CPAN. If you wish to update one of these modules, you don't need to
wait for a new perl release. From within the cpan shell, running the
'r' command will report on modules with upgrades available. See
<code class="inline"><span class="w">perldoc</span> <span class="w">CPAN</span></code>
for more information.</p>
<a id="Pragmata-Changes"></a><h3 class='h3' >Pragmata Changes</h3>
<ul>
<li><a id="feature"></a><strong><code class="inline"><span class="w">feature</span></code>
</strong>
<p>The new pragma <code class="inline"><span class="w">feature</span></code>
is used to enable new features that might break
old code. See <a href="#The-feature-pragma">The feature pragma</a> above.</p>
</li>
<li><a id="mro"></a><strong><code class="inline"><span class="w">mro</span></code>
</strong>
<p>This new pragma enables to change the algorithm used to resolve inherited
methods. See <a href="#New-Pragma%2c-mro">New Pragma, mro</a> above.</p>
</li>
<li><a id="Scoping-of-the-sort-pragma"></a><strong>Scoping of the <code class="inline"><a class="l_k" href="functions/sort.html">sort</a></code> pragma</strong>
<p>The <code class="inline"><a class="l_k" href="functions/sort.html">sort</a></code> pragma is now lexically scoped. Its effect used to be global.</p>
</li>
<li><a id="Scoping-of-bignum%2c-bigint%2c-bigrat"></a><strong>Scoping of <code class="inline"><span class="w">bignum</span></code>
, <code class="inline"><span class="w">bigint</span></code>
, <code class="inline"><span class="w">bigrat</span></code>
</strong>
<p>The three numeric pragmas <code class="inline"><span class="w">bignum</span></code>
, <code class="inline"><span class="w">bigint</span></code>
and <code class="inline"><span class="w">bigrat</span></code>
are now
lexically scoped. (Tels)</p>
</li>
<li><a id="base"></a><strong><code class="inline"><span class="w">base</span></code>
</strong>
<p>The <code class="inline"><span class="w">base</span></code>
pragma now warns if a class tries to inherit from itself.
(Curtis "Ovid" Poe)</p>
</li>
<li><a id="strict-and-warnings"></a><strong><code class="inline"><span class="w">strict</span></code>
and <code class="inline"><span class="w">warnings</span></code>
</strong>
<p><code class="inline"><span class="w">strict</span></code>
and <code class="inline"><span class="w">warnings</span></code>
will now complain loudly if they are loaded via
incorrect casing (as in <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">Strict</span><span class="sc">;</span></code>
). (Johan Vromans)</p>
</li>
<li><a id="version"></a><strong><code class="inline"><span class="w">version</span></code>
</strong>
<p>The <code class="inline"><span class="w">version</span></code>
module provides support for version objects.</p>
</li>
<li><a id="warnings"></a><strong><code class="inline"><span class="w">warnings</span></code>
</strong>
<p>The <code class="inline"><span class="w">warnings</span></code>
pragma doesn't load <code class="inline"><span class="w">Carp</span></code>
anymore. That means that code
that used <code class="inline"><span class="w">Carp</span></code>
routines without having loaded it at compile time might
need to be adjusted; typically, the following (faulty) code won't work
anymore, and will require parentheses to be added after the function name:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/use.html">use</a> <span class="w">warnings</span><span class="sc">;</span></li><li> <a class="l_k" href="functions/require.html">require</a> <span class="w">Carp</span><span class="sc">;</span></li><li> <span class="w">Carp::confess</span> <span class="q">'argh'</span><span class="sc">;</span></li></ol></pre></li>
<li><a id="less"></a><strong><code class="inline"><span class="w">less</span></code>
</strong>
<p><code class="inline"><span class="w">less</span></code>
now does something useful (or at least it tries to). In fact, it
has been turned into a lexical pragma. So, in your modules, you can now
test whether your users have requested to use less CPU, or less memory,
less magic, or maybe even less fat. See <a href="less.html">less</a> for more. (Joshua ben
Jore)</p>
</li>
</ul>
<a id="New-modules"></a><h3 class='h3' >New modules</h3>
<ul>