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Gurusamy Sarathy


perldelta - what's new for perl5.006 (as of 5.005_56)


This document describes differences between the 5.005 release and this one.

Incompatible Changes

Perl Source Incompatibilities

None known at this time.

C Source Incompatibilities


Release 5.005 grandfathered old global symbol names by providing preprocessor macros for extension source compatibility. As of release 5.006, these preprocessor definitions are not available by default. You need to explicitly compile perl with -DPERL_POLLUTE to get these definitions. For extensions still using the old symbols, this option can be specified via MakeMaker:

    perl Makefile.PL POLLUTE=1

Enabling Perl's malloc in release 5.005 and earlier caused the namespace of system versions of the malloc family of functions to be usurped by the Perl versions, since by default they used the same names.

Besides causing problems on platforms that do not allow these functions to be cleanly replaced, this also meant that the system versions could not be called in programs that used Perl's malloc. Previous versions of Perl have allowed this behaviour to be suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor definitions.

As of release 5.006, Perl's malloc family of functions have default names distinct from the system versions. You need to explicitly compile perl with -DPERL_POLLUTE_MALLOC to get the older behaviour. HIDEMYMALLOC and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now the default.

Note that these functions do not constitute Perl's memory allocation API. See "Memory Allocation" in perlguts for further information about that.

PL_na and dTHR Issues

The PL_na global is now thread local, so a dTHR declaration is needed in the scope in which the global appears. XSUBs should handle this automatically, but if you have used PL_na in support functions, you either need to change the PL_na to a local variable (which is recommended), or put in a dTHR.

Compatible C Source API Changes


The cpp macros PERL_REVISION, PERL_VERSION, and PERL_SUBVERSION are now available by default from perl.h, and reflect the base revision, patchlevel, and subversion respectively. PERL_REVISION had no prior equivalent, while PERL_VERSION and PERL_SUBVERSION were previously available as PATCHLEVEL and SUBVERSION.

The new names cause less pollution of the cpp namespace and reflect what the numbers have come to stand for in common practice. For compatibility, the old names are still supported when patchlevel.h is explicitly included (as required before), so there is no source incompatibility from the change.

Binary Incompatibilities

This release is not binary compatible with the 5.005 release or its maintenance versions.

Core Changes

Unicode and UTF-8 support

Perl can optionally use UTF-8 as its internal representation for character strings. The use utf8 pragma enables this support in the current lexical scope. See utf8 for more information.

Lexically scoped warning categories

You can now control the granularity of warnings emitted by perl at a finer level using the use warning pragma. See warning for details.

Binary numbers supported

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

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

syswrite() ease-of-use

The length argument of syswrite() is now optional.

64-bit support

Better 64-bit support -- but full support still a distant goal. One must Configure with -Duse64bits to get Configure to probe for the extent of 64-bit support. Depending on the platform (hints file) more or less 64-awareness becomes available. As of 5.005_54 at least somewhat 64-bit aware platforms are HP-UX 11 or better, Solaris 2.6 or better, IRIX 6.2 or better. Naturally 64-bit platforms like Digital Unix and UNICOS also have 64-bit support.

Better syntax checks on parenthesized unary operators

Expressions such as:

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

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

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

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

remains unchanged. See perlop.

Improved qw// operator

The qw// operator is now evaluated at compile time into a true list instead of being replaced with a run time call to split(). This removes the confusing misbehaviour of qw// in scalar context, which had inherited that behaviour from split().


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

now correctly prints "3|a", instead of "2|a".

pack() format 'Z' supported

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

pack() format modifier '!' supported

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

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

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

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

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

Significant bug fixes

<HANDLE> on empty files

With $/ set to undef, slurping an empty file returns a string of zero length (instead of undef, as it used to) the first time the HANDLE is read. Further reads yield undef.

This means that the following will append "foo" to an empty file (it used to do nothing):

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

The behaviour of:

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

is unchanged (it continues to leave the file empty).

eval '...' improvements

Line numbers (as reflected by caller() and most diagnostics) within eval '...' were often incorrect when here documents were involved. This has been corrected.

Lexical lookups for variables appearing in eval '...' within functions that were themselves called within an eval '...' were searching the wrong place for lexicals. The lexical search now correctly ends at the subroutine's block boundary.

Parsing of here documents used to be flawed when they appeared as the replacement expression in eval 's/.../.../e'. This has been fixed.

Automatic flushing of output buffers

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

Supported Platforms

  • VM/ESA is now supported.

  • Siemens BS2000 is now supported under the POSIX Shell.

  • The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread extension.

  • GNU/Hurd is now supported.

  • Rhapsody is now supported.

New tests


IO constants (SEEK_*, _IO*).


Directory-related IO methods (new, read, close, rewind, tied delete).


INET sockets with multi-homed hosts.


IO poll().


UNIX sockets.


File test operators.


Verify operations that access pad objects (lexicals and temporaries).

Modules and Pragmata



Added Dumpvalue module provides screen dumps of Perl data.


You can now run tests for n seconds instead of guessing the right number of tests to run: e.g. timethese(-5, ...) will run each code for at least 5 CPU seconds. Zero as the "number of repetitions" means "for at least 3 CPU seconds". The output format has also changed. For example:

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

will now output something like this:

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

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


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


More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for large (more than 4G) file access (64-bit support is not yet working, though, so no need to get overly excited), Free/Net/OpenBSD locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.


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


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

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

instead of

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

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


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


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


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


The timelocal() and timegm() functions used to silently return bogus results when the date exceeded the machine's integer range. They now consistently croak() if the date falls in an unsupported range.


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


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

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

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

DBM Filters

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


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


use utf8 to enable UTF-8 and Unicode support.

Lexical warnings pragma, use warning;, to control optional warnings.

use filetest to control the behaviour of filetests (-r -w ...). Currently only one subpragma implemented, "use filetest 'access';", that enables the use of access(2) or equivalent to check permissions instead of using stat(2) as usual. This matters in filesystems where there are ACLs (access control lists): the stat(2) might lie, but access(2) knows better.

Utility Changes


Documentation Changes


A tutorial on using open() effectively.


A tutorial that introduces the essentials of references.


A tutorial on managing class data for object modules.

New Diagnostics

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

(W) You used a backslash-character combination which is not recognized by Perl. This combination appears in an interpolated variable or a '-delimited regular expression.

Unrecognized escape \\%c passed through

(W) You used a backslash-character combination which is not recognized by Perl.

Missing command in piped open

(W) You used the open(FH, "| command") or open(FH, "command |") construction, but the command was missing or blank.

Obsolete Diagnostics


Configuration Changes

You can use "Configure -Uinstallusrbinperl" which causes installperl to skip installing perl also as /usr/bin/perl. This is useful if you prefer not to modify /usr/bin for some reason or another but harmful because many scripts assume to find Perl in /usr/bin/perl.


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

If you believe you have an unreported bug, please run the perlbug program included with your release. Make 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.com to be analysed by the Perl porting team.


The Changes file for exhaustive details on what changed.

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.


Written by Gurusamy Sarathy <gsar@umich.edu>, with many contributions from The Perl Porters.

Send omissions or corrections to <perlbug@perl.com>.

2 POD Errors

The following errors were encountered while parsing the POD:

Around line 460:

'=item' outside of any '=over'

Around line 476:

You forgot a '=back' before '=head1'