PERL5004DELTA(1) Perl Programmers Reference GuidePERL5004DELTA(1)
NAME
perldelta - what's new for perl5.004
DESCRIPTION
This document describes differences between the 5.003
release (as documented in Programming Perl, second
edition--the Camel Book) and this one.
Supported Environments
Perl5.004 builds out of the box on Unix, Plan 9, LynxOS,
VMS, OS/2, QNX, AmigaOS, and Windows NT. Perl runs on
Windows 95 as well, but it cannot be built there, for lack
of a reasonable command interpreter.
Core Changes
Most importantly, many bugs were fixed, including several
security problems. See the Changes file in the
distribution for details.
List assignment to %ENV works
%ENV = () and %ENV = @list now work as expected (except on
VMS where it generates a fatal error).
""Can't locate Foo.pm in @INC"" error now lists @INC
Compilation option: Binary compatibility with 5.003
There is a new Configure question that asks if you want to
maintain binary compatibility with Perl 5.003. If you
choose binary compatibility, you do not have to recompile
your extensions, but you might have symbol conflicts if
you embed Perl in another application, just as in the
5.003 release. By default, binary compatibility is
preserved at the expense of symbol table pollution.
$PERL5OPT environment variable
You may now put Perl options in the $PERL5OPT environment
variable. Unless Perl is running with taint checks, it
will interpret this variable as if its contents had
appeared on a "#!perl" line at the beginning of your
script, except that hyphens are optional. PERL5OPT may
only be used to set the following switches: -[DIMUdmw].
Limitations on -M, -m, and -T options
The -M and -m options are no longer allowed on the #! line
of a script. If a script needs a module, it should invoke
it with the use pragma.
The -T option is also forbidden on the #! line of a
script, unless it was present on the Perl command line.
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Due to the way #! works, this usually means that -T must
be in the first argument. Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as
scriptname, while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix
systems will probably not follow this rule.) But perl
scriptname is guaranteed to fail, since then there is no
chance of -T being found on the command line before it is
found on the #! line.
More precise warnings
If you removed the -w option from your Perl 5.003 scripts
because it made Perl too verbose, we recommend that you
try putting it back when you upgrade to Perl 5.004. Each
new perl version tends to remove some undesirable
warnings, while adding new warnings that may catch bugs in
your scripts.
Deprecated: Inherited AUTOLOAD for non-methods
Before Perl 5.004, AUTOLOAD functions were looked up as
methods (using the @ISA hierarchy), even when the function
to be autoloaded was called as a plain function (e.g.
Foo::bar()), not a method (e.g. Foo->bar() or
$obj->bar()).
Perl 5.005 will use method lookup only for methods'
AUTOLOADs. However, there is a significant base of
existing code that may be using the old behavior. So, as
an interim step, Perl 5.004 issues an optional warning
when a non-method uses an inherited AUTOLOAD.
The simple rule is: Inheritance will not work when
autoloading non-methods. The simple fix for old code is:
In any module that used to depend on inheriting AUTOLOAD
for non-methods from a base class named BaseClass, execute
*AUTOLOAD = \&BaseClass::AUTOLOAD during startup.
Previously deprecated %OVERLOAD is no longer usable
Using %OVERLOAD to define overloading was deprecated in
5.003. Overloading is now defined using the overload
pragma. %OVERLOAD is still used internally but should not
be used by Perl scripts. See the overload manpage for more
details.
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Subroutine arguments created only when they're modified
In Perl 5.004, nonexistent array and hash elements used as
subroutine parameters are brought into existence only if
they are actually assigned to (via @_).
Earlier versions of Perl vary in their handling of such
arguments. Perl versions 5.002 and 5.003 always brought
them into existence. Perl versions 5.000 and 5.001
brought them into existence only if they were not the
first argument (which was almost certainly a bug).
Earlier versions of Perl never brought them into
existence.
For example, given this code:
undef @a; undef %a;
sub show { print $_[0] };
sub change { $_[0]++ };
show($a[2]);
change($a{b});
After this code executes in Perl 5.004, $a{b} exists but
$a[2] does not. In Perl 5.002 and 5.003, both $a{b} and
$a[2] would have existed (but $a[2]'s value would have
been undefined).
Group vector changeable with $)
The $) special variable has always (well, in Perl 5, at
least) reflected not only the current effective group, but
also the group list as returned by the getgroups() C
function (if there is one). However, until this release,
there has not been a way to call the setgroups() C
function from Perl.
In Perl 5.004, assigning to $) is exactly symmetrical with
examining it: The first number in its string value is used
as the effective gid; if there are any numbers after the
first one, they are passed to the setgroups() C function
(if there is one).
Fixed parsing of $$<digit>, &$<digit>, etc.
Perl versions before 5.004 misinterpreted any type marker
followed by "$" and a digit. For example, "$$0" was
incorrectly taken to mean "${$}0" instead of "${$0}".
This bug is (mostly) fixed in Perl 5.004.
However, the developers of Perl 5.004 could not fix this
bug completely, because at least two widely-used modules
depend on the old meaning of "$$0" in a string. So Perl
5.004 still interprets "$$<digit>" in the old (broken) way
inside strings; but it generates this message as a
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warning. And in Perl 5.005, this special treatment will
cease.
Fixed localization of $<digit>, $&, etc.
Perl versions before 5.004 did not always properly
localize the regex-related special variables. Perl 5.004
does localize them, as the documentation has always said
it should. This may result in $1, $2, etc. no longer
being set where existing programs use them.
No resetting of $. on implicit close
The documentation for Perl 5.0 has always stated that $.
is not reset when an already-open file handle is reopened
with no intervening call to close. Due to a bug, perl
versions 5.000 through 5.003 did reset $. under that
circumstance; Perl 5.004 does not.
wantarray may return undef
The wantarray operator returns true if a subroutine is
expected to return a list, and false otherwise. In Perl
5.004, wantarray can also return the undefined value if a
subroutine's return value will not be used at all, which
allows subroutines to avoid a time-consuming calculation
of a return value if it isn't going to be used.
eval EXPR determines value of EXPR in scalar context
Perl (version 5) used to determine the value of EXPR
inconsistently, sometimes incorrectly using the
surrounding context for the determination. Now, the value
of EXPR (before being parsed by eval) is always determined
in a scalar context. Once parsed, it is executed as
before, by providing the context that the scope
surrounding the eval provided. This change makes the
behavior Perl4 compatible, besides fixing bugs resulting
from the inconsistent behavior. This program:
@a = qw(time now is time);
print eval @a;
print '|', scalar eval @a;
used to print something like "timenowis881399109|4", but
now (and in perl4) prints "4|4".
Changes to tainting checks
A bug in previous versions may have failed to detect some
insecure conditions when taint checks are turned on.
(Taint checks are used in setuid or setgid scripts, or
when explicitly turned on with the -T invocation option.)
Although it's unlikely, this may cause a previously-
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working script to now fail -- which should be construed as
a blessing, since that indicates a potentially-serious
security hole was just plugged.
The new restrictions when tainting include:
No glob() or <*>
These operators may spawn the C shell (csh), which
cannot be made safe. This restriction will be lifted
in a future version of Perl when globbing is
implemented without the use of an external program.
No spawning if tainted $CDPATH, $ENV, $BASH_ENV
These environment variables may alter the behavior of
spawned programs (especially shells) in ways that
subvert security. So now they are treated as
dangerous, in the manner of $IFS and $PATH.
No spawning if tainted $TERM doesn't look like a terminal
name
Some termcap libraries do unsafe things with $TERM.
However, it would be unnecessarily harsh to treat all
$TERM values as unsafe, since only shell
metacharacters can cause trouble in $TERM. So a
tainted $TERM is considered to be safe if it contains
only alphanumerics, underscores, dashes, and colons,
and unsafe if it contains other characters (including
whitespace).
New Opcode module and revised Safe module
A new Opcode module supports the creation, manipulation
and application of opcode masks. The revised Safe module
has a new API and is implemented using the new Opcode
module. Please read the new Opcode and Safe
documentation.
Embedding improvements
In older versions of Perl it was not possible to create
more than one Perl interpreter instance inside a single
process without leaking like a sieve and/or crashing. The
bugs that caused this behavior have all been fixed.
However, you still must take care when embedding Perl in a
C program. See the updated perlembed manpage for tips on
how to manage your interpreters.
Internal change: FileHandle class based on IO::* classes
File handles are now stored internally as type IO::Handle.
The FileHandle module is still supported for backwards
compatibility, but it is now merely a front end to the
IO::* modules -- specifically, IO::Handle, IO::Seekable,
and IO::File. We suggest, but do not require, that you
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use the IO::* modules in new code.
In harmony with this change, *GLOB{FILEHANDLE} is now just
a backward-compatible synonym for *GLOB{IO}.
Internal change: PerlIO abstraction interface
It is now possible to build Perl with AT&T's sfio IO
package instead of stdio. See the perlapio manpage for
more details, and the INSTALL file for how to use it.
New and changed syntax
$coderef->(PARAMS)
A subroutine reference may now be suffixed with an
arrow and a (possibly empty) parameter list. This
syntax denotes a call of the referenced subroutine,
with the given parameters (if any).
This new syntax follows the pattern of
$hashref->{FOO} and $aryref->[$foo]: You may now
write &$subref($foo) as $subref->($foo). All of
these arrow terms may be chained; thus,
&{$table->{FOO}}($bar) may now be written
$table->{FOO}->($bar).
New and changed builtin constants
__PACKAGE__
The current package name at compile time, or the
undefined value if there is no current package (due
to a package; directive). Like __FILE__ and
__LINE__, __PACKAGE__ does not interpolate into
strings.
New and changed builtin variables
$^E Extended error message on some platforms. (Also
known as $EXTENDED_OS_ERROR if you use English).
$^H The current set of syntax checks enabled by use
strict. See the documentation of strict for more
details. Not actually new, but newly documented.
Because it is intended for internal use by Perl core
components, there is no use English long name for
this variable.
$^M By default, running out of memory it is not
trappable. However, if compiled for this, Perl may
use the contents of $^M as an emergency pool after
die()ing with this message. Suppose that your Perl
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were compiled with -DPERL_EMERGENCY_SBRK and used
Perl's malloc. Then
$^M = 'a' x (1<<16);
would allocate a 64K buffer for use when in
emergency. See the INSTALL file for information on
how to enable this option. As a disincentive to
casual use of this advanced feature, there is no use
English long name for this variable.
New and changed builtin functions
delete on slices
This now works. (e.g. delete @ENV{'PATH',
'MANPATH'})
flock
is now supported on more platforms, prefers fcntl to
lockf when emulating, and always flushes before
(un)locking.
printf and sprintf
Perl now implements these functions itself; it
doesn't use the C library function sprintf() any
more, except for floating-point numbers, and even
then only known flags are allowed. As a result, it
is now possible to know which conversions and flags
will work, and what they will do.
The new conversions in Perl's sprintf() are:
%i a synonym for %d
%p a pointer (the address of the Perl value, in hexadecimal)
%n special: *stores* the number of characters output so far
into the next variable in the parameter list
The new flags that go between the % and the
conversion are:
# prefix octal with "0", hex with "0x"
h interpret integer as C type "short" or "unsigned short"
V interpret integer as Perl's standard integer type
Also, where a number would appear in the flags, an
asterisk ("*") may be used instead, in which case
Perl uses the next item in the parameter list as the
given number (that is, as the field width or
precision). If a field width obtained through "*" is
negative, it has the same effect as the '-' flag:
left-justification.
See the sprintf entry in the perlfunc manpage for a
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complete list of conversion and flags.
keys as an lvalue
As an lvalue, keys allows you to increase the number
of hash buckets allocated for the given hash. This
can gain you a measure of efficiency if you know the
hash is going to get big. (This is similar to pre-
extending an array by assigning a larger number to
$#array.) If you say
keys %hash = 200;
then %hash will have at least 200 buckets allocated
for it. These buckets will be retained even if you
do %hash = (); use undef %hash if you want to free
the storage while %hash is still in scope. You can't
shrink the number of buckets allocated for the hash
using keys in this way (but you needn't worry about
doing this by accident, as trying has no effect).
my() in Control Structures
You can now use my() (with or without the
parentheses) in the control expressions of control
structures such as:
while (defined(my $line = <>)) {
$line = lc $line;
} continue {
print $line;
}
if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
user_agrees();
} elsif ($answer =~ /^n(o)?$/i) {
user_disagrees();
} else {
chomp $answer;
die "`$answer' is neither `yes' nor `no'";
}
Also, you can declare a foreach loop control variable
as lexical by preceding it with the word "my". For
example, in:
foreach my $i (1, 2, 3) {
some_function();
}
$i is a lexical variable, and the scope of $i extends
to the end of the loop, but not beyond it.
Note that you still cannot use my() on global
punctuation variables such as $_ and the like.
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pack() and unpack()
A new format 'w' represents a BER compressed integer
(as defined in ASN.1). Its format is a sequence of
one or more bytes, each of which provides seven bits
of the total value, with the most significant first.
Bit eight of each byte is set, except for the last
byte, in which bit eight is clear.
If 'p' or 'P' are given undef as values, they now
generate a NULL pointer.
Both pack() and unpack() now fail when their
templates contain invalid types. (Invalid types used
to be ignored.)
sysseek()
The new sysseek() operator is a variant of seek()
that sets and gets the file's system read/write
position, using the lseek(2) system call. It is the
only reliable way to seek before using sysread() or
syswrite(). Its return value is the new position, or
the undefined value on failure.
use VERSION
If the first argument to use is a number, it is
treated as a version number instead of a module name.
If the version of the Perl interpreter is less than
VERSION, then an error message is printed and Perl
exits immediately. Because use occurs at compile
time, this check happens immediately during the
compilation process, unlike require VERSION, which
waits until runtime for the check. This is often
useful if you need to check the current Perl version
before useing library modules which have changed in
incompatible ways from older versions of Perl. (We
try not to do this more than we have to.)
use Module VERSION LIST
If the VERSION argument is present between Module and
LIST, then the use will call the VERSION method in
class Module with the given version as an argument.
The default VERSION method, inherited from the
UNIVERSAL class, croaks if the given version is
larger than the value of the variable
$Module::VERSION. (Note that there is not a comma
after VERSION!)
This version-checking mechanism is similar to the one
currently used in the Exporter module, but it is
faster and can be used with modules that don't use
the Exporter. It is the recommended method for new
code.
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prototype(FUNCTION)
Returns the prototype of a function as a string (or
undef if the function has no prototype). FUNCTION is
a reference to or the name of the function whose
prototype you want to retrieve. (Not actually new;
just never documented before.)
srand
The default seed for srand, which used to be time,
has been changed. Now it's a heady mix of difficult-
to-predict system-dependent values, which should be
sufficient for most everyday purposes.
Previous to version 5.004, calling rand without first
calling srand would yield the same sequence of random
numbers on most or all machines. Now, when perl sees
that you're calling rand and haven't yet called
srand, it calls srand with the default seed. You
should still call srand manually if your code might
ever be run on a pre-5.004 system, of course, or if
you want a seed other than the default.
$_ as Default
Functions documented in the Camel to default to $_
now in fact do, and all those that do are so
documented in the perlfunc manpage.
m//gc does not reset search position on failure
The m//g match iteration construct has always reset
its target string's search position (which is visible
through the pos operator) when a match fails; as a
result, the next m//g match after a failure starts
again at the beginning of the string. With Perl
5.004, this reset may be disabled by adding the "c"
(for "continue") modifier, i.e. m//gc. This feature,
in conjunction with the \G zero-width assertion,
makes it possible to chain matches together. See the
perlop manpage and the perlre manpage.
m//x ignores whitespace before ?*+{}
The m//x construct has always been intended to ignore
all unescaped whitespace. However, before Perl
5.004, whitespace had the effect of escaping repeat
modifiers like "*" or "?"; for example, /a *b/x was
(mis)interpreted as /a\*b/x. This bug has been fixed
in 5.004.
nested sub{} closures work now
Prior to the 5.004 release, nested anonymous
functions didn't work right. They do now.
formats work right on changing lexicals
Just like anonymous functions that contain lexical
variables that change (like a lexical index variable
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for a foreach loop), formats now work properly. For
example, this silently failed before (printed only
zeros), but is fine now:
my $i;
foreach $i ( 1 .. 10 ) {
write;
}
format =
my i is @#
$i
.
However, it still fails (without a warning) if the
foreach is within a subroutine:
my $i;
sub foo {
foreach $i ( 1 .. 10 ) {
write;
}
}
foo;
format =
my i is @#
$i
.
New builtin methods
The UNIVERSAL package automatically contains the following
methods that are inherited by all other classes:
isa(CLASS)
isa returns true if its object is blessed into a
subclass of CLASS
isa is also exportable and can be called as a sub
with two arguments. This allows the ability to check
what a reference points to. Example:
use UNIVERSAL qw(isa);
if(isa($ref, 'ARRAY')) {
...
}
can(METHOD)
can checks to see if its object has a method called
METHOD, if it does then a reference to the sub is
returned; if it does not then undef is returned.
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VERSION( [NEED] )
VERSION returns the version number of the class
(package). If the NEED argument is given then it
will check that the current version (as defined by
the $VERSION variable in the given package) not less
than NEED; it will die if this is not the case. This
method is normally called as a class method. This
method is called automatically by the VERSION form of
use.
use A 1.2 qw(some imported subs);
# implies:
A->VERSION(1.2);
NOTE: can directly uses Perl's internal code for method
lookup, and isa uses a very similar method and caching
strategy. This may cause strange effects if the Perl code
dynamically changes @ISA in any package.
You may add other methods to the UNIVERSAL class via Perl
or XS code. You do not need to use UNIVERSAL in order to
make these methods available to your program. This is
necessary only if you wish to have isa available as a
plain subroutine in the current package.
TIEHANDLE now supported
See the perltie manpage for other kinds of tie()s.
TIEHANDLE classname, LIST
This is the constructor for the class. That means it
is expected to return an object of some sort. The
reference can be used to hold some internal
information.
sub TIEHANDLE {
print "<shout>\n";
my $i;
return bless \$i, shift;
}
PRINT this, LIST
This method will be triggered every time the tied
handle is printed to. Beyond its self reference it
also expects the list that was passed to the print
function.
sub PRINT {
$r = shift;
$$r++;
return print join( $, => map {uc} @_), $\;
}
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PRINTF this, LIST
This method will be triggered every time the tied
handle is printed to with the printf() function.
Beyond its self reference it also expects the format
and list that was passed to the printf function.
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."\n";
}
READ this LIST
This method will be called when the handle is read
from via the read or sysread functions.
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
READLINE this
This method will be called when the handle is read
from. The method should return undef when there is no
more data.
sub READLINE {
$r = shift;
return "PRINT called $$r times\n"
}
GETC this
This method will be called when the getc function is
called.
sub GETC { print "Don't GETC, Get Perl"; return "a"; }
DESTROY this
As with the other types of ties, this method will be
called when the tied handle is about to be destroyed.
This is useful for debugging and possibly for
cleaning up.
sub DESTROY {
print "</shout>\n";
}
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Malloc enhancements
If perl is compiled with the malloc included with the perl
distribution (that is, if perl -V:d_mymalloc is 'define')
then you can print memory statistics at runtime by running
Perl thusly:
env PERL_DEBUG_MSTATS=2 perl your_script_here
The value of 2 means to print statistics after compilation
and on exit; with a value of 1, the statistics are printed
only on exit. (If you want the statistics at an arbitrary
time, you'll need to install the optional module
Devel::Peek.)
Three new compilation flags are recognized by malloc.c.
(They have no effect if perl is compiled with system
malloc().)
-DPERL_EMERGENCY_SBRK
If this macro is defined, running out of memory need
not be a fatal error: a memory pool can allocated by
assigning to the special variable $^M. See the
section on $^M.
-DPACK_MALLOC
Perl memory allocation is by bucket with sizes close
to powers of two. Because of these malloc overhead
may be big, especially for data of size exactly a
power of two. If PACK_MALLOC is defined, perl uses a
slightly different algorithm for small allocations
(up to 64 bytes long), which makes it possible to
have overhead down to 1 byte for allocations which
are powers of two (and appear quite often).
Expected memory savings (with 8-byte alignment in
alignbytes) is about 20% for typical Perl usage.
Expected slowdown due to additional malloc overhead
is in fractions of a percent (hard to measure,
because of the effect of saved memory on speed).
-DTWO_POT_OPTIMIZE
Similarly to PACK_MALLOC, this macro improves
allocations of data with size close to a power of
two; but this works for big allocations (starting
with 16K by default). Such allocations are typical
for big hashes and special-purpose scripts,
especially image processing.
On recent systems, the fact that perl requires 2M
from system for 1M allocation will not affect speed
of execution, since the tail of such a chunk is not
going to be touched (and thus will not require real
memory). However, it may result in a premature out-
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of-memory error. So if you will be manipulating very
large blocks with sizes close to powers of two, it
would be wise to define this macro.
Expected saving of memory is 0-100% (100% in
applications which require most memory in such 2**n
chunks); expected slowdown is negligible.
Miscellaneous efficiency enhancements
Functions that have an empty prototype and that do nothing
but return a fixed value are now inlined (e.g. sub PI () {
3.14159 }).
Each unique hash key is only allocated once, no matter how
many hashes have an entry with that key. So even if you
have 100 copies of the same hash, the hash keys never have
to be reallocated.
Support for More Operating Systems
Support for the following operating systems is new in Perl
5.004.
Win32
Perl 5.004 now includes support for building a "native"
perl under Windows NT, using the Microsoft Visual C++
compiler (versions 2.0 and above) or the Borland C++
compiler (versions 5.02 and above). The resulting perl
can be used under Windows 95 (if it is installed in the
same directory locations as it got installed in Windows
NT). This port includes support for perl extension
building tools like the MakeMaker manpage and the h2xs
manpage, so that many extensions available on the
Comprehensive Perl Archive Network (CPAN) can now be
readily built under Windows NT. See http://www.perl.com/
for more information on CPAN and README.win32 in the perl
distribution for more details on how to get started with
building this port.
There is also support for building perl under the Cygwin32
environment. Cygwin32 is a set of GNU tools that make it
possible to compile and run many UNIX programs under
Windows NT by providing a mostly UNIX-like interface for
compilation and execution. See README.cygwin32 in the
perl distribution for more details on this port and how to
obtain the Cygwin32 toolkit.
Plan 9
See README.plan9 in the perl distribution.
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QNX
See README.qnx in the perl distribution.
AmigaOS
See README.amigaos in the perl distribution.
Pragmata
Six new pragmatic modules exist:
use autouse MODULE => qw(sub1 sub2 sub3)
Defers require MODULE until someone calls one of the
specified subroutines (which must be exported by
MODULE). This pragma should be used with caution,
and only when necessary.
use blib
use blib 'dir'
Looks for MakeMaker-like 'blib' directory structure
starting in dir (or current directory) and working
back up to five levels of parent directories.
Intended for use on command line with -M option as a
way of testing arbitrary scripts against an
uninstalled version of a package.
use constant NAME => VALUE
Provides a convenient interface for creating compile-
time constants, See the section on Constant Functions
in the perlsub manpage.
use locale
Tells the compiler to enable (or disable) the use of
POSIX locales for builtin operations.
When use locale is in effect, the current LC_CTYPE
locale is used for regular expressions and case
mapping; LC_COLLATE for string ordering; and
LC_NUMERIC for numeric formating in printf and
sprintf (but not in print). LC_NUMERIC is always
used in write, since lexical scoping of formats is
problematic at best.
Each use locale or no locale affects statements to
the end of the enclosing BLOCK or, if not inside a
BLOCK, to the end of the current file. Locales can
be switched and queried with POSIX::setlocale().
See the perllocale manpage for more information.
use ops
Disable unsafe opcodes, or any named opcodes, when
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compiling Perl code.
use vmsish
Enable VMS-specific language features. Currently,
there are three VMS-specific features available:
'status', which makes $? and system return genuine
VMS status values instead of emulating POSIX; 'exit',
which makes exit take a genuine VMS status value
instead of assuming that exit 1 is an error; and
'time', which makes all times relative to the local
time zone, in the VMS tradition.
Modules
Required Updates
Though Perl 5.004 is compatible with almost all modules
that work with Perl 5.003, there are a few exceptions:
Module Required Version for Perl 5.004
------ -------------------------------
Filter Filter-1.12
LWP libwww-perl-5.08
Tk Tk400.202 (-w makes noise)
Also, the majordomo mailing list program, version 1.94.1,
doesn't work with Perl 5.004 (nor with perl 4), because it
executes an invalid regular expression. This bug is fixed
in majordomo version 1.94.2.
Installation directories
The installperl script now places the Perl source files
for extensions in the architecture-specific library
directory, which is where the shared libraries for
extensions have always been. This change is intended to
allow administrators to keep the Perl 5.004 library
directory unchanged from a previous version, without
running the risk of binary incompatibility between
extensions' Perl source and shared libraries.
Module information summary
Brand new modules, arranged by topic rather than strictly
alphabetically:
CGI.pm Web server interface ("Common Gateway Interface")
CGI/Apache.pm Support for Apache's Perl module
CGI/Carp.pm Log server errors with helpful context
CGI/Fast.pm Support for FastCGI (persistent server process)
CGI/Push.pm Support for server push
CGI/Switch.pm Simple interface for multiple server types
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CPAN Interface to Comprehensive Perl Archive Network
CPAN::FirstTime Utility for creating CPAN configuration file
CPAN::Nox Runs CPAN while avoiding compiled extensions
IO.pm Top-level interface to IO::* classes
IO/File.pm IO::File extension Perl module
IO/Handle.pm IO::Handle extension Perl module
IO/Pipe.pm IO::Pipe extension Perl module
IO/Seekable.pm IO::Seekable extension Perl module
IO/Select.pm IO::Select extension Perl module
IO/Socket.pm IO::Socket extension Perl module
Opcode.pm Disable named opcodes when compiling Perl code
ExtUtils/Embed.pm Utilities for embedding Perl in C programs
ExtUtils/testlib.pm Fixes up @INC to use just-built extension
FindBin.pm Find path of currently executing program
Class/Struct.pm Declare struct-like datatypes as Perl classes
File/stat.pm By-name interface to Perl's builtin stat
Net/hostent.pm By-name interface to Perl's builtin gethost*
Net/netent.pm By-name interface to Perl's builtin getnet*
Net/protoent.pm By-name interface to Perl's builtin getproto*
Net/servent.pm By-name interface to Perl's builtin getserv*
Time/gmtime.pm By-name interface to Perl's builtin gmtime
Time/localtime.pm By-name interface to Perl's builtin localtime
Time/tm.pm Internal object for Time::{gm,local}time
User/grent.pm By-name interface to Perl's builtin getgr*
User/pwent.pm By-name interface to Perl's builtin getpw*
Tie/RefHash.pm Base class for tied hashes with references as keys
UNIVERSAL.pm Base class for *ALL* classes
Fcntl
New constants in the existing Fcntl modules are now
supported, provided that your operating system happens to
support them:
F_GETOWN F_SETOWN
O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
O_EXLOCK O_SHLOCK
These constants are intended for use with the Perl
operators sysopen() and fcntl() and the basic database
modules like SDBM_File. For the exact meaning of these
and other Fcntl constants please refer to your operating
system's documentation for fcntl() and open().
In addition, the Fcntl module now provides these constants
for use with the Perl operator flock():
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LOCK_SH LOCK_EX LOCK_NB LOCK_UN
These constants are defined in all environments (because
where there is no flock() system call, Perl emulates it).
However, for historical reasons, these constants are not
exported unless they are explicitly requested with the
":flock" tag (e.g. use Fcntl ':flock').
IO
The IO module provides a simple mechanism to load all of
the IO modules at one go. Currently this includes:
IO::Handle
IO::Seekable
IO::File
IO::Pipe
IO::Socket
For more information on any of these modules, please see
its respective documentation.
Math::Complex
The Math::Complex module has been totally rewritten, and
now supports more operations. These are overloaded:
+ - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
And these functions are now exported:
pi i Re Im arg
log10 logn ln cbrt root
tan
csc sec cot
asin acos atan
acsc asec acot
sinh cosh tanh
csch sech coth
asinh acosh atanh
acsch asech acoth
cplx cplxe
Math::Trig
This new module provides a simpler interface to parts of
Math::Complex for those who need trigonometric functions
only for real numbers.
DB_File
There have been quite a few changes made to DB_File. Here
are a few of the highlights:
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- Fixed a handful of bugs.
- By public demand, added support for the standard hash
function exists().
- Made it compatible with Berkeley DB 1.86.
- Made negative subscripts work with RECNO interface.
- Changed the default flags from O_RDWR to
O_CREAT|O_RDWR and the default mode from 0640 to
0666.
- Made DB_File automatically import the open()
constants (O_RDWR, O_CREAT etc.) from Fcntl, if
available.
- Updated documentation.
Refer to the HISTORY section in DB_File.pm for a complete
list of changes. Everything after DB_File 1.01 has been
added since 5.003.
Net::Ping
Major rewrite - support added for both udp echo and real
icmp pings.
Object-oriented overrides for builtin operators
Many of the Perl builtins returning lists now have object-
oriented overrides. These are:
File::stat
Net::hostent
Net::netent
Net::protoent
Net::servent
Time::gmtime
Time::localtime
User::grent
User::pwent
For example, you can now say
use File::stat;
use User::pwent;
$his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
Utility Changes
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pod2html
Sends converted HTML to standard output
The pod2html utility included with Perl 5.004 is
entirely new. By default, it sends the converted
HTML to its standard output, instead of writing it to
a file like Perl 5.003's pod2html did. Use the
--outfile=FILENAME option to write to a file.
xsubpp
void XSUBs now default to returning nothing
Due to a documentation/implementation bug in previous
versions of Perl, XSUBs with a return type of void
have actually been returning one value. Usually that
value was the GV for the XSUB, but sometimes it was
some already freed or reused value, which would
sometimes lead to program failure.
In Perl 5.004, if an XSUB is declared as returning
void, it actually returns no value, i.e. an empty
list (though there is a backward-compatibility
exception; see below). If your XSUB really does
return an SV, you should give it a return type of SV
*.
For backward compatibility, xsubpp tries to guess
whether a void XSUB is really void or if it wants to
return an SV *. It does so by examining the text of
the XSUB: if xsubpp finds what looks like an
assignment to ST(0), it assumes that the XSUB's
return type is really SV *.
C Language API Changes
gv_fetchmethod and perl_call_sv
The gv_fetchmethod function finds a method for an
object, just like in Perl 5.003. The GV it returns
may be a method cache entry. However, in Perl 5.004,
method cache entries are not visible to users;
therefore, they can no longer be passed directly to
perl_call_sv. Instead, you should use the GvCV macro
on the GV to extract its CV, and pass the CV to
perl_call_sv.
The most likely symptom of passing the result of
gv_fetchmethod to perl_call_sv is Perl's producing an
"Undefined subroutine called" error on the second
call to a given method (since there is no cache on
the first call).
perl_eval_pv
A new function handy for eval'ing strings of Perl
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code inside C code. This function returns the value
from the eval statement, which can be used instead of
fetching globals from the symbol table. See the
perlguts manpage, the perlembed manpage and the
perlcall manpage for details and examples.
Extended API for manipulating hashes
Internal handling of hash keys has changed. The old
hashtable API is still fully supported, and will
likely remain so. The additions to the API allow
passing keys as SV*s, so that tied hashes can be
given real scalars as keys rather than plain strings
(nontied hashes still can only use strings as keys).
New extensions must use the new hash access functions
and macros if they wish to use SV* keys. These
additions also make it feasible to manipulate HE*s
(hash entries), which can be more efficient. See the
perlguts manpage for details.
Documentation Changes
Many of the base and library pods were updated. These new
pods are included in section 1:
the perldelta manpage
This document.
the perlfaq manpage
Frequently asked questions.
the perllocale manpage
Locale support (internationalization and
localization).
the perltoot manpage
Tutorial on Perl OO programming.
the perlapio manpage
Perl internal IO abstraction interface.
the perlmodlib manpage
Perl module library and recommended practice for
module creation. Extracted from the perlmod manpage
(which is much smaller as a result).
the perldebug manpage
Although not new, this has been massively updated.
the perlsec manpage
Although not new, this has been massively updated.
New Diagnostics
Several new conditions will trigger warnings that were
silent before. Some only affect certain platforms. The
following new warnings and errors outline these. These
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messages are classified as follows (listed in increasing
order of desperation):
(W) A warning (optional).
(D) A deprecation (optional).
(S) A severe warning (mandatory).
(F) A fatal error (trappable).
(P) An internal error you should never see (trappable).
(X) A very fatal error (nontrappable).
(A) An alien error message (not generated by Perl).
""""my"""" variable %s masks earlier declaration in same
scope
(W) A lexical variable has been redeclared in the
same scope, effectively eliminating all access to the
previous instance. This is almost always a
typographical error. Note that the earlier variable
will still exist until the end of the scope or until
all closure referents to it are destroyed.
%s argument is not a HASH element or slice
(F) The argument to delete() must be either a hash
element, such as
$foo{$bar}
$ref->[12]->{"susie"}
or a hash slice, such as
@foo{$bar, $baz, $xyzzy}
@{$ref->[12]}{"susie", "queue"}
Allocation too large: %lx
(X) You can't allocate more than 64K on an MS-DOS
machine.
Allocation too large
(F) You can't allocate more than 2^31+"small amount"
bytes.
Applying %s to %s will act on scalar(%s)
(W) The pattern match (//), substitution (s///), and
transliteration (tr///) operators work on scalar
values. If you apply one of them to an array or a
hash, it will convert the array or hash to a scalar
value -- the length of an array, or the population
info of a hash -- and then work on that scalar value.
This is probably not what you meant to do. See the
grep entry in the perlfunc manpage and the map entry
in the perlfunc manpage for alternatives.
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Attempt to free nonexistent shared string
(P) Perl maintains a reference counted internal table
of strings to optimize the storage and access of hash
keys and other strings. This indicates someone tried
to decrement the reference count of a string that can
no longer be found in the table.
Attempt to use reference as lvalue in substr
(W) You supplied a reference as the first argument to
substr() used as an lvalue, which is pretty strange.
Perhaps you forgot to dereference it first. See the
substr entry in the perlfunc manpage.
Bareword """"%s"""" refers to nonexistent package
(W) You used a qualified bareword of the form Foo::,
but the compiler saw no other uses of that namespace
before that point. Perhaps you need to predeclare a
package?
Can't redefine active sort subroutine %s
(F) Perl optimizes the internal handling of sort
subroutines and keeps pointers into them. You tried
to redefine one such sort subroutine when it was
currently active, which is not allowed. If you
really want to do this, you should write sort { &func
} @x instead of sort func @x.
Can't use bareword '%s' as %s ref while """"strict
refs"""" in use
(F) Only hard references are allowed by "strict
refs". Symbolic references are disallowed. See the
perlref manpage.
Cannot resolve method `%s' overloading `%s' in package
`%s'
(P) Internal error trying to resolve overloading
specified by a method name (as opposed to a
subroutine reference).
Constant subroutine %s redefined
(S) You redefined a subroutine which had previously
been eligible for inlining. See the section on
Constant Functions in the perlsub manpage for
commentary and workarounds.
Constant subroutine %s undefined
(S) You undefined a subroutine which had previously
been eligible for inlining. See the section on
Constant Functions in the perlsub manpage for
commentary and workarounds.
Copy method did not return a reference
(F) The method which overloads "=" is buggy. See the
section on Copy Constructor in the overload manpage.
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Died (F) You passed die() an empty string (the equivalent
of die "") or you called it with no args and both $@
and $_ were empty.
Exiting pseudo-block via %s
(W) You are exiting a rather special block construct
(like a sort block or subroutine) by unconventional
means, such as a goto, or a loop control statement.
See the sort entry in the perlfunc manpage.
Identifier too long
(F) Perl limits identifiers (names for variables,
functions, etc.) to 252 characters for simple names,
somewhat more for compound names (like $A::B).
You've exceeded Perl's limits. Future versions of
Perl are likely to eliminate these arbitrary
limitations.
Illegal character %s (carriage return)
(F) A carriage return character was found in the
input. This is an error, and not a warning, because
carriage return characters can break multi-line
strings, including here documents (e.g., print
<<EOF;).
Illegal switch in PERL5OPT: %s
(X) The PERL5OPT environment variable may only be
used to set the following switches: -[DIMUdmw].
Integer overflow in hex number
(S) The literal hex number you have specified is too
big for your architecture. On a 32-bit architecture
the largest hex literal is 0xFFFFFFFF.
Integer overflow in octal number
(S) The literal octal number you have specified is
too big for your architecture. On a 32-bit
architecture the largest octal literal is
037777777777.
internal error: glob failed
(P) Something went wrong with the external program(s)
used for glob and <*.c>. This may mean that your csh
(C shell) is broken. If so, you should change all of
the csh-related variables in config.sh: If you have
tcsh, make the variables refer to it as if it were
csh (e.g. full_csh='/usr/bin/tcsh'); otherwise, make
them all empty (except that d_csh should be 'undef')
so that Perl will think csh is missing. In either
case, after editing config.sh, run ./Configure -S and
rebuild Perl.
Invalid conversion in %s: """"%s""""
(W) Perl does not understand the given format
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conversion. See the sprintf entry in the perlfunc
manpage.
Invalid type in pack: '%s'
(F) The given character is not a valid pack type.
See the pack entry in the perlfunc manpage.
Invalid type in unpack: '%s'
(F) The given character is not a valid unpack type.
See the unpack entry in the perlfunc manpage.
Name """"%s::%s"""" used only once: possible typo
(W) Typographical errors often show up as unique
variable names. If you had a good reason for having
a unique name, then just mention it again somehow to
suppress the message (the use vars pragma is provided
for just this purpose).
Null picture in formline
(F) The first argument to formline must be a valid
format picture specification. It was found to be
empty, which probably means you supplied it an
uninitialized value. See the perlform manpage.
Offset outside string
(F) You tried to do a read/write/send/recv operation
with an offset pointing outside the buffer. This is
difficult to imagine. The sole exception to this is
that sysread()ing past the buffer will extend the
buffer and zero pad the new area.
Out of memory!
(X|F) The malloc() function returned 0, indicating
there was insufficient remaining memory (or virtual
memory) to satisfy the request.
The request was judged to be small, so the
possibility to trap it depends on the way Perl was
compiled. By default it is not trappable. However,
if compiled for this, Perl may use the contents of
$^M as an emergency pool after die()ing with this
message. In this case the error is trappable once.
Out of memory during request for %s
(F) The malloc() function returned 0, indicating
there was insufficient remaining memory (or virtual
memory) to satisfy the request. However, the request
was judged large enough (compile-time default is
64K), so a possibility to shut down by trapping this
error is granted.
panic: frexp
(P) The library function frexp() failed, making
printf("%f") impossible.
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Possible attempt to put comments in qw() list
(W) qw() lists contain items separated by whitespace;
as with literal strings, comment characters are not
ignored, but are instead treated as literal data.
(You may have used different delimiters than the
parentheses shown here; braces are also frequently
used.)
You probably wrote something like this:
@list = qw(
a # a comment
b # another comment
);
when you should have written this:
@list = qw(
a
b
);
If you really want comments, build your list the old-
fashioned way, with quotes and commas:
@list = (
'a', # a comment
'b', # another comment
);
Possible attempt to separate words with commas
(W) qw() lists contain items separated by whitespace;
therefore commas aren't needed to separate the items.
(You may have used different delimiters than the
parentheses shown here; braces are also frequently
used.)
You probably wrote something like this:
qw! a, b, c !;
which puts literal commas into some of the list
items. Write it without commas if you don't want
them to appear in your data:
qw! a b c !;
Scalar value @%s{%s} better written as $%s{%s}
(W) You've used a hash slice (indicated by @) to
select a single element of a hash. Generally it's
better to ask for a scalar value (indicated by $).
The difference is that $foo{&bar} always behaves like
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a scalar, both when assigning to it and when
evaluating its argument, while @foo{&bar} behaves
like a list when you assign to it, and provides a
list context to its subscript, which can do weird
things if you're expecting only one subscript.
Stub found while resolving method `%s' overloading `%s' in
package `%s'
(P) Overloading resolution over @ISA tree may be
broken by importing stubs. Stubs should never be
implicitly created, but explicit calls to can may
break this.
Too late for """"-T"""" option
(X) The #! line (or local equivalent) in a Perl
script contains the -T option, but Perl was not
invoked with -T in its argument list. This is an
error because, by the time Perl discovers a -T in a
script, it's too late to properly taint everything
from the environment. So Perl gives up.
untie attempted while %d inner references still exist
(W) A copy of the object returned from tie (or tied)
was still valid when untie was called.
Unrecognized character %s
(F) The Perl parser has no idea what to do with the
specified character in your Perl script (or eval).
Perhaps you tried to run a compressed script, a
binary program, or a directory as a Perl program.
Unsupported function fork
(F) Your version of executable does not support
forking.
Note that under some systems, like OS/2, there may be
different flavors of Perl executables, some of which
may support fork, some not. Try changing the name you
call Perl by to perl_, perl__, and so on.
Use of """"$$<digit>"""" to mean """"${$}<digit>"""" is
deprecated
(D) Perl versions before 5.004 misinterpreted any
type marker followed by "$" and a digit. For
example, "$$0" was incorrectly taken to mean "${$}0"
instead of "${$0}". This bug is (mostly) fixed in
Perl 5.004.
However, the developers of Perl 5.004 could not fix
this bug completely, because at least two widely-used
modules depend on the old meaning of "$$0" in a
string. So Perl 5.004 still interprets "$$<digit>"
in the old (broken) way inside strings; but it
generates this message as a warning. And in Perl
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5.005, this special treatment will cease.
Value of %s can be """"0""""; test with defined()
(W) In a conditional expression, you used <HANDLE>,
<*> (glob), each(), or readdir() as a boolean value.
Each of these constructs can return a value of "0";
that would make the conditional expression false,
which is probably not what you intended. When using
these constructs in conditional expressions, test
their values with the defined operator.
Variable """"%s"""" may be unavailable
(W) An inner (nested) anonymous subroutine is inside
a named subroutine, and outside that is another
subroutine; and the anonymous (innermost) subroutine
is referencing a lexical variable defined in the
outermost subroutine. For example:
sub outermost { my $a; sub middle { sub { $a } } }
If the anonymous subroutine is called or referenced
(directly or indirectly) from the outermost
subroutine, it will share the variable as you would
expect. But if the anonymous subroutine is called or
referenced when the outermost subroutine is not
active, it will see the value of the shared variable
as it was before and during the *first* call to the
outermost subroutine, which is probably not what you
want.
In these circumstances, it is usually best to make
the middle subroutine anonymous, using the sub {}
syntax. Perl has specific support for shared
variables in nested anonymous subroutines; a named
subroutine in between interferes with this feature.
Variable """"%s"""" will not stay shared
(W) An inner (nested) named subroutine is referencing
a lexical variable defined in an outer subroutine.
When the inner subroutine is called, it will probably
see the value of the outer subroutine's variable as
it was before and during the *first* call to the
outer subroutine; in this case, after the first call
to the outer subroutine is complete, the inner and
outer subroutines will no longer share a common value
for the variable. In other words, the variable will
no longer be shared.
Furthermore, if the outer subroutine is anonymous and
references a lexical variable outside itself, then
the outer and inner subroutines will never share the
given variable.
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This problem can usually be solved by making the
inner subroutine anonymous, using the sub {} syntax.
When inner anonymous subs that reference variables in
outer subroutines are called or referenced, they are
automatically rebound to the current values of such
variables.
Warning: something's wrong
(W) You passed warn() an empty string (the equivalent
of warn "") or you called it with no args and $_ was
empty.
Ill-formed logical name |%s| in prime_env_iter
(W) A warning peculiar to VMS. A logical name was
encountered when preparing to iterate over %ENV which
violates the syntactic rules governing logical names.
Since it cannot be translated normally, it is
skipped, and will not appear in %ENV. This may be a
benign occurrence, as some software packages might
directly modify logical name tables and introduce
nonstandard names, or it may indicate that a logical
name table has been corrupted.
Got an error from DosAllocMem
(P) An error peculiar to OS/2. Most probably you're
using an obsolete version of Perl, and this should
not happen anyway.
Malformed PERLLIB_PREFIX
(F) An error peculiar to OS/2. PERLLIB_PREFIX should
be of the form
prefix1;prefix2
or
prefix1 prefix2
with nonempty prefix1 and prefix2. If prefix1 is
indeed a prefix of a builtin library search path,
prefix2 is substituted. The error may appear if
components are not found, or are too long. See
"PERLLIB_PREFIX" in README.os2.
PERL_SH_DIR too long
(F) An error peculiar to OS/2. PERL_SH_DIR is the
directory to find the sh-shell in. See "PERL_SH_DIR"
in README.os2.
Process terminated by SIG%s
(W) This is a standard message issued by OS/2
applications, while *nix applications die in silence.
It is considered a feature of the OS/2 port. One can
easily disable this by appropriate sighandlers, see
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the section on Signals in the perlipc manpage. See
also "Process terminated by SIGTERM/SIGINT" in
README.os2.
BUGS
If you find what you think is a bug, you might check the
headers of recently posted articles in 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 you
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.
SEE ALSO
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl. This file has
been significantly updated for 5.004, so even veteran
users should look through it.
The README file for general stuff.
The Copying file for copyright information.
HISTORY
Constructed by Tom Christiansen, grabbing material with
permission from innumerable contributors, with kibitzing
by more than a few Perl porters.
Last update: Wed May 14 11:14:09 EDT 1997
29/Apr/1999 perl 5.005, patch 03 31
PERL5004DELTA(1) Perl Programmers Reference GuidePERL5004DELTA(1)
29/Apr/1999 perl 5.005, patch 03 32
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others. |
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