MirBSD manpage: perl5004delta(1)

PERL5004DELTA(1)Perl Programmers Reference Guide PERL5004DELTA(1)


     perl5004delta - what's new for perl5.004


     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 Win-
     dows 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).

     Change to "Can't locate Foo.pm in @INC" error

     The error "Can't locate Foo.pm in @INC" now lists the con-
     tents of @INC for easier debugging.

     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

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     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.  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

     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

     Perl 5.005 will use method lookup only for methods'
     "AUTOLOAD"s. However, there is a significant base of exist-
     ing 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 auto-
     loading 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.

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     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 overload for more details.

     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]++ };

     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

     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 func-
     tion (if there is one). However, until this release, there
     has not been a way to call the "setgroups()" C function from

     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

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     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 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 local-
     ize 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 incon-
     sistently, sometimes incorrectly using the surrounding con-
     text for the determination. Now, the value of EXPR (before
     being parsed by eval) is always determined in a scalar con-
     text.  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

         @a = qw(time now is time);
         print eval @a;
         print '|', scalar eval @a;

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     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 expli-
     citly turned on with the "-T" invocation option.)  Although
     it's unlikely, this may cause a previously-working script to
     now fail -- which should be construed as a blessing, since
     that indicates a potentially-serious security hole was just

     The new restrictions when tainting include:

     No glob() or <*>
         These operators may spawn the C shell (csh), which can-
         not 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 sub-
         vert 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 con-
         sidered to be safe if it contains only alphanumerics,
         underscores, dashes, and colons, and unsafe if it con-
         tains 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

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     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 com-
     patibility, 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 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 perlapio for more details, and the
     INSTALL file for how to use it.

     New and changed syntax

         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->($foo)".  All these arrow
         terms may be chained; thus, "&{$table->{FOO}}($bar)" may
         now be written "$table->{FOO}->($bar)".

     New and changed builtin constants

         The current package name at compile time, or the unde-
         fined 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

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     $^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 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'}")

         is now supported on more platforms, prefers fcntl to
         lockf when emulating, and always flushes before

     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

            #    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

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         field width obtained through "*" is negative, it has the
         same effect as the '-' flag: left-justification.

         See "sprintf" in perlfunc for a complete list of conver-
         sion 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

             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

             while (defined(my $line = <>)) {
                 $line = lc $line;
             } continue {
                 print $line;

             if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
             } elsif ($answer =~ /^n(o)?$/i) {
             } 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 exam-
         ple, in:

             foreach my $i (1, 2, 3) {

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         $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 punctua-
         tion variables such as $_ and the like.

     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 gen-
         erate a NULL pointer.

         Both pack() and unpack() now fail when their templates
         contain invalid types.  (Invalid types used to be

         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 VER-
         SION, then an error message is printed and Perl exits
         immediately.  Because "use" occurs at compile time, this
         check happens immediately during the compilation pro-
         cess, unlike "require VERSION", which waits until run-
         time for the check.  This is often useful if you need to
         check the current Perl version before "use"ing 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!)

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         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.

         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 proto-
         type you want to retrieve. (Not actually new; just never
         documented before.)

         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 suffi-
         cient 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

     "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 "con-
         tinue") modifier, i.e. "m//gc".  This feature, in con-
         junction with the "\G" zero-width assertion, makes it
         possible to chain matches together.  See perlop and

     "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.

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     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 vari-
         ables that change (like a lexical index variable for a
         "foreach" loop), formats now work properly.  For exam-
         ple, this silently failed before (printed only zeros),
         but is fine now:

             my $i;
             foreach $i ( 1 .. 10 ) {
             format =
                 my i is @#

         However, it still fails (without a warning) if the
         foreach is within a subroutine:

             my $i;
             sub foo {
               foreach $i ( 1 .. 10 ) {
             format =
                 my i is @#

     New builtin methods

     The "UNIVERSAL" package automatically contains the following
     methods that are inherited by all other classes:

         "isa" returns true if its object is blessed into a sub-
         class 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);

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             if(isa($ref, 'ARRAY')) {

         "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.

     VERSION( [NEED] )
         "VERSION" returns the version number of the class (pack-
         age).  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 nor-
         mally 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:

     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 subrou-
     tine in the current package.

     TIEHANDLE now supported

     See perltie 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.

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             sub PRINT {
                 $r = shift;
                 return print join( $, => map {uc} @_), $\;

     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 {
                   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

             sub READLINE {
                 $r = shift;
                 return "PRINT called $$r times\n"

     GETC this
         This method will be called when the "getc" function is

             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

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             sub DESTROY {
                 print "</shout>\n";

     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

     Three new compilation flags are recognized by malloc.c.
     (They have no effect if perl is compiled with system mal-

         If this macro is defined, running out of memory need not
         be a fatal error: a memory pool can allocated by assign-
         ing to the special variable $^M.  See "$^M".

         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 dif-
         ferent 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).

         Similarly to "PACK_MALLOC", this macro improves alloca-
         tions 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 process-

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         On recent systems, the fact that perl requires 2M from
         system for 1M allocation will not affect speed of execu-
         tion, since the tail of such a chunk is not going to be
         touched (and thus will not require real memory).  How-
         ever, it may result in a premature out-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 applica-
         tions 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


     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 (ver-
     sions 5.02 and above). The resulting perl can be used under
     Windows 95 (if it is installed in the same directory loca-
     tions as it got installed in Windows NT).  This port
     includes support for perl extension building tools like Mak-
     eMaker and h2xs, 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 distribu-
     tion 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

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     Plan 9

     See README.plan9 in the perl distribution.


     See README.qnx in the perl distribution.


     See README.amigaos in the perl distribution.


     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 ver-
         sion of a package.

     use constant NAME => VALUE
         Provides a convenient interface for creating compile-
         time constants, See "Constant Functions" in perlsub.

     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 formatting in printf and sprintf (but not in
         print).  LC_NUMERIC is always used in write, since lexi-
         cal 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 perllocale for more information.

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     use ops
         Disable unsafe opcodes, or any named opcodes, when com-
         piling 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 assum-
         ing that "exit 1" is an error; and 'time', which makes
         all times relative to the local time zone, in the VMS


     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 administra-
     tors 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

     Module information summary

     Brand new modules, arranged by topic rather than strictly

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         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

         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


     New constants in the existing Fcntl modules are now sup-
     ported, provided that your operating system happens to sup-
     port them:


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     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 documenta-
     tion for fcntl() and open().

     In addition, the Fcntl module now provides these constants
     for use with the Perl operator flock():


     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'").


     The IO module provides a simple mechanism to load all the IO
     modules at one go.  Currently this includes:


     For more information on any of these modules, please see its
     respective documentation.


     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
         csc sec cot
         asin acos atan
         acsc asec acot
         sinh cosh tanh
         csch sech coth
         asinh acosh atanh
         acsch asech acoth
         cplx cplxe

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     This new module provides a simpler interface to parts of
     Math::Complex for those who need trigonometric functions
     only for real numbers.


     There have been quite a few changes made to DB_File. Here
     are a few of the highlights:

     +   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.


     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:


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     For example, you can now say

         use File::stat;
         use User::pwent;
         $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);

Utility Changes


     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.


     "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

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         call to a given method (since there is no cache on the
         first call).

         A new function handy for eval'ing strings of Perl 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 perlguts, perlembed
         and perlcall 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 exten-
         sions 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 perlguts for details.

Documentation Changes

     Many of the base and library pods were updated.  These new
     pods are included in section 1:

         This document.

         Frequently asked questions.

         Locale support (internationalization and localization).

         Tutorial on Perl OO programming.

         Perl internal IO abstraction interface.

         Perl module library and recommended practice for module
         creation. Extracted from perlmod (which is much smaller
         as a result).

         Although not new, this has been massively updated.

         Although not new, this has been massively updated.

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New Diagnostics

     Several new conditions will trigger warnings that were
     silent before.  Some only affect certain platforms. The fol-
     lowing new warnings and errors outline these. These messages
     are classified as follows (listed in increasing order of

        (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 previ-
         ous 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 ele-
         ment, such as


         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

     Allocation too large
         (F) You can't allocate more than 2^31+"small amount"

     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 "grep" in perlfunc and
         "map" in perlfunc 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
         "substr" in perlfunc.

     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

     Can't redefine active sort subroutine %s
         (F) Perl optimizes the internal handling of sort subrou-
         tines and keeps pointers into them.  You tried to rede-
         fine 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 perlref.

     Cannot resolve method `%s' overloading `%s' in package `%s'
         (P) Internal error trying to resolve overloading speci-
         fied by a method name (as opposed to a subroutine refer-

     Constant subroutine %s redefined
         (S) You redefined a subroutine which had previously been
         eligible for inlining.  See "Constant Functions" in
         perlsub for commentary and workarounds.

     Constant subroutine %s undefined
         (S) You undefined a subroutine which had previously been
         eligible for inlining.  See "Constant Functions" in
         perlsub for commentary and workarounds.

     Copy method did not return a reference
         (F) The method which overloads "=" is buggy. See "Copy
         Constructor" in overload.

         (F) You passed die() an empty string (the equivalent of

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         "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
         "sort" in perlfunc.

     Identifier too long
         (F) Perl limits identifiers (names for variables, func-
         tions, etc.) to 252 characters for simple names, some-
         what 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, includ-
         ing 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 conver-
         sion. See "sprintf" in perlfunc.

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     Invalid type in pack: '%s'
         (F) The given character is not a valid pack type.  See
         "pack" in perlfunc.

     Invalid type in unpack: '%s'
         (F) The given character is not a valid unpack type.  See
         "unpack" in perlfunc.

     Name "%s::%s" used only once: possible typo
         (W) Typographical errors often show up as unique vari-
         able 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

     Null picture in formline
         (F) The first argument to formline must be a valid for-
         mat picture specification.  It was found to be empty,
         which probably means you supplied it an uninitialized
         value.  See perlform.

     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 possi-
         bility to shut down by trapping this error is granted.

     panic: frexp
         (P) The library function frexp() failed, making
         printf("%f") impossible.

     Possible attempt to put comments in qw() list

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         (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(

         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

         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 a scalar, both
         when assigning to it and when evaluating its argument,
         while @foo{&bar} behaves like a list when you assign to

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         it, and provides a list context to its subscript, which
         can do weird things if you're expecting only one sub-

     Stub found while resolving method `%s' overloading `%s' in %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 5.005, this special treatment will

     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.

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         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 con-
         structs 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 subrou-
         tine; 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 sub-
         routine; 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

         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 automati-
         cally rebound to the current values of such variables.

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     Warning: something's wrong
         (W) You passed warn() an empty string (the equivalent of
         "warn """) or you called it with no args and $_ was

     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

         with nonempty prefix1 and prefix2.  If "prefix1" is
         indeed a prefix of a builtin library search path, pre-
         fix2 is substituted.  The error may appear if components
         are not found, or are too long.  See "PERLLIB_PREFIX" in

     PERL_SH_DIR too long
         (F) An error peculiar to OS/2. PERL_SH_DIR is the direc-
         tory to find the "sh"-shell in.  See "PERL_SH_DIR" in

     Process terminated by SIG%s
         (W) This is a standard message issued by OS/2 applica-
         tions, 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 "Signals"
         in perlipc.  See also "Process terminated by
         SIGTERM/SIGINT" in README.os2.


     If you find what you think is a bug, you might check the

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     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


     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.


     Constructed by Tom Christiansen, grabbing material with per-
     mission from innumerable contributors, with kibitzing by
     more than a few Perl porters.

     Last update: Wed May 14 11:14:09 EDT 1997

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