func would create $h{foo} if it did not already exist, causing exists $h{foo} to become true and keys %h to return
Perl 5.004 returns to the pre-5.002 behavior of not autovivifying array and hash elements used as subroutine parameters.
$$."0", but rather to ${$0}. To get the old behavior, change ``$$'' followed by a digit to ``${$}''.
-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
plugged.
In harmony with this change, *GLOB{FILEHANDLE} is now a backward-compatible synonym for *STDOUT{IO}.
$EXTENDED_OS_ERROR if you use English).
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 as an emergency pool after dieing with this message. Suppose that your Perl were compiled with
-DEMERGENCY_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.
delete @ENV{'PATH', 'MANPATH'})
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 (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.
require VERSION, which waits until run-time 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.)
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.
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.
$_ now in fact
do, and all those that do are so documented in the perlfunc manpage.
m//g match iteration construct used to reset the iteration when it failed to
match (so that the next m//g match would start at the beginning of the string). You now have to
explicitly do a
pos $str = 0; to reset the ``last match'' position, or modify the string in some way.
This change makes it practical to chain m//g
matches together in conjunction with ordinary matches using the \G
zero-width assertion. See the perlop manpage and the perlre manpage.
foreach loop), formats now work properly. For example, this silently failed before,
and is fine now:
my $i;
foreach $i ( 1 .. 10 ) {
format =
my i is @#
$i
.
write;
}
UNIVERSAL package automatically contains the following methods that are inherited by
all other classes:
isa returns true if its object is blessed into a sub-class of CLASS
isa is also exportable and can be called as a sub with two arguments. This
allows the ability to check what a reference points to. Example:
use UNIVERSAL qw(isa);
if(isa($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 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);
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.
ties.
sub TIEHANDLE {
print "<shout>\n";
my $i;
return bless \$i, shift;
}
sub PRINT {
$r = shift;
$$r++;
return print join( $, => map {uc} @_), $\;
}
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
sub READLINE {
$r = shift;
return "PRINT called $$r times\n"
}
sub GETC { print "Don't GETC, Get Perl"; return "a"; }
sub DESTROY {
print "</shout>\n";
}
malloc.)
DEBUGGING_MSTATS defined, 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 ares printed only on exit. (If you want the statistics at an arbitrary time, you'll need to install the optional module Devel::Peek.)
$^M. See $^M.
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).
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-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.
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 re-allocated.
Intended for use on command line with -M option as a way of testing arbitrary scripts against an uninstalled version of a package.
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.
$? 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.
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:
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').
CPAN interface to Comprehensive Perl Archive Network
CPAN::FirstTime create a CPAN configuration file
CPAN::Nox run 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/Template.pm Structure/member template builder
File/stat.pm Object-oriented wrapper around CORE::stat
Net/hostent.pm Object-oriented wrapper around CORE::gethost*
Net/netent.pm Object-oriented wrapper around CORE::getnet*
Net/protoent.pm Object-oriented wrapper around CORE::getproto*
Net/servent.pm Object-oriented wrapper around CORE::getserv*
Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
Time/localtime.pm Object-oriented wrapper around CORE::localtime
Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
User/grent.pm Object-oriented wrapper around CORE::getgr*
User/pwent.pm Object-oriented wrapper around CORE::getpw*
Tie/RefHash.pm Base class for tied hashes with references as keys
UNIVERSAL.pm Base class for *ALL* classes
IO::Handle
IO::Seekable
IO::File
IO::Pipe
IO::Socket
For more information on any of these modules, please see its respective documentation.
+ - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
And these functions are now exported:
pi i Re Im arg
log10 logn cbrt root
tan cotan asin acos atan acotan
sinh cosh tanh cotanh asinh acosh atanh acotanh
cplx cplxe
exists.
open constants
(O_RDWR,
O_CREAT etc.) from Fcntl, if available.
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);
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, it assumes that the XSUB's return type is really SV *.
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).
SV*s, so that tied hashes can be given real scalars as keys rather than plain strings
(non-tied 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.
(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 (non-trappable). (A) An alien error message (not generated by Perl).
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"}
substr used as an lvalue, which is pretty strange. Perhaps you
forgot to dereference it first. See substr.
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.
%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 non-standard names, or it may indicate that a logical name table has been corrupted.
die an empty string (the
equivalent of die "") or you called it with no args and both $@ and $_ were empty.
use vars pragma is provided for just this purpose).
@ISA tree
may be broken by importing stubs. Stubs should never be implicitely
created, but explicit calls to can
may break this.
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 dieing with this message. In this
case the error is trappable once.
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.
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 exclamation marks 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
);
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 !;
$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 it, and provides a list context to
its subscript, which can do weird things if you're expecting only one
subscript.
tied) was still valid when untie was called.
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.
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.
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 re-bound to the current values of such variables.
warn an empty string (the
equivalent of warn "") or you called it with no args and $_ was empty.
prefix1;prefix2
or
prefix1 prefix2
with non-empty 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 perlos2.
sh-shell in. See perlos2.
*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. See perlos2.
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.
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.
Last update: Sat Mar 8 19:51:26 EST 1997