Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
-chr(0x263a) is a Unicode smiley face. Note that characters from 127
-to 255 (inclusive) are by default not encoded in Unicode for backward
-compatibility reasons (but see L<encoding>).
+chr(0x263a) is a Unicode smiley face. Note that characters from 128
+to 255 (inclusive) are by default not encoded in UTF-8 Unicode for
+backward compatibility reasons (but see L<encoding>).
If NUMBER is omitted, uses C<$_>.
element in the hash.
Entries are returned in an apparently random order. The actual random
-order is subject to change in future versions of perl, but it is guaranteed
-to be in the same order as either the C<keys> or C<values> function
-would produce on the same (unmodified) hash.
+order is subject to change in future versions of perl, but it is
+guaranteed to be in the same order as either the C<keys> or C<values>
+function would produce on the same (unmodified) hash. Since Perl
+5.8.1 the ordering is different even between different runs of Perl
+for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
When the hash is entirely read, a null array is returned in list context
(which when assigned produces a false (C<0>) value), and C<undef> in
fcntl($filehandle, F_GETFL, $packed_return_buffer)
or die "can't fcntl F_GETFL: $!";
-You don't have to check for C<defined> on the return from C<fnctl>.
+You don't have to check for C<defined> on the return from C<fcntl>.
Like C<ioctl>, it maps a C<0> return from the system call into
C<"0 but true"> in Perl. This string is true in boolean context and C<0>
in numeric context. It is also exempt from the normal B<-w> warnings
=item keys HASH
-Returns a list consisting of all the keys of the named hash. (In
-scalar context, returns the number of keys.) The keys are returned in
-an apparently random order. The actual random order is subject to
-change in future versions of perl, but it is guaranteed to be the same
-order as either the C<values> or C<each> function produces (given
-that the hash has not been modified). As a side effect, it resets
-HASH's iterator.
+Returns a list consisting of all the keys of the named hash.
+(In scalar context, returns the number of keys.)
+
+The keys are returned in an apparently random order. The actual
+random order is subject to change in future versions of perl, but it
+is guaranteed to be the same order as either the C<values> or C<each>
+function produces (given that the hash has not been modified). Since
+Perl 5.8.1 the ordering is different even between different runs of
+Perl for security reasons (see L<perlsec/"Algorithmic Complexity
+Attacks">).
+
+As a side effect, calling keys() resets the HASH's internal iterator,
+see L</each>.
Here is yet another way to print your environment:
kill 9, @goners;
If SIGNAL is zero, no signal is sent to the process. This is a
-useful way to check that the process is alive and hasn't changed
+useful way to check that a child process is alive and hasn't changed
its UID. See L<perlport> for notes on the portability of this
construct.
process groups instead of processes. (On System V, a negative I<PROCESS>
number will also kill process groups, but that's not portable.) That
means you usually want to use positive not negative signals. You may also
-use a signal name in quotes. See L<perlipc/"Signals"> for details.
+use a signal name in quotes.
+
+See L<perlipc/"Signals"> for more details.
=item last LABEL
=item no Module
-See the C<use> function, which C<no> is the opposite of.
+See the C<use> function, of which C<no> is the opposite.
=item oct EXPR
}
You may also, in the Bourne shell tradition, specify an EXPR beginning
-with C<< '>&' >>, in which case the rest of the string is interpreted as the
-name of a filehandle (or file descriptor, if numeric) to be
-duped and opened. You may use C<&> after C<< > >>, C<<< >> >>>,
-C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>. The
-mode you specify should match the mode of the original filehandle.
-(Duping a filehandle does not take into account any existing contents of
-IO buffers.) If you use the 3 arg form then you can pass either a number,
-the name of a filehandle or the normal "reference to a glob".
+with C<< '>&' >>, in which case the rest of the string is interpreted
+as the name of a filehandle (or file descriptor, if numeric) to be
+duped (as L<dup(2)>) and opened. You may use C<&> after C<< > >>,
+C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>.
+The mode you specify should match the mode of the original filehandle.
+(Duping a filehandle does not take into account any existing contents
+of IO buffers.) If you use the 3 arg form then you can pass either a
+number, the name of a filehandle or the normal "reference to a glob".
Here is a script that saves, redirects, and restores C<STDOUT> and
C<STDERR> using various methods:
print STDOUT "stdout 2\n";
print STDERR "stderr 2\n";
-If you specify C<< '<&=N' >>, where C<N> is a number, then Perl will
-do an equivalent of C's C<fdopen> of that file descriptor; this is
-more parsimonious of file descriptors. For example:
+If you specify C<< '<&=X' >>, where C<X> is a file descriptor number
+or a filehandle, then Perl will do an equivalent of C's C<fdopen> of
+that file descriptor (and not call L<dup(2)>); this is more
+parsimonious of file descriptors. For example:
+ # open for input, reusing the fileno of $fd
open(FILEHANDLE, "<&=$fd")
or
open(FILEHANDLE, "<&=", $fd)
-Note that if Perl is using the standard C libraries' fdopen() then on
-many UNIX systems, fdopen() is known to fail when file descriptors
-exceed a certain value, typically 255. If you need more file
-descriptors than that, consider rebuilding Perl to use the C<PerlIO>.
+or
+
+ # open for append, using the fileno of OLDFH
+ open(FH, ">>&=", OLDFH)
+
+or
+
+ open(FH, ">>&=OLDFH")
+
+Being parsimonious on filehandles is also useful (besides being
+parsimonious) for example when something is dependent on file
+descriptors, like for example locking using flock(). If you do just
+C<< open(A, '>>&B') >>, the filehandle A will not have the same file
+descriptor as B, and therefore flock(A) will not flock(B), and vice
+versa. But with C<< open(A, '>>&=B') >> the filehandles will share
+the same file descriptor.
+
+Note that if you are using Perls older than 5.8.0, Perl will be using
+the standard C libraries' fdopen() to implement the "=" functionality.
+On many UNIX systems fdopen() fails when file descriptors exceed a
+certain value, typically 255. For Perls 5.8.0 and later, PerlIO is
+most often the default.
You can see whether Perl has been compiled with PerlIO or not by
running C<perl -V> and looking for C<useperlio=> line. If C<useperlio>
=item *
-If the pattern begins with a C<U>, the resulting string will be treated
-as Unicode-encoded. You can force UTF8 encoding on in a string with an
-initial C<U0>, and the bytes that follow will be interpreted as Unicode
-characters. If you don't want this to happen, you can begin your pattern
-with C<C0> (or anything else) to force Perl not to UTF8 encode your
-string, and then follow this with a C<U*> somewhere in your pattern.
+If the pattern begins with a C<U>, the resulting string will be
+treated as UTF-8-encoded Unicode. You can force UTF-8 encoding on in a
+string with an initial C<U0>, and the bytes that follow will be
+interpreted as Unicode characters. If you don't want this to happen,
+you can begin your pattern with C<C0> (or anything else) to force Perl
+not to UTF-8 encode your string, and then follow this with a C<U*>
+somewhere in your pattern.
=item *
Attempts to read LENGTH I<characters> of data into variable SCALAR
from the specified FILEHANDLE. Returns the number of characters
actually read, C<0> at end of file, or undef if there was an error (in
-the latter case C<$!> is also set). SCALAR will be grown or shrunk to
-the length actually read. If SCALAR needs growing, the new bytes will
-be zero bytes. An OFFSET may be specified to place the read data into
-some other place in SCALAR than the beginning. The call is actually
-implemented in terms of either Perl's or system's fread() call. To
-get a true read(2) system call, see C<sysread>.
+the latter case C<$!> is also set). SCALAR will be grown or shrunk
+so that the last character actually read is the last character of the
+scalar after the read.
+
+An OFFSET may be specified to place the read data at some place in the
+string other than the beginning. A negative OFFSET specifies
+placement at that many characters counting backwards from the end of
+the string. A positive OFFSET greater than the length of SCALAR
+results in the string being padded to the required size with C<"\0">
+bytes before the result of the read is appended.
+
+The call is actually implemented in terms of either Perl's or system's
+fread() call. To get a true read(2) system call, see C<sysread>.
Note the I<characters>: depending on the status of the filehandle,
either (8-bit) bytes or characters are read. By default all
filehandles operate on bytes, but for example if the filehandle has
been opened with the C<:utf8> I/O layer (see L</open>, and the C<open>
-pragma, L<open>), the I/O will operate on characters, not bytes.
+pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode
+characters, not bytes. Similarly for the C<:encoding> pragma:
+in that case pretty much any characters can be read.
=item readdir DIRHANDLE
(8-bit) bytes or characters are received. By default all sockets
operate on bytes, but for example if the socket has been changed using
binmode() to operate with the C<:utf8> I/O layer (see the C<open>
-pragma, L<open>), the I/O will operate on characters, not bytes.
+pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode
+characters, not bytes. Similarly for the C<:encoding> pragma:
+in that case pretty much any characters can be read.
=item redo LABEL
Note the I<characters>: depending on the status of the socket, either
(8-bit) bytes or characters are sent. By default all sockets operate
on bytes, but for example if the socket has been changed using
-binmode() to operate with the C<:utf8> I/O layer (see L</open>, or
-the C<open> pragma, L<open>), the I/O will operate on characters, not
-bytes.
+binmode() to operate with the C<:utf8> I/O layer (see L</open>, or the
+C<open> pragma, L<open>), the I/O will operate on UTF-8 encoded
+Unicode characters, not bytes. Similarly for the C<:encoding> pragma:
+in that case pretty much any characters can be sent.
=item setpgrp PID,PGRP
sometimes saying the opposite, for example) the results are not
well-defined.
+Because C<< <=> >> returns C<undef> when either operand is C<NaN>
+(not-a-number), and because C<sort> will trigger a fatal error unless the
+result of a comparison is defined, when sorting with a comparison function
+like C<< $a <=> $b >>, be careful about lists that might contain a C<NaN>.
+The following example takes advantage of the fact that C<NaN != NaN> to
+eliminate any C<NaN>s from the input.
+
+ @result = sort { $a <=> $b } grep { $_ == $_ } @input;
+
=item splice ARRAY,OFFSET,LENGTH,LIST
=item splice ARRAY,OFFSET,LENGTH
($login, $passwd, $remainder) = split(/:/, $_, 3);
-When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT
-one larger than the number of variables in the list, to avoid
+When assigning to a list, if LIMIT is omitted, or zero, Perl supplies
+a LIMIT one larger than the number of variables in the list, to avoid
unnecessary work. For the list above LIMIT would have been 4 by
default. In time critical applications it behooves you not to split
into more fields than you really need.
$symlink_exists = eval { symlink("",""); 1 };
-=item syscall LIST
+=item syscall NUMBER, LIST
Calls the system call specified as the first element of the list,
passing the remaining elements as arguments to the system call. If
from the Fcntl module. Use of the constants is also more portable
than relying on 0, 1, and 2. For example to define a "systell" function:
- use Fnctl 'SEEK_CUR';
+ use Fcntl 'SEEK_CUR';
sub systell { sysseek($_[0], 0, SEEK_CUR) }
Returns the new position, or the undefined value on failure. A position
You can check all the failure possibilities by inspecting
C<$?> like this:
- $exit_value = $? >> 8;
- $signal_num = $? & 127;
- $dumped_core = $? & 128;
+ if ($? == -1) {
+ print "failed to execute: $!\n";
+ }
+ elsif ($? & 127) {
+ printf "child died with signal %d, %s coredump\n",
+ ($? & 127), ($? & 128) ? 'with' : 'without';
+ }
+ else {
+ printf "child exited with value %d\n", $? >> 8;
+ }
+
or more portably by using the W*() calls of the POSIX extension;
see L<perlport> for more information.
that many characters counting backwards from the end of the string.
In the case the SCALAR is empty you can use OFFSET but only zero offset.
-Note that if the filehandle has been marked as C<:utf8>,
-Unicode characters are written instead of bytes (the LENGTH, OFFSET,
-and the return value of syswrite() are in Unicode characters).
+Note that if the filehandle has been marked as C<:utf8>, Unicode
+characters are written instead of bytes (the LENGTH, OFFSET, and the
+return value of syswrite() are in UTF-8 encoded Unicode characters).
The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer.
See L</binmode>, L</open>, and the C<open> pragma, L<open>.
Undefines the value of EXPR, which must be an lvalue. Use only on a
scalar value, an array (using C<@>), a hash (using C<%>), a subroutine
-(using C<&>), or a typeglob (using <*>). (Saying C<undef $hash{$key}>
+(using C<&>), or a typeglob (using C<*>). (Saying C<undef $hash{$key}>
will probably not do what you expect on most predefined variables or
DBM list values, so don't do that; see L<delete>.) Always returns the
undefined value. You can omit the EXPR, in which case nothing is
C<import> method any way it likes, though most modules just choose to
derive their C<import> method via inheritance from the C<Exporter> class that
is defined in the C<Exporter> module. See L<Exporter>. If no C<import>
-method can be found then the call is skipped.
+method can be found then the call is skipped, even if there is an AUTOLOAD
+method.
If you do not want to call the package's C<import> method (for instance,
to stop your namespace from being altered), explicitly supply the empty list:
There's a corresponding C<no> command that unimports meanings imported
by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import>.
+It behaves exactly as C<import> does with respect to VERSION, an
+omitted LIST, empty LIST, or no unimport method being found.
no integer;
no strict 'refs';
=item values HASH
-Returns a list consisting of all the values of the named hash. (In a
-scalar context, returns the number of values.) The values are
-returned in an apparently random order. The actual random order is
-subject to change in future versions of perl, but it is guaranteed to
-be the same order as either the C<keys> or C<each> function would
-produce on the same (unmodified) hash.
+Returns a list consisting of all the values of the named hash.
+(In a scalar context, returns the number of values.)
+
+The values are returned in an apparently random order. The actual
+random order is subject to change in future versions of perl, but it
+is guaranteed to be the same order as either the C<keys> or C<each>
+function would produce on the same (unmodified) hash. Since Perl
+5.8.1 the ordering is different even between different runs of Perl
+for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
+
+As a side effect, calling values() resets the HASH's internal iterator,
+see L</each>.
Note that the values are not copied, which means modifying them will
modify the contents of the hash:
for (values %hash) { s/foo/bar/g } # modifies %hash values
for (@hash{keys %hash}) { s/foo/bar/g } # same
-As a side effect, calling values() resets the HASH's internal iterator.
See also C<keys>, C<each>, and C<sort>.
=item vec EXPR,OFFSET,BITS
to try to write off the beginning of the string (i.e. negative OFFSET).
The string should not contain any character with the value > 255 (which
-can only happen if you're using UTF8 encoding). If it does, it will be
-treated as something which is not UTF8 encoded. When the C<vec> was
+can only happen if you're using UTF-8 encoding). If it does, it will be
+treated as something which is not UTF-8 encoded. When the C<vec> was
assigned to, other parts of your program will also no longer consider the
-string to be UTF8 encoded. In other words, if you do have such characters
+string to be UTF-8 encoded. In other words, if you do have such characters
in your string, vec() will operate on the actual byte string, and not the
conceptual character string.
projects / p5sagit/p5-mst-13.2.git / blobdiff