fcntl($filehandle, F_GETFL, $packed_return_buffer)
or die "can't fcntl F_GETFL: $!";
-You don't have to check for C<defined> on the return from C<fnctl>.
+You don't have to check for C<defined> on the return from C<fcntl>.
Like C<ioctl>, it maps a C<0> return from the system call into
C<"0 but true"> in Perl. This string is true in boolean context and C<0>
in numeric context. It is also exempt from the normal B<-w> warnings
kill 9, @goners;
If SIGNAL is zero, no signal is sent to the process. This is a
-useful way to check that the process is alive and hasn't changed
+useful way to check that a child process is alive and hasn't changed
its UID. See L<perlport> for notes on the portability of this
construct.
process groups instead of processes. (On System V, a negative I<PROCESS>
number will also kill process groups, but that's not portable.) That
means you usually want to use positive not negative signals. You may also
-use a signal name in quotes. See L<perlipc/"Signals"> for details.
+use a signal name in quotes.
+
+See L<perlipc/"Signals"> for more details.
=item last LABEL
Attempts to read LENGTH I<characters> of data into variable SCALAR
from the specified FILEHANDLE. Returns the number of characters
actually read, C<0> at end of file, or undef if there was an error (in
-the latter case C<$!> 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(/:/, $_, 3);
-When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT
-one larger than the number of variables in the list, to avoid
+When assigning to a list, if LIMIT is omitted, or zero, Perl supplies
+a LIMIT one larger than the number of variables in the list, to avoid
unnecessary work. For the list above LIMIT would have been 4 by
default. In time critical applications it behooves you not to split
into more fields than you really need.
from the Fcntl module. Use of the constants is also more portable
than relying on 0, 1, and 2. For example to define a "systell" function:
- use Fnctl 'SEEK_CUR';
+ use Fcntl 'SEEK_CUR';
sub systell { sysseek($_[0], 0, SEEK_CUR) }
Returns the new position, or the undefined value on failure. A position
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
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