In the first form, the return value of EXPR is parsed and executed as if it
were a little Perl program. The value of the expression (which is itself
determined within scalar context) is first parsed, and if there weren't any
-errors, executed in the context of the current Perl program, so that any
-variable settings or subroutine and format definitions remain afterwards.
-Note that the value is parsed every time the eval executes. If EXPR is
-omitted, evaluates C<$_>. This form is typically used to delay parsing
-and subsequent execution of the text of EXPR until run time.
+errors, executed in the lexical context of the current Perl program, so
+that any variable settings or subroutine and format definitions remain
+afterwards. Note that the value is parsed every time the eval executes.
+If EXPR is omitted, evaluates C<$_>. This form is typically used to
+delay parsing and subsequent execution of the text of EXPR until run time.
In the second form, the code within the BLOCK is parsed only once--at the
same time the code surrounding the eval itself was parsed--and executed
@foo = grep {!/^#/} @bar; # weed out comments
-Note that, because C<$_> is a reference into the list value, it can
-be used to modify the elements of the array. While this is useful and
-supported, it can cause bizarre results if the LIST is not a named array.
+Note that C<$_> is an alias to the list value, so it can be used to
+modify the elements of the LIST. While this is useful and supported,
+it can cause bizarre results if the elements of LIST are not variables.
Similarly, grep returns aliases into the original list, much as a for
loop's index variable aliases the list elements. That is, modifying an
element of a list returned by grep (for example, in a C<foreach>, C<map>
$hash{getkey($_)} = $_;
}
-Note that, because C<$_> is a reference into the list value, it can
-be used to modify the elements of the array. While this is useful and
-supported, it can cause bizarre results if the LIST is not a named array.
+Note that C<$_> is an alias to the list value, so it can be used to
+modify the elements of the LIST. While this is useful and supported,
+it can cause bizarre results if the elements of LIST are not variables.
Using a regular C<foreach> loop for this purpose would be clearer in
most cases. See also L</grep> for an array composed of those items of
the original list for which the BLOCK or EXPR evaluates to true.
then ARG must be a variable which will hold the returned C<msqid_ds>
structure. Returns like C<ioctl>: the undefined value for error,
C<"0 but true"> for zero, or the actual return value otherwise. See also
-C<IPC::SysV> and C<IPC::Semaphore> documentation.
+L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::Semaphore> documentation.
=item msgget KEY,FLAGS
Calls the System V IPC function msgget(2). Returns the message queue
-id, or the undefined value if there is an error. See also C<IPC::SysV>
-and C<IPC::Msg> documentation.
+id, or the undefined value if there is an error. See also
+L<perlipc/"SysV IPC"> and C<IPC::SysV> and C<IPC::Msg> documentation.
=item msgrcv ID,VAR,SIZE,TYPE,FLAGS
native long integer will be the first thing in VAR, followed by the
actual message. This packing may be opened with C<unpack("l! a*")>.
Taints the variable. Returns true if successful, or false if there is
-an error. See also C<IPC::SysV> and C<IPC::SysV::Msg> documentation.
+an error. See also L<perlipc/"SysV IPC">, C<IPC::SysV>, and
+C<IPC::SysV::Msg> documentation.
=item msgsnd ID,MSG,FLAGS
=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.
+
+=item *
+
You must yourself do any alignment or padding by inserting for example
enough C<'x'>es while packing. There is no way to pack() and unpack()
could know where the bytes are going to or coming from. Therefore
the undefined value for error, "C<0 but true>" for zero, or the actual
return value otherwise. The ARG must consist of a vector of native
short integers, which may be created with C<pack("s!",(0)x$nsem)>.
-See also C<IPC::SysV> and C<IPC::Semaphore> documentation.
+See also L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::Semaphore>
+documentation.
=item semget KEY,NSEMS,FLAGS
Calls the System V IPC function semget. Returns the semaphore id, or
-the undefined value if there is an error. See also C<IPC::SysV> and
-C<IPC::SysV::Semaphore> documentation.
+the undefined value if there is an error. See also
+L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::SysV::Semaphore>
+documentation.
=item semop KEY,OPSTRING
$semop = pack("sss", $semnum, -1, 0);
die "Semaphore trouble: $!\n" unless semop($semid, $semop);
-To signal the semaphore, replace C<-1> with C<1>. See also C<IPC::SysV>
-and C<IPC::SysV::Semaphore> documentation.
+To signal the semaphore, replace C<-1> with C<1>. See also
+L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::SysV::Semaphore>
+documentation.
=item send SOCKET,MSG,FLAGS,TO
the C<eval ''>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>, and C<END {}>
constructs.
-See also C<unshift>, C<push>, and C<pop>. C<shift()> and C<unshift> do the
+See also C<unshift>, C<push>, and C<pop>. C<shift> and C<unshift> do the
same thing to the left end of an array that C<pop> and C<push> do to the
right end.
then ARG must be a variable which will hold the returned C<shmid_ds>
structure. Returns like ioctl: the undefined value for error, "C<0> but
true" for zero, or the actual return value otherwise.
-See also C<IPC::SysV> documentation.
+See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
=item shmget KEY,SIZE,FLAGS
Calls the System V IPC function shmget. Returns the shared memory
segment id, or the undefined value if there is an error.
-See also C<IPC::SysV> documentation.
+See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
=item shmread ID,VAR,POS,SIZE
hold the data read. When writing, if STRING is too long, only SIZE
bytes are used; if STRING is too short, nulls are written to fill out
SIZE bytes. Return true if successful, or false if there is an error.
-shmread() taints the variable. See also C<IPC::SysV> documentation and
-the C<IPC::Shareable> module from CPAN.
+shmread() taints the variable. See also L<perlipc/"SysV IPC">,
+C<IPC::SysV> documentation, and the C<IPC::Shareable> module from CPAN.
=item shutdown SOCKET,HOW
whitespace produces a null first field. A C<split> with no arguments
really does a C<split(' ', $_)> internally.
+A PATTERN of C</^/> is treated as if it were C</^/m>, since it isn't
+much use otherwise.
+
Example:
open(PASSWD, '/etc/passwd');
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