Implement "my $_".

[perl5.git] / pod / perlvar.pod

diff --git a/pod/perlvar.pod b/pod/perlvar.pod
index df456cb..8fc7441 100644 (file)
--- a/pod/perlvar.pod
+++ b/pod/perlvar.pod
@@ -177,6 +177,11 @@ test.  Outside a C<while> test, this will not happen.
 
 =back
 
 
 =back
 

+As C<$_> is a global variable, this may lead in some cases to unwanted
+side-effects.  As of perl 5.9.1, you can now use a lexical version of
+C<$_> by declaring it in a file or in a block with C<my>.  Moreover,
+declaring C<our $> restores the global C<$_> in the current scope.
+

 (Mnemonic: underline is understood in certain operations.)
 
 =back
 (Mnemonic: underline is understood in certain operations.)
 
 =back


@@ -189,10 +194,9 @@ test.  Outside a C<while> test, this will not happen.
 
 Special package variables when using sort(), see L<perlfunc/sort>.
 Because of this specialness $a and $b don't need to be declared
 
 Special package variables when using sort(), see L<perlfunc/sort>.
 Because of this specialness $a and $b don't need to be declared

-(using local(), use vars, or our()) even when using the strict
-vars pragma.  Don't lexicalize them with C<my $a> or C<my $b>
-if you want to be able to use them in the sort() comparison block
-or function.
+(using use vars, or our()) even when using the C<strict 'vars'> pragma.
+Don't lexicalize them with C<my $a> or C<my $b> if you want to be
+able to use them in the sort() comparison block or function.

 
 =back
 
 
 =back
 


@@ -294,26 +298,6 @@ past where $2 ends, and so on.  You can use C<$#+> to determine
 how many subgroups were in the last successful match.  See the
 examples given for the C<@-> variable.
 
 how many subgroups were in the last successful match.  See the
 examples given for the C<@-> variable.
 

-=item $MULTILINE_MATCHING
-
-=item $*
-
-Set to a non-zero integer value to do multi-line matching within a
-string, 0 (or undefined) to tell Perl that it can assume that strings
-contain a single line, for the purpose of optimizing pattern matches.
-Pattern matches on strings containing multiple newlines can produce
-confusing results when C<$*> is 0 or undefined. Default is undefined.
-(Mnemonic: * matches multiple things.) This variable influences the
-interpretation of only C<^> and C<$>. A literal newline can be searched
-for even when C<$* == 0>.
-
-Use of C<$*> is deprecated in modern Perl, supplanted by 
-the C</s> and C</m> modifiers on pattern matching.
-
-Assigning a non-numerical value to C<$*> triggers a warning (and makes
-C<$*> act if C<$* == 0>), while assigning a numerical value to C<$*>
-makes that an implicit C<int> is applied on the value.
-

 =item HANDLE->input_line_number(EXPR)
 
 =item $INPUT_LINE_NUMBER
 =item HANDLE->input_line_number(EXPR)
 
 =item $INPUT_LINE_NUMBER


@@ -491,8 +475,6 @@ taken for something more important.)
 Consider using "real" multidimensional arrays as described
 in L<perllol>.
 
 Consider using "real" multidimensional arrays as described
 in L<perllol>.
 

-=item $OFMT
-

 =item $#
 
 The output format for printed numbers.  This variable is a half-hearted
 =item $#
 
 The output format for printed numbers.  This variable is a half-hearted


@@ -695,7 +677,7 @@ In the above I<meaningless> stands for anything: zero, non-zero,
 C<undef>.  A successful system or library call does B<not> set
 the variable to zero.
 
 C<undef>.  A successful system or library call does B<not> set
 the variable to zero.
 

-If used an a string, yields the corresponding system error string.
+If used as a string, yields the corresponding system error string.

 You can assign a number to C<$!> to set I<errno> if, for instance,
 you want C<"$!"> to return the string for error I<n>, or you want
 to set the exit value for the die() operator.  (Mnemonic: What just
 You can assign a number to C<$!> to set I<errno> if, for instance,
 you want C<"$!"> to return the string for error I<n>, or you want
 to set the exit value for the die() operator.  (Mnemonic: What just


@@ -858,20 +840,36 @@ and C<$)> can be swapped only on machines supporting setregid().
 
 =item $0
 
 
 =item $0
 

-Contains the name of the program being executed.  On some operating
-systems assigning to C<$0> modifies the argument area that the B<ps>
-program sees.  This is more useful as a way of indicating the current
-program state than it is for hiding the program you're running.
-(Mnemonic: same as B<sh> and B<ksh>.)
+Contains the name of the program being executed.
+
+On some (read: not all) operating systems assigning to C<$0> modifies
+the argument area that the C<ps> program sees.  On some platforms you
+may have to use special C<ps> options or a different C<ps> to see the
+changes.  Modifying the $0 is more useful as a way of indicating the
+current program state than it is for hiding the program you're
+running.  (Mnemonic: same as B<sh> and B<ksh>.)
+
+Note that there are platform specific limitations on the the maximum
+length of C<$0>.  In the most extreme case it may be limited to the
+space occupied by the original C<$0>.
+
+In some platforms there may be arbitrary amount of padding, for
+example space characters, after the modified name as shown by C<ps>.
+In some platforms this padding may extend all the way to the original
+length of the argument area, no matter what you do (this is the case
+for example with Linux 2.2).

 
 Note for BSD users: setting C<$0> does not completely remove "perl"
 
 Note for BSD users: setting C<$0> does not completely remove "perl"

-from the ps(1) output.  For example, setting C<$0> to C<"foobar"> will
-result in C<"perl: foobar (perl)">.  This is an operating system
-feature.
+from the ps(1) output.  For example, setting C<$0> to C<"foobar"> may
+result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix
+and the " (perl)" suffix are shown depends on your exact BSD variant
+and version).  This is an operating system feature, Perl cannot help it.

 
 In multithreaded scripts Perl coordinates the threads so that any
 thread may modify its copy of the C<$0> and the change becomes visible
 
 In multithreaded scripts Perl coordinates the threads so that any
 thread may modify its copy of the C<$0> and the change becomes visible

-to ps(1) (assuming the operating system plays along).
+to ps(1) (assuming the operating system plays along).  Note that the
+the view of C<$0> the other threads have will not change since they
+have their own copies of it.

 
 =item $[
 
 
 =item $[
 


@@ -883,8 +881,14 @@ subscripting and when evaluating the index() and substr() functions.
 
 As of release 5 of Perl, assignment to C<$[> is treated as a compiler
 directive, and cannot influence the behavior of any other file.
 
 As of release 5 of Perl, assignment to C<$[> is treated as a compiler
 directive, and cannot influence the behavior of any other file.

+(That's why you can only assign compile-time constants to it.)

 Its use is highly discouraged.
 
 Its use is highly discouraged.
 

+Note that, unlike other compile-time directives (such as L<strict>),
+assignment to $[ can be seen from outer lexical scopes in the same file.
+However, you can use local() on it to strictly bound its value to a
+lexical block.
+

 =item $]
 
 The version + patchlevel / 1000 of the Perl interpreter.  This variable
 =item $]
 
 The version + patchlevel / 1000 of the Perl interpreter.  This variable


@@ -916,7 +920,8 @@ C<$^C = 1> is similar to calling C<B::minus_c>.
 =item $^D
 
 The current value of the debugging flags.  (Mnemonic: value of B<-D>
 =item $^D
 
 The current value of the debugging flags.  (Mnemonic: value of B<-D>

-switch.)
+switch.) May be read or set. Like its command-line equivalent, you can use
+numeric or symbolic values, eg C<$^D = 10> or C<$^D = "st">.

 
 =item $SYSTEM_FD_MAX
 
 
 =item $SYSTEM_FD_MAX
 


@@ -1075,6 +1080,10 @@ Provide informative "file" names for evals based on the place they were compiled
 Provide informative names to anonymous subroutines based on the place they
 were compiled.
 
 Provide informative names to anonymous subroutines based on the place they
 were compiled.
 

+=item 0x400
+
+Debug assertion subroutines enter/exit.
+

 =back
 
 Some bits may be relevant at compile-time only, some at
 =back
 
 Some bits may be relevant at compile-time only, some at


@@ -1329,20 +1338,11 @@ Be sure not to use a bareword as the name of a signal handler,
 lest you inadvertently call it. 
 
 If your system has the sigaction() function then signal handlers are
 lest you inadvertently call it. 
 
 If your system has the sigaction() function then signal handlers are

-installed using it.  This means you get reliable signal handling.  If
-your system has the SA_RESTART flag it is used when signals handlers are
-installed.  This means that system calls for which restarting is supported
-continue rather than returning when a signal arrives.  If you want your
-system calls to be interrupted by signal delivery then do something like
-this:
-
-    use POSIX ':signal_h';
-
-    my $alarm = 0;
-    sigaction SIGALRM, new POSIX::SigAction sub { $alarm = 1 }
-       or die "Error setting SIGALRM handler: $!\n";
+installed using it.  This means you get reliable signal handling.

 
 

-See L<POSIX>.
+The default delivery policy of signals changed in Perl 5.8.0 from 
+immediate (also known as "unsafe") to deferred, also known as 
+"safe signals".  See L<perlipc> for more information.

 
 Certain internal hooks can be also set using the %SIG hash.  The
 routine indicated by C<$SIG{__WARN__}> is called when a warning message is
 
 Certain internal hooks can be also set using the %SIG hash.  The
 routine indicated by C<$SIG{__WARN__}> is called when a warning message is