=head1 NAME
-perlfaq7 - General Perl Language Issues ($Revision: 1.7 $, $Date: 2002/01/31 04:27:55 $)
+perlfaq7 - General Perl Language Issues ($Revision: 1.11 $, $Date: 2002/11/10 17:35:47 $)
=head1 DESCRIPTION
Another way is to use undef as an element on the left-hand-side:
($dev, $ino, undef, undef, $uid, $gid) = stat($file);
+
+You can also use a list slice to select only the elements that
+you need:
+
+ ($dev, $ino, $uid, $gid) = ( stat($file) )[0,1,4,5];
=head2 How do I temporarily block warnings?
=item Passing Filehandles
-To pass filehandles to subroutines, use the C<*FH> or C<\*FH> notations.
+As of Perl 5.6, you can represent filehandles with scalar variables
+which you treat as any other scalar.
+
+ open my $fh, $filename or die "Cannot open $filename! $!";
+ func( $fh );
+
+ sub func {
+ my $passed_fh = shift;
+
+ my $line = <$fh>;
+ }
+
+Before Perl 5.6, you had to use the C<*FH> or C<\*FH> notations.
These are "typeglobs"--see L<perldata/"Typeglobs and Filehandles">
and especially L<perlsub/"Pass by Reference"> for more information.
-Here's an excerpt:
-
-If you're passing around filehandles, you could usually just use the bare
-typeglob, like *STDOUT, but typeglobs references would be better because
-they'll still work properly under C<use strict 'refs'>. For example:
-
- splutter(\*STDOUT);
- sub splutter {
- my $fh = shift;
- print $fh "her um well a hmmm\n";
- }
-
- $rec = get_rec(\*STDIN);
- sub get_rec {
- my $fh = shift;
- return scalar <$fh>;
- }
-
-If you're planning on generating new filehandles, you could do this:
-
- sub openit {
- my $path = shift;
- local *FH;
- return open (FH, $path) ? *FH : undef;
- }
- $fh = openit('< /etc/motd');
- print <$fh>;
-
=item Passing Regexes
To pass regexes around, you'll need to be using a release of Perl
=head2 How can I access a dynamic variable while a similarly named lexical is in scope?
-You can do this via symbolic references, provided you haven't set
-C<use strict "refs">. So instead of $var, use C<${'var'}>.
+If you know your package, you can just mention it explicitly, as in
+$Some_Pack::var. Note that the notation $::var is B<not> the dynamic $var
+in the current package, but rather the one in the "main" package, as
+though you had written $main::var.
- local $var = "global";
- my $var = "lexical";
+ use vars '$var';
+ local $var = "global";
+ my $var = "lexical";
- print "lexical is $var\n";
+ print "lexical is $var\n";
+ print "global is $main::var\n";
- no strict 'refs';
- print "global is ${'var'}\n";
+Alternatively you can use the compiler directive our() to bring a
+dynamic variable into the current lexical scope.
-If you know your package, you can just mention it explicitly, as in
-$Some_Pack::var. Note that the notation $::var is I<not> the dynamic
-$var in the current package, but rather the one in the C<main>
-package, as though you had written $main::var. Specifying the package
-directly makes you hard-code its name, but it executes faster and
-avoids running afoul of C<use strict "refs">.
+ require 5.006; # our() did not exist before 5.6
+ use vars '$var';
+
+ local $var = "global";
+ my $var = "lexical";
+
+ print "lexical is $var\n";
+
+ {
+ our $var;
+ print "global is $var\n";
+ }
=head2 What's the difference between deep and shallow binding?
print "No such command: $string\n";
}
-=head2 How can I catch accesses to undefined variables/functions/methods?
+=head2 How can I catch accesses to undefined variables, functions, or methods?
The AUTOLOAD method, discussed in L<perlsub/"Autoloading"> and
L<perltoot/"AUTOLOAD: Proxy Methods">, lets you capture calls to
undefined functions and methods.
When it comes to undefined variables that would trigger a warning
-under C<-w>, you can use a handler to trap the pseudo-signal
-C<__WARN__> like this:
-
- $SIG{__WARN__} = sub {
-
- for ( $_[0] ) { # voici un switch statement
+under C<use warnings>, you can promote the warning to an error.
- /Use of uninitialized value/ && do {
- # promote warning to a fatal
- die $_;
- };
-
- # other warning cases to catch could go here;
-
- warn $_;
- }
-
- };
+ use warnings FATAL => qw(uninitialized);
=head2 Why can't a method included in this same file be found?
=head2 How can I comment out a large block of perl code?
-Use embedded POD to discard it:
+You can use embedded POD to discard it. The =for directive
+lasts until the next paragraph (two consecutive newlines).
# program is here
# program continues
+The =begin and =end directives can contain multiple
+paragraphs.
+
=begin comment text
all of this stuff
=end comment text
- =cut
+The pod directives cannot go just anywhere. You must put a
+pod directive where the parser is expecting a new statement,
+not just in the middle of an expression or some other
+arbitrary s grammar production.
-This can't go just anywhere. You have to put a pod directive where
-the parser is expecting a new statement, not just in the middle
-of an expression or some other arbitrary yacc grammar production.
+See L<perlpod> for more details.
=head2 How do I clear a package?
projects / p5sagit/p5-mst-13.2.git / blobdiff