=head1 NAME
-perlfaq7 - General Perl Language Issues ($Revision: 1.11 $, $Date: 2002/11/10 17:35:47 $)
+perlfaq7 - General Perl Language Issues ($Revision: 1.13 $, $Date: 2003/01/26 17:45:46 $)
=head1 DESCRIPTION
Note that <FILE> is I<neither> the type specifier for files
nor the name of the handle. It is the C<< <> >> operator applied
to the handle FILE. It reads one line (well, record--see
-L<perlvar/$/>) from the handle FILE in scalar context, or I<all> lines
+L<perlvar/$E<sol>>) from the handle FILE in scalar context, or I<all> lines
in list context. When performing open, close, or any other operation
besides C<< <> >> on files, or even when talking about the handle, do
I<not> use the brackets. These are correct: C<eof(FH)>, C<seek(FH, 0,
Another way is to use undef as an element on the left-hand-side:
($dev, $ino, undef, undef, $uid, $gid) = stat($file);
-
+
You can also use a list slice to select only the elements that
you need:
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.
variables. It gives a global variable a temporary value. my() is
what you're looking for if you want private variables.
-See L<perlsub/"Private Variables via my()"> and
+See L<perlsub/"Private Variables via my()"> and
L<perlsub/"Temporary Values via local()"> for excruciating details.
=head2 How can I access a dynamic variable while a similarly named lexical is in scope?
are effectively shallowly bound. Consider this just one more reason
not to use them. See the answer to L<"What's a closure?">.
-=head2 Why doesn't "my($foo) = <FILE>;" work right?
+=head2 Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
C<my()> and C<local()> give list context to the right hand side
of C<=>. The <FH> read operation, like so many of Perl's
elsif (/pat2/) { } # do something else
elsif (/pat3/) { } # do something else
else { } # default
- }
+ }
Here's a simple example of a switch based on pattern matching, this
time lined up in a way to make it look more like a switch statement.
}
-See C<perlsyn/"Basic BLOCKs and Switch Statements"> for many other
+See C<perlsyn/"Basic BLOCKs and Switch Statements"> for many other
examples in this style.
Sometimes you should change the positions of the constant and the variable.
elsif ("LIST" =~ /^\Q$answer/i) { print "Action is list\n" }
elsif ("EDIT" =~ /^\Q$answer/i) { print "Action is edit\n" }
-A totally different approach is to create a hash of function references.
+A totally different approach is to create a hash of function references.
my %commands = (
"happy" => \&joy,
$commands{$string}->();
} else {
print "No such command: $string\n";
- }
+ }
=head2 How can I catch accesses to undefined variables, functions, or methods?
sub scrub_package {
no strict 'refs';
my $pack = shift;
- die "Shouldn't delete main package"
+ die "Shouldn't delete main package"
if $pack eq "" || $pack eq "main";
my $stash = *{$pack . '::'}{HASH};
my $name;
}
}
-Or, if you're using a recent release of Perl, you can
+Or, if you're using a recent release of Perl, you can
just use the Symbol::delete_package() function instead.
=head2 How can I use a variable as a variable name?
$name = "fred";
$$name{WIFE} = "wilma"; # set %fred
- $name = "barney";
+ $name = "barney";
$$name{WIFE} = "betty"; # set %barney
This is still a symbolic reference, and is still saddled with the
for my $name (@colors) {
no strict 'refs'; # renege for the block
*$name = sub { "<FONT COLOR='$name'>@_</FONT>" };
- }
+ }
All those functions (red(), blue(), green(), etc.) appear to be separate,
but the real code in the closure actually was compiled only once.
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