the beginning or the end of the script. However, if you're using
lexically-scoped private variables created with my(), you'll have to make sure
your format or subroutine definition is within the same block scope
-as the my if you expect to to be able to access those private variables.
+as the my if you expect to be able to access those private variables.
Declaring a subroutine allows a subroutine name to be used as if it were a
list operator from that point forward in the program. You can declare a
side effects. Every simple statement must be terminated with a
semicolon, unless it is the final statement in a block, in which case
the semicolon is optional. (A semicolon is still encouraged there if the
-block takes up more than one line, since you may eventually add another line.)
+block takes up more than one line, because you may eventually add another line.)
Note that there are some operators like C<eval {}> and C<do {}> that look
like compound statements, but aren't (they're just TERMs in an expression),
and thus need an explicit termination if used as the last item in a statement.
} until $line eq ".\n";
See L<perlfunc/do>. Note also that the loop control
-statements described later will I<NOT> work in this construct, since
+statements described later will I<NOT> work in this construct, because
modifiers don't take loop labels. Sorry. You can always wrap
another block around it to do that sort of thing.
open(FOO) ? 'hi mom' : die "Can't open $FOO: $!";
# a bit exotic, that last one
-The C<if> statement is straightforward. Since BLOCKs are always
+The C<if> statement is straightforward. Because BLOCKs are always
bounded by curly brackets, there is never any ambiguity about which
C<if> an C<else> goes with. If you use C<unless> in place of C<if>,
the sense of the test is reversed.
test is reversed, but the conditional is still tested before the first
iteration.
-In either the C<if> or the C<while> statement, you may replace "(EXPR)"
-with a BLOCK, and the conditional is true if the value of the last
-statement in that block is true. While this "feature" continues to work in
-version 5, it has been deprecated, so please change any occurrences of "if BLOCK" to
-"if (do BLOCK)".
+The form C<while/if BLOCK BLOCK>, available in Perl 4, is no longer
+available. Replace any occurrence of C<if BLOCK> by C<if (do BLOCK)>.
=head2 For Loops
See how much easier this is? It's cleaner, safer, and faster. It's
cleaner because it's less noisy. It's safer because if code gets added
between the inner and outer loops later on, the new code won't be
-accidentally executed, the C<next> explicitly iterates the other loop
+accidentally executed. The C<next> explicitly iterates the other loop
rather than merely terminating the inner one. And it's faster because
Perl executes a C<foreach> statement more rapidly than it would the
equivalent C<for> loop.
.........
}
-Note that pod translators should only look at paragraphs beginning
+Note that pod translators should look at only paragraphs beginning
with a pod directive (it makes parsing easier), whereas the compiler
actually knows to look for pod escapes even in the middle of a
paragraph. This means that the following secret stuff will be
You probably shouldn't rely upon the warn() being podded out forever.
Not all pod translators are well-behaved in this regard, and perhaps
the compiler will become pickier.
+
+One may also use pod directives to quickly comment out a section
+of code.
+
+=head2 Plain Old Comments (Not!)
+
+Much like the C preprocessor, perl can process line directives. Using
+this, one can control perl's idea of filenames and line numbers in
+error or warning messages (especially for strings that are processed
+with eval()). The syntax for this mechanism is the same as for most
+C preprocessors: it matches the regular expression
+C</^#\s*line\s+(\d+)\s*(?:\s"([^"]*)")?/> with C<$1> being the line
+number for the next line, and C<$2> being the optional filename
+(specified within quotes).
+
+Here are some examples that you should be able to type into your command
+shell:
+
+ % perl
+ # line 200 "bzzzt"
+ # the `#' on the previous line must be the first char on line
+ die 'foo';
+ __END__
+ foo at bzzzt line 201.
+
+ % perl
+ # line 200 "bzzzt"
+ eval qq[\n#line 2001 ""\ndie 'foo']; print $@;
+ __END__
+ foo at - line 2001.
+
+ % perl
+ eval qq[\n#line 200 "foo bar"\ndie 'foo']; print $@;
+ __END__
+ foo at foo bar line 200.
+
+ % perl
+ # line 345 "goop"
+ eval "\n#line " . __LINE__ . ' "' . __FILE__ ."\"\ndie 'foo'";
+ print $@;
+ __END__
+ foo at goop line 345.
+
+=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff