C<"">; and when used as a reference that isn't being assigned
to, it is treated as an error. If you enable warnings, you'll
be notified of an uninitialized value whenever you treat C<undef>
-as a string or a number. Well, usually. Boolean ("don't-care")
-contexts and operators such as C<++>, C<-->, C<+=>, C<-=>, and
-C<.=> are always exempt from such warnings.
+as a string or a number. Well, usually. Boolean contexts, such as:
+
+ my $a;
+ if ($a) {}
+
+are exempt from warnings (because they care about truth rather than
+definedness). Operators such as C<++>, C<-->, C<+=>,
+C<-=>, and C<.=>, that operate on undefined left values such as:
+
+ my $a;
+ $a++;
+
+are also always exempt from such warnings.
A declaration can be put anywhere a statement can, but has no effect on
the execution of the primary sequence of statements--declarations all
# now process $line
}
-Note that if there were a C<continue> block on the above code, it would get
-executed even on discarded lines. This is often used to reset line counters
-or C<?pat?> one-time matches.
+Note that if there were a C<continue> block on the above code, it would
+get executed only on lines discarded by the regex (since redo skips the
+continue block). A continue block is often used to reset line counters
+or C<?pat?> one-time matches:
# inspired by :1,$g/fred/s//WILMA/
while (<>) {
they aren't loops. You can double the braces to make them such, though.
if (/pattern/) {{
- next if /fred/;
- next if /barney/;
- # so something here
+ last if /fred/;
+ next if /barney/; # same effect as "last", but doesn't document as well
+ # do something here
}}
+This is caused by the fact that a block by itself acts as a loop that
+executes once, see L<"Basic BLOCKs and Switch Statements">.
+
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)>.
"read-only";
};
-Or if you are certainly that all the C<&&> clauses are true, you can use
+Or if you are certain that all the C<&&> clauses are true, you can use
something like this, which "switches" on the value of the
C<HTTP_USER_AGENT> environment variable.