[win32] merge changes#872,873 from maintbranch

[perl5.git] / pod / perltrap.pod

diff --git a/pod/perltrap.pod b/pod/perltrap.pod
index d5aeafc..9d861e3 100644 (file)
--- a/pod/perltrap.pod
+++ b/pod/perltrap.pod
@@ -6,7 +6,8 @@ perltrap - Perl traps for the unwary
 
 The biggest trap of all is forgetting to use the B<-w> switch; see
 L<perlrun>.  The second biggest trap is not making your entire program
-runnable under C<use strict>.
+runnable under C<use strict>.  The third biggest trap is not reading
+the list of changes in this version of Perl; see L<perldelta>.
 
 =head2 Awk Traps
 
@@ -34,7 +35,7 @@ Curly brackets are required on C<if>s and C<while>s.
 
 =item *
 
-Variables begin with "$" or "@" in Perl.
+Variables begin with "$", "@" or "%" in Perl.
 
 =item *
 
@@ -167,7 +168,7 @@ There's no switch statement.  (But it's easy to build one on the fly.)
 
 =item *
 
-Variables begin with "$" or "@" in Perl.
+Variables begin with "$", "@" or "%" in Perl.
 
 =item *
 
@@ -437,6 +438,12 @@ whether this should be classed as a bug or not.
     # perl4 prints: x=10
     # perl5 prints: Can't find string terminator "'" anywhere before EOF
 
+You can avoid this problem, and remain compatible with perl4, if you
+always explicitly include the package name:
+
+    $x = 10 ;
+    print "x=${main'x}\n" ;
+
 Also see precedence traps, for parsing C<$:>.
 
 =item * BugFix
@@ -750,15 +757,11 @@ variable is localized subsequent to the assignment
     # perl4 prints: This is Perl 4
     # perl5 prints:
 
-    # Another example
-
-    *fred = *barney; # fred is aliased to barney
-    @barney = (1, 2, 4);
-    # @fred;
-    print "@fred";  # should print "1, 2, 4"
+=item * (Globs)
 
-    # perl4 prints: 1 2 4
-    # perl5 prints: In string, @fred now must be written as \@fred
+Assigning C<undef> to a glob has no effect in Perl 5.   In Perl 4
+it undefines the associated scalar (but may have other side effects
+including SEGVs).
 
 =item * (Scalar String)
 
@@ -922,7 +925,9 @@ Perl4-to-Perl5 traps involving precedence order.
 
 =item * Precedence
 
-LHS vs. RHS when both sides are getting an op.
+LHS vs. RHS of any assignment operator.  LHS is evaluated first
+in perl4, second in perl5; this can affect the relationship
+between side-effects in sub-expressions.
 
     @arr = ( 'left', 'right' );
     $a{shift @arr} = shift @arr;
@@ -998,18 +1003,6 @@ concatenation precedence over filetest operator?
     # perl4 prints: no output
     # perl5 prints: Can't modify -e in concatenation
 
-=item * Precedence
-
-Assignment to value takes precedence over assignment to key in
-perl5 when using the shift operator on both sides.
-
-    @arr = ( 'left', 'right' );
-    $a{shift @arr} = shift @arr;
-    print join( ' ', keys %a );
-
-    # perl4 prints: left
-    # perl5 prints: right
-
 =back
 
 =head2 General Regular Expression Traps using s///, etc.
@@ -1454,9 +1447,7 @@ Everything else.
 
 =over 5
 
-=item * Unclassified
-
-C<require>/C<do> trap using returned value
+=item * C<require>/C<do> trap using returned value
 
 If the file doit.pl has:
 
@@ -1477,6 +1468,14 @@ Running doit.pl gives the following:
 
 Same behavior if you replace C<do> with C<require>.
 
+=item * C<split> on empty string with LIMIT specified
+
+       $string = '';
+    @list = split(/foo/, $string, 2)
+
+Perl4 returns a one element list containing the empty string but Perl5
+returns an empty list.
+
 =back
 
 As always, if any of these are ever officially declared as bugs,