=item *
Reading an input line does not split it for you. You get to split it
-yourself to an array. And split() operator has different
+yourself to an array. And the split() operator has different
arguments.
=item *
=item *
-printf() does not implement the "*" format for interpolating
+C<printf()> does not implement the "*" format for interpolating
field widths, but it's trivial to use interpolation of double-quoted
strings to achieve the same effect.
=item *
-The backtick operator does variable interpretation without regard to
+The backtick operator does variable interpolation without regard to
the presence of single quotes in the command.
=item *
default to $_, or @ARGV, or whatever, but that others which
you might expect to do not.
-=item *
+=item *
The <FH> construct is not the name of the filehandle, it is a readline
operation on that handle. The data read is only assigned to $_ if the
while ($_ = <FH>) { }..
<FH>; # data discarded!
-=item *
+=item *
Remember not to use "C<=>" when you need "C<=~>";
these two constructs are quite different:
=item *
-Use my() for local variables whenever you can get away with
+Use C<my()> for local variables whenever you can get away with
it (but see L<perlform> for where you can't).
-Using local() actually gives a local value to a global
+Using C<local()> actually gives a local value to a global
variable, which leaves you open to unforeseen side-effects
of dynamic scoping.
=back
-=head2 Perl4 Traps
+=head2 Perl4 to Perl5 Traps
-Penitent Perl 4 Programmers should take note of the following
-incompatible changes that occurred between release 4 and release 5:
+Practicing Perl4 Programmers should take note of the following
+Perl4-to-Perl5 specific traps.
+
+They're crudely ordered according to the following list:
=over 4
-=item *
+=item Discontinuance, Deprecation, and BugFix traps
-C<@> now always interpolates an array in double-quotish strings. Some programs
-may now need to use backslash to protect any C<@> that shouldn't interpolate.
+Anything that's been fixed as a perl4 bug, removed as a perl4 feature
+or deprecated as a perl4 feature with the intent to encourage usage of
+some other perl5 feature.
-=item *
+=item Parsing Traps
-Barewords that used to look like strings to Perl will now look like subroutine
-calls if a subroutine by that name is defined before the compiler sees them.
-For example:
+Traps that appear to stem from the new parser.
- sub SeeYa { die "Hasta la vista, baby!" }
- $SIG{'QUIT'} = SeeYa;
+=item Numerical Traps
-In Perl 4, that set the signal handler; in Perl 5, it actually calls the
-function! You may use the B<-w> switch to find such places.
+Traps having to do with numerical or mathematical operators.
-=item *
+=item General data type traps
-Symbols starting with C<_> are no longer forced into package C<main>, except
-for $_ itself (and @_, etc.).
+Traps involving perl standard data types.
-=item *
+=item Context Traps - scalar, list contexts
+
+Traps related to context within lists, scalar statements/declarations.
+
+=item Precedence Traps
+
+Traps related to the precedence of parsing, evaluation, and execution of
+code.
+
+=item General Regular Expression Traps using s///, etc.
+
+Traps related to the use of pattern matching.
+
+=item Subroutine, Signal, Sorting Traps
+
+Traps related to the use of signals and signal handlers, general subroutines,
+and sorting, along with sorting subroutines.
+
+=item OS Traps
+
+OS-specific traps.
+
+=item DBM Traps
+
+Traps specific to the use of C<dbmopen()>, and specific dbm implementations.
+
+=item Unclassified Traps
+
+Everything else.
+
+=back
+
+If you find an example of a conversion trap that is not listed here,
+please submit it to Bill Middleton F<wjm@best.com> for inclusion.
+Also note that at least some of these can be caught with C<-w>.
+
+=head2 Discontinuance, Deprecation, and BugFix traps
+
+Anything that has been discontinued, deprecated, or fixed as
+a bug from perl4.
-Double-colon is now a valid package separator in an identifier. Thus these
-behave differently in perl4 vs. perl5:
+=over 4
+
+=item * Discontinuance
+
+Symbols starting with "_" are no longer forced into package main, except
+for C<$_> itself (and C<@_>, etc.).
+
+ package test;
+ $_legacy = 1;
- print "$a::$b::$c\n";
+ package main;
+ print "\$_legacy is ",$_legacy,"\n";
+
+ # perl4 prints: $_legacy is 1
+ # perl5 prints: $_legacy is
+
+=item * Deprecation
+
+Double-colon is now a valid package separator in a variable name. Thus these
+behave differently in perl4 vs. perl5, since the packages don't exist.
+
+ $a=1;$b=2;$c=3;$var=4;
+ print "$a::$b::$c ";
print "$var::abc::xyz\n";
+
+ # perl4 prints: 1::2::3 4::abc::xyz
+ # perl5 prints: 3
-=item *
+Given that C<::> is now the preferred package delimiter, it is debatable
+whether this should be classed as a bug or not.
+(The older package delimiter, ' ,is used here)
-C<s'$lhs'$rhs'> now does no interpolation on either side. It used to
-interpolate C<$lhs> but not C<$rhs>.
+ $x = 10 ;
+ print "x=${'x}\n" ;
+
+ # perl4 prints: x=10
+ # perl5 prints: Can't find string terminator "'" anywhere before EOF
-=item *
+Also see precedence traps, for parsing C<$:>.
-The second and third arguments of splice() are now evaluated in scalar
-context (as the book says) rather than list context.
+=item * BugFix
-=item *
+The second and third arguments of C<splice()> are now evaluated in scalar
+context (as the Camel says) rather than list context.
-These are now semantic errors because of precedence:
+ sub sub1{return(0,2) } # return a 2-elem array
+ sub sub2{ return(1,2,3)} # return a 3-elem array
+ @a1 = ("a","b","c","d","e");
+ @a2 = splice(@a1,&sub1,&sub2);
+ print join(' ',@a2),"\n";
+
+ # perl4 prints: a b
+ # perl5 prints: c d e
- shift @list + 20;
- $n = keys %map + 20;
+=item * Discontinuance
-Because if that were to work, then this couldn't:
+You can't do a C<goto> into a block that is optimized away. Darn.
- sleep $dormancy + 20;
+ goto marker1;
-=item *
+ for(1){
+ marker1:
+ print "Here I is!\n";
+ }
+
+ # perl4 prints: Here I is!
+ # perl5 dumps core (SEGV)
+
+=item * Discontinuance
+
+It is no longer syntactically legal to use whitespace as the name
+of a variable, or as a delimiter for any kind of quote construct.
+Double darn.
+
+ $a = ("foo bar");
+ $b = q baz ;
+ print "a is $a, b is $b\n";
+
+ # perl4 prints: a is foo bar, b is baz
+ # perl5 errors: Bare word found where operator expected
+
+=item * Discontinuance
+
+The archaic while/if BLOCK BLOCK syntax is no longer supported.
+
+ if { 1 } {
+ print "True!";
+ }
+ else {
+ print "False!";
+ }
+
+ # perl4 prints: True!
+ # perl5 errors: syntax error at test.pl line 1, near "if {"
+
+=item * BugFix
+
+The C<**> operator now binds more tightly than unary minus.
+It was documented to work this way before, but didn't.
+
+ print -4**2,"\n";
+
+ # perl4 prints: 16
+ # perl5 prints: -16
+
+=item * Discontinuance
+
+The meaning of C<foreach{}> has changed slightly when it is iterating over a
+list which is not an array. This used to assign the list to a
+temporary array, but no longer does so (for efficiency). This means
+that you'll now be iterating over the actual values, not over copies of
+the values. Modifications to the loop variable can change the original
+values.
+
+ @list = ('ab','abc','bcd','def');
+ foreach $var (grep(/ab/,@list)){
+ $var = 1;
+ }
+ print (join(':',@list));
+
+ # perl4 prints: ab:abc:bcd:def
+ # perl5 prints: 1:1:bcd:def
+
+To retain Perl4 semantics you need to assign your list
+explicitly to a temporary array and then iterate over that. For
+example, you might need to change
+
+ foreach $var (grep(/ab/,@list)){
+
+to
+
+ foreach $var (@tmp = grep(/ab/,@list)){
+
+Otherwise changing $var will clobber the values of @list. (This most often
+happens when you use C<$_> for the loop variable, and call subroutines in
+the loop that don't properly localize C<$_>.)
+
+=item * Deprecation
+
+Some error messages will be different.
+
+=item * Discontinuance
+
+Some bugs may have been inadvertently removed. :-)
+
+=back
+
+=head2 Parsing Traps
+
+Perl4-to-Perl5 traps from having to do with parsing.
+
+=over 4
+
+=item * Parsing
+
+Note the space between . and =
+
+ $string . = "more string";
+ print $string;
+
+ # perl4 prints: more string
+ # perl5 prints: syntax error at - line 1, near ". ="
+
+=item * Parsing
+
+Better parsing in perl 5
+
+ sub foo {}
+ &foo
+ print("hello, world\n");
+
+ # perl4 prints: hello, world
+ # perl5 prints: syntax error
+
+=item * Parsing
+
+"if it looks like a function, it is a function" rule.
+
+ print
+ ($foo == 1) ? "is one\n" : "is zero\n";
+
+ # perl4 prints: is zero
+ # perl5 warns: "Useless use of a constant in void context" if using -w
+
+=back
+
+=head2 Numerical Traps
+
+Perl4-to-Perl5 traps having to do with numerical operators,
+operands, or output from same.
+
+=over 5
+
+=item * Numerical
+
+Formatted output and significant digits
+
+ print 7.373504 - 0, "\n";
+ printf "%20.18f\n", 7.373504 - 0;
+
+ # Perl4 prints:
+ 7.375039999999996141
+ 7.37503999999999614
+
+ # Perl5 prints:
+ 7.373504
+ 7.37503999999999614
+
+=item * Numerical
+
+Large integer trap with autoincrement
+
+ $a = $b = 2147483647;
+ print "$a $b\n";
+ $a += 1;
+ $b++;
+ print "$a $b\n";
+
+ # perl4 prints:
+ 2147483647 2147483647
+ 2147483648 2147483648
+
+ # perl5 prints:
+ 2147483647 2147483647
+ 2147483648 -2147483648
+
+=item * Numerical
+
+Assignment of return values from numeric equality tests
+does not work in perl5 when the test evaluates to false (0).
+Logical tests now return an null, instead of 0
+
+ $p = ($test == 1);
+ print $p,"\n";
+
+ # perl4 prints: 0
+ # perl5 prints:
+
+Also see the L<General Regular Expression Traps> tests for another example
+of this new feature...
+
+=back
+
+=head2 General data type traps
+
+Perl4-to-Perl5 traps involving most data-types, and their usage
+within certain expressions and/or context.
+
+=over 5
+
+=item * (Arrays)
+
+Negative array subscripts now count from the end of the array.
+
+ @a = (1, 2, 3, 4, 5);
+ print "The third element of the array is $a[3] also expressed as $a[-2] \n";
+
+ # perl4 prints: The third element of the array is 4 also expressed as
+ # perl5 prints: The third element of the array is 4 also expressed as 4
+
+=item * (Arrays)
+
+Setting C<$#array> lower now discards array elements, and makes them
+impossible to recover.
+
+ @a = (a,b,c,d,e);
+ print "Before: ",join('',@a);
+ $#a =1;
+ print ", After: ",join('',@a);
+ $#a =3;
+ print ", Recovered: ",join('',@a),"\n";
+
+ # perl4 prints: Before: abcde, After: ab, Recovered: abcd
+ # perl5 prints: Before: abcde, After: ab, Recovered: ab
+
+=item * (Hashes)
+
+Hashes get defined before use
+
+ local($s,@a,%h);
+ die "scalar \$s defined" if defined($s);
+ die "array \@a defined" if defined(@a);
+ die "hash \%h defined" if defined(%h);
+
+ # perl4 prints:
+ # perl5 dies: hash %h defined
+
+=item * (Globs)
+
+glob assignment from variable to variable will fail if the assigned
+variable is localized subsequent to the assignment
+
+ @a = ("This is Perl 4");
+ *b = *a;
+ local(@a);
+ print @b,"\n";
+
+ # 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"
+
+ # perl4 prints: 1 2 4
+ # perl5 prints: Literal @fred now requires backslash
+
+=item * (Scalar String)
+
+Changes in unary negation (of strings)
+This change effects both the return value and what it
+does to auto(magic)increment.
+
+ $x = "aaa";
+ print ++$x," : ";
+ print -$x," : ";
+ print ++$x,"\n";
+
+ # perl4 prints: aab : -0 : 1
+ # perl5 prints: aab : -aab : aac
+
+=item * (Constants)
+
+perl 4 lets you modify constants:
+
+ $foo = "x";
+ &mod($foo);
+ for ($x = 0; $x < 3; $x++) {
+ &mod("a");
+ }
+ sub mod {
+ print "before: $_[0]";
+ $_[0] = "m";
+ print " after: $_[0]\n";
+ }
+
+ # perl4:
+ # before: x after: m
+ # before: a after: m
+ # before: m after: m
+ # before: m after: m
+
+ # Perl5:
+ # before: x after: m
+ # Modification of a read-only value attempted at foo.pl line 12.
+ # before: a
+
+=item * (Scalars)
+
+The behavior is slightly different for:
+
+ print "$x", defined $x
+
+ # perl 4: 1
+ # perl 5: <no output, $x is not called into existence>
+
+=item * (Variable Suicide)
+
+Variable suicide behavior is more consistent under Perl 5.
+Perl5 exhibits the same behavior for associative arrays and scalars,
+that perl4 exhibits only for scalars.
+
+ $aGlobal{ "aKey" } = "global value";
+ print "MAIN:", $aGlobal{"aKey"}, "\n";
+ $GlobalLevel = 0;
+ &test( *aGlobal );
+
+ sub test {
+ local( *theArgument ) = @_;
+ local( %aNewLocal ); # perl 4 != 5.001l,m
+ $aNewLocal{"aKey"} = "this should never appear";
+ print "SUB: ", $theArgument{"aKey"}, "\n";
+ $aNewLocal{"aKey"} = "level $GlobalLevel"; # what should print
+ $GlobalLevel++;
+ if( $GlobalLevel<4 ) {
+ &test( *aNewLocal );
+ }
+ }
+
+ # Perl4:
+ # MAIN:global value
+ # SUB: global value
+ # SUB: level 0
+ # SUB: level 1
+ # SUB: level 2
+
+ # Perl5:
+ # MAIN:global value
+ # SUB: global value
+ # SUB: this should never appear
+ # SUB: this should never appear
+ # SUB: this should never appear
+
+=back
+
+=head2 Context Traps - scalar, list contexts
+
+=over 5
+
+=item * (list context)
+
+The elements of argument lists for formats are now evaluated in list
+context. This means you can interpolate list values now.
+
+ @fmt = ("foo","bar","baz");
+ format STDOUT=
+ @<<<<< @||||| @>>>>>
+ @fmt;
+ .
+ write;
+
+ # perl4 errors: Please use commas to separate fields in file
+ # perl5 prints: foo bar baz
+
+=item * (scalar context)
+
+The C<caller()> function now returns a false value in a scalar context
+if there is no caller. This lets library files determine if they're
+being required.
+
+ caller() ? (print "You rang?\n") : (print "Got a 0\n");
+
+ # perl4 errors: There is no caller
+ # perl5 prints: Got a 0
+
+=item * (scalar context)
+
+The comma operator in a scalar context is now guaranteed to give a
+scalar context to its arguments.
+
+ @y= ('a','b','c');
+ $x = (1, 2, @y);
+ print "x = $x\n";
+
+ # Perl4 prints: x = c # Thinks list context interpolates list
+ # Perl5 prints: x = 3 # Knows scalar uses length of list
+
+=item * (list, builtin)
+
+C<sprintf()> funkiness (array argument converted to scalar array count)
+This test could be added to t/op/sprintf.t
+
+ @z = ('%s%s', 'foo', 'bar');
+ $x = sprintf(@z);
+ if ($x eq 'foobar') {print "ok 2\n";} else {print "not ok 2 '$x'\n";}
+
+ # perl4 prints: ok 2
+ # perl5 prints: not ok 2
+
+C<printf()> works fine, though:
+
+ printf STDOUT (@z);
+ print "\n";
+
+ # perl4 prints: foobar
+ # perl5 prints: foobar
+
+Probably a bug.
+
+=back
+
+=head2 Precedence Traps
+
+Perl4-to-Perl5 traps involving precedence order.
+
+=item *
+
+These are now semantic errors because of precedence:
+
+ @list = (1,2,3,4,5);
+ %map = ("a",1,"b",2,"c",3,"d",4);
+ $n = shift @list + 2; # first item in list plus 2
+ print "n is $n, ";
+ $m = keys %map + 2; # number of items in hash plus 2
+ print "m is $m\n";
+
+ # perl4 prints: n is 3, m is 6
+ # perl5 errors and fails to compile
+
+=item * Precedence
The precedence of assignment operators is now the same as the precedence
of assignment. Perl 4 mistakenly gave them the precedence of the associated
operator. So you now must parenthesize them in expressions like
/foo/ ? ($a += 2) : ($a -= 2);
-
+
Otherwise
- /foo/ ? $a += 2 : $a -= 2;
+ /foo/ ? $a += 2 : $a -= 2
would be erroneously parsed as
On the other hand,
- $a += /foo/ ? 1 : 2;
+ $a += /foo/ ? 1 : 2;
now works as a C programmer would expect.
-=item *
+=item * Precedence
-C<open FOO || die> is now incorrect. You need parens around the filehandle.
-While temporarily supported, using such a construct will
-generate a non-fatal (but non-suppressible) warning.
+ open FOO || die;
-=item *
+is now incorrect. You need parens around the filehandle.
+Otherwise, perl5 leaves the statement as it's default precedence:
-The elements of argument lists for formats are now evaluated in list
-context. This means you can interpolate list values now.
+ open(FOO || die);
+
+ # perl4 opens or dies
+ # perl5 errors: Precedence problem: open FOO should be open(FOO)
-=item *
+=item * Precedence
-You can't do a C<goto> into a block that is optimized away. Darn.
+perl4 gives the special variable, C<$:> precedence, where perl5
+treats C<$::> as main C<package>
-=item *
+ $a = "x"; print "$::a";
+
+ # perl 4 prints: -:a
+ # perl 5 prints: x
+
+=item * Precedence
-It is no longer syntactically legal to use whitespace as the name
-of a variable, or as a delimiter for any kind of quote construct.
-Double darn.
+concatenation precedence over filetest operator?
-=item *
+ -e $foo .= "q"
+
+ # perl4 prints: no output
+ # perl5 prints: Can't modify -e in concatenation
-The caller() function now returns a false value in a scalar context if there
-is no caller. This lets library files determine if they're being required.
+=item * Precedence
-=item *
+Assignment to value takes precedence over assignment to key in
+perl5 when using the shift operator on both sides.
+
+ @arr = ( 'left', 'right' );
+ $a{shift @arr} = shift @arr;
+ print join( ' ', keys %a );
+
+ # perl4 prints: left
+ # perl5 prints: right
+
+=back
+
+=head2 General Regular Expression Traps using s///, etc.
+
+All types of RE traps.
+
+=over 5
+
+=item * Regular Expression
+
+C<s'$lhs'$rhs'> now does no interpolation on either side. It used to
+interpolate C<$lhs> but not C<$rhs>. (And still does not match a literal
+'$' in string)
+
+ $a=1;$b=2;
+ $string = '1 2 $a $b';
+ $string =~ s'$a'$b';
+ print $string,"\n";
+
+ # perl4 prints: $b 2 $a $b
+ # perl5 prints: 1 2 $a $b
+
+=item * Regular Expression
C<m//g> now attaches its state to the searched string rather than the
-regular expression.
+regular expression. (Once the scope of a block is left for the sub, the
+state of the searched string is lost)
+
+ $_ = "ababab";
+ while(m/ab/g){
+ &doit("blah");
+ }
+ sub doit{local($_) = shift; print "Got $_ "}
+
+ # perl4 prints: blah blah blah
+ # perl5 prints: infinite loop blah...
+
+=item * Regular Expression
+
+If no parentheses are used in a match, Perl4 sets C<$+> to
+the whole match, just like C<$&>. Perl5 does not.
+
+ "abcdef" =~ /b.*e/;
+ print "\$+ = $+\n";
+
+ # perl4 prints: bcde
+ # perl5 prints:
+
+=item * Regular Expression
+
+substitution now returns the null string if it fails
+
+ $string = "test";
+ $value = ($string =~ s/foo//);
+ print $value, "\n";
+
+ # perl4 prints: 0
+ # perl5 prints:
+
+Also see L<Numerical Traps> for another example of this new feature.
+
+=item * Regular Expression
+
+C<s`lhs`rhs`> (using backticks) is now a normal substitution, with no
+backtick expansion
+
+ $string = "";
+ $string =~ s`^`hostname`;
+ print $string, "\n";
+
+ # perl4 prints: <the local hostname>
+ # perl5 prints: hostname
+
+=item * Regular Expression
+
+Stricter parsing of variables used in regular expressions
+
+ s/^([^$grpc]*$grpc[$opt$plus$rep]?)//o;
+
+ # perl4: compiles w/o error
+ # perl5: with Scalar found where operator expected ..., near "$opt$plus"
+
+an added component of this example, apparently from the same script, is
+the actual value of the s'd string after the substitution.
+C<[$opt]> is a character class in perl4 and an array subscript in perl5
+
+ $grpc = 'a';
+ $opt = 'r';
+ $_ = 'bar';
+ s/^([^$grpc]*$grpc[$opt]?)/foo/;
+ print ;
+
+ # perl4 prints: foo
+ # perl5 prints: foobar
+
+=item * Regular Expression
+
+Under perl5, C<m?x?> matches only once, like C<?x?>. Under perl4, it matched
+repeatedly, like C</x/> or C<m!x!>.
+
+ $test = "once";
+ sub match { $test =~ m?once?; }
+ &match();
+ if( &match() ) {
+ # m?x? matches more then once
+ print "perl4\n";
+ } else {
+ # m?x? matches only once
+ print "perl5\n";
+ }
+
+ # perl4 prints: perl4
+ # perl5 prints: perl5
-=item *
-C<reverse> is no longer allowed as the name of a sort subroutine.
+=back
+
+=head2 Subroutine, Signal, Sorting Traps
-=item *
+The general group of Perl4-to-Perl5 traps having to do with
+Signals, Sorting, and their related subroutines, as well as
+general subroutine traps. Includes some OS-Specific traps.
-B<taintperl> is no longer a separate executable. There is now a B<-T>
-switch to turn on tainting when it isn't turned on automatically.
+=over 5
-=item *
+=item * (Signals)
-Double-quoted strings may no longer end with an unescaped C<$> or C<@>.
+Barewords that used to look like strings to Perl will now look like subroutine
+calls if a subroutine by that name is defined before the compiler sees them.
-=item *
+ sub SeeYa { warn"Hasta la vista, baby!" }
+ $SIG{'TERM'} = SeeYa;
+ print "SIGTERM is now $SIG{'TERM'}\n";
+
+ # perl4 prints: SIGTERM is main'SeeYa
+ # perl5 prints: SIGTERM is now main::1
-The archaic C<while/if> BLOCK BLOCK syntax is no longer supported.
+Use B<-w> to catch this one
+=item * (Sort Subroutine)
-=item *
+reverse is no longer allowed as the name of a sort subroutine.
-Negative array subscripts now count from the end of the array.
+ sub reverse{ print "yup "; $a <=> $b }
+ print sort reverse a,b,c;
+
+ # perl4 prints: yup yup yup yup abc
+ # perl5 prints: abc
-=item *
+=back
-The comma operator in a scalar context is now guaranteed to give a
-scalar context to its arguments.
+=head2 OS Traps
+
+=over 5
+
+=item * (SysV)
+
+Under HPUX, and some other SysV OS's, one had to reset any signal handler,
+within the signal handler function, each time a signal was handled with
+perl4. With perl5, the reset is now done correctly. Any code relying
+on the handler _not_ being reset will have to be reworked.
+
+5.002 and beyond uses sigaction() under SysV
+
+ sub gotit {
+ print "Got @_... ";
+ }
+ $SIG{'INT'} = 'gotit';
+
+ $| = 1;
+ $pid = fork;
+ if ($pid) {
+ kill('INT', $pid);
+ sleep(1);
+ kill('INT', $pid);
+ } else {
+ while (1) {sleep(10);}
+ }
+
+ # perl4 (HPUX) prints: Got INT...
+ # perl5 (HPUX) prints: Got INT... Got INT...
+
+=item * (SysV)
+
+Under SysV OS's, C<seek()> on a file opened to append C<E<gt>E<gt>> now does
+the right thing w.r.t. the fopen() man page. e.g. - When a file is opened
+for append, it is impossible to overwrite information already in
+the file.
+
+ open(TEST,">>seek.test");
+ $start = tell TEST ;
+ foreach(1 .. 9){
+ print TEST "$_ ";
+ }
+ $end = tell TEST ;
+ seek(TEST,$start,0);
+ print TEST "18 characters here";
+
+ # perl4 (solaris) seek.test has: 18 characters here
+ # perl5 (solaris) seek.test has: 1 2 3 4 5 6 7 8 9 18 characters here
-=item *
-The C<**> operator now binds more tightly than unary minus.
-It was documented to work this way before, but didn't.
-=item *
+=back
-Setting C<$#array> lower now discards array elements.
+=head2 Interpolation Traps
-=item *
+=over 5
-delete() is not guaranteed to return the old value for tie()d arrays,
-since this capability may be onerous for some modules to implement.
+=item * Interpolation
-=item *
+@ now always interpolates an array in double-quotish strings.
+
+ print "To: someone@somewhere.com\n";
+
+ # perl4 prints: To:someone@somewhere.com
+ # perl5 errors : Literal @somewhere now requires backslash
+
+=item * Interpolation
+
+Perl4-to-Perl5 traps having to do with how things get interpolated
+within certain expressions, statements, contexts, or whatever.
+
+Double-quoted strings may no longer end with an unescaped $ or @.
+
+ $foo = "foo$";
+ $bar = "bar@";
+ print "foo is $foo, bar is $bar\n";
+
+ # perl4 prints: foo is foo$, bar is bar@
+ # perl5 errors: Final $ should be \$ or $name
+
+Note: perl5 DOES NOT error on the terminating @ in $bar
+
+=item * Interpolation
The construct "this is $$x" used to interpolate the pid at that
-point, but now tries to dereference $x. C<$$> by itself still
+point, but now apparently tries to dereference C<$x>. C<$$> by itself still
works fine, however.
-=item *
+ print "this is $$x\n";
-The meaning of foreach has changed slightly when it is iterating over a
-list which is not an array. This used to assign the list to a
-temporary array, but no longer does so (for efficiency). This means
-that you'll now be iterating over the actual values, not over copies of
-the values. Modifications to the loop variable can change the original
-values. To retain Perl 4 semantics you need to assign your list
-explicitly to a temporary array and then iterate over that. For
-example, you might need to change
+ # perl4 prints: this is XXXx (XXX is the current pid)
+ # perl5 prints: this is
+
+=item * Interpolation
+
+Creation of hashes on the fly with C<eval "EXPR"> now requires either both
+C<$>'s to be protected in the specification of the hash name, or both curlies
+to be protected. If both curlies are protected, the result will be compatible
+with perl4 and perl5. This is a very common practice, and should be changed
+to use the block form of C<eval{}> if possible.
- foreach $var (grep /x/, @list) { ... }
+ $hashname = "foobar";
+ $key = "baz";
+ $value = 1234;
+ eval "\$$hashname{'$key'} = q|$value|";
+ (defined($foobar{'baz'})) ? (print "Yup") : (print "Nope");
+
+ # perl4 prints: Yup
+ # perl5 prints: Nope
+
+Changing
+
+ eval "\$$hashname{'$key'} = q|$value|";
to
- foreach $var (my @tmp = grep /x/, @list) { ... }
+ eval "\$\$hashname{'$key'} = q|$value|";
-Otherwise changing C<$var> will clobber the values of @list. (This most often
-happens when you use C<$_> for the loop variable, and call subroutines in
-the loop that don't properly localize C<$_>.)
+causes the following result:
-=item *
+ # perl4 prints: Nope
+ # perl5 prints: Yup
-Some error messages will be different.
+or, changing to
-=item *
+ eval "\$$hashname\{'$key'\} = q|$value|";
+
+causes the following result:
+
+ # perl4 prints: Yup
+ # perl5 prints: Yup
+ # and is compatible for both versions
+
+
+=item * Interpolation
+
+perl4 programs which unconsciously rely on the bugs in earlier perl versions.
+
+ perl -e '$bar=q/not/; print "This is $foo{$bar} perl5"'
+
+ # perl4 prints: This is not perl5
+ # perl5 prints: This is perl5
+
+=item * Interpolation
+
+You also have to be careful about array references.
+
+ print "$foo{"
+
+ perl 4 prints: {
+ perl 5 prints: syntax error
+
+=item * Interpolation
+
+Similarly, watch out for:
+
+ $foo = "array";
+ print "\$$foo{bar}\n";
+
+ # perl4 prints: $array{bar}
+ # perl5 prints: $
+
+Perl 5 is looking for C<$array{bar}> which doesn't exist, but perl 4 is
+happy just to expand $foo to "array" by itself. Watch out for this
+especially in C<eval>'s.
+
+=item * Interpolation
+
+C<qq()> string passed to C<eval>
+
+ eval qq(
+ foreach \$y (keys %\$x\) {
+ \$count++;
+ }
+ );
+
+ # perl4 runs this ok
+ # perl5 prints: Can't find string terminator ")"
-Some bugs may have been inadvertently removed.
+=back
+
+=head2 DBM Traps
+
+General DBM traps.
+
+=over 5
+
+=item * DBM
+
+Existing dbm databases created under perl4 (or any other dbm/ndbm tool)
+may cause the same script, run under perl5, to fail. The build of perl5
+must have been linked with the same dbm/ndbm as the default for C<dbmopen()>
+to function properly without C<tie>'ing to an extension dbm implementation.
+
+ dbmopen (%dbm, "file", undef);
+ print "ok\n";
+
+ # perl4 prints: ok
+ # perl5 prints: ok (IFF linked with -ldbm or -lndbm)
+
+
+=item * DBM
+
+Existing dbm databases created under perl4 (or any other dbm/ndbm tool)
+may cause the same script, run under perl5, to fail. The error generated
+when exceeding the limit on the key/value size will cause perl5 to exit
+immediately.
+
+ dbmopen(DB, "testdb",0600) || die "couldn't open db! $!";
+ $DB{'trap'} = "x" x 1024; # value too large for most dbm/ndbm
+ print "YUP\n";
+
+ # perl4 prints:
+ dbm store returned -1, errno 28, key "trap" at - line 3.
+ YUP
+
+ # perl5 prints:
+ dbm store returned -1, errno 28, key "trap" at - line 3.
=back
+
+=head2 Unclassified Traps
+
+Everything else.
+
+=item * Unclassified
+
+C<require>/C<do> trap using returned value
+
+If the file doit.pl has:
+
+ sub foo {
+ $rc = do "./do.pl";
+ return 8;
+ }
+ print &foo, "\n";
+
+And the do.pl file has the following single line:
+
+ return 3;
+
+Running doit.pl gives the following:
+
+ # perl 4 prints: 3 (aborts the subroutine early)
+ # perl 5 prints: 8
+
+Same behavior if you replace C<do> with C<require>.
+
+=back
+
+As always, if any of these are ever officially declared as bugs,
+they'll be fixed and removed.
+
projects / p5sagit/p5-mst-13.2.git / commitdiff