(By way of Andrew Stesin):

From: wjm@best.com (William J. Middleton)
Newsgroups: comp.lang.perl.announce,comp.lang.perl.misc
Subject: PATCH: perltrap.pod <- 425traps
Date: 1 Jul 1996 14:49:58 GMT
Approved: merlyn@stonehenge.com (comp.lang.perl.announce)
Message-ID: <4r8oim$e5q@nadine.teleport.com>
NNTP-Posting-Host: julie.teleport.com

[The rush to 5.003 couldn't integrate this, so here it is]

The following is a patch for perltrap.pod, from 5.003 (also 5.002).
It integrates the latest version of my simple 425traps
document.  425traps demonstrated, with examples, all of the traps
which have been discovered and sent to me, which have bitten
folks making the transition from perl4 to perl5.  It also gave
an example for each one, including all of the existing perl4
traps in perltrap.pod.

As always, if you discover something that isn't documented in
one form or another in here, and isn't an official (or at least
reported) bug, drop me a line with it.  Also, when or if any
of these is ever formally declared a bug, I'll take it out.

1 files changed, 1077 insertions, 0 deletions

diff --git a/lang/perl5.10/files/patch-ac b/lang/perl5.10/files/patch-ac
new file mode 100644
index 000000000000..451a47418899
--- /dev/null
+++ b/lang/perl5.10/files/patch-ac
@@ -0,0 +1,1077 @@
+--- ./pod/perltrap.pod.orig	Tue Jan 30 20:23:50 1996
++++ ./pod/perltrap.pod	Sun Jul 14 17:33:46 1996
+@@ -172,7 +172,7 @@
+ 
+ =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.
+ 
+@@ -318,7 +318,7 @@
+ 
+ =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 
+ variable, which leaves you open to unforeseen side-effects
+@@ -332,75 +332,540 @@
+ 
+ =back
+ 
+-=head2 Perl4 Traps
+ 
+-Penitent Perl 4 Programmers should take note of the following
+-incompatible changes that occurred between release 4 and release 5:
++=head2 Perl4 to Perl5  Traps
++
++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, Depracation, 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.
++=item Parsing Traps
+ 
+-=item *
++=item Numerical 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:
++=item General data type traps
+ 
+-    sub SeeYa { die "Hasta la vista, baby!" }
+-    $SIG{'QUIT'} = SeeYa;
++=item Context Traps - scalar, list contexts
+ 
+-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.
++=item Precedence Traps
+ 
+-=item *
++=item General Regular Expression Traps using s///, etc.
+ 
+-Symbols starting with C<_> are no longer forced into package C<main>, except
+-for $_ itself (and @_, etc.).
++=item Subroutine, Signal, Sorting Traps
+ 
+-=item *
++=item OS Traps
++
++=item Unclassified Traps
++
++=back
++
++If you find an example of a conversion trap that is not listed here,
++please submit it to Bill Middleton F<wjm@best.com> for inclusion.
++Also note that at least some of these can be caught with C<-w>.
++
++=head2 Discontinuance, Depracation, and BugFix traps
++
++Anything that has been discontinued, depracated, or fixed as
++a bug from perl4.  
++
++=over 4
++
++=item * Discontinuance 
++
++Symbols starting with "_" are no longer forced into package main, except
++for C<$_> itself (and C<@_>, etc.).
++
++    package test;
++    $_legacy = 1;
++
++    package main;
++    print "\$_legacy is ",$_legacy,"\n";
++ 
++    # perl4 prints: $_legacy is 1
++    # perl5 prints: $_legacy is
++
++=item * Depracation 
+ 
+ Double-colon is now a valid package separator in an identifier.  Thus these
+-behave differently in perl4 vs. perl5:
++behave differently in perl4 vs. perl5, since the packages dont exist.
+ 
+-    print "$a::$b::$c\n";
++    $a=1;$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.
++    
++    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 
+ 
+-These are now semantic errors because of precedence:
++=item * Discontinuance 
+ 
+-    shift @list + 20;	
+-    $n = keys %map + 20; 
++You can't do a C<goto> into a block that is optimized away.  Darn.
+ 
+-Because if that were to work, then this couldn't:
++    goto marker1;
+ 
+-    sleep $dormancy + 20;
++    for(1){         
++    marker1:
++        print "Here I is!\n";
++    } 
++ 
++    # perl4 prints: Here I is!
++    # perl5 dumps core (SEGV)
+ 
+-=item *
++=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 * Depracation
++
++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
+ 
+@@ -408,115 +873,418 @@
+ 
+ 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.
++concatatination precedence over filetest operator?  
+ 
+-=item *
++    -e $foo .= "q" 
++  
++    # perl4 prints: no output
++    # perl5 prints: Can't modify -e in concatenation
+ 
+-The caller() function now returns a false value in a scalar context if there
+-is no caller.  This lets library files determine if they're being required.
++=back
+ 
+-=item *
++=head2 General Regular Expression Traps using s///, etc.
++
++All types of RE traps.
++
++=over 5
++
++=item * Regular Expression
++
++C<s'$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)
+ 
+-=item *
++    $_ = "ababab";
++    while(m/ab/g){
++        &doit("blah");
++    }
++    sub doit{local($_) = shift; print "Got $_ "}
++ 
++    # perl4 prints: blah blah blah
++    # perl5 prints: infinite loop blah...
+ 
+-C<reverse> is no longer allowed as the name of a sort subroutine.
++=item * Regular Expression
+ 
+-=item *
++If no parentheses are used in a match, Perl4 sets C<$+> to
++the whole match, just like C<$&>. Perl5 does not.
+ 
+-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.
++    "abcdef" =~ /b.*e/;
++    print "\$+ = $+\n";
++ 
++    # perl4 prints: bcde
++    # perl5 prints:
+ 
+-=item *
++=item * Regular Expression
+ 
+-Double-quoted strings may no longer end with an unescaped C<$> or C<@>.
++substitution now returns the null string if it fails
+ 
+-=item *
++    $string = "test";
++    $value = ($string =~ s/foo//);
++    print $value, "\n";
++ 
++    # perl4 prints: 0
++    # perl5 prints:
+ 
+-The archaic C<while/if> BLOCK BLOCK syntax is no longer supported.
++Also see L<Numerical Traps> for another example of this new feature.
+ 
++=item * Regular Expression
+ 
+-=item *
++C<s`lhs`rhs`> (using backticks) is now a normal substitution, with no 
++backtick expansion
+ 
+-Negative array subscripts now count from the end of the array.
++    $string = "";
++    $string =~ s`^`hostname`;
++    print $string, "\n";
++ 
++    # perl4 prints: <the local hostname>
++    # perl5 prints: hostname
+ 
+-=item *
++=item * Regular Expression
+ 
+-The comma operator in a scalar context is now guaranteed to give a
+-scalar context to its arguments.
++Stricter parsing of variables used in regular expressions
+ 
+-=item *
++    s/^([^$grpc]*$grpc[$opt$plus$rep]?)//o;
++ 
++    # perl4: compiles w/o error
++    # perl5: with Scalar found where operator expected ..., near "$opt$plus"
+ 
+-The C<**> operator now binds more tightly than unary minus.  
+-It was documented to work this way before, but didn't.
++an added component of this example, apparantly 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
+ 
+-=item *
++    $grpc = 'a'; 
++    $opt  = 'r';
++    $_ = 'bar';
++    s/^([^$grpc]*$grpc[$opt]?)/foo/;
++    print ;
++ 
++    # perl4 prints: foo
++    # perl5 prints: foobar
+ 
+-Setting C<$#array> lower now discards array elements.
++=item * Regular Expression
+ 
+-=item *
++Under perl5, C<m?x?> matches only once, like C<?x?>. Under perl4, it matched
++repeatedly, like C</x/> or C<m!x!>.
+ 
+-delete() is not guaranteed to return the old value for tie()d arrays,
+-since this capability may be onerous for some modules to implement.
++    $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 *
++
++=back
++
++=head2 Subroutine, Signal, Sorting Traps
++
++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.
++
++=over 5
++
++=item * (Signals)
++
++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.
++
++    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
++
++Use -w to catch this one
++
++=item * (Sort Subroutine)
++
++reverse is no longer allowed as the name of a sort subroutine.
++
++    sub reverse{ print "yup "; $a <=> $b }
++    print sort reverse a,b,c;  
++ 
++    # perl4 prints: yup yup yup yup abc
++    # perl5 prints: abc 
++
++=back
++
++=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
++
++
++
++=back
++
++=head2 Interpolation Traps
++
++=over 5
++
++=item * Interpolation
++
++@ 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 apparantly 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
+ 
+-    foreach $var (grep /x/, @list) { ... }
++=item * Interpolation
++
++Creation of hashes on the fly with C<eval "EXPR"> now requires either both 
++C<$>'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.
++
++    $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|";
+ 
+-Some bugs may have been inadvertently removed.
++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 ")" 
++
++=back
++
++=head2 Unclassified Traps
++
++Everything else.
++
++=over 5
++
++=item * Unclassified
++
++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 * 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.
++